Yes it is true. I made the biggest mistake of my life. I was working in a company of 4000 people manufacturing hitech equipment for fertiliser, petroleum and petrochemicals, nuclear, power,defense and other industries. I was No.2 in the organisation. I was controlling about a dozen departments. I was running a well equipped R&D department which was developing missile components. In short I was working in a place which I was proud of. Suddenly I had an offer from a company in Chennai as Technical Director and I was recommended by one of my assistants who was working with me earlier and who has joined this company. At that time I was not aware of terms such as "Cost to the company". The salary offered appeared to be good but it was the "Cost to the Company. I later learnt that the salary included the rent for the flat, drivers salary etc. which effectively brought down my "Take home pay" which was not much higher from what I was getting from my previous job. For example, in my previous job I had an independent bungalow in half an acre of land with a garden, with subsidised electricity, water, a gardener, subsidised health benefits etc.By joining this the new company I lost all these benefits That was the first shock I got by joining the company. The next shock was my visit to the work shop which was located about 30 KM from Chennai. It was smaller than my R&D work shop in my previous organisation. There were some five or six welding machines which I learnt later was the property of the subcontractor. All the work was subcontracted hence there were no permanent workers. With such an arrangement quality was sacrificed. There was a GM who had no powers. His role was to beg for men and materials directly from MD. I was shattered and started wondering how long I will last in this Company. Incidentally, the turn over of the company was around Rupees twenty crores. The company I came from had a turn over of Rs.350 crores. Hence I was forced to think small.
The new company was manufacturing Filter and cleaning systems for Power Plants. The Managing Director was a middle aged man and there were three people who was MD's Ears and Eyes. One was M supposed to be an "Expert" in design and "Installation", another was R supposed to be a financial wizard and another was RK who was supposed to be an expert in Corporate Affairs.All the three spied on their colleagues and reported on them to MD every evening. Whom ever they found to be a potential competitor to them he was massacred by filling the ears of the MD.(Incidentally I was one of the victims). MD never even cross cross checked the info given to him. Such was the mislaid confidence in the THREE. These were the not the only people who were spying on the others. Even the lowest peon can walk in to MD's room and tell him on any one whom he disliked. This was not so in the previous organisation. There was hierarchy and only those who were directly reporting to MD can meet him only after fixing an appointment. Here it was chaos. Every body was telling on every body and hence the whole atmosphere was one of distrust. Once I made a comment that MD should sit in a different place so that even a messenger will not have access to him. This was twisted out of shape and R reported to MD that I want MD to leave his place and hand it over to me!
Orders were not got on merit. Officers at the execution level in Power Plants had no confidence in the equipment supplied. Whenever such difference of opinion occurred, the higher ups stepped and a deal was struck and the order was secured. Those who were stubborn not to recommend the order were neutralized. The MD had stooped to such a low level that he asked my secretary to furnish him at the end of the day who all met me and at time I went to work and what time I left for home. Those who were spying on their colleagues were rewarded and those who refused were punished.Obviously M, R and RK were rewarded beyond their expectations.
In such a dirty atmosphere I knew I cannot survive for long. M felt I am a stumbling block to his progress. He poisoned the mind of MD and a day came that I decided to quit by giving the mandatory three months notice. On my last working day MD wanted to give me three months pay as gratis. I had the supreme satisfaction of telling him "GO to Hell". Of course the company is doing well and has expanded and I hope that with growth openness has come to the company. Of course, M and R have become Directors and if they have to change their jobs then at best they can be accommodated as Senior Managers in a new company. Any one wants to join a tiny family owned company must be ready to give up his dignity and self respect.
Saturday, December 19, 2009
Saturday, November 7, 2009
LIFE IN RUSSIAN HOSTEL-2
HOT SHOWERS IN THE HOSTEL
We lived in a four storied building identified as Foreign Students Hostel.You must be wondering why I am writing about HOT Showers is in many undergraduate hostels there were no showers. Many of the Indian students living in such hostels used to come to our hostel regularly for a shower!
The showers were located in the ground floor. The showers were working round the clock. Three days were reserved for girls and the remaining days were for boys. Sunday was for girls when all the girls in the hostel used the shower. Many used the showers once a week.
We Indians used the showers all the seven days in a week. Russians used to ask us why there is necessity to take bath everyday when we don't sweat. With so many clothes we were wearing to protect ourselves from cold we were sweating inside. Moreover many Indians are accustomed to take bath every day. So we continued our daily routine. We invariably showered just before going to bed. There were about six showers and all of us showered in our birth day suit. Initially it was embarrassing but we got used. Just to mask their bad body odor they Russians used cheap scents which only enhanced their bad smell.
We lived in a four storied building identified as Foreign Students Hostel.You must be wondering why I am writing about HOT Showers is in many undergraduate hostels there were no showers. Many of the Indian students living in such hostels used to come to our hostel regularly for a shower!
The showers were located in the ground floor. The showers were working round the clock. Three days were reserved for girls and the remaining days were for boys. Sunday was for girls when all the girls in the hostel used the shower. Many used the showers once a week.
We Indians used the showers all the seven days in a week. Russians used to ask us why there is necessity to take bath everyday when we don't sweat. With so many clothes we were wearing to protect ourselves from cold we were sweating inside. Moreover many Indians are accustomed to take bath every day. So we continued our daily routine. We invariably showered just before going to bed. There were about six showers and all of us showered in our birth day suit. Initially it was embarrassing but we got used. Just to mask their bad body odor they Russians used cheap scents which only enhanced their bad smell.
Friday, November 6, 2009
LIFE IN A RUSSIAN HOSTEL-1
KGB IS WATCHING YOU
Last time I had written that we had to share a room with a Russian who did not know English. Invariably he was a member of the communist party. His main job was to keep a watch on who comes to meet us and how often we meet. In addition we used to visit Indian Embassy twice a week to collect our mail. His job was to inform KGB how often we visit the embassy and what type of mail we got. He always questioned about our attitude to Soviet way of life. Our standard answer was we like USSR. After we suffered his company for one or two years he was shifted to other new comers room.
Another ploy employed by KGB was to call us on telephone and accuse us of having an affair with a Russian girl and they have enough evidence to prove it. If we accept it then they will blackmail us that they report the Indian Embassy and ensure that we will be sent back. If we agree to cooperate with them when we go back to India, they will hush the whole thing up and we can continue as usual. When we faced such a situation our seniors had already warned us that we should abuse the caller and tell the caller that we are being harassed we are bringing this to the notice of our Embassy. Then such calls will stop. They did not want our Embassy to know that we are being watched.
Other than such minor incidents life in USSR was very interesting. We were free to roam freely in Moscow.
Last time I had written that we had to share a room with a Russian who did not know English. Invariably he was a member of the communist party. His main job was to keep a watch on who comes to meet us and how often we meet. In addition we used to visit Indian Embassy twice a week to collect our mail. His job was to inform KGB how often we visit the embassy and what type of mail we got. He always questioned about our attitude to Soviet way of life. Our standard answer was we like USSR. After we suffered his company for one or two years he was shifted to other new comers room.
Another ploy employed by KGB was to call us on telephone and accuse us of having an affair with a Russian girl and they have enough evidence to prove it. If we accept it then they will blackmail us that they report the Indian Embassy and ensure that we will be sent back. If we agree to cooperate with them when we go back to India, they will hush the whole thing up and we can continue as usual. When we faced such a situation our seniors had already warned us that we should abuse the caller and tell the caller that we are being harassed we are bringing this to the notice of our Embassy. Then such calls will stop. They did not want our Embassy to know that we are being watched.
Other than such minor incidents life in USSR was very interesting. We were free to roam freely in Moscow.
Monday, November 2, 2009
Government of India Scholarship
LEARNING RUSSIAN LANGUAGE
I was a Research Scholar in Indian Institute of Science working for my M.Sc degree in Mechanical Engineering. I had applied for a scholarship to do Ph.D from a Canadian University. I was offered a scholarship with a condition that I must produce a letter from my professor that I have submitted my Thesis for M.Sc. Unfortunately I could not get such a letter and for no fault of mine I lost the opportunity to study in Canada.
After completing my degree I got a job in CSIR and left for Durgapur in West Bengal.CSIR encouraged us to apply for Government of India Scholarships to study abroad. Countries such as U.K, Canada, West Germany, USSR were offering scholarships to Indian Scholars to pursue Ph.D programs in their country. Children of influential people cornered scholarships to study in the West but people like me had to be contented with scholarships offered by USSR and other countries. By the time I finished my Ph.D I was glad that I went to study in Moscow.
When I went to Moscow I did not know one word of Russian Language. We were assigned to various professors depending upon what topic we wanted to specialise for Ph.D programme. Since we did not know Russian language we were asked to learn for six Month's Russian language. Hence we were directed to the Russian language faculty. One young and beautiful Russian girl was assigned to teach six students. Perhaps assigning a young and beautiful teacher was sort of incentive for us not to bunk classes. The teacher knew English well.She used to talk to us in English for few weeks and once we learnt to recognise alphabets she stopped talking to us in English and switched over to Russian. We had tutorials lasting for about six hours a day for five days in a week. Further we were loaded with enough home work to last for another four to five hours. We were put up in a hostel and your room mate is a Russian who could not speak one word of English.Hence we were forced to communicate with him in our broken Russian which also helped us to learn Russian faster.Later we learnt that he was put up with us more for spying on us than to help us to learn Russian.
We went to buy daily necessities such as bread, butter jam etc. We will pick up the article and ask the sales girl its name and write down and in this way we learnt names of commodities which were not taught to us in class room.
My Professor insisted that I must come to the faculty after Russian classes. He introduced me to the fellow scholars and workers. The workers taught me the names of tools such as wrenches. screw driver, file etc. which were not taught in the Russian class room. In addition they taught me slang language without teaching the meaning which I used in one of my Russian classes. The teacher was shocked and asked me to repeat the word which I repeated without being aware of the meaning.She asked me who taught this slang and I told her the workers in the lab. She asked me whether I knew the meaning. I said no. She let it go at that but complained to my Professor that in the company of workers I am learning vulgar language. The professor warned the workers not to teach me vulgar language. When I fully learnt the language I understood what I had uttered and was ashamed of it. But I was not to be blamed.
Russian grammar is similar to Sanskrit grammar. In Sanskrit grammar we have "ekavachana, dwivachana, and bahuvachana". In Russian Language also we have "ekavachana, dwiavchana and bahuvachana" In Sanskrit the verb changes with number and gender. Same in Russian also. Hence Indians had no difficulty in accepting that the verb changes with gender and number. But students from Vietnam, France and even U.K had a lot of difficulty to accept that verb changes with number and gender.
There are a number of words in Russian which are similar to Sanskrit words, For example, OGON in Russian is AGNI in Sanskrit, VADA in Russian is UDAKA in Sanskrit, SYESTRA in Russain is SAHODARY in Sanaskrit etc. Hence it was not difficult for Indians to accept that verb changes with gender and number.
In addition to teaching Russian, our teacher took us to Museums, Ballets and plays. Next day she would ask us to narrate in our own words what we saw. We were asked to read the news paper and narrate in our own words what we have understood.
With such rigorous training in Russian for six months we were ready to enter our faculties. But learning Russian never ended. The technical language we have to master was a different kettle of fish. Here the colleagues and professors helped us a lot and we can never forget their love and affection.
I was a Research Scholar in Indian Institute of Science working for my M.Sc degree in Mechanical Engineering. I had applied for a scholarship to do Ph.D from a Canadian University. I was offered a scholarship with a condition that I must produce a letter from my professor that I have submitted my Thesis for M.Sc. Unfortunately I could not get such a letter and for no fault of mine I lost the opportunity to study in Canada.
After completing my degree I got a job in CSIR and left for Durgapur in West Bengal.CSIR encouraged us to apply for Government of India Scholarships to study abroad. Countries such as U.K, Canada, West Germany, USSR were offering scholarships to Indian Scholars to pursue Ph.D programs in their country. Children of influential people cornered scholarships to study in the West but people like me had to be contented with scholarships offered by USSR and other countries. By the time I finished my Ph.D I was glad that I went to study in Moscow.
When I went to Moscow I did not know one word of Russian Language. We were assigned to various professors depending upon what topic we wanted to specialise for Ph.D programme. Since we did not know Russian language we were asked to learn for six Month's Russian language. Hence we were directed to the Russian language faculty. One young and beautiful Russian girl was assigned to teach six students. Perhaps assigning a young and beautiful teacher was sort of incentive for us not to bunk classes. The teacher knew English well.She used to talk to us in English for few weeks and once we learnt to recognise alphabets she stopped talking to us in English and switched over to Russian. We had tutorials lasting for about six hours a day for five days in a week. Further we were loaded with enough home work to last for another four to five hours. We were put up in a hostel and your room mate is a Russian who could not speak one word of English.Hence we were forced to communicate with him in our broken Russian which also helped us to learn Russian faster.Later we learnt that he was put up with us more for spying on us than to help us to learn Russian.
We went to buy daily necessities such as bread, butter jam etc. We will pick up the article and ask the sales girl its name and write down and in this way we learnt names of commodities which were not taught to us in class room.
My Professor insisted that I must come to the faculty after Russian classes. He introduced me to the fellow scholars and workers. The workers taught me the names of tools such as wrenches. screw driver, file etc. which were not taught in the Russian class room. In addition they taught me slang language without teaching the meaning which I used in one of my Russian classes. The teacher was shocked and asked me to repeat the word which I repeated without being aware of the meaning.She asked me who taught this slang and I told her the workers in the lab. She asked me whether I knew the meaning. I said no. She let it go at that but complained to my Professor that in the company of workers I am learning vulgar language. The professor warned the workers not to teach me vulgar language. When I fully learnt the language I understood what I had uttered and was ashamed of it. But I was not to be blamed.
Russian grammar is similar to Sanskrit grammar. In Sanskrit grammar we have "ekavachana, dwivachana, and bahuvachana". In Russian Language also we have "ekavachana, dwiavchana and bahuvachana" In Sanskrit the verb changes with number and gender. Same in Russian also. Hence Indians had no difficulty in accepting that the verb changes with gender and number. But students from Vietnam, France and even U.K had a lot of difficulty to accept that verb changes with number and gender.
There are a number of words in Russian which are similar to Sanskrit words, For example, OGON in Russian is AGNI in Sanskrit, VADA in Russian is UDAKA in Sanskrit, SYESTRA in Russain is SAHODARY in Sanaskrit etc. Hence it was not difficult for Indians to accept that verb changes with gender and number.
In addition to teaching Russian, our teacher took us to Museums, Ballets and plays. Next day she would ask us to narrate in our own words what we saw. We were asked to read the news paper and narrate in our own words what we have understood.
With such rigorous training in Russian for six months we were ready to enter our faculties. But learning Russian never ended. The technical language we have to master was a different kettle of fish. Here the colleagues and professors helped us a lot and we can never forget their love and affection.
Tuesday, October 27, 2009
Hastelloy-G welding
In late 1970's the emission from existing power plants and chemical plants came under Governments scrutiny and laws were enacted to control emission of sulphur di oxide phosphoric acids and other harmful emissions. Flue gas desulpharisation was insisted upon and there was a need to look in to the material which can withstand corrosive products emitted by the stack. We looked in to the problem from material angle and decided that we need to study Hastelloy-G as a candidate material.
Hastelloy-G is a columbium stabilised nickel based alloy with additions of chromium,molybdenum and iron as major constituents in the alloy. The chemical composition of this alloy
is chosen to resist both acidic and alkaline media. It can also resist both oxdising and reducing media. This alloy is eminently suited to handle sulphuric acid which changes from oxidising to reducing depending upon concentration and temperature. Hastelloy-G has outstanding resistance to mixed acids,flurosilisic acid, sulphate compounds,contaminated nitric acid,flue gases and hydrofluoric acid. The alloy resists pitting, crevice corrosion and also stress corrosion cracking.
Hastelloy-G is welded either by manual metal arc or by TIG process.In manual metal arc welding electrode confirming to ENiCrMo-1 which deposits a weld metal whose composition is close to plate material is used.Some minor problems are encountered during welding. Hastelloy-G being a nickel rich material flowability is poor which makes it difficult to place the weld where it is required. But this problem can be over come by training of welders.
Hastelloy-G plates are supplied in solution treated condition. Solution treatment consists of heating to 1175 degC, holding at this temperature for sufficient length of time and rapid air cooling or water quench.
Hastelloy- G being high nickel alloy the flowability of molten metal is poor. It is necessary to place the weld metal where it is required. Large bevel angles and small root face is necessary. Side wall fusion is another problem with welding of Hastelloy-G- It is difficult to obtain full penetration. In such cases back chipping and placing sealing weld is necessary to ensure good radiography quality welds. Magnetic arc blow which is problem with all high nickel alloy is also experienced by Hastelloy-G. But the problem can be overcome by suitably locating ground clamps. Porosity is another problem which is encountered often. By using short arc and proper cleaning of base metal and baking the electrode porosity can be eliminated. A large number of trials were carried out by varying heat in put over a wide range. Mechanical tests were carried out to establish the strength and ductility of welds. From these results we established the optimum heat input for welding Hastelloy-G.
In TIG welding the filler wire used is ERNiCrMo-1. Similar problems which we experienced with manual welding were also experienced with TIG welding.
The test specimens from both the methods of welding were subjected to corrosion tests in sulphuric acid with concentration ranging from 10% to 70%. At 70% concentration the acid becomes oxidizing and the corrosion rate is extremely high.
Weldments showed excellent corrosion resistance in entire range of concentration in phosphoric acid.
Weldments were subjected to stress corrosion cracking tests in 42% boiling Magnesium Chloride solution. Hastelloy-G did not show any signs of cracking even after hundreds of hours of test.
We passed on these results to the manufacturing section of BHPV for fabricating equipment with Hastelloy-G.
Hastelloy-G is a columbium stabilised nickel based alloy with additions of chromium,molybdenum and iron as major constituents in the alloy. The chemical composition of this alloy
is chosen to resist both acidic and alkaline media. It can also resist both oxdising and reducing media. This alloy is eminently suited to handle sulphuric acid which changes from oxidising to reducing depending upon concentration and temperature. Hastelloy-G has outstanding resistance to mixed acids,flurosilisic acid, sulphate compounds,contaminated nitric acid,flue gases and hydrofluoric acid. The alloy resists pitting, crevice corrosion and also stress corrosion cracking.
Hastelloy-G is welded either by manual metal arc or by TIG process.In manual metal arc welding electrode confirming to ENiCrMo-1 which deposits a weld metal whose composition is close to plate material is used.Some minor problems are encountered during welding. Hastelloy-G being a nickel rich material flowability is poor which makes it difficult to place the weld where it is required. But this problem can be over come by training of welders.
Hastelloy-G plates are supplied in solution treated condition. Solution treatment consists of heating to 1175 degC, holding at this temperature for sufficient length of time and rapid air cooling or water quench.
Hastelloy- G being high nickel alloy the flowability of molten metal is poor. It is necessary to place the weld metal where it is required. Large bevel angles and small root face is necessary. Side wall fusion is another problem with welding of Hastelloy-G- It is difficult to obtain full penetration. In such cases back chipping and placing sealing weld is necessary to ensure good radiography quality welds. Magnetic arc blow which is problem with all high nickel alloy is also experienced by Hastelloy-G. But the problem can be overcome by suitably locating ground clamps. Porosity is another problem which is encountered often. By using short arc and proper cleaning of base metal and baking the electrode porosity can be eliminated. A large number of trials were carried out by varying heat in put over a wide range. Mechanical tests were carried out to establish the strength and ductility of welds. From these results we established the optimum heat input for welding Hastelloy-G.
In TIG welding the filler wire used is ERNiCrMo-1. Similar problems which we experienced with manual welding were also experienced with TIG welding.
The test specimens from both the methods of welding were subjected to corrosion tests in sulphuric acid with concentration ranging from 10% to 70%. At 70% concentration the acid becomes oxidizing and the corrosion rate is extremely high.
Weldments showed excellent corrosion resistance in entire range of concentration in phosphoric acid.
Weldments were subjected to stress corrosion cracking tests in 42% boiling Magnesium Chloride solution. Hastelloy-G did not show any signs of cracking even after hundreds of hours of test.
We passed on these results to the manufacturing section of BHPV for fabricating equipment with Hastelloy-G.
Thursday, October 15, 2009
superplastic forming
After developing welding and forming commercially pure titanium and titanium alloy Ti-6Al-4V, we turned our attention to superpastic forming of Ti-6Al-4V.We had been manufacturing gas bottles of titanium alloy for missile application. We wanted to examine whether we can adopt superplastic forming for manufacture of gas bottles.
Superplasticity is the property of certain metals and alloys to be stretched many times their intial length without fracture.Elongations of the order of 800% to 1000% can be expected if certain conditions such as temperature, strain rate, microstructure of the alloy can be controlled.Ti-6Al-4V shows excellent superplastic forming properties in the temperature range of 750degC to 1000degC.Maximum elongation is observe around 930 deg C. The Microstructure must be fine grained and the deforming temperature must be higher than half th melting temperature.In addition to the grain size, grain size distribution. grain aspect ratio and percentage of alpha -beta in the microsructure are also important. Without getting in to more details on theory of superplastic forming let us look into how we did free blowing of a sphere and some other shapes.
We selected a 3mm thin Ti-6Al-4V sheet for free blowing. We attempted free blowing a sphere. Circular blanks were trepanned by holding the plate in a vacuum chuck. The two blanks were held in a jig and the edges were welded by TIG welding. In of the blanks a thick walled tube of commercially pure titanium was welded. The welded blank was coated with a protective coating which reduced oxidation of the blanks during heating, An electric furnace which was earlier calibrated with the temperature uniformity of plus or minus 5degC was used for experiments. A thermocouple was attached to the nozzle and the temperature indicated by digital temperature recorder was accepted as the temperature of blank. The furnace was purged with argon and low volume flow was maintained throughout blowing,When the temperature of the blank reached 930 degC Argon was admitted in to the sandwich and the pressure was increased in increments of few Psi.After the assuring that the free blowing was completed, the pressure was released slowly and the furnace switched off. After the sphere was cooled to room temperature the surface was examined and the thickness was measured by ultrasonic thickness gauge.The thickness at the pole of the sphere was between 2.1mm to 2,2 and at the pole was 1,7mm to 1.8mm.
Although we demonstrated the feasibility of forming a sphere by free blowing we realised that the process is slow and hence we abandoned further trails. We continued with hot forming, machining,welding and testing. But if the number of components required was not many free blowing is a viable option.
Superplasticity is the property of certain metals and alloys to be stretched many times their intial length without fracture.Elongations of the order of 800% to 1000% can be expected if certain conditions such as temperature, strain rate, microstructure of the alloy can be controlled.Ti-6Al-4V shows excellent superplastic forming properties in the temperature range of 750degC to 1000degC.Maximum elongation is observe around 930 deg C. The Microstructure must be fine grained and the deforming temperature must be higher than half th melting temperature.In addition to the grain size, grain size distribution. grain aspect ratio and percentage of alpha -beta in the microsructure are also important. Without getting in to more details on theory of superplastic forming let us look into how we did free blowing of a sphere and some other shapes.
We selected a 3mm thin Ti-6Al-4V sheet for free blowing. We attempted free blowing a sphere. Circular blanks were trepanned by holding the plate in a vacuum chuck. The two blanks were held in a jig and the edges were welded by TIG welding. In of the blanks a thick walled tube of commercially pure titanium was welded. The welded blank was coated with a protective coating which reduced oxidation of the blanks during heating, An electric furnace which was earlier calibrated with the temperature uniformity of plus or minus 5degC was used for experiments. A thermocouple was attached to the nozzle and the temperature indicated by digital temperature recorder was accepted as the temperature of blank. The furnace was purged with argon and low volume flow was maintained throughout blowing,When the temperature of the blank reached 930 degC Argon was admitted in to the sandwich and the pressure was increased in increments of few Psi.After the assuring that the free blowing was completed, the pressure was released slowly and the furnace switched off. After the sphere was cooled to room temperature the surface was examined and the thickness was measured by ultrasonic thickness gauge.The thickness at the pole of the sphere was between 2.1mm to 2,2 and at the pole was 1,7mm to 1.8mm.
Although we demonstrated the feasibility of forming a sphere by free blowing we realised that the process is slow and hence we abandoned further trails. We continued with hot forming, machining,welding and testing. But if the number of components required was not many free blowing is a viable option.
Tuesday, October 6, 2009
Welding Maraging Steel
Maraging steel is vacuum induction melted plus vacuum arc melted, low carbon Nickel-Cobalt-Molybdenum High Temperature Alloy capable of attaining yield strength in excess of 240 ksi through a heat treatment. The steel exhibits good ductility coupled with high strength and is readily weldable. A aging heat treatment in the temperature range of 454-514 deg C from the solution treated condition will results in high strength.
The chemical composition of the steel is given below:
C-0.03max Mn-0.10max P-0.01max S-0.01max Si-0.10max Ni-18.50 Mo-4.80
Co-7.50 Ti-0.40 Al-0.10 B-0.003 Zr-0.01
Welding was performed on two thicknesses,namely, 5mm and 10mm. Gas tungsten arc welding was adopted using ultra high purity Argon. Matching filler wire was used in all welding trials.Test coupons were welded in solution annealed condition and the weldment was aged after welding and also welding was carried out after solution treatment and aging. The aim was to optimise heat-input to ensure that the development meets the stringent fracture toughness specified apart from meeting the tensile requirements. All the experiments done and the results obtained were compiled in a report which was handed over to MIDHANI which in turn forwarded the report to the customer. This was one of the contract development by R&D of BHPV.
The chemical composition of the steel is given below:
C-0.03max Mn-0.10max P-0.01max S-0.01max Si-0.10max Ni-18.50 Mo-4.80
Co-7.50 Ti-0.40 Al-0.10 B-0.003 Zr-0.01
Welding was performed on two thicknesses,namely, 5mm and 10mm. Gas tungsten arc welding was adopted using ultra high purity Argon. Matching filler wire was used in all welding trials.Test coupons were welded in solution annealed condition and the weldment was aged after welding and also welding was carried out after solution treatment and aging. The aim was to optimise heat-input to ensure that the development meets the stringent fracture toughness specified apart from meeting the tensile requirements. All the experiments done and the results obtained were compiled in a report which was handed over to MIDHANI which in turn forwarded the report to the customer. This was one of the contract development by R&D of BHPV.
Tuesday, September 1, 2009
Welding Maraging Steel
In the initial stage of rocket development ISRO was using a quenched and tempered high strength steel designated as 15CdV6. Demand for more powerful rockets necessitated to identify a material which has higher strength and better weldability than 15CdV6. The material identified was a high strength steel Maraging 250 steel. Mishra Dhatu Nigam (Midhani), which is a factory which is set up to manufacture special special steels and alloys agreed to supply Maraging 250 steel. But there was a hitch. No body had welded maraging steel in India. Midhani was asked by ISRO to supply not only the material but also the welding technology. Midhani looked up to R&D of BHPV to develop the welding technology by placing a developmental contract. The development was a tough assignment. The developed technology must not only meet the strength requirements but also meet the fracture toughness specified by ISRO, Hence we had to optimise the welding procedure. But it must be repeatable and produce consistence results. How we went about developing the welding technology is the essence of this blog which will follow.
Tuesday, August 25, 2009
Meeting at DMRL
There was a high level meeting in DMRL which was attended by all big bosses of ordnance factory board (OFB). The Director of DMRL and his associates made a detailed presentation of the development and the various tests conducted by them. Discussions went on and on. The questions asked by the OFB board members were answered patiently by DMRL staff even though many questions were flimsy in nature. Then it was my turn to present the experiments done and interpretations of the results obtained. I had already mentioned that OFB's were way behind in their standards for armour testing. Hence the method of testing adopted by us was challenged. I presented enough data and informed the committee that the testing procedures adopted by us was in line with the British armour testing specifications. This seems to have convinced them that we were on the right track. In addition to the CTS test we had welded one meter long plates and after conducting radiography we carried out conventional tests such as tensile test, bend test and charpy impact test at low temperature. All tests were in acceptable limits. One of the persons who was very sarcastic during the review suddenly told me that welding one meter does not prove that the steel is weldable as the armoured personnel carrier has hundreds of meters of weld. I retorted by saying that in my company we just weld a test coupon which is 450 mm long and if the test coupon passes all the tests based upon that procedure we weld thousands of meters. He did not like my answer because no body has ever talked to him like that. Later I learnt that he was one of the top people in the army. He was not accustomed to a civilian snubbing him. In spite of DMRL clearing all doubts OFB insisted that DMRL should weld a full scale hull of the APC, fit the engine and the transmission, carry all sorts of tests and if the tets are satisfactory then only army will agree for the Jackal steel to be used as a replacement steel for APC. DMRL requested BHPV to manufacture one hull with the drawings supplied by them. We did produce a hull which was fitted with the engine and transmission. This prototype APC went through all trials and was finally accepted by the army. During these trials not a single weld failed certifying that the technology developed by us met all the requirements of OFB.The welding technology supplied by us is even now used for welding indigenous armour plate developed by DMRL.
In the end we told DMRL we can weld armour steel!
In the end we told DMRL we can weld armour steel!
Wednesday, August 19, 2009
CTC Test
Controlled thermal severity test is very sensitive test to evaluate a steel for its propensity for underbead cracking. This test is in use for a number of years. We used a modified CTS test developed by The Welding Institute, UK, which was more severe than the classical test.
Controlled therma severity test is done using plates which have propensity for hydrogen induced cracking, also called as underbead cracking. The test spcimen consists of a bottom plate and a top plate which are bolted together. The bottom plate has the dimensions of 175x175 mm x thickness of plate under test. The top plate has the dimension 75x75 mm ,thickness being same as the bottom plate. Both the plates are bolted together securely.Two fillet welds, called anchor welds,are laid between the top plate and the bottom plate.The bolt is again tightened. The test plate is allowed to cool to the room temperature. Using the selected electrode test welds on the remaining sides of the assembly were laid taking care to see that test specimen is not over heated.The welded assmbly is stored for 72 hour for any cracks to develop. After 72 hours the test welds are cross sectioned and polished to see if there any cracks in the heat affected zone. The cross sectioned pieces are subjected to magnetic particle testing to reveal any hidden cracks. Finally the specimen is polished, etched and examined under microscope at 200x magnification to detect any microcracks in the heat affected zone.During testing we had recorded the heat input for which we had developed a gadget. We conducted several tests with various heat inputs.
We selected three types stainless steel electrodes available in the market from three different manufacturers. Initial tests suggested that the standard electrodes which were supplied off the shelf were not meeting our requirements. We called all the electrode manufacturers and requested them to slightly modify the weld chemistry. Only one electrode manufacturer agreed for our proposal and he cooperated with us. Of the three specifications of electrode tested by us one specification fully met our requirements. This electrode was finally recommended to DMRL for welding Jackal steel.
When DMRL presented the data before the ordnance board several questions were raised. Ordnance board followed a method of testing which is no longer in vouge. Board members insisted that we conduct the test to meet their test procedure. Even though their method of testing is outdated to satisfy their ego and bail out DMRL we again did several test as per the standards of ordnance board. Ordnance board fixed another date for final evaluation and I was invited to be present to clarify doubts to ordnance board officials.
Controlled therma severity test is done using plates which have propensity for hydrogen induced cracking, also called as underbead cracking. The test spcimen consists of a bottom plate and a top plate which are bolted together. The bottom plate has the dimensions of 175x175 mm x thickness of plate under test. The top plate has the dimension 75x75 mm ,thickness being same as the bottom plate. Both the plates are bolted together securely.Two fillet welds, called anchor welds,are laid between the top plate and the bottom plate.The bolt is again tightened. The test plate is allowed to cool to the room temperature. Using the selected electrode test welds on the remaining sides of the assembly were laid taking care to see that test specimen is not over heated.The welded assmbly is stored for 72 hour for any cracks to develop. After 72 hours the test welds are cross sectioned and polished to see if there any cracks in the heat affected zone. The cross sectioned pieces are subjected to magnetic particle testing to reveal any hidden cracks. Finally the specimen is polished, etched and examined under microscope at 200x magnification to detect any microcracks in the heat affected zone.During testing we had recorded the heat input for which we had developed a gadget. We conducted several tests with various heat inputs.
We selected three types stainless steel electrodes available in the market from three different manufacturers. Initial tests suggested that the standard electrodes which were supplied off the shelf were not meeting our requirements. We called all the electrode manufacturers and requested them to slightly modify the weld chemistry. Only one electrode manufacturer agreed for our proposal and he cooperated with us. Of the three specifications of electrode tested by us one specification fully met our requirements. This electrode was finally recommended to DMRL for welding Jackal steel.
When DMRL presented the data before the ordnance board several questions were raised. Ordnance board followed a method of testing which is no longer in vouge. Board members insisted that we conduct the test to meet their test procedure. Even though their method of testing is outdated to satisfy their ego and bail out DMRL we again did several test as per the standards of ordnance board. Ordnance board fixed another date for final evaluation and I was invited to be present to clarify doubts to ordnance board officials.
Weldability of Jackal Steel
I had talked about armour steel welding.While we were doing literature survey we found that all western countries were using stainless steel electrodes where as Russians were welding with carbon and low alloy steel electrodes.These are classified as ferritic electrode The argument given by the western countries were since armour steels are susceptible for hydrogen induced cracking they decided to use austenitic electrodes for welding.
This needs to be explained. While welding armour steel slightest amount of hydrogen in the weld causes under bead cracking. This hydrogen come from various sources, such as, improperly dried electrodes, rust and grime on the plate, paint marks or condensed water etc.When the plate is welded with a ferritic electrode the hydrogen is first absorbed in the weld metal and as the weld metal cools hydrogen migrates to heat affected zone which contains martensite and in course of time a crack develops. The hydrogen induced cracks take at least 72 hours to develop.
The solubility of hydrogen in the austenitic weld metal is high and is not liberated to heat affected zone after cooling as in the case of ferritic weld metal. Since the migration of hydrogen to heat affected zone is absent the chances of hydrogen induced cracking when armour steel is welded with austenitic stainless steel electrodes are less.
The question arises then why Russians weld with ferritic electrode. They are not dumb. The Russians have a valid argument.
In the manufacture of steel Russians follow a technology of steel making which contains very less hydrogen. More over all their armored vehicles are welded by MIG welding which is known to contain less Hydrogen. More over they used to manufacture large number of armoured vehicles for supplying to their allies almost free. Hence they used ferritic weld metal which is cheaper.
We put all these facts before DMRL and DMRL suggested that we should use austenitic electrodes. Hence we did all our experiments with austenitic elrctrodes,
This needs to be explained. While welding armour steel slightest amount of hydrogen in the weld causes under bead cracking. This hydrogen come from various sources, such as, improperly dried electrodes, rust and grime on the plate, paint marks or condensed water etc.When the plate is welded with a ferritic electrode the hydrogen is first absorbed in the weld metal and as the weld metal cools hydrogen migrates to heat affected zone which contains martensite and in course of time a crack develops. The hydrogen induced cracks take at least 72 hours to develop.
The solubility of hydrogen in the austenitic weld metal is high and is not liberated to heat affected zone after cooling as in the case of ferritic weld metal. Since the migration of hydrogen to heat affected zone is absent the chances of hydrogen induced cracking when armour steel is welded with austenitic stainless steel electrodes are less.
The question arises then why Russians weld with ferritic electrode. They are not dumb. The Russians have a valid argument.
In the manufacture of steel Russians follow a technology of steel making which contains very less hydrogen. More over all their armored vehicles are welded by MIG welding which is known to contain less Hydrogen. More over they used to manufacture large number of armoured vehicles for supplying to their allies almost free. Hence they used ferritic weld metal which is cheaper.
We put all these facts before DMRL and DMRL suggested that we should use austenitic electrodes. Hence we did all our experiments with austenitic elrctrodes,
Tuesday, August 18, 2009
Controlled Thermal Severity Test
Armour steels are generally low alloy steels which are hardenable. The steel develops high strength and high hardness with adequate fracture toughness. Hence a fine balance should be maintained in the chemistry of the steel and its heat treatment. As told earlier the steel had passed all the ballistic tests and what was required to be proved was that the steel can be welded.
High hardness steels are susceptible for what is called underbead cracking. These cracks are buried cracks which develop under the weld bead and extremely dangerous since they are not detected after welding and generally take some time to develop. Three conditions are essential for this type of cracks to develop.
1. There must be adequate hydrogen in the weld. This hydrogen comes from the coating on the electrode or from some external agent such as grease or oil used for preserving the steel.
2. Tensile stresses must be present in the welded structure.
3. There should be susceptible microstructure, that is , microstructure such as martensite.
Since we had no earlier knowledge of welding armour steel we did a literature survey. We could not get much information, naturally, as the welding of armour steel was a classified information. We decided to start from fundamentals. All high hardness steels are tested for underbead cracking by a test called Controlled Thermal Severity Test. We decided to apply this test to the armour steel with some modification which was permitted for acceptance of the results obtained. The tests are to be done in a controlled fashion which means that the test conditions have to be standardised. We developed a gadget which allowed us to measure the heat input precisely. How we performed the tests and how we interpreted the tests will be explained later.
High hardness steels are susceptible for what is called underbead cracking. These cracks are buried cracks which develop under the weld bead and extremely dangerous since they are not detected after welding and generally take some time to develop. Three conditions are essential for this type of cracks to develop.
1. There must be adequate hydrogen in the weld. This hydrogen comes from the coating on the electrode or from some external agent such as grease or oil used for preserving the steel.
2. Tensile stresses must be present in the welded structure.
3. There should be susceptible microstructure, that is , microstructure such as martensite.
Since we had no earlier knowledge of welding armour steel we did a literature survey. We could not get much information, naturally, as the welding of armour steel was a classified information. We decided to start from fundamentals. All high hardness steels are tested for underbead cracking by a test called Controlled Thermal Severity Test. We decided to apply this test to the armour steel with some modification which was permitted for acceptance of the results obtained. The tests are to be done in a controlled fashion which means that the test conditions have to be standardised. We developed a gadget which allowed us to measure the heat input precisely. How we performed the tests and how we interpreted the tests will be explained later.
Monday, August 17, 2009
Can you develop technology for welding armour steel?
We received a message from the Director of Defense Metallurgical Research Laboratory(DMRL), Hyderabad, that he wanted to visit BHPV and in particular R&D laboratory. On the appointed day he visited BHPV and R&D. The first question he asked us was whether we knew how to weld armour steel. Our honest answer was that we had no need to weld armour steel in our business but definitely we can try.
DMRL had developed an armour steel as a replacement for the steel India was importing from Russia for the armoured personnel carrier(APC) which India was building under license.
It was am excellent steel much better than the Russian steel in its ballistic performance. When DMRL proposed to Army to use this steel for armoured personnel carrier (APC) Army had its own reservations.DMRL had manufactured small size plates in its own facilities starting from melting, forging and heat treatment for its trials . The development was remarkable considering the constraint DMRL had. Very few people could understand the manufacture of armour steel and the precise heat treatment it has to undergo to meet the ballistic requirements.In addition, APC will have various thicknesses and the ballistic performance must satisfy various requirements.Credit should be given to the Director, DMRL and his band of enthusiastic young scientists who pulled out a difficult task successfully. You have to remember that this development was in early 1980's. Army, rightly, told DMRL that they need large size plates and in huge quantities. DMRL tied up with one of the steel manufacturers to produce these plates. Once every objection by the Army was neutralised,Army asked DMRL to prove that the steel is weldable and DMRL should supply the welding technology.This is where we came in. We shall discuss next time how we proved that the steel is weldable and the welding technology needed to weld APC's.
DMRL had developed an armour steel as a replacement for the steel India was importing from Russia for the armoured personnel carrier(APC) which India was building under license.
It was am excellent steel much better than the Russian steel in its ballistic performance. When DMRL proposed to Army to use this steel for armoured personnel carrier (APC) Army had its own reservations.DMRL had manufactured small size plates in its own facilities starting from melting, forging and heat treatment for its trials . The development was remarkable considering the constraint DMRL had. Very few people could understand the manufacture of armour steel and the precise heat treatment it has to undergo to meet the ballistic requirements.In addition, APC will have various thicknesses and the ballistic performance must satisfy various requirements.Credit should be given to the Director, DMRL and his band of enthusiastic young scientists who pulled out a difficult task successfully. You have to remember that this development was in early 1980's. Army, rightly, told DMRL that they need large size plates and in huge quantities. DMRL tied up with one of the steel manufacturers to produce these plates. Once every objection by the Army was neutralised,Army asked DMRL to prove that the steel is weldable and DMRL should supply the welding technology.This is where we came in. We shall discuss next time how we proved that the steel is weldable and the welding technology needed to weld APC's.
Saturday, August 15, 2009
Repairing LOX and LN2 tanks
Stress corrosion cracks can be identified easily. The cracks appear as branches of a tree, that is, there is stem and from the stem branches radiate. When we entered the tank we noticed a number of stress corrosion cracks at the sites where the inner tank was anchored to the outer tank. We did dye penetrant test to reveal the cracks. Some times the cracks are buried inside the material. One way of making the cracks come to the surface is to heat the metal which causes internal cracks to break out to the surface.After ensuring that there are no sub surface cracks, which were revealed by dye penetrant tests, repair work was started. The cracked portion was marked and grinding was done till the cracks were removed. Then the ground portion was welded and checked by dye penetrant test. This method was continued till all the cracks were removed. Then hydraulic test was done and the tank was handed over to the customer.
All five tanks which had developed stress corrosion cracks were successfully repaired and handed over to the customer after hydraulic test. These tanks are performing successfully for the past 15 years.
The repairing of all the tanks took nearly six months not 15 days as expected by MD. If we had not detected the cracks and had done the hydraulic testing all the tanks would have collapsed causing a huge loss to the company. But our MD never realised the gravity of the problem because he was ignorant nor did he appreciate the work done by us. Had we worked in a private company we would have been rewarded by the management. We did not get even one word of appreciation by the management. Such are the motivation people have while working in PSU's!
All five tanks which had developed stress corrosion cracks were successfully repaired and handed over to the customer after hydraulic test. These tanks are performing successfully for the past 15 years.
The repairing of all the tanks took nearly six months not 15 days as expected by MD. If we had not detected the cracks and had done the hydraulic testing all the tanks would have collapsed causing a huge loss to the company. But our MD never realised the gravity of the problem because he was ignorant nor did he appreciate the work done by us. Had we worked in a private company we would have been rewarded by the management. We did not get even one word of appreciation by the management. Such are the motivation people have while working in PSU's!
Sunday, August 2, 2009
What is stress corrosion cracking
Most of the metals are prone to stress corrosion cracking.Stainless steel is more prone to stress corrosion cracking compared to other metals and alloys.Stress corrosion cracks are generally subsurface cracks which are not detected early enough to take corrective measure.
Three conditions are essential for the stress corrosion cracks to occur:
1.The metal temperature must be high, above 70 deg celsius.
2.Tensile stresses must be present in the structure.
3.The atmosphere in which the structure is working must be salty.
Let us look at the LOX and LN2 tanks erected by us for the shore based steel plant.
In the mornings when the atmospheric temperature was around 40 deg.C the metal temperature can be as high as 140 deg.C.
Where the outer stainless steel wall was anchored to the inner carbon steel wall by wedges with fillet welds the stress distribution in the fillet calculated showed high tensile stresses at the stainless steel wall,
Since the tank was erected near the sea moist air saturated with salt condensed inside the tank when the atmospheric temperature fell in the night and deposited salt especially at the fillet joints.In course of time the concentration of salts reached sufficiently high to initiate cracking.These are the cracks we discovered on the steel surface.Stress corrosion cracks generally are buried but in the inner tank where fillet weld was made the cracks were extensive and also cracks can be seen on the inner surface of the tank.How we repaired forms the subject of next blog.
Three conditions are essential for the stress corrosion cracks to occur:
1.The metal temperature must be high, above 70 deg celsius.
2.Tensile stresses must be present in the structure.
3.The atmosphere in which the structure is working must be salty.
Let us look at the LOX and LN2 tanks erected by us for the shore based steel plant.
In the mornings when the atmospheric temperature was around 40 deg.C the metal temperature can be as high as 140 deg.C.
Where the outer stainless steel wall was anchored to the inner carbon steel wall by wedges with fillet welds the stress distribution in the fillet calculated showed high tensile stresses at the stainless steel wall,
Since the tank was erected near the sea moist air saturated with salt condensed inside the tank when the atmospheric temperature fell in the night and deposited salt especially at the fillet joints.In course of time the concentration of salts reached sufficiently high to initiate cracking.These are the cracks we discovered on the steel surface.Stress corrosion cracks generally are buried but in the inner tank where fillet weld was made the cracks were extensive and also cracks can be seen on the inner surface of the tank.How we repaired forms the subject of next blog.
Thursday, July 30, 2009
Repair of LOX & LN2 tanks affected by SCC
Field erected storage tanks for storing liquid oxygen and liquid nitrogen are high tech storage devices. A typical tank is a double walled tank, the inner tank is made of stainless steel and the outer tank wall is made of carbon steel.The inter space between the inner tank and the outer tank is evacuated and filled with low thermal conductivity perlite powder.The inner tank and the outer tank is held in place by stainless steel wedges. One end of the Stainless steel wedge is welded to the out side of the inner stainless steel tank and the other end is welded to the inside of the carbon steel tank.The tanks were erected close to the sea shore. The atmosphere is humid and salt laden. When the tanks were ready we asked the steel plant authorities to provide raw water for hydraulic testing. Steel plant authorities could not provide the water required and asked us to postpone hydraulic testing. After one year steel plant authorities asked us to carry out hydraulic testing. When we went inside the stainless steel tank we were surprised to find a number of cracks on the surface. Examination of the cracks closely led us to conclude that the cracks are stress corrosion cracks. We will explain how we came to this conclusion later.
Wednesday, July 22, 2009
"The Crack is in Your Head"
This is how a Managing Director Of BHPV reacted when I told him that the liquid oxygen and liquid nitrogen storage tanks erected at a shore based steel plant cannot be hydraulic tested as the tanks have developed STRESS CORROSION CRACKS.
Perhaps he must have heard the word stress corrosion cracking for the first time in his life. Granting that many would not know about stress corrosion cracking he did not want know what is stress corrosion cracking. In order to camouflage his ignorance on many things he always resorted to insult the person who brought any problem to him. I would like to say few things about his style of functioning.
He was an ordinary engineering graduate. I doubt whether he passed his B.E examination in first class.He had powerful political connections which he used effectively to climb up the ladder in Public Sector Undertakings. At a relatively young age he became the CMD of a company which was famous for manufacturing Three Jaw Chucks! The turnover of that company was around Rs.30 crores.He had no experience in heavy fabrication. Before coming to BHPV,I am sure, he did not know what a pressure vessel or a heat exchanger is let alone knowing how they are designed and manufactured. When the post of MD became vacant in BHPV using his connections he jockeyed to get that post. At that time BHPV was a company with a turn over of over Rs.350 crores. BHPV had good a design and manufacturing team staffed by post graduate engineers. The top was full of people who had put in more than 20 years experience in heavy fabrication. He came to such a place ill equipped with necessary skills to run BHPV. What he lacked in managerial skills he made up by insulting people without any regard for age, experience and qualification.He terrorized all including workers. Unfortunately we had to work with him for nearly five years. When he left BHPV he left a team which was demoralized and demotivated. Hence when he told me that" Crack is in your head" I did not get offended because I knew that I was dealing with a mental case. He demanded that I should repair the tanks in two weeks. Then I told him that he can find a person who could repair the tanks in that time as I was not capable of meeting his dead line and I walked out of the meeting. He threatened me that he will post me out of Vizag and harass me. I stood my ground and finally he agreed to my terms and conditions.Probably he learnt from his coterie that no one expect me can solve this problem. I will explain what is stress corrosion cracking and how we repaired the tank later.
Perhaps he must have heard the word stress corrosion cracking for the first time in his life. Granting that many would not know about stress corrosion cracking he did not want know what is stress corrosion cracking. In order to camouflage his ignorance on many things he always resorted to insult the person who brought any problem to him. I would like to say few things about his style of functioning.
He was an ordinary engineering graduate. I doubt whether he passed his B.E examination in first class.He had powerful political connections which he used effectively to climb up the ladder in Public Sector Undertakings. At a relatively young age he became the CMD of a company which was famous for manufacturing Three Jaw Chucks! The turnover of that company was around Rs.30 crores.He had no experience in heavy fabrication. Before coming to BHPV,I am sure, he did not know what a pressure vessel or a heat exchanger is let alone knowing how they are designed and manufactured. When the post of MD became vacant in BHPV using his connections he jockeyed to get that post. At that time BHPV was a company with a turn over of over Rs.350 crores. BHPV had good a design and manufacturing team staffed by post graduate engineers. The top was full of people who had put in more than 20 years experience in heavy fabrication. He came to such a place ill equipped with necessary skills to run BHPV. What he lacked in managerial skills he made up by insulting people without any regard for age, experience and qualification.He terrorized all including workers. Unfortunately we had to work with him for nearly five years. When he left BHPV he left a team which was demoralized and demotivated. Hence when he told me that" Crack is in your head" I did not get offended because I knew that I was dealing with a mental case. He demanded that I should repair the tanks in two weeks. Then I told him that he can find a person who could repair the tanks in that time as I was not capable of meeting his dead line and I walked out of the meeting. He threatened me that he will post me out of Vizag and harass me. I stood my ground and finally he agreed to my terms and conditions.Probably he learnt from his coterie that no one expect me can solve this problem. I will explain what is stress corrosion cracking and how we repaired the tank later.
Tuesday, July 21, 2009
Details of heat exchangers brazed
17 numbers of heat exchangers were to be brazed, some of aluminium and some of stainless steel.
The minimum core weight of the aluminium heat exchanger(Liquid-Air HE) was o.28 Kg and the finished weight of the same heat exchanger was 0.85 Kg.
The maximum core weight of the aluminium heat exchanger(Secondary HE) was 8.78 Kg the finished weight was 12.0 Kg.
The aluminium fins are as thin as 0,0762 mm.
There were a number of stainless steel heat exchangers.
The minimum core weight of the heat exchanger(Precooler) was 8.8 Kg and the finished weight was 12.0 Kg.
The maximum core weight(Primary HE} was 15.6 Kg and the maximum finished weight was 23.0 Kg.
The fin thickness was 0.0762 mm.
If you look at the thickness of the fins the difficulty in brazing can be gauged. CLOSE CONTROL OF THE BRAZING TEMPERATURE WAS ESSENTIAL FOR THE SUCCESS OF THE BRAZING OF THESE HEAT EXCHANGERS.
All these heat exchangers are performing successfully in the Supersonic air craft developed by Aeronautical Development Agency ,LCA TEJAS, and have clocked hundreds of flight hours. India is one of the few countries which have such a sophisticated technology.
My association with this project was in the initial brazing trials as I left BHPV in 1995. Credit should go to R&D team led by Mr. Panigrahi DGM(R&D) who completed the project. Recently ADA has placed an order worth Rs.20 crores for a few sets of these heat exchangers.
The minimum core weight of the aluminium heat exchanger(Liquid-Air HE) was o.28 Kg and the finished weight of the same heat exchanger was 0.85 Kg.
The maximum core weight of the aluminium heat exchanger(Secondary HE) was 8.78 Kg the finished weight was 12.0 Kg.
The aluminium fins are as thin as 0,0762 mm.
There were a number of stainless steel heat exchangers.
The minimum core weight of the heat exchanger(Precooler) was 8.8 Kg and the finished weight was 12.0 Kg.
The maximum core weight(Primary HE} was 15.6 Kg and the maximum finished weight was 23.0 Kg.
The fin thickness was 0.0762 mm.
If you look at the thickness of the fins the difficulty in brazing can be gauged. CLOSE CONTROL OF THE BRAZING TEMPERATURE WAS ESSENTIAL FOR THE SUCCESS OF THE BRAZING OF THESE HEAT EXCHANGERS.
All these heat exchangers are performing successfully in the Supersonic air craft developed by Aeronautical Development Agency ,LCA TEJAS, and have clocked hundreds of flight hours. India is one of the few countries which have such a sophisticated technology.
My association with this project was in the initial brazing trials as I left BHPV in 1995. Credit should go to R&D team led by Mr. Panigrahi DGM(R&D) who completed the project. Recently ADA has placed an order worth Rs.20 crores for a few sets of these heat exchangers.
Friday, July 10, 2009
Building vacuum furnace
Imported vacuum furnaces are very expensive. Hence we decided to build a vacuum furnace in-house.
A vacuum furnace can be divided in to three subsystems:
1. A double walled chamber to create vacuum and maintain vacuum.
2. Heating system consisting of electrical heating elements and shields to reflect the heat inwards.
3. Power supply and control gear to maintain required temperature in the furnace.
We looked at our strengths and weaknesses to build the vacuum furnace.
We had people who are good at building vacuum tight vessels.
We had people who can design the vacuum system as well as size up the required
vacuum pumps
One of our engineers came forward to design the heating elements.
What we lacked was people who can design the control system.
We decided to off-load control system to a professional company.
Taking in to account the brazing requirement we firmed up the size of the vacuum furnace as follows;
External size : 1200mmID x 800mm long.
Hot zone: 450mm x 450mm x 450mm
Vacuum: 5 x 10-4 mbar
Maximum power required: 60kw.
We arrived at this figure to take in to account the rapid rate of of heating needed for aluminium brazing.
Largest size that can be loaded: 250mm x 250mm x 250mm.
The furnace was double walled furnace with the inner shell of stainless steel and the outer shell of carbon steel.Water circulated in the annular space. Several feed throughs were provided for electrical connections,thermocouples and vacuum gauge.
Vacuum chamber with all the feed throughs were subjected helium leak test.
Vacuum system consisted of a fore vacuum pump, roots blower and a diffusion pump.
The control system was designed to take care of starting the pumps, raising the temperature in the furnace at a controlled rate,holding the temperature constant during brazing and shutting down the heating at a controlled rate. In addition temperature was constantly monitored from the thermocouples fixed in the vacuum chamber. We calibrated the furnace and started our brazing activities.
We built one more high temperature vacuum brazing furnace later to vacuum braze stainless steel These furnaces are in no way inferior to imported furnaces.
We will give details of heat exchangers brazed in the next blog.
A vacuum furnace can be divided in to three subsystems:
1. A double walled chamber to create vacuum and maintain vacuum.
2. Heating system consisting of electrical heating elements and shields to reflect the heat inwards.
3. Power supply and control gear to maintain required temperature in the furnace.
We looked at our strengths and weaknesses to build the vacuum furnace.
We had people who are good at building vacuum tight vessels.
We had people who can design the vacuum system as well as size up the required
vacuum pumps
One of our engineers came forward to design the heating elements.
What we lacked was people who can design the control system.
We decided to off-load control system to a professional company.
Taking in to account the brazing requirement we firmed up the size of the vacuum furnace as follows;
External size : 1200mmID x 800mm long.
Hot zone: 450mm x 450mm x 450mm
Vacuum: 5 x 10-4 mbar
Maximum power required: 60kw.
We arrived at this figure to take in to account the rapid rate of of heating needed for aluminium brazing.
Largest size that can be loaded: 250mm x 250mm x 250mm.
The furnace was double walled furnace with the inner shell of stainless steel and the outer shell of carbon steel.Water circulated in the annular space. Several feed throughs were provided for electrical connections,thermocouples and vacuum gauge.
Vacuum chamber with all the feed throughs were subjected helium leak test.
Vacuum system consisted of a fore vacuum pump, roots blower and a diffusion pump.
The control system was designed to take care of starting the pumps, raising the temperature in the furnace at a controlled rate,holding the temperature constant during brazing and shutting down the heating at a controlled rate. In addition temperature was constantly monitored from the thermocouples fixed in the vacuum chamber. We calibrated the furnace and started our brazing activities.
We built one more high temperature vacuum brazing furnace later to vacuum braze stainless steel These furnaces are in no way inferior to imported furnaces.
We will give details of heat exchangers brazed in the next blog.
Wednesday, July 8, 2009
vacuum brazed aluminium heat exhangers for aero space applications
Aeronautical Development Agency gave R&D of BHPV a development contract for the design of compact heat exchangers for the supersonic air craft which they were designing.The heat exchangers were to be fitted in an envelope volume specified by ADA. The smallest aluminium heat exchanger had dimensions of 130mm x 30mm x 55mm and the largest heat exchanger had dimensions of 250mm x 140mm x 370mm.
The smallest stainless steel heat exchanger had dimensions of 175mm x 118mm x 200mm and the largest heat exchanger had dimensions of 250mm x 140m x 282 mm.
The challenge was to optimise the design with in the space provided so that the heat exchangers meet the heat dissipating requirements. Our design engineers developed computer programmes to optimise the heat exchangers. It took us over an year to fit all the heat exchangers in the given envelope. Our work was finished.
Brazing of the heat exchangers was the responsibility of another metallurgical laboratory in the defence sector. ADA financed procuring a vacuum furnace for aluminum brazing. Even after several trials over a period of one year they were no where near achieving the brazing. The scientists in the laboratory were so secretive that they did not want us to see the brazing furnace. After much pursuation we were allowed to visit the laboratory where brazing was being carried out. Our visit convinced us that the brazing furnace is defective which was the cause for their failure in brazing. Even after several attempts the laboratory was not successful in brazing. At that time we made a proposal to ADA. We proposed that the brazing also should be a part of our design contract. ADA's scope was to import the components for brazing and supply to us.Once we acheved brazing the technology was the property of BHPV. ADA agreed to our proposal. Imported vacuum brazing furnaces are very expensive and hence we decided to manufacture a brazing furnace designed by us. The next blog describes how we went about the design of the vacuum brazing furnace.
The smallest stainless steel heat exchanger had dimensions of 175mm x 118mm x 200mm and the largest heat exchanger had dimensions of 250mm x 140m x 282 mm.
The challenge was to optimise the design with in the space provided so that the heat exchangers meet the heat dissipating requirements. Our design engineers developed computer programmes to optimise the heat exchangers. It took us over an year to fit all the heat exchangers in the given envelope. Our work was finished.
Brazing of the heat exchangers was the responsibility of another metallurgical laboratory in the defence sector. ADA financed procuring a vacuum furnace for aluminum brazing. Even after several trials over a period of one year they were no where near achieving the brazing. The scientists in the laboratory were so secretive that they did not want us to see the brazing furnace. After much pursuation we were allowed to visit the laboratory where brazing was being carried out. Our visit convinced us that the brazing furnace is defective which was the cause for their failure in brazing. Even after several attempts the laboratory was not successful in brazing. At that time we made a proposal to ADA. We proposed that the brazing also should be a part of our design contract. ADA's scope was to import the components for brazing and supply to us.Once we acheved brazing the technology was the property of BHPV. ADA agreed to our proposal. Imported vacuum brazing furnaces are very expensive and hence we decided to manufacture a brazing furnace designed by us. The next blog describes how we went about the design of the vacuum brazing furnace.
Thursday, July 2, 2009
Machinery and tools designed for the manufacture of cryo containers
One of the most difficult operations in the manufacture of cryo containers was the winding of super insulated blanket on the inner vessel.
One roll of aluminum foil and one roll of paper was mounted on a frame 180 degrees apart. This frame had provision for adjusting the tension to release paper and foil at required rate. The frame was connected to a gear box through a drive to rotate at a slow speed. Separately from this frame a shaft was mounted on another drive rotating at a slow speed. This shaft can be tilted at various angles up or down. The inner vessel was mounted on this shaft.
By varying the inclination and the speed of the shaft one can vary the pitch at which foil and paper can be wound on the inner vessel of the cryo container. By varying the tension we can wind the paper and foil tightly or otherwise. This machine was a marvelous piece of development.
We needed one more tool.This tool should allow the assembled cryo container to be evacuated and seal the evacuated vessel. He designed a gadget which met these conditions.
The cryo containers required heating to accelerate degassing and remove moisture in the space between inner vessel and the outer vessel. A system was developed to heat and evacuate a number of cryo containers simultaneously. Heating temperature was controlled by a number of thermocouples. During evacuation vacuum was monitored continuously.
With all these systems in place we manufactured and sold hundreds of cryo containers to various customers.
This development gave us confidence to enter a new field of transporting liquid nitrogen and liquid oxygen over long distances without much loss.
One roll of aluminum foil and one roll of paper was mounted on a frame 180 degrees apart. This frame had provision for adjusting the tension to release paper and foil at required rate. The frame was connected to a gear box through a drive to rotate at a slow speed. Separately from this frame a shaft was mounted on another drive rotating at a slow speed. This shaft can be tilted at various angles up or down. The inner vessel was mounted on this shaft.
By varying the inclination and the speed of the shaft one can vary the pitch at which foil and paper can be wound on the inner vessel of the cryo container. By varying the tension we can wind the paper and foil tightly or otherwise. This machine was a marvelous piece of development.
We needed one more tool.This tool should allow the assembled cryo container to be evacuated and seal the evacuated vessel. He designed a gadget which met these conditions.
The cryo containers required heating to accelerate degassing and remove moisture in the space between inner vessel and the outer vessel. A system was developed to heat and evacuate a number of cryo containers simultaneously. Heating temperature was controlled by a number of thermocouples. During evacuation vacuum was monitored continuously.
With all these systems in place we manufactured and sold hundreds of cryo containers to various customers.
This development gave us confidence to enter a new field of transporting liquid nitrogen and liquid oxygen over long distances without much loss.
Tuesday, June 30, 2009
superinsulsting cryo contaikners
In an ordinary glass thermos flask heat transfer from the hot or cold liquid takes place by conduction, convection and radiation. Heat is conducted by the neck of the thermos flak. Heat is lost by convection which is minimized by evacuating the system and radiation is controlled by giving a mirror finish to the outer wall of the inner vessel and inner wall of the outer vessel.In spite of these precautions heat is lost. These techniques are not effective if you have to store liquid nitrogen for prolonged periods. Liquid Nitrogen boils at -193 deg C.If the evaporation rate from the liquid Nitrogen container is 2 to 3 per cent per day conventional manufacturing techniques of glass thermos flask will not meet the evapolration rate as mentioned above. Hence an advanced manufatureing method is empolyed as described below.
A thin low thermal conductivity fiber glass tube is attached to to the inner aluminium shell by an epoxy resin capable of withstanding liquid nitrogen temperature. This fabrication method reduces conduction loss.
Multiple radiation shields reduce radiation loss. Multiple radiation shields consist of alternate layers of 5 micron polished aluminium strips 60 mm wide and low thermal conductivity cellulose paper wound on the inner shell in a pre determined fashion. The thickness of this blanket is determined by experimentation in a calorimeter to give minimum cold loss. A number of holes are punched through this blanket to allow air to escape during evacuation. The inner shell so prepared is connected to the outer shell by low thermal conductivity fiber glass tube.
Heat transfer through convection is reduced by evacuating the space between inner shell and the outer shell to a low vacuum of about 10 to the power minus 4 mm Hg.
A getter is used to take care of the out gassing that may occur during evacuation The entire assembly is heated from outside to aid degassing during evacuation.Evacuation may take one two days to reach the desired vacuum level. After checking the vacuum level heating is stopped and the container is allowed to come to room temperature. The container is checked for evaporation loss and the container is ready for dispatch to customer.
A thin low thermal conductivity fiber glass tube is attached to to the inner aluminium shell by an epoxy resin capable of withstanding liquid nitrogen temperature. This fabrication method reduces conduction loss.
Multiple radiation shields reduce radiation loss. Multiple radiation shields consist of alternate layers of 5 micron polished aluminium strips 60 mm wide and low thermal conductivity cellulose paper wound on the inner shell in a pre determined fashion. The thickness of this blanket is determined by experimentation in a calorimeter to give minimum cold loss. A number of holes are punched through this blanket to allow air to escape during evacuation. The inner shell so prepared is connected to the outer shell by low thermal conductivity fiber glass tube.
Heat transfer through convection is reduced by evacuating the space between inner shell and the outer shell to a low vacuum of about 10 to the power minus 4 mm Hg.
A getter is used to take care of the out gassing that may occur during evacuation The entire assembly is heated from outside to aid degassing during evacuation.Evacuation may take one two days to reach the desired vacuum level. After checking the vacuum level heating is stopped and the container is allowed to come to room temperature. The container is checked for evaporation loss and the container is ready for dispatch to customer.
Saturday, June 20, 2009
Cryo containers
Operation Flood was conceived for increasing the availability of milk and milk products in the country.Artificial insemination of cows was a part of this programme.Semen from healthy bulls was collected, stored in liquid nitrogen containers and transported to various animal husbandry centers which in turn distributed it to various user centers.These portable liquid nitrogen containers are also called as cryo containers.
The cryo container is similar to a thermos flask.There is an inner container and an outer container. The inner container is connected to the outer container by a low thermal conductivity fiber tube. Just as in the thermos flask the gap between the inner and the outer container was evacuated to a low pressure. But there is one main difference.
In a conventional thermos flask space between the inner and outer container is evacuated to reduce heat transfer. The outer wall of the inner glass container and inner wall of the outer glass container is silvered to reduce the heat loss by radiation. But in spite of vacuum some heat is transferred by convection.Heat is also lost by conduction through the neck. In a cryo container all these losses are reduced to a low value by unique design which we shall see later.
The cryo container is similar to a thermos flask.There is an inner container and an outer container. The inner container is connected to the outer container by a low thermal conductivity fiber tube. Just as in the thermos flask the gap between the inner and the outer container was evacuated to a low pressure. But there is one main difference.
In a conventional thermos flask space between the inner and outer container is evacuated to reduce heat transfer. The outer wall of the inner glass container and inner wall of the outer glass container is silvered to reduce the heat loss by radiation. But in spite of vacuum some heat is transferred by convection.Heat is also lost by conduction through the neck. In a cryo container all these losses are reduced to a low value by unique design which we shall see later.
Site stress relieving at Mathura Refinery
Our first opportunity for stress relieving of sphere was given by the management of Mathura Refinery. We had built a number of spheres for storage of LPG. Each sphere was 18 meters in diameter with a wall thickness of 65mm.
When we arrived at Mathura refinery our team was interviewed by the management to find out whether we knew our business or not. After satisfying themselves we were given permission to go ahead and start the work.
LPG was supplied by an LPG tanker. Since the withdrawal of LPG was very high natural evaporation from the tanker was inadequate.Hence we connected the LPG tanker to an evaporator which drew the liquid from the tank and the liquid passed through heat exchanger converting the liquid in to gas. Air for combustion was supplied by a blower. We had a stand by blower in case the blower failed during operation.
A number of thermocouples were fixed on the sphere and these thermocouples were connected to strip chart recorders. The entire sphere was insulated.We fired the burner out side the sphere to test its performance at various gas and air flows. After ascertaining the performance we fixed the burner at the bottom of the sphere. The top exit of the sphere was kept partially open for the combustion gases to escape. After checking all connections we fired the burner. The gas and air flow was adjusted to give a temperature raise of around 50 deg C per hour.As the temperature reached the specified stress relieving temperature the rate of heating was brought down considerably and once the temperature reached the stress relieving temperature the flame was adjusted to give a heat input which was just sufficient to compensate for heat loss from the sphere.After maintaining the temperature constant for specified time the heat input was slowly reduced and when the temperature reached around 300 deg C the burner was was switched off and the sphere was allowed to cool to room temperature. The cycle took nearly 20 hours.
Full credit of successful stress relieving should go to the head of chemical engineering and his dedicated team. Later a number spheres in Mathura Refinery were stress relieved using the same technology. We stopped requesting foreign help. More than 100 spheres have been stress relieved by now using the technology developed by R&D.
When we arrived at Mathura refinery our team was interviewed by the management to find out whether we knew our business or not. After satisfying themselves we were given permission to go ahead and start the work.
LPG was supplied by an LPG tanker. Since the withdrawal of LPG was very high natural evaporation from the tanker was inadequate.Hence we connected the LPG tanker to an evaporator which drew the liquid from the tank and the liquid passed through heat exchanger converting the liquid in to gas. Air for combustion was supplied by a blower. We had a stand by blower in case the blower failed during operation.
A number of thermocouples were fixed on the sphere and these thermocouples were connected to strip chart recorders. The entire sphere was insulated.We fired the burner out side the sphere to test its performance at various gas and air flows. After ascertaining the performance we fixed the burner at the bottom of the sphere. The top exit of the sphere was kept partially open for the combustion gases to escape. After checking all connections we fired the burner. The gas and air flow was adjusted to give a temperature raise of around 50 deg C per hour.As the temperature reached the specified stress relieving temperature the rate of heating was brought down considerably and once the temperature reached the stress relieving temperature the flame was adjusted to give a heat input which was just sufficient to compensate for heat loss from the sphere.After maintaining the temperature constant for specified time the heat input was slowly reduced and when the temperature reached around 300 deg C the burner was was switched off and the sphere was allowed to cool to room temperature. The cycle took nearly 20 hours.
Full credit of successful stress relieving should go to the head of chemical engineering and his dedicated team. Later a number spheres in Mathura Refinery were stress relieved using the same technology. We stopped requesting foreign help. More than 100 spheres have been stress relieved by now using the technology developed by R&D.
Wednesday, June 17, 2009
High heat flux and high velocity burner
Preliminary calculations indicated that the burner should meet the following conditions:
Heat output of the burner : I million BTU per hour.
The combustion must be complete.
The hot gases coming out of the burner must be given a tangential velocity so that the walls of the sphere gets scrubbed by the hot gases.
The flame must be stable at all conditions of air flow.
The burner must be easy to start in case of flame outage during stress relieving.
In case the air supply fails accidentally, the gas flow must stop immediately.
With such stringent conditions, we realised that we do not have the expertise in designing a stable high velocity high heat flux burner. We approached Indian Institute of Science, Bangalore and National Aerospace Laboratories, Bangalore for designing the burner. A development contract was placed with the understanding that the manufacturing of burner is our responsibility. Both the laboratories started the work simultaneously and with in one year we had two burners of different designs each meeting laid down specifications.
Meanwhile we developed the burner management system The burner management system consisted of an electronic system with infrared sensors to monitor the flame and activate a hooter in case of flame outage and shuts off LPG flow immediately. It also supplied high frequency power to the spark plug to ignite the flame. We did extensive trials with burner simulating all conditions of stress relieving and ensured that the burner can operate with out any problem. Then we were ready for site stress relieving.
Heat output of the burner : I million BTU per hour.
The combustion must be complete.
The hot gases coming out of the burner must be given a tangential velocity so that the walls of the sphere gets scrubbed by the hot gases.
The flame must be stable at all conditions of air flow.
The burner must be easy to start in case of flame outage during stress relieving.
In case the air supply fails accidentally, the gas flow must stop immediately.
With such stringent conditions, we realised that we do not have the expertise in designing a stable high velocity high heat flux burner. We approached Indian Institute of Science, Bangalore and National Aerospace Laboratories, Bangalore for designing the burner. A development contract was placed with the understanding that the manufacturing of burner is our responsibility. Both the laboratories started the work simultaneously and with in one year we had two burners of different designs each meeting laid down specifications.
Meanwhile we developed the burner management system The burner management system consisted of an electronic system with infrared sensors to monitor the flame and activate a hooter in case of flame outage and shuts off LPG flow immediately. It also supplied high frequency power to the spark plug to ignite the flame. We did extensive trials with burner simulating all conditions of stress relieving and ensured that the burner can operate with out any problem. Then we were ready for site stress relieving.
Monday, June 15, 2009
How we developed technology for site stress of sphere.
In refineries and fertilizer plants liquefied petroleum gas and ethylene are stored at room temperature in spheres. These spheres are built from individual steel petals hot or cold pressed and assembled at site Depending upon the pressure and the diameter of the sphere the steel plate thickness can be as high as 65mm. The total weight of the sphere can be few hundred tons. BHPV,for some time had a monopoly in this business. After welding the sphere it has to be stress relieved. Stress relieving involves heating the sphere to a temperature of 580degC to 620degC depending on the plate thickness and composition and holding at this temperature for one two hours depending upon the thickness and cooling it slowly to room temperature. Since the sphere cannot be put in a furnace, the sphere itself is converted in to a furnace. A high velocity gas burner is fitted at the bottom of the sphere. The sphere is externally insulated and a number of thermocouples are fixed on the surface of the sphere which are used to monitor the sphere temperature.
The heart of the process is the high velocity gas burner. Initially a company from UK was contracted to carry out the stress relieving. This involved spending foreign exchange which was, before 1990 was not available easily and the logistics of getting the UK firm to come and perform stress relieving was very daunting.
The Management gave the assignment to R&D to develop the burner and stress relieving technology. We decided that chemical engineering group should handle this assignment.
The heart of the process is the high velocity gas burner. Initially a company from UK was contracted to carry out the stress relieving. This involved spending foreign exchange which was, before 1990 was not available easily and the logistics of getting the UK firm to come and perform stress relieving was very daunting.
The Management gave the assignment to R&D to develop the burner and stress relieving technology. We decided that chemical engineering group should handle this assignment.
Friday, June 12, 2009
conclusions
You have to remeber that all this development was done in mid 1980's.A research institute set up with UNDP help was publicising, at that time, that they have successfully repaired a tolling bell of a church and put it back in to operation!
Our success can be attributed to a team of young graduates who came to us with no baggage. They were willing to try any thing new. They were not afraid of failures as Management had realised that when you are working in high technolgy areas some failures have to be accepted.
The other factor responsible for our success was the working atmosphere in R&D. Whenever we met with a problem we used to call for a meeting of all people from various sections of R&D and the problem was thrown open for discussions. Welding engineers suggested solutions to chemical engineers and chemical engineers suggested solutions to manufacturing engeneers etc!. Some times we involved workers to suggest alternate methods of manufacturing. This approach helped us to think out of the box.
In the next blogs you can read the various pathbreaking developments we did in R&D.
Our success can be attributed to a team of young graduates who came to us with no baggage. They were willing to try any thing new. They were not afraid of failures as Management had realised that when you are working in high technolgy areas some failures have to be accepted.
The other factor responsible for our success was the working atmosphere in R&D. Whenever we met with a problem we used to call for a meeting of all people from various sections of R&D and the problem was thrown open for discussions. Welding engineers suggested solutions to chemical engineers and chemical engineers suggested solutions to manufacturing engeneers etc!. Some times we involved workers to suggest alternate methods of manufacturing. This approach helped us to think out of the box.
In the next blogs you can read the various pathbreaking developments we did in R&D.
Wednesday, June 10, 2009
Hydraulic testing of gas bottles
The acid test of the development of gas bottle is the hydraulic test,burst test and the stretch.
Out of the many bottles which had passed radiography, five bottles were picked at random by the customer and these five bottles formed a lot which are sent for hydraulic test. One bottle picked from this lot randomly is sent for burst test after hydraulic test.
The hydraulic test pressure is in excess of 350 atm. and burst pressure is in excess of 700 atm. Since these pressure are very high, for the sake of safety, the gas bottle prepared for hydraulic test was kept in a pit and covered with sand bags.The hydraulic pressure has to be raised in an incremental manner as given in the specification.We used a computer controlled hydraulic testing machine.The Incremental pressure raise and the final hydraulic pressure was programmed. Once the hydraulic test was started the machine took over and stopped when the desired hydraulic pressure was achieved. The hydraulic test continued to establish the burst pressure of the selected bottle. At the end of the test the hydraulic test pressure and burst pressure was read out from the machine. The full testing sequence was recorded and a print out could be taken at the end of the test.
Initially, when we used commercially pure titanium wire for welding larger bottle of 8.5mm thickness we had some failures.But once we switched over to 3Al-2V filler wire we did not have a single failure.
Hundreds of bottles have been supplied to DRDL for their use. Even today BHPV is the preferred vendor for these bottles.
Out of the many bottles which had passed radiography, five bottles were picked at random by the customer and these five bottles formed a lot which are sent for hydraulic test. One bottle picked from this lot randomly is sent for burst test after hydraulic test.
The hydraulic test pressure is in excess of 350 atm. and burst pressure is in excess of 700 atm. Since these pressure are very high, for the sake of safety, the gas bottle prepared for hydraulic test was kept in a pit and covered with sand bags.The hydraulic pressure has to be raised in an incremental manner as given in the specification.We used a computer controlled hydraulic testing machine.The Incremental pressure raise and the final hydraulic pressure was programmed. Once the hydraulic test was started the machine took over and stopped when the desired hydraulic pressure was achieved. The hydraulic test continued to establish the burst pressure of the selected bottle. At the end of the test the hydraulic test pressure and burst pressure was read out from the machine. The full testing sequence was recorded and a print out could be taken at the end of the test.
Initially, when we used commercially pure titanium wire for welding larger bottle of 8.5mm thickness we had some failures.But once we switched over to 3Al-2V filler wire we did not have a single failure.
Hundreds of bottles have been supplied to DRDL for their use. Even today BHPV is the preferred vendor for these bottles.
Tuesday, June 9, 2009
Welding gas bottles
A trailing shield is essential for welding titanium or titanium alloy. In this method of welding certain amount of oxygen and nitrogen will be picked up from air by the weld.The pick up of these gases lowers the fracture toughness of the welds. For aerospace applications welding in open air is not allowed. Hence we used a chamber for welding.The welding chamber is a plexiglass dome mounted on a steel base.The chamber is connected to a vacuum pump which can evacuate the chamber at a fast rate.There are several feed throughs which allow current tobe carried to the welding torch, a welding positioner,an electric lamp etc. and a system of valves for gas inlet,gas outlet and evacuation of the chamber. The welder stands outside and performs welding through a glove port.
The chamber is first evacuated by a vacuum pump to a low pressure and then back filled with high purity argon.This argon filled chamber is again evacuated and high purity argon is filled for the second time.The chamber is maintained at a positive presuure by the flow of a small quantity of gas. The welder stands outside the chamber and manipulates the welding torch through a glove port and carries out welding
The machined hemispheres are sent to the metrology department to check uniformity of thickness and contour. If these are within the permissible limits,they are taken up for welding. Before the spheres are welded they are thoroughly degreased and the weld edges are etched with a solution of HF-HNO3. The welding wires are also degreased and etched with the above etching solutions.
Assembled hemispheres, filler wire and the other tools for welding are placed in the chamber before the start of the evacuation.To remove any residual oxygen and nitrogen in the chamber the welder welds on a scrap titanium plate. The welded titanium plate acts as a getter absorbing the residual gases, if any ,in the chamber. The welding operator standing out side lays the root bead by manipulating the welding torch.When the root bead is finished, the welded sphere is taken out and sent for radiography. If the radiography is cleared the sphere is taken for further welding in the chamber. For higher thickness spheres one more radiography test is performed at the mid thickness of the weld. These tests are done to detect any defects and rectify them and not wait till the sphere is completely welded. Specification allows rectification of the defects only two times. After the welding is completed the job is allowed to cool in the chamber. Then the job is taken out and sent for final radiography.If the bottle has passed the radiography test bottle is sent for hydraulic testing.
The chamber is first evacuated by a vacuum pump to a low pressure and then back filled with high purity argon.This argon filled chamber is again evacuated and high purity argon is filled for the second time.The chamber is maintained at a positive presuure by the flow of a small quantity of gas. The welder stands outside the chamber and manipulates the welding torch through a glove port and carries out welding
The machined hemispheres are sent to the metrology department to check uniformity of thickness and contour. If these are within the permissible limits,they are taken up for welding. Before the spheres are welded they are thoroughly degreased and the weld edges are etched with a solution of HF-HNO3. The welding wires are also degreased and etched with the above etching solutions.
Assembled hemispheres, filler wire and the other tools for welding are placed in the chamber before the start of the evacuation.To remove any residual oxygen and nitrogen in the chamber the welder welds on a scrap titanium plate. The welded titanium plate acts as a getter absorbing the residual gases, if any ,in the chamber. The welding operator standing out side lays the root bead by manipulating the welding torch.When the root bead is finished, the welded sphere is taken out and sent for radiography. If the radiography is cleared the sphere is taken for further welding in the chamber. For higher thickness spheres one more radiography test is performed at the mid thickness of the weld. These tests are done to detect any defects and rectify them and not wait till the sphere is completely welded. Specification allows rectification of the defects only two times. After the welding is completed the job is allowed to cool in the chamber. Then the job is taken out and sent for final radiography.If the bottle has passed the radiography test bottle is sent for hydraulic testing.
Saturday, June 6, 2009
Establishing welding procedure
After the hemisphere was machined,on each hemisphere one nozzle was welded in the specified location. These nozzles are specially machined to close tolerances.The nozzles have special threads so that once the gas is filled in to the bottle and closed by a plug the leakage from the gas bottle is almost zero.Two
hemispheres were tack welded and was ready for final welding.
We had to develop two types of gas bottles,namely,a smaller diameter gas bottle with a wall thickness of 5.5-0+0.5mm and a larger diameter gas bottle with a wall thickness of 8.5 -0+0.5mm
Customer had specified that the gas bottle should meet a certain stretch value at hydraulic test. This could only be achieved if weld test coupon had an elongation in excess of 8percent.
Welding procedure was established for a nominal thickness of 5.5mm and 8.5mm. When the test coupon was welded with matching composition filler wire.i.e,6Al-4V filler wire the desired elongation was not achievable.
When 5.5mm test coupon was welded with commercially pure titanium wire we could achieve the required elongation and the UTS as given in the specification. The weld bead picked up aluminium and vanadium from the parent plate which was responsible for meeting the required UTS and elongation.
8.5mm test coupon was welded with commercially pure titanium filler wire. The test coupon failed to develop the specified UTS. Detailed metallurgical analysis of the weld bead led to the conclusion that enough aluminium and vanadium was not picked up from the base plate as it happened in case of 5.5mm thickness plate. At the center of the weld bead the chemical composition was pure titanium and not an alloy of titanium.This was the cause for lower UTS observed. We realized that somehow we have to introduce aluminum and vanadium in to the weld without using 6Al-4V. We hit upon the idea of using two wires twisted together,one of commercially pure titanium and another of 6Al-4V and using the composite wire as filler wire for welding.When welded with this composite wire the test coupons passed all the tests.
We did extensive tests to ensure that the weld bead deposited with the combination wire did not lead to non uniformity of composition or gross segregation in weld bead.
We welded several gas bottles with this composite wire and the bottles passed all the tests.
Later the customer supplied TIG wire of composition Ti-3Al-2V which was used for welding large diameter bottles.
hemispheres were tack welded and was ready for final welding.
We had to develop two types of gas bottles,namely,a smaller diameter gas bottle with a wall thickness of 5.5-0+0.5mm and a larger diameter gas bottle with a wall thickness of 8.5 -0+0.5mm
Customer had specified that the gas bottle should meet a certain stretch value at hydraulic test. This could only be achieved if weld test coupon had an elongation in excess of 8percent.
Welding procedure was established for a nominal thickness of 5.5mm and 8.5mm. When the test coupon was welded with matching composition filler wire.i.e,6Al-4V filler wire the desired elongation was not achievable.
When 5.5mm test coupon was welded with commercially pure titanium wire we could achieve the required elongation and the UTS as given in the specification. The weld bead picked up aluminium and vanadium from the parent plate which was responsible for meeting the required UTS and elongation.
8.5mm test coupon was welded with commercially pure titanium filler wire. The test coupon failed to develop the specified UTS. Detailed metallurgical analysis of the weld bead led to the conclusion that enough aluminium and vanadium was not picked up from the base plate as it happened in case of 5.5mm thickness plate. At the center of the weld bead the chemical composition was pure titanium and not an alloy of titanium.This was the cause for lower UTS observed. We realized that somehow we have to introduce aluminum and vanadium in to the weld without using 6Al-4V. We hit upon the idea of using two wires twisted together,one of commercially pure titanium and another of 6Al-4V and using the composite wire as filler wire for welding.When welded with this composite wire the test coupons passed all the tests.
We did extensive tests to ensure that the weld bead deposited with the combination wire did not lead to non uniformity of composition or gross segregation in weld bead.
We welded several gas bottles with this composite wire and the bottles passed all the tests.
Later the customer supplied TIG wire of composition Ti-3Al-2V which was used for welding large diameter bottles.
Friday, June 5, 2009
Machining the hemisphere
After the hemisphere was tested ultrasonically to ensure that there are no buried cracks, the hemisphere was sent for machining. Machining was done to removes the gas saturated layer and to maintain the desired wall thickness. Normally machining of hemisphere is done on a CNC lathe. We did not posses a CNC machine. But we had a brilliant engineer. He came forward and took the challenge of machining using the copying attachment to the ordinary lathe we had in the work shop.As the machining parameters such as speed,feed etc.are similar for machining stainless steel and Ti-6Al-4V he first experimented with a stainless steel hemisphere of the same diameter as the titaniun alloy hemisphere. In two or three trials he achieved the dimensions and shape. Then he took up the task of machining titanium sphere with the knowledge he had gained from copy turning stainless steel hemisphere.He could achieve the required shape as well as the required uniformity in thickness.We crossed one more hurdle. We were now ready for welding.
After the production process of machining was stabilized we invested in a custom built CNC machining center.
After the production process of machining was stabilized we invested in a custom built CNC machining center.
Thursday, June 4, 2009
Preparation of the blank
After deciding about the thickness of the blank, the next step was to prepare the blank for pressing.
The diameter of the hemisphere to be pressed decided the diameter of the flat plate required for forming. This diameter was further increased by about 10-15mm. The blank was cut by an oxyacetylene gas torch. When the blank is cut by oxyacetylene
gas torch two important points are to be kept in mind,namely, gas saturated layer and minute cracks that develop while cutting. Gas saturated layer increases the hardness and minute cracks can grow during pressing. Hence the blanks were machined till the gas saturated layer was removed and dye penetrant test was carried out.If no cracks are visible the blank is ready for pressing.
Elongation of Ti-6Al-4V increases with temperature.In the temperature range of 850-950 degC, the material will be in the super plastic range. Hence the blanks were heated in a gas fired furnace with excess oxygen to a temperature around 850degC.
When the blank is taken out from the furnace the blank loses temperature rapidly by radiation. When the blank is placed on the die for pressing the blank loses temperature by conduction. As the temperature falls the elongation of the material also falls. Our aim is to see that the blank does not fall below 500degC Hence to reduce conduction loss the top punch and the bottom die are heated to a temperature of 500degC approx.After ensuring that the dies have reached the desired temperature the heated blank was transferred rapidly to the press and the pressing was done without any loss of time. The pressed hemisphere was checked for approximate dimensions and was sent for shot blasting. After shot blasting dye penetrant test and ultrasonic test was carried out detect any cracks before the hemisphere went for machining.
The diameter of the hemisphere to be pressed decided the diameter of the flat plate required for forming. This diameter was further increased by about 10-15mm. The blank was cut by an oxyacetylene gas torch. When the blank is cut by oxyacetylene
gas torch two important points are to be kept in mind,namely, gas saturated layer and minute cracks that develop while cutting. Gas saturated layer increases the hardness and minute cracks can grow during pressing. Hence the blanks were machined till the gas saturated layer was removed and dye penetrant test was carried out.If no cracks are visible the blank is ready for pressing.
Elongation of Ti-6Al-4V increases with temperature.In the temperature range of 850-950 degC, the material will be in the super plastic range. Hence the blanks were heated in a gas fired furnace with excess oxygen to a temperature around 850degC.
When the blank is taken out from the furnace the blank loses temperature rapidly by radiation. When the blank is placed on the die for pressing the blank loses temperature by conduction. As the temperature falls the elongation of the material also falls. Our aim is to see that the blank does not fall below 500degC Hence to reduce conduction loss the top punch and the bottom die are heated to a temperature of 500degC approx.After ensuring that the dies have reached the desired temperature the heated blank was transferred rapidly to the press and the pressing was done without any loss of time. The pressed hemisphere was checked for approximate dimensions and was sent for shot blasting. After shot blasting dye penetrant test and ultrasonic test was carried out detect any cracks before the hemisphere went for machining.
Saturday, May 30, 2009
HOW WE HOT PRESSED A HEMISPHERE FROM A SHEET OF Ti-6Al-4V
Our success in welding Ti-6Al-4V was noticed by Defense Research and Development Organization(DRDL) in Hyderabad. They had a need for spherical titanium gas bottles for their missile applications. DRDL was importing these bottles from France. The hemispheres were forged in France and after machining the two hemispheres were welded by Electron Beam welding. When DRDL approached R&D of BHPV, we told DRDL that we don't have forging facilities and we have no plans to install an Electron Beam Welding machine but we may able to hot press Ti-6Al-4V hemispheres. machine it to the required contour and weld the hemispheres by conventional TIG welding. We also guaranteed that we will meet their specifications regarding hydraulic test,increase in volume during hydraulic test and burst pressure. DRDL reposed confidence in us and gave us a trial order.
If I look back I wonder the self confidence we had to tackle such a complex problem. We had to develop whole lot of technologies from scratch. We had to develop tools for hot pressing, machining the hemispheres on a lathe to close tolerances and weld the hemispheres. Possibly because our team members were young and full of enthusiasm and self confidence. We will tell you later how we went about the development.
If I look back I wonder the self confidence we had to tackle such a complex problem. We had to develop whole lot of technologies from scratch. We had to develop tools for hot pressing, machining the hemispheres on a lathe to close tolerances and weld the hemispheres. Possibly because our team members were young and full of enthusiasm and self confidence. We will tell you later how we went about the development.
Friday, May 29, 2009
Thursday, May 28, 2009
WELDING Ti-6Al-4V
Welding Ti-6Al-4V
Having mastered welding of commercially pure titanium we decided to continue our work on Ti-6Al-4V alloy of titanium which is called the work horse alloy in defence and aerospace industries.
This alloy has the following mechanical properties:
Ultimate tensile strength: 950MPa or 138kpsi
Yield strength: 880MPa or 128kpsi
Elongation: 10 to 14 percent.
These are typical values. Since Ti-6Al-4V is a heat treatable alloy the above strengths can be increased by suitable heat treatment.
For aerospace applications, the above alloy containing very low oxygen and nitrogen designated as ELI grade(Extra low interstitial) is used.
The welding of Ti-6Al-4V is not different from that of commercially pure titanium except that we used ultra pure argon gas to keep the interstitial low. Ti-6Al-4V is welded by TIG welding using commercially pure titanium filler wire or by matching composition filler wire or by the so called half alloy which is Ti-3Al-2V filler wire. The selection of wire depends upon the final property desired in the final weld.
We welded Ti-6Al-4V in annealed condition, solution annealed and solution annealed and aged condition. We also used commercially pure filler wire, matching composition filler wire and also half alloy wire. Welded test coupons were subjected to extensive testing. Test results were tabulated so that we have data bank to select what type of filler wire to use for a specific application.
The data so collected by us was used for defence application about which I will tell later.
Tuesday, May 26, 2009
Organising R&D in BHPV
I was selected to establish R&D in BHPV. We trnaferred some postgraduate engineers from various department to form the nucleus. Full freedom was given to me to organise the R&D.
We decided to form four groups in consultations with the user groups, namely,
1. Chemical enginering group.
2. Cryogenic engineering group.
3. Manufacturing technology group.
4. Welding technology group.
Chemical engineering group concentrated on the develolpment of computer programmes for the design of various equipment such as heat exchangers, columns etc.
Cryogenic engineering group concentrated on the development of cryogenic equipment such as cryogenic storage systems, liquid nitrogen and oxygen transfer sysytems etc,
Sunday, May 24, 2009
welding titanium
This goes back to 1976. When welding technologists in India were finding it difficult to weld alloy steels we were developing welding technology for commercially pure titanium.
Titanium is a highly reactive material which has great affinity for oxygen and nitrogen. Titanium cannot be welded by shielded metal arc welding. Similarly, at that time neither submerged arc welding or MIG welding. In recent times Russians have developed submerged arc welding technique. The preferred method of welding is by gas tungsten arc welding also called as TIG welding.
Welding titanium is different from welding stainless steel. While welding stainless steel by TIG welding the gas shielding is provided to the weld pool from the gas flowing through the torch and a separate gas flow is provided to the bottom side of the weld (called back purge) to prevent the weldment getting oxidized.
While welding titanium in addition to the the gas flow through the torch and back purge you have what is called a travelling shield.The travelling shield is an attachment fixed to TIG torch which blankets the molten side of the pool as the torch moves forward and also on either side of center of the weld. This is because titanium continues to absorb oxygen and nitrogen right down to temperature down to 500 deg. celsius. When nitrogen and oxygen are absorbed the weldment becomes brittle. The UTS of weldment will be high and hardness increases.
The sucecess of welding titanium depends upon the clealiness you maintain and the design of the trailing shield. We developed a method of designing the trailing shield based on calculated temperature distribution for a given welding parameter. We had developed trailing shields for butt weld, tube to sheet welding, corner welding etc. Using the technolgy developed in
R&D we manufactured titanium lined urea reactor, titanium heat exchangers, titaniun anodes and number of equipments of titanium.
Titanium is a highly reactive material which has great affinity for oxygen and nitrogen. Titanium cannot be welded by shielded metal arc welding. Similarly, at that time neither submerged arc welding or MIG welding. In recent times Russians have developed submerged arc welding technique. The preferred method of welding is by gas tungsten arc welding also called as TIG welding.
Welding titanium is different from welding stainless steel. While welding stainless steel by TIG welding the gas shielding is provided to the weld pool from the gas flowing through the torch and a separate gas flow is provided to the bottom side of the weld (called back purge) to prevent the weldment getting oxidized.
While welding titanium in addition to the the gas flow through the torch and back purge you have what is called a travelling shield.The travelling shield is an attachment fixed to TIG torch which blankets the molten side of the pool as the torch moves forward and also on either side of center of the weld. This is because titanium continues to absorb oxygen and nitrogen right down to temperature down to 500 deg. celsius. When nitrogen and oxygen are absorbed the weldment becomes brittle. The UTS of weldment will be high and hardness increases.
The sucecess of welding titanium depends upon the clealiness you maintain and the design of the trailing shield. We developed a method of designing the trailing shield based on calculated temperature distribution for a given welding parameter. We had developed trailing shields for butt weld, tube to sheet welding, corner welding etc. Using the technolgy developed in
R&D we manufactured titanium lined urea reactor, titanium heat exchangers, titaniun anodes and number of equipments of titanium.
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