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!