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 Even though their method of testing is outdated to satisfy their ego and bail out DMRL we again did several test as per the standards of ordnance board.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.