TWI Industrial Member Report Summary 225/1983
By A R Jones and P H M Hart
A programme of work was carried out to investigate the validity of predictions for welding procedures for the avoidance of hydrogen cracking, as given by TWI nomogram and BS 5135: 1974 (and the proposed current revision of this standard). Attention was paid to the flux-cored wire (FCW) and submerged-arc processes and to manual metal arc (MMA) welding on thick section plate. Controlled thermal severity (CTS) tests have been carried out primarily to define conditions avoiding heat affected zone (HAZ) cracking using FCW and submerged-arc welding in conjunction with C-Mn-Si-Nb-Al plates of a range of thicknesses (25-50mm) and CE values (0.35-0.45). Manual metal arc welds have been deposited on CTS blocks prepared from l00mm thick C-Mn-Si-Nb-Al plate. Restrained Lehigh type butt welds have been used to investigate the conditions of hydrogen level and preheat/interpass temperature for avoidance of weld metal hydrogen cracking in highly restrained multipass submerged-arc welds. For the consumables used, the results indicate that the present TWI nomogram could be used to predict welding conditions for avoiding HAZ hydrogen cracking for both submerged-arc and flux-cored wire welding processes. For welding of thick section material (>200mm combined thickness), the results indicate that when using Scale A or B hydrogen levels, a minimum preheat of 150°C should be used. The butt weld cracking test showed that for submerged-arc welding of 50mm thick plate at ~3kJ/mm and using Scale C hydrogen levels, preheats of <l00°C predicted from TWI nomogram, should be raised to 100°C to avoid transverse weld metal hydrogen cracking. The original modification of TWI nomogram for use in BS 5135: 1974 (and its revision) is considered appropriate also for FCW and submerged-arc welding. However, for the avoidance of cracking when welding thick sections, and of weld metal hydrogen cracking in restrained submerged-arc welds, the changes proposed above for TWI nomogram should be applied directly to BS 5135:1974 (and its revision). This can be done by using the proposed changes, and also increasing the calculated plate CE value by 0.02.