Studies on Delayed Cracking in Steel Weldments (Report 2)

Prevention of Cracking in Restraint Multi-run Weldments

Abstract

The root cracking in the root-pass welds was studied in the Report 1. It may be too conservative to employ the critical preheating temperature obtained from root-pass cracking tests for the necessary preheating temperature.
In this study, the critical preheating temperatures for preventing cracking in the root-pass welds and multi-run welds have been compared for steels including mild steel, pressure vessel steel and high strength steel. The cracks investigated in these cracking tests include root crack, toe crack and under-head crack.
The findings in this study are as follows:
1) The cad cracking susceptibility of carbon manganese steels and low alloy steels with carbon more than 0.16 % may be better evaluated by Ceq(WES) than PCM. For steels with carbon less than 0.16 %, PCM may be a proper parameter rather than Ceq.
2) The critical preheating temperature for preventing root cracking in multi-run welds is less than that for root-pass welds by 50 to 75°C, mainly because of a decrease in hydrogen accumulation at the root by a post heating effect of subsequent passes.
3) The critical preheating temperature for preventing toe and under-bead cracking in restrained multi-run butt weldments is lower than that for multi-run root cracking, especially in a lower Ceq range.
4) It may be practical to select the preheating and inter-pass temperature based on the toe cracking prevention preheating temperature rather than that for root cracking in root-pass welds.