L51415 Prediction of Weld Crack Susceptibility

The vast majority of research on hydrogen induced cracking has been towards heat affected zone cracking. This has resulted in methods for estimating crack sensitivity of steels through carbon equivalent formulae, schemes for predicting safe welding procedures based on hardness or on hydrogen diffusion, and test techniques for assessing HAZ susceptibility (such as the implant test) that have proved useful in the weldability aspect of steel development. The traditional carbon equivalent formula have proven to be inadequate for some of the modern, lower carbon steels and alternate approaches have recently been suggested. This work assesses the carbon equivalent correlations in which HAZ crack susceptibility of a range of pipeline steels was studied. The results showed that traditional carbon equivalent formula did not rate the steel accurately, and that more recent formula emphasizing the role of carbon were more accurate. It was also observed in the tests that cracking often occurred in the weld metal, thus confusing the use of the test as a HAZ test, but indicating that the weld metal cracking may well control the level of preheat required. Indeed, experience indicates that in many practical situations, and particularly with modern low carbon steels, the required preheat, or the total joint crack susceptibility is controlled by weld metal cracking. This study was made to ascertain the factors that influence the susceptibility of high strength, low alloy (HSLA) steels to hydrogen induced cracking. A small-scale high- restraint, cracking test was used to examine the cracking behavior with six different steels and four electrodes.