In late 2007 and early 2008, 2 1/4Cr1MoV heavy reactors fabrication has undergone some weld metal reheat cracking issues that became a serious situation as roughly 25 large vessels were affected. Strong efforts from the whole production chain were put in trying to isolate the root cause of the crack appearance and solve this particular matter. Many investigations were conducted by independent laboratories in the first months of 2008.
In particular, a hot tensile Gleeble® test indicated a decrease in ductility in the critical temperature range of Intermediate Stress Relieving (ISR) treatment (650–680 °C) of the affected welding consumables compared to those that did not cause cracking. This mechanical test was successfully combined with high sensitivity chemical analyses (Glow Discharge Mass Spectroscopy – GDMS) to find the root cause of such batch-to-batch differences in ductility. A chemical composition factor, called Kfactor, was defined and statistically linked to the Gleeble® test in July 2008. Altogether, it permitted to solve the issue.
Even if reliable and well documented, the Gleeble® test was originally developed to understand the root cause of the cracking. But due to lack of other solutions, its role was largely extended and it became a kind of standard test to qualify 2 1/4Cr1MoV SAW filler material. It was decided to optimize this test, keeping its general philosophy but making it feasible by a larger number of laboratories. In order to do that, a one-year Joint Industrial Program (JIP) was proposed to the community, accepted, sponsored and launched at the beginning of 2010. The target was to create a new test protocol able to discriminate batches of filler material.
The objective of this paper is to summarize the investigations performed and the optimization of the original Gleeble® test during the project that led to the definition of a new hot tensile mechanical test successfully benchmarked by independent laboratories and now balloted to be incorporated in American Petroleum Institute (API) recommended practice API RP 934-A as a new appendix.
