Utilizing high strength steels in hydrogen pipelines provides an opportunity to reduce material costs while permitting higher operating pressures; however, current design codes restrict or severely penalize use of higher strength steels. Severe design restrictions are primarily the result of a lack of experimental research on high strength pipelines, particularly of high strength steel welds which have the potential to be more severely embrittled by hydrogen than the base metals. In this study, four different high strength steel welds were subjected to fatigue in high pressure hydrogen gas in order to measure the effects of hydrogen on fatigue crack growth rate. The welds were fabricated from the same X100 base metal. Fatigue crack growth rates (FCGR) in hydrogen were accelerated by over an order of magnitude compared to companion tests performed in air. Residual stress measurements were performed on companion weld specimens. The measured residual stress was used to determine the influence on stress intensity factor, Kres, and FCGR curves were corrected, accordingly. Removal of residual stress effects resulted in shifts of the FCGR data and provided a more complete characterization of the fatigue behavior of high strength pipeline welds. Fatigue behavior of high strength welds in hydrogen were compared to previously tested lower strength pipeline steel welds in an effort to evaluate the role of strength in hydrogen susceptibility. In general, the higher strength X100 welds exhibited higher FCGR than lower strength welds, particularly in the lower ΔK range. Measurements of FCGR on high strength steel welds in hydrogen inform the potential acceptance of these materials and are necessary for structural assessment in hydrogen infrastructure.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.