Abstract
Prior to 2003, hydrogen induced cracking (HIC) testing was not incorporated into NACE MR0175 / ISO 15156(1) and generally was not required for mildly sour environments (i.e. Region 0) and thus assets operating in CO2-containing environments with potentially very low levels of H2S were commonly built using ‘sweet’ steel grades. A consideration of HIC, even for traces of H2S, became mandatory in the 2003 revision, but the associated threat has not been quantified. Very few instances of pipeline leakages due to HIC have however been reported. Recent work carried out by the European Pipeline Research Group(2) suggested that there could be a threshold below which HIC may not be a credible threat. That study, however, used ‘modern’ linepipe materials and it well known that ‘heritage’ or vintage materials are inherently more susceptible to HIC, due to a lesser degree of control of inclusions, leading to HIC in rolled materials. Safe operating limits of vintage steels need to be defined to ensure reliable and inherently safe operations. In the present work, four vintage steels have been tested using small and full-scale testing, coupled with non-destructive monitor/inspection. Safe operating limits of heritage materials have been established and the roles played by inclusions on crack initiation, and by banded microstructure on crack propagation, have been clarified.
