1.1 This standard is intended to be a primary source of information on cracking in wet H2S petroleum refinery environments and provides guidelines on the detection, repair, and mitigation of cracking of existing carbon steel refinery pressure vessels in wet H2S environments. Refinery pressure vessels include items such as, but not limited to, columns, heat exchangers, drums, reboilers, and separators. Piping is not included in the scope of this standard; inspection requirements for new pressure vessels (never in service) are also beyond the scope of this standard.

1.2 For the purposes of this standard, wet H2S service is defined as refinery process environments in which the concentration of H2S is 50 ppmw or greater in the aqueous phase. However, as indicated by the survey results reported in Section 3, the threshold concentration of H2S in the aqueous phase required for cracking to occur has not been clearly established. Therefore, selective application of this standard may be appropriate when past experience has indicated the presence of cracking or blistering in comparable service, regardless of H2S concentration.

1.3 Cracking of carbon steel pressure vessels, due to various causes, has been a problem faced by the industry almost since its inception. However, increased industry attention to the potential for cracking of carbon steel pressure vessels began in 1984 with the rupture of a monoethanolamine (MEA) absorber tower at a Lemont, Illinois, refinery. The resultant explosion and fire resulted in fatalities and extensive damage to the facility. In response to this incident, NACE Task Group T-8-14 on Stress Corrosion Cracking of Carbon Steel in Amine Solutions was formed in the fall of 1984. The results of the T-8-14 effort have been reported separately.

1.4 In 1988, some new results on vessel inspections and the cracking found were reported to the industry.Among the significant findings was the observation that cracking problems were occurring in other wet H2S environments, not just in MEA. It was further reported that inspection techniques commonly used at the time (visual, liquid penetrant, and dry magnetic particle testing) were not sensitive enough to find these cracks. In response to this new information, NACE Task Group T-8-16 on Cracking in Wet H2S Environments was formed in the spring of 1988.

 Historical Document 1995