API RP 945:2003 pdf download

API RP 945:2003 pdf download.Avoiding Environmental Crackingin Amine Units.
The first three mechanisms are most prevalent in carbon steels that have been exposed to rich amine solutions loaded with HS, including the lower sections of absorber or contactor towers. In contrast, ASCC is more common in carbon steel components that have been exposed to lean amine service. Cracking can occur both with and without significant metal loss. Definitions of these cracking mechanisms and photomicrographs are presented in Appendix A.
Several serious cracking problems have been reported over the past 50 years. ASCC of carbon steel by amine solutions was first mentioned in a report published in 1951 by the NACE Technical Practices Committee 5C on Sub-Surface Corrosion by Alkaline Solutions Ill. The report noted that piping, regenerators (strippers), absorbers, and heat exchanger shells and heads made from carbon steel had cracked after 6 months to 10 years of exposure to 15-percent monoethanolamine in water (containing unspecified amounts of both hydrogen sulfide and carbon dioxide) at temperatures up to 149°C (300°F). Complete stress relieving was recommended as a solution to the problem.
In 1953, ASCC was reported in MEA solutions in gas treatment plants [2]. Requirements for cracking included the presence of both a high stress and a particular corrosive amine solution. The elimination of either factor was found to prevent cracking. Recommended preventive measures included maintaining the reboiler temperature and the regenerator pressure at the lowest practical levels, using reclaimers, and preventing air contact to minimize the corrosiveness of the amine solutions. Frequently, such process changes cannot be readily implemented, so stress relieving was recommended as an effective alternative to the recommended practices.
Other instances of ASCC were reported in non-stress- relieved equipment operating in 20-percent (by weight) monoethanolamine [3]. Affected equipment included two amine storage tanks, four absorber towers, one rich amine flash drum, one lean amine treater, and various piping. Cracking was found primarily at welds exposed to amine solutions where temperatures ranged from 53°C to 93°C (127°F to 200°F). The cracking was intergranular. and the crack surfaces were covered by a thin film of magnetite (Fe304). No cracking was found in postweld heat treated (PWHT) piping that operated at temperatures as high as 154°C (310°F). Although the exact reason for the extensive cracking was not clear, it was concluded that PWHT could be used to prevent the problem.
A major problem occurred in 1984, when an MEA absorber tower ruptured at a U.S. refinery. This failure initiated as SSC in the hardened area of the heat-affected zone of a rewelded shell seam and propagated by SOHIC through the base metal [4]. The weld repair had been performed 10 years earlier as part of a procedure to replace a shell course.
In 1986 extensive leaking of piping welds was reported in lean MEA service [5]. The leaking was attributed to ASCC. Most leaks occurred at piping welds that had been in lean amine service for 4 to 8 years. Cracks were found in the weld deposits, heat-affected zones, and areas of the base metal adjacent to heat-affected zones. Typically, the cracks propagated parallel to the weld. Shear-wave ultrasonic inspection confirmed the presence of cracks at many other welds in lean amine piping. None of the cracked piping welds had received
PWHT.
As a result of these occurrences, in 1985 the NACE Group Committee T-8 on Refining industry Corrosion, in cooperation with the API Subcommittee on Corrosion and Materials, sponsored an industry-wide survey of cracking problems in amine services [6]. The results of this survey indicated that cracking was most prevalent in MEA service, and that it occurred in all types of equipment at temperatures as low as ambient. PWHT of welds was identified as the single most effective means of preventing cracking. Additional data on stress corrosion cracking of carbon steel in DEA and DIPA services were reported in 1991 [7] and in DEA. DIPA. and MDEA service in 1993 [8].