Case Study On Environmental Cracking Resistance Assessment Of Welded Segments Of An Interconnecting Sour Gas Feed Pipeline
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South Pars Gas Complex (SPGC), as operator of the mega gas plants in the south of Iran, aims to bring the level of gas flaring in the giant South Pars Gas Field to zero and prevent up to 400 million cubic meters of associated petroleum gases from burning off annually. Hence, SPGC as the gas export hub in the zone, is conducting important studies and assessment on the pipeline materials for to be constructed interconnecting export lines of sour gas to the petrochemical plants for ethanol production. Regarding previous experiences in the region, as a cost effective and feasible material, A234 carbon steel, selected as the most applicable material. Thus, considering the environmental cracking corrosion risks, HIC and SSC tests conducted on the newly produced and welded A234, 24” pipeline to check the material resistance. The pipeline transfer a gas containing 2500 ppm H2S. Tests conducted according to the NACE TM0177 and NACE TM0284. Results and acceptance criteria evaluated as per NACE MR0175-2. All test parameters such as CSR, CTR and CLR resulted in zero, but 1% hydrogen blister observed on the specimens. Therefore, complementary tests of EFC16-2009-method B-FPB and ISO 7539-2 performed on base metal, HAC and welded sections. Micrographs from the raw material, proved the absence of any metallurgical or welding defects. In conclusion, the observed blisters was considered as a hydrogen crack and associated risks calculated. This paper discusses the full method and calculations to solve an environmental related engineering problem and shows how the materials is finally accepted with a minimum risk for human and environmental hazards.
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