加氢裂化泵入口管线三通失效原因分析

通过对某公司加氢裂化装置液化气泵入口不锈钢管线失效三通进行宏观检验、化学成分分析、金相分析与扫描电镜分析等,认为三通失效的原因为湿环境下氯离子和硫化氢共同作用下的应力腐蚀开裂。该不锈钢三通在制造过程中未严格执行制造工艺,导致金相组织中出现σ相析出,制造后又未经过固溶处理,使材料的耐蚀性降低,在腐蚀性介质中由于氯离子的长期作用,产生点蚀坑,成为诱发裂纹的起源。有害物质硫化氢的质量浓度由过去的低于1 g/L增加到7～10 g/L,有害物质硫化氢的质量浓度出现了激增,氯离子质量浓度最高达124 mg/L。同时介质中氯离子的存在使硫化氢应力腐蚀速率加快,从而导致三通失效。

Failure Cause Analysis of Tees on Pump Inlet Line of Hydrocracking Unit

The macro examination,chemical analysis and metallographic analysis and SEM of failed tees on stainless steel inlet pipelines of LPG pump of hydrocracking unit concluded that the cause of failure was the stress corrosion cracking under the common effect of chlorine ions and H2S in wet environment.The stainless steel tee had been fabricated without strictly following the required fabrication procedures,and à phase educt appeared in the metallographic structure.Furthermore,as the tee had not been treated by solution after fabrication,the corrosion resistance of the material was reduced.The pit corrosion occurred under the long-term effect of chlorine ions in the corrosive media,which was the culprit of cracking.The mass concentration of hazardous H2S was increased to 7～10 g/L from 1 g/L and the maximum mass concentration of chlorine ions was as high as 124 mg/L.The presence of chlorine ions in the media had accelerated the stress corrosion rate of H2S,which led to the failure of the tee.