某化工装置中S32750管道的开裂原因

Cause Analysis for Crack Occurred in S32750 Piping in One Chemical Plant

某化工装置中材质为S32750的主管道在其支管高压注胶堵漏一段时间后,于卡具固定部位发生严重开裂,通过宏观检查、断口形貌分析、金相组织分析、能谱分析(EDS)、化学成分分析和力学性能试验等方法,对管道失效原因进行了分析,结果表明:S32750管道的失效机理为氯化物应力腐蚀开裂(CLSCC);由于带压堵漏后的介质仍存在一定量渗漏,随着介质挥发其中的腐蚀性物质(Cl-)在卡箍结构内的管道表面富集,且因卡具固定在主管道上,卡具紧固操作对失效部位施加了巨大的应力,较高的运行温度增加了开裂的敏感性,以上因素的共同作用导致对CLSCC具有一定敏感性的双相不锈钢管道发生开裂失效。

In the main pipeline made of S32750 in a chemical plant there was serious crack occurred at the position of the fixture which had been used for high-pressure gel injection plugging in the branch piping a period before.The failure analysis was performed by using macroscopic examination,fracture morphology analysis,metallographic structure analysis,energy spectrum analysis(EDS),chemical composition analysis and mechanical property test.The results showed that the failure mechanism of the S32750 pipeline was chloride stress corrosion cracking(CLSCC).Since there was still a certain amount of leakage of the pressure fluid after plugging,the corrosive substances(Cl^(−))in the volatile fluid were enriched on the surface of the pipe in the clamp structure,and because the fixture was fixed on the main pipe,which imposed great stresses on the failure part,and the relatively high operating temperature increased the cracking sensitivity.The combined effect of the above factors led to the cracking of the duplex stainless steel which had a certain degree of sensitivity to CLSCC.