A failure analysis of welded pipes (ASTM A312 Grade TP 316L) in a water treatment plant was done and it is presented in this paper. The premature failure was detected by several water leakages caused by pitting corrosion three months after hydrostatic tests and before transferring the plant to the operator. The leakages were located near the bottom of the circumferential butt welds of the entire piping system. The samples were analyzed using visual inspection, radiographic examination, optical emission spectrometry, ferrite number (FN) measurements, metallographic examination and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectrometry (EDS). The results showed that the corrosion rate was extremely high compared to other studies available in the literature for austenitic stainless steel and the pits were in the weld metal and the Heat Affected Zone (HAZ) of the circumferential welds. The lack or deficiency of a purging gas during the field welding generated heat-tinted zones around the welds. Visual inspection showed that the pits were preferentially located at heat-tinted zones and they have large sub-surface cavities. The SEM inspection confirmed the presence of structures compatible with sulfate-reducing bacteria and iron-oxidizing bacteria and revealed that the failure was caused by microbiologically-influenced corrosion (MIC). The review of standards and codes used to perform hydrostatic testing of austenitic stainless steel piping systems showed that the water used for hydrostatic tests should have been treated before testing or the surfaces should have been deeply drained and dried. The failure was caused by the water used during the hydrostatic testing since it was not fully drained from the piping system and remained stagnant leading to MIC.

进行了水处理厂焊管（ASTM A312 TP 316L级）的失效分析，并在本文中进行了介绍。在静水压测试后三个月以及在将设备移交给操作员之前三个月，由于点蚀腐蚀而导致的数次漏水检测出了过早的故障。泄漏点位于整个管道系统的圆周对接焊缝的底部附近。使用目视检查，射线照相检查，光学发射光谱，铁素体数（FN）测量，金相检查和扫描电子显微镜（SEM）结合能量色散光谱（EDS）对样品进行了分析。结果表明，与文献中对奥氏体不锈钢进行的其他研究相比，腐蚀速率极高，并且凹坑位于焊缝金属和圆周焊缝的热影响区（HAZ）中。现场焊接过程中缺乏吹扫气体会在焊缝周围产生热着色区域。目视检查表明，凹坑优先位于热着色区，并且它们具有较大的地下空腔。SEM检查证实了与硫酸盐还原细菌和铁氧化细菌兼容的结构的存在，并表明该失效是由微生物影响的腐蚀（MIC）引起的。对用于执行奥氏体不锈钢管道系统静水压测试的标准和规范的审查表明，用于静水压测试的水应在测试前进行处理，或者应将表面深层排干。该故障是由于静水压力试验期间使用的水引起的，因为该水没有从管道系统中完全排出，并且保持通向MIC的状态。