某核电厂碱液管道弯头开裂原因分析

Cause Analysis of Cracking of Lye Pipeline Elbow in A Nuclear Power Plant

某核电厂日常期间发现凝结水精处理系统一阀门下游管道弯头处出现大量碱结晶,清理干净后检查发现弯头焊缝附近存在裂纹。通过成分、硬度、金相及夹杂物分析等测试手段,发现送检的开裂弯头为奥氏体不锈钢,服役过程中与浓碱环境介质接触,弯头开裂部位同时存在加工硬化和焊接带来的残余应力,长期综合作用下使弯头靠近焊缝位置发生了应力腐蚀开裂。

During the daily operation of a nuclear power plant,a large number of alkali crystals were found at the elbow of the pipeline downstream of a valve in the condensate polishing system.After cleaning,the cracks were found near the elbow weld.Through the analysis of composition,hardness,metallography and inclusions,it was found that cracked elbow submitted for inspection was austenitic stainless steel.During service,the elbow was in contact with concentrated alkali environment medium,and there were residual stresses caused by work hardening and welding at the cracked part of the elbow.Under the long-term comprehensive action,stress corrosion cracking occurred near the weld of the elbow.