酸气后冷器封头开裂原因分析

Analysis of cracking cause of acid gas post-cooler head

某天然气净化厂酸气后冷器浮头式封头内壁出现鼓包和裂纹,采用宏观检验、化学成分分析、硬度测试、金相检验、能谱分析、断口分析及EBSD测试等方法,对鼓包和裂纹产生的原因进行了分析。结果表明,封头内壁鼓包和开裂为氢鼓包(HB)和氢致开裂(HIC)。由于该封头材料(20g钢)显微组织沿轧制方向呈(铁素体+珠光体)带状分布,且在1/2板厚位置存在因元素偏析所致的贝氏体组织和较多MnS夹杂物,而该封头的服役环境中含有湿H2 S介质,与钢材发生电化学反应后产生了氢,氢在板厚1/2缺陷处聚集,导致了封头内壁的鼓包和开裂。

Bulges and cracks appeared in the inner wall of floating head of acid gas post-cooler in a natural gas purification plant.The causes of bulges and cracks were analyzed by means of macroscopic examination,chemical composition analysis,hardness test,metallographic examination,energy spectrum analysis,fracture analysis and EBSD test.The results show that the bulge and cracking of the inner wall of the head are hydrogen bulge(HB)and hydrogen-induced cracking(HIC).Since the microstructure of the head material(20g steel)is banded ferrite+pearlite along the rolling direction,with bainite and more MnS inclusions appearing at the position of 1/2 plate thickness caused by element segregation,and the service environment of the head contains wet H2 S medium which generates hydrogen after electrochemical reaction with the steel,then the hydrogen accumulates at the defects of 1/2 plate thickness,leading to bulge and cracking of the inner wall of the head.