某大型石油化工生产企业在常规检查中发现,硫磺回收仪表阀门螺栓断裂。采用宏观观察、化学成分分析、金相检验、硬度测试和断口分析等方法,分析了该螺栓断裂的原因。结果表明:螺栓的固溶处理工艺不恰当,使其晶界两侧形成了贫铬区,造成晶间碳化物的析出,从而发生晶间腐蚀,同时该螺栓中的镍和铬元素含量偏低,使其耐蚀性偏低,且螺栓的服役温度较低,未达到敏化温度,在腐蚀性介质的作用下,螺栓的非敏化型晶间腐蚀加重,最终导致螺栓断裂。

During routine inspection, a large petrochemical production enterprise found that the bolt of a sulfur recovery instrument valve was fractured. By means of macroscopic observation, chemical composition analysis, metallographic inspection, hardness test and fracture analysis, the reasons for the fracture of bolt were analyzed. The results showed that the solution treatment process of the bolt was not appropriate, so that a chromium-depleted area was formed on both sides of grain boundaries and caused the precipitation of intergranular carbides, resulting in intergranular corrosion. At the same time, the content of nickel and chromium elements in the bolt was relatively low, which made its corrosion resistance low. And service temperature of the bolt was low and did not reach the sensitization temperature. Under the action of corrosive medium, non-sensitized intergranular corrosion of the bolt was aggravated, which eventually led to bolt fracture.