某化工企业火炬气分液罐不锈钢法兰发生断裂失效。通过化学成分分析、硬度测定、金相检查和断口形貌和成分分析研究了法兰的失效原因。结果表明:失效法兰母材中硫含量超标、硬度超标;断口位于热影响区、表面呈脆性断裂特征;断口处内壁和外壁均存在裂纹,裂纹从表面向内部扩展,呈树枝状分叉,沿晶界扩展,符合敏化-晶间腐蚀失效的特征。焊接导致热影响区敏化,在应力和腐蚀环境的共同作用下,裂纹沿晶扩展,最终导致不锈钢法兰在热影响区发生晶间腐蚀断裂。

Fracture failure occurred at a stainless steel flange of a flare gas liquid seperation tank in a chemical enterprise. The failure causes of the flange were studied by chemical composition analysis, hardness measurement, metallographic examination, fracture morphology and composition analysis. The results showed that the sulfur content and hardness of the base metal of the failed flange exceeded their standards. The fracture was located in the heat affected zone (HAZ) of the weld with the characteristics of brittle fracture. The cracks on the inner and outer walls near the fracture extended from surface to inside, showing dendritic bifurcation and extending along grain boundaries, which accorded with the characteristics of sensitization-intergranular corrosion failure. Welding caused the sensitization of the HAZ. Cracks propagated along the grain boundaries under the combined action of stress and corrosion environment, which eventually leaded to intergranular corrosion fracture of stainless steel flange in HAZ.