某公司304不锈钢弯头在使用5 a（年）后出现周向裂纹而失效，通过宏观观察、金相检验、扫描电镜分析、化学成分分析、力学性能试验和晶间腐蚀试验等方法，对弯头失效原因进行了分析。结果表明：该304不锈钢弯头裂纹为应力腐蚀形成的沿晶裂纹。弯头暴露在空气中并附着有长期因雨水、盐分产生的弱腐蚀介质，再加上管道输送的氧气对管壁外表面产生的拉应力以及弯头材料本身抗晶间腐蚀性差，最终弯头发生开裂失效。

The 304 stainless steel elbow of a company failed due to circumferential cracks after 5 years of service. The failure causes of the elbow cracks were analyzed by means of macroscopic observation, metallographic examination, scanning electron microscopic analysis, chemical composition analysis, mechanical properties test and intergranular corrosion test. The results show that the cracks of 304 stainless steel elbow were intergranular cracks formed by stress corrosion. The elbow was exposed to air and adhered to the weak corrosion medium produced by rain water and salt for a long time. In addition, the tensile stress on the outer surface of pipe wall caused by oxygen conveyed by pipe and poor intergranular corrosion resistance of the elbow material itself. Finally, the elbow cracked and failed.