20钢等径三通失效分析

通过断口分析、化学成分分析、显微组织、布氏硬度以及电化学腐蚀性能测试,并结合该类三通的生产工艺,对发生脆断开裂的20钢计量撬等径三通进行了失效原因分析。结果表明,20钢无缝管采用液压冷胀成形工艺制造的三通未按标准要求进行正火或退火处理,加工硬化引起的材料脆化未能通过正确的热处理加以消除,导致三通本体缺陷容限的降低,诱发脆性断裂,并且冷变形还会使三通材料的电化学腐蚀性能显著下降,加速三通本体腐蚀,三通内壁上的腐蚀坑成为脆性断裂的裂纹源。建议加强对三通的质量监督和出厂检验。

Failure analysis of 20 steel equal-diameter tee

Failure causes of failed 20 steel equal-diameter tee used in a metering skid were investigated through the fracture analysis, chemical composition analysis, microstructure analysis, Brinell hardness and electrochemical corrosion test combining with the manufacture process of the tee. The results show that the tee made of 20 steel seamless pipe by hydraulic cold expansion forming process does not meet the standard requirements of normalizing or annealing treatment. The embrittlement caused by work hardening is not eliminated, which leads to the reduction of defect tolerance of the tee, and then the brittle fracture. Moreover, the electrochemical corrosion properties of the failed tee decline clearly due to the cold deformation, and the corrosion of inner wall of the tee is aggravated, and then the corrosion pit on inner wall of the tee becomes the crack source of brittle fracture. It is recommended to enhance the quality supervision and ex-factory inspection of the tee.