不锈钢换热管泄漏失效的原因

Reasons for Leakage Failure of Stainless Steel Heat Exchange Tubes

某化工企业多台管壳式换热器在服役3~4 a后陆续发生泄漏,拆卸后检查发现换热器内部大量304不锈钢换热管存在开裂或穿孔现象。通过宏观形貌分析,扫描电镜及能谱分析,金相检测,化学成分分析、晶间腐蚀试验、残余应力测试等手段对不锈钢管失效原因进行分析。结果表明:换热管出现穿孔和开裂失效的主要原因是材料发生了晶间腐蚀及应力腐蚀。换热管材料304不锈钢具有晶间腐蚀敏感性,换热管内外壁都存在明显的残余拉应力,且介质中存在S、Cl等腐蚀性元素,换热管材料同时具备以上3种应力腐蚀开裂的必要条件而发生应力腐蚀开裂。

A number of shell and tube heat exchangers in a chemical enterprise leaked one after another after 3-4 years of service.After disassembly,a large number of 304 stainless steel heat exchange tubes were found to be cracked or perforated.The failure reasons of stainless steel tubes were analyzed by means of macroscopic morphology analysis,scanning electron microscopy and energy spectrum analysis,metallographic examination,chemical composition analysis,intergranular corrosion test and residual stress measurement.The results showed that intergranular corrosion and stress corrosion were the main reasons for the cracking and perforation of the heat exchange tubes.The heat exchange tube material 304 stainless steel was sensitive to intergranular corrosion.There was obvious residual tensile stress on both the inner and outer walls of the heat exchange tubes.And there were corrosive elements such as S and Cl in the medium.Stress corrosion cracking happened in the heat exchange tube material due to the coexistance of the above three necessary conditions for stress corrosion cracking at the same time.