某电厂Super304H钢管晶间腐蚀开裂原因分析

某电厂Super304H钢过热器和再热器在机组试运行过程中,连接短管和管屏的焊接接头附近出现晶间腐蚀,导致多处泄漏。通过对材料化学成分分析、能谱分析、金相组织和扫描电镜观察,以及钢管敏化后的晶间腐蚀试验,结果表明:Super304H钢基体为等轴奥氏体组织,无论是否经过敏化处理,经晶间腐蚀试验并弯曲后均会出现开裂;钢管的含铌量与含碳量之比仅为5.4,碳含量偏高而铌含量偏低易导致晶间腐蚀,并且钢管在堆放过程中受到介质的腐蚀,焊缝收缩所产生的拉应力促进了裂纹的产生和扩展。

CAUSE ANALYSIS OF CRACKING DUE TO INTERCRYSTALLINE CORROSION FOR Sper304H TUBES

The intercrystalline corrosion had appeared on the superheater and reheater with Super304H steel tubes,leading to leakage at many locations.The cracked Super304H steel tubes have been sampled,through chemical components analysis,energy spectrum analysis,as well as observation of metallographic structure and using scanning eletron microscope etc.,the causes leading to intercrystalline corrosion of said steel tubes have been obtained.Results show that the basic body of Super304H steel is isoaxial austenitic structure,regardless of sensibilization treanment or not,after test of crystalline corrosion and bending,cracks have appeared.The ratio between niobium content and carbon content is only 5.4,the higher corbon content and lower niobium content are easy to result in intercrystalline corrosion.