S31803双相不锈钢换热器管束腐蚀穿孔的原因

Reason for Corrosion Perforation of Heat Exchanger Bundle of S31803 Duplex Stainless Steel

某化工厂S31803双相不锈钢换热器管在投入使用14个月后发生腐蚀穿孔。利用化学成分和物相分析、显微组织和微观形貌观察、硬度测试、微区成分测定等方法分析了其腐蚀穿孔的原因。结果表明:钢管在冷拔成形过程中析出富铬σ相,导致周围贫铬而降低了钢管的耐腐蚀性能;在壳程工艺气中的H+2S、NH_4^+等介质的腐蚀作用下,钢管外壁发生腐蚀减薄甚至穿孔,管程循环水通过穿孔进入壳程,在钢管外表面沉积疏松结构的CaCO_3,造成腐蚀介质富集,从而加速并形成全面腐蚀。

S31803duplex stainless steel tubes in heat exchanger of a chemical factory failed by corrosion perforation after using for 14months.The reason for corrosion perforation was investigated by chemical and phase composition analysis,microstructure and micromorphology observation,hardness testing and microarea composition measurement.The results show that chromium-depletedσphase precipitated in the steel tube during cold drawing,leading to poor chromium around,and therefore reducd the corrosion resistance of the steel tube.Corrosion thinning or perforation occurred on the outer-wall of the steel tube under the action of corrosion of H2S,NH+4 and other media in the shell gas.The pipe-circulating water entered the shell side through the perforation,and a loose structure of CaCO3 was deposited on the outer surface of the steel tube,causing the enrichment of corrosive mediums,thereby accelerating and forming a comprehensive corrosion.