高温潮湿含氯环境中304不锈钢腐蚀失效分析

Analysis on Corrossion Failure of 304 Stainless Steel in High-temperature and Humid Environment with Chlorine Ion

304不锈钢的应用很广,但对304不锈钢长期处于高温潮湿含氯环境中的腐蚀研究较少。利用光学显微镜、扫描电子显微镜、能谱仪等分析手段对失效的不锈钢进行组织结构、元素和断口分析。结果表明:Cr含量基本符合要求,Ni含量偏低,这是导致不锈钢不耐蚀的主要原因。另外由于内胆与保温层长期处于高温潮湿含氯气氛中,内胆与保温层形状突变处正好是焊缝区,该区域腐蚀最严重,焊接应力腐蚀伴随晶间腐蚀。断面Cl和S含量增加,进一步促进应力腐蚀开裂。内胆与保温层形变突变处的缝隙可能也加剧腐蚀。确保材料合格、工艺规范,防止水渗入内胆与保温层之间,避免腐蚀介质的滞流是提高类似环境中不锈钢使用寿命的重要措施。

304 stainless steel is widely used,but little research on the corrosion of 304 stainless steel in high temperature and humid chlorine environment for a long time has been done.The microstructure,elements and fracture of failed stainless steel were analyzed by the optical microscope,scanning electron microscope(SEM),and energy spectrometer(EDS).The results showed that the Cr content basically met the criterion,and the Ni content was a little low,which were the main causes of little corrosion resistance for 304 stainless steel.In addition,due to the internal bile and thermal insulation layer were in a high temperature and humid chlorine atmosphere for a long time,the shape mutation between the internal bile and thermal insulation layer was just the weld area,which was the most serious corrosion,and the welding stress corrosion was accompanied by the intercrystal corrosion.Increasing content of Cl and S further promoted the stress corrosion cracking.The gap between the internal bile and the insulation layer might be also aggravate the corrosion.The important measures to improve the service life of stainless steel in a similar environment were sure to use qualified materials and techniche process,to prevent water infiltrating into the internal bile and the insulation layer and to avoid corrosion medium stagnation.