模拟浓缩液桶内干燥过程干燥桶腐蚀原因分析

目的通过对模拟浓缩液桶内干燥试验过程中出现泄漏的干燥桶泄漏处取样分析,明确干燥桶泄漏的主要原因。方法采用切割取样的方式在干燥桶泄漏处取样,根据后续分析测试手段对样片进行分解制样。对干燥桶材质进行化学组分分析和金相组织及晶粒度测试,通过扫描电镜对干燥桶腐蚀区域微观形貌进行观察,此外对腐蚀产物进行能谱分析,并和相关标准进行比较。结果干燥桶材质符合ASME A240中304不锈钢化学成分含量规定,非金属夹杂物满足一般工程用钢对非金属夹杂物的要求,其金相组织为奥氏体和条状铁素体,与304不锈钢金相不符,晶粒度为6.5级。样品存在大量腐蚀坑点,孔洞及坑点周围附着有较多腐蚀产物,坑点内呈现"冰糖块"状形貌,未形成坑点的区域同样存在腐蚀现象,观察到清晰的晶粒,腐蚀属于不锈钢的点腐蚀,在腐蚀产物中发现了Cl,F元素。结论桶体材质存在奥氏体和铁素体两相金相组织引发不锈钢点蚀是导致干燥桶腐蚀泄漏的主要原因,此外,不能排除Cl和F离子对干燥桶腐蚀的影响。

Causes of Corrosion in Simulating Drying Process in Concentrate Drum

Objective To sample and analyze leaking areas of drum in simulating drying test in concentrate drum to understand main causes of drum leakage. Methods Leaking areas of the drying drum was sampled by cutting. The sample pieces were decomposed based on subsequent analysis and test. The chemical composition, metallographic structure and grain size of the material of drying drum were analyzed and tested. The morphology in the corrosion area was been observed by SEM. Furthermore, the corrosion product was analyzed by energy spectrum. Afterwards, the results of analysis were compared with interrelated standards. Results The chemical composition of the material of drying drum conformed to regulation values of 304 stainless steel in ASME A240. The content of nonmetallic satisfied requirements of general engineering steel. The level of grain size was 6.5, but there were austenite and ferrite in the material of drying drum. This disagreed with the metallographic phase of 304 stainless steel. Lots of pit points and "rock candy shaped" corrosion product were observed in the sample. Corrosion also existed in areas without pit. Clear grain could be observed. The type of corrosion was pitting corrosion of stainless steel. Moreover, the Cl and F were also found in the corrosion product. Conclusion The corrosion of the container is induced mainly by the austenitic and ferrite metallographic in the container material. In addition, the existence of Cl and F also play certain role in the corrosion case.