撒哈拉地区不锈钢输水设施点蚀原因分析

目的研究撒哈拉地区某输水项目不锈钢设施点蚀的原因及解决方案。方法通过对输水项目管线、过滤器、膨胀节、换热器等不锈钢设施进行腐蚀形貌观察,在现场取原水水样、腐蚀样品和腐蚀产物进行实验室水质分析、扫描电镜及能谱分析,并对腐蚀情况进行综合评价。通过动电位扫描Tafel曲线和Rp拟合分析方法,对DIN 1.4301不锈钢在不同温度原水中的电化学性能进行测试和分析。结果该不锈钢主要腐蚀形态为点蚀,位置集中在管线底部焊缝,高温比低温环境腐蚀点更多。原水矿化度达1947 mg/L,水中氯离子质量浓度为600 mg/L,室温条件下RI值为7.7,有较强的腐蚀性。该不锈钢抗点蚀当量PREN较低。通过电化学测试发现,管线用不锈钢材料DIN 1.4301在原水中20℃条件下有较好的耐蚀性,当温度高于40℃时其耐蚀性急剧下降,因此该地区的强辐射高温环境和停输过程进一步加剧了原水中各类不锈钢的腐蚀。结论发生点蚀主要原因是水质差,所选用材质耐点蚀性能差,另外停输和环境因素引起的高温进一步加剧了点蚀的发生。可通过水源净化、更换耐点蚀材质、涂层内防护、减少停输、避免高温辐射等方案,减少点蚀的发生。

Corrosion Analysis of Water Facilities Pittings in Sahara Desert

ABSTRACT:Objective To figure out the reasons of stainless steel corrosion in a water transmission project in Sahara desert, and propose the solutions accordingly.Methodsfield investigation was performed by corrosion appearance observation on pip-ings, filters, expansion joints and heat exchangers, raw water, corrosion samples and corrosion products were collected and ana-lyzed in laboratory. Tafel curves of DIN 1.4301 stainless steel were tested in raw water with different temperatures, and ana-lyzed with Rp simulation.Results pittings were found in girth welds bottom of the pipings, more pittings were found in pipings with higher temperature. Mineralization and chloride ions content were 1947 mg/L and 600 mg/L respectively in the raw water, the RI value in ambient is 7.7, which was corrosive. PREN values of the stainless steel used in this project is low. The electro-chemical tests showed that DIN 1.4301 was corrosion resistance in raw water in 20℃, but not suitable to serve in a temperature higher than 40℃. Therefore the high temperature and shut down process deteriorated the situation.Conclusion reasons of pit- tings in this project include corrosive water quality, materials which are sensitive to pitting, and the high temperature caused by shut down process and sunshine. Solutions of corrosion protection include water purification, change materials with high pitting resistance, internal coating protection, reducing the effects by high temperature and shut down progress, etc.