海水温度和浓缩度对316L不锈钢点蚀性能的影响

EFFECT OF TEMPERATURE AND CONCENTRATION RATIO ON PITTING RESISTANCE OF 316L STAINLESS STEEL IN SEAWATER

运用循环阳极极化曲线研究了不同温度和浓缩度的海水介质中316L不锈钢的点蚀行为．结果表明，在1～3倍浓缩度范围内，316L不锈钢的点蚀电位和再钝化电位均随着温度的升高而线性降低，但当浓缩度高于2倍、温度大于85℃时，点蚀电位变化较小；在25～95℃温度范围内，点蚀电位和再钝化电位与海水浓缩度的对数呈线性关系．浓缩度对316L不锈钢点蚀性能的影响比温度更小，并根据点缺陷理论分析了二者对点蚀的作用机制．

Due to a serious shortage of natural fresh water in many areas all over the world, the seawater desalination has emerged as an effective compensation way to meet the consumption requirements. Due to the good corrosion resistance and low cost, stainless steels have been used extensively to construct the multi effect distillation （MED） plants, especially type 316L stainless steel for the evaporation chambers. However, with the application and development of low temperature MED, there is increasingly need of higher temperature distillation and higher brine concentration in the desalinators to reduce the drainage of hot brine and increase the water production ratio, which may cause more serious corrosion on the stainless steel components in the plants. Pitting corrosion of 316L stainless steel was studied in the concentrated environments of seawater with different temperatures （25, 50, 63, 72, 85 and 95 ℃） and concentration ratios （1, 1.5, 2, 2.5 and 3 times） by using cyclic anodic polarization measurement and SEM surface observation. The results show that both pitting potential and repassivation potential of 316L stainless steel decrease linearly with temperature in the concentration ratio range of 1 to 3 times for seawater, but the change of pitting potential is very slight when the solution temperature is higher than 85℃ in the case of concentration ratio larger than 2 times. Both pitting potential and repassivation potential reduce linearly with the logarithm of the concentration ratio of seawater in the range of 25 to 95℃. It is apparent that increasing temperature and concentration ratio of seawater will deteriorate the pitting resistance of 316L stainless steel noticeably. The influence of temperature and concentration ratio is analyzed on the basis of the point defect model. Nevertheless, the concentration ratio of seawater has a weaker influence on pitting resistance of 316L stainless steel in comparison with temperature as revealed by the pitting potential changes resulted from the concentration ratio around 1.5 times and solution temperature around 72 ℃. Therefore, compared with temperature, the corrosion resistance of 316L stainless steel for low temperature MED plants may be relatively tolerant of the adjustment or fluctuation of seawater concentration.