ABSTRACT

The present study compares corrosion behaviour of three austenitic stainless steels 316L, 317L and 904L (base materials and welds) in wet-process phosphoric acid (WPA) and reagent grade phosphoric acid with impurities, e.g., Cl-, F- and SO₄^2-. The corrosion study was done by performing electrochemical polarisations at 50°C followed by Tafel extrapolation. Welds always had higher corrosion rates than their respective base materials. The corrosion rates of stainless steels in plant WPA were much less compared to that in reagent grade phosphoric acid with almost similar levels of Cl⁻, F⁻ and ${\mathrm{SO}}_4^{2-}$. This is due to the presence of a variety of dissolved metallic ions in WPA that reduces its corrosiveness. Among the three metallic cations (Fe³⁺, Mg²⁺ and Al³⁺) examined in this study, the inhibiting action increased in the order Fe³⁺< Mg²⁺ < Al³⁺. SS 904L was the most corrosion-resistant alloy in WPA followed by SS 317L and 316L.

摘要

本研究比较了三种奥氏体不锈钢 316L、317L 和 904L（母材和焊缝）在湿法磷酸 (WPA) 和试剂级磷酸中的腐蚀行为，其中含有杂质，例如 Cl-、F- 和 SO ₄ ^{2 -} . 腐蚀研究是通过在 50°C 下进行电化学极化然后进行 Tafel 外推来完成的。焊缝的腐蚀速率总是高于它们各自的母材。不锈钢在工厂 WPA 中的腐蚀速率远低于试剂级磷酸中的腐蚀速率，其中 Cl ^-、F ^-和${\mathrm{所以}}_4^{2-}$. 这是因为 WPA 中存在多种溶解的金属离子，从而降低了其腐蚀性。在本研究中检测的三种金属阳离子（Fe ³⁺、Mg ²⁺和Al ³⁺）中，抑制作用按照Fe ³⁺ < Mg ²⁺  < Al ³⁺的顺序增加。SS 904L 是 WPA 中最耐腐蚀的合金，其次是 SS 317L 和 316L。