Effect of Post-weld Cleanup Method on the Localized Corrosion Resistance of Duplex Stainless Steels

摘要

Recent experience with duplex stainless steels in wet flue gas desulfurization service has shown rapid localized attack in some cases. This paper discusses field observations, laboratory results, and a brief historical perspective on the corrosion phenomena. Early observations of attacked wet flue gas desulfurization absorbers showed pitting and crevice corrosion near welds in the immersion zone and inside spray headers. The post weld cleanup methods that were used were not consistent from plant to plant, offering a variety of data to analyze. Some of the common methods were wire brushing, sanding with flapper wheels, pickle-passivation treatment, and grinding. The surface preparation methods were applied to coupons for laboratory testing. Laboratory testing consisted of galvanic corrosion tests and cyclic potentiodynamic polarization testing, and microscopy. The surface finish and the presence of crevices played key roles in determining each alloys corrosion resistance.