INVESTIGATION OF CONTROL MEASURES FOR GALVANIC CORROSION

摘要

The coupling of dissimilar alloys in conducting, corrosive solutions such as seawater can lead to accelerated, galvanic corrosion of the more anodic, electronegative alloy. The driving force for galvanic corrosion is the potential difference between two or more metals or alloys in a conductive medium that allows current flow between the anodic and cathodic members. The extent of galvanic corrosion between two or more coupled dissimilar alloys depends on many, often dynamic, factors. Alternative galvanic control methods were investigated to eliminate the need for inspection, improve safety, and control corrosion in piping systems. Mitigation of galvanic corrosion can offer designers more possible material options within piping systems. Several possible candidate methods for controlling galvanic corrosion were considered: (1) coating the cathodic member of the couple (alloy 625 or titanium) to reduce the overall cathodic reaction; (2) cathodic protection applied to the more anodic member of the galvanic couple; and (3) use of a bi-electrode device between the anodic and cathodic piping members of the dissimilar alloy interface. Use of cathodic protection, the bi-electrode, and a coating on the cathodic member of the couple were effective to varying degrees (30 to 99%) in controlling galvanic corrosion.