A new copper/copper sulfate reference electrode for external corrosion monitoring of buried pipelines

摘要

The external corrosion of cathodically protected buried pipelines can be monitored by using carbon steel corrosion coupons. These coupons are installed near buried pipelines and they are electrically connected to the pipelines through test points. Coupon weight loss, coupon visual and microscopic inspection, AC and DC pipeline/soil potential and electrical current measurements are very important to predict the pipeline external corrosion processes. To measure AC and DC pipeline/soil potential, copper/copper sulfate reference electrodes are installed near corrosion coupons to minimize IR-drop. However, these reference electrodes have shown premature failures due to the transport of copper ions from the reference electrode through the soil toward the coupon surfaces. These ions are reduced at the carbon steel surface through a galvanic displacement reaction forming a thin copper coating on the steel surfaces which causes permanent damages to the steel coupons. To solve this problem, the traditional copper/copper sulfate reference electrodes were modified and a new copper/copper sulfate reference electrode was developed. The modification was to replace the ceramic junction of the traditional reference electrodes by a metallic junction. This work has the objectives of describing the new reference electrode and presenting lab electrochemical test results performed to validate the new reference electrode.