Corrosion Monitoring Techniques of X65 Pipeline Steel in Brine Solution

Through a special design of electronic coupons, on-line monitoring of corrosion rate for the same coupon of X65 steel in 3.5% (mass fraction) NaCl solution for 50 d was carried out by electrical resistance (ER) and electrochemical methods. The measurement results by on-line monitoring were compared with those monitored by weight-loss method. The results show that the rust layer had an excellent inhibition for the corrosion of X65 steel. The corrosion rate reduced to 1/6 of the initial corrosion rate after 30 days. The ER monitoring results had a measurement error at the beginning due to the nonuniform corrosion on the specimen surface. The corrosion rates measured by ER technique and weight-loss method had a good accordance after corrosion for 20 days. The corrosion rate measured by electrochemical methods agreed with the other two kinds of methods during the initial period. However, after corrosion for 30 days, the electrochemical measurement results were much higher than the real corrosion rate of the specimen. It means that electrochemical methods are not applicable for long term corrosion monitoring in ocean surroundings.