Evaluation of anticorrosive properties of welded junctions of pipes and profiles made of a galvanized strip on a continuous electric-weld pipe mill

In this research the method of metallographic examinations and corrosion tests of galvanized pipes and profiles was developed. The zone of a welded joint of pipes and profiles made of a galvanized strip by high-frequency welding on a continuous electric-weld pipe mill was investigated. A general character and the degree of the anticorrosive coating damage in the weld junction zone were defined. It was determined that the character of the damage in all investigated samples was the same, while the damage degree in the coating width and depth is different and depends on welding modes. On the outer surface of the pipe an additional zinc coating is usually deformed and thinned as a result of profiling-calibration. Corrosion tests were carried out using accelerated test methods. The effect of the degree of the coating damage in the zone of the weld junction on corrosion resistance was evaluated. A comparative analysis of corrosion resistance of the damaged coating zone of the weld junction and the base coating of the base pipe metal was carrried out. Corrosion resistance of weld junctions of pipes and profiles with various zinc alloy coatings was evaluated. The damaged area of the zinc coating in the weld junction zone is a corrosion center of the base metal. Under certain conditions the corrosion resistance is different and depends on the degree of the coating damage. The wider and the deeper is the area of the damaged coating that exceeds the action of the anode protection, the more corrosion centers of the base metal exist.