The reason for the presence of a noticeable cluster of corrosion pits on the surface of welded steel pipes after pickling

After pickling, welded steel pipes are prone to developing corrosion pits along the longitudinal weld seam, leading to the occurrence of such defects particularly in gas-welded and furnace-welded steel pipes. The primary cause of these weld seam corrosion pit clusters is the temperature difference between the weld seam and the base metal during the welding process, which results in internal stresses. Areas with internal stresses are susceptible to varying degrees of corrosion by the pickling solution. Additionally, oxides and other impurities pressed into the dissolved weld seam during welding undergo differential corrosion rates in the pickling solution due to their different electrical potentials, leading to uneven corrosion pits.