Factors of Pits on The Surface of Hot-dip Galvanized Steel Pipe

The steel pipe blank is corroded too badly, and a thick iron oxide layer appears on the surface. Because the elements in the steel matrix are not necessarily uniform, some places are rusted deeply, and some places are rusted shallowly, and unevenness appears after pickling. Large uneven pits, such a surface still leave pits after hot-dip galvanizing. When the steel pipe was pickled, numerous pits were caused by over pickling, especially at the weld seam, which was caused by the action of the micro battery. Oversized pits cannot be filled in during hot-dip galvanizing. The amount of carbon (C) in the steel pipe matrix, iron carbide (Fe3C), silicon, aluminum, copper, phosphorus, sulfur, and nitrogen, etc. will cause pits due to different dissolution rates during pickling. Alkaline converter steel is exposed to this situation, so it is also prone to over pickling. The pickling steam scars formed in the pickling are ring-shaped or bird's nest-shaped, which easily cause pits.