Galvanized seamless steel pipes have very little galvanizing, only 10-50g/m2, and their corrosion resistance is much worse than that of hot-dip galvanized pipes. Regular galvanized pipe manufacturers use quenched galvanized pipes as water and gas pipes. The galvanized layer of the cold-galvanized steel pipe is an electroplated layer, and the zinc layer and the steel pipe base are separately layered. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe base and is easy to fall off. Therefore, its corrosion resistance is poor. In newly built houses, the use of cold-galvanized steel pipes as feedwater pipes is prohibited.
Anyone who has been in contact with galvanized seamless steel pipes for a long time will analyze the appearance of galvanized seamless steel tubes from the appearance of galvanized seamless steel tubes.
Made a detailed summary:
The galvanized seamless steel tube galvanized layer is passivated by chromate to improve corrosion resistance by 6-8 times. Therefore, galvanizing passivation treatment is an indispensable step. Organic dyeing on the passivation film can be used as a protective coating for low-document products.
Zinc is easily corroded when it is in contact with volatiles (low molecular carboxylic acids, aldehydes, phenols, ammonia, etc.) of non-metallic materials in a closed or poorly ventilated, humid air condition, producing a white loose corrosion product, commonly known as " Hoar frost." Zinc-plated steel pipe in high temperature, high humidity, closed conditions, with bakelite, paint, wood. The volatiles released by the material are in contact with zinc, which has a tendency to grow filamentous single crystals.
Zinc's standard potential is more negative than iron and is anodized for steel, providing reliable electrochemical protection. In the industrial atmosphere, the steel products used in the rural atmosphere and the maritime atmosphere can be selected as the protective layer of zinc, and the protective life is almost proportional to the thickness of the zinc layer. In the atmosphere of industrial waste gas pollution, zinc plating of galvanized steel pipe is better than cadmium plating, and vice versa in sea or seawater.
The appearance of the galvanized seamless steel pipe coating is blue-white, the standard electrode potential is -0.76V, soluble in acid, soluble in alkali, and is a typical amphoteric metal. Zinc hardly changes in dry air. The critical humidity of zinc corrosion is more than 70%. Therefore, it can react with carbon dioxide and oxygen in a humid atmosphere to form a film mainly composed of basic zinc carbonate. This film has certain Corrosion inhibition, zinc reacts with sulfides such as hydrogen sulfide to form zinc sulfide; zinc is easily etched by chloride ions, so it is unstable in seawater.
