Color Analysis of Galvanized Seamless Steel Pipes

The galvanized seamless steel pipe is very few, only 10-50g / m2, and its corrosion resistance is much worse than that of hot dip galvanized pipe. Conventional galvanized pipe manufacturers use hardened galvanized pipes as water and gas pipes. The galvanized layer of cold galvanized steel pipe is electroplated layer, and the zinc layer and steel pipe substrate are laminated respectively. The zinc layer is very thin. The zinc layer is simply attached to the base of the steel pipe, which is easy to fall off. Therefore, its corrosion resistance is poor. In new buildings, it is forbidden to use cold galvanized steel pipes as water supply pipes.


Those who have long-term contact with galvanized seamless steel pipe will analyze the appearance of galvanized seamless steel pipe according to the appearance of galvanized seamless steel pipe.


A detailed summary is made:
The zinc coating of galvanized seamless steel pipe is passivated by chromate to improve the corrosion resistance by 6-8 times. Therefore, passivation treatment of zinc plating is an essential step. The organic dye on the passivation film can be used as the protective coating of low certification products.


Under the condition of closed or poorly ventilated humid air, zinc is easy to corrode when contacting with the volatiles of non-metallic materials (low molecular carboxylic acid, aldehyde, phenol, ammonia, etc.), resulting in white loose corrosion products, which are usually called "white frost". High temperature, high humidity, closed condition galvanized steel pipe, with bakelite, paint, wood. The volatiles released from the materials are in contact with zinc, which tends to grow filamentous single crystals.


The standard potential of zinc is more negative than that of iron, and the steel is anodized to provide reliable electrochemical protection. In the industrial atmosphere, the steel products used in the rural atmosphere and marine atmosphere can be chosen as the protective layer of zinc, whose protective life is almost proportional to the thickness of the zinc layer. In the environment polluted by industrial waste gas, zinc coating of galvanized steel pipe is better than cadmium coating, and vice versa in seawater or seawater.


The appearance of galvanized seamless steel pipe coating is blue white, the standard electrode potential is - 0.76v, soluble in acid, soluble in alkali, which is a typical amphoteric metal. Zinc is almost constant in dry air. The critical humidity of zinc corrosion is over 70%. Therefore, it can react with carbon dioxide and oxygen in a humid atmosphere to form a film mainly composed of alkaline zinc carbonate. The film has a certain corrosion inhibition effect, zinc reacts with sulfide such as hydrogen sulfide to form zinc sulfide; zinc is easily corroded by chloride ion, so it is unstable in seawater.