Galvanized steel pipe galvanized layer by chromate passivation, corrosion resistance can be increased by 6--8 times. The passivation treatment is necessary steps. The organic dye on the passivation film, can be used forlow file product protection, decorative coating.
Zinc in the closed or poor ventilation, air wet conditions, and non-metallic materials volatiles (low molecular carboxylic acid, aldehyde, phenol, ammonia) contact, zinc and prone to corrosion, corrosion products of white loose, commonly known as "frost". The zinc galvanized steel pipe in high temperature, high humidity, airtight conditions, and bakelite, wood paint, release of the volatile contact, zinc has a tendency to grow filaments of single crystal, commonly known as "long hair".
Zinc standard potential than iron steel is negative, the anode coating, can provide reliable electrochemical protection. In the industrial atmosphere, rural atmosphere and ocean atmosphere in the iron and steel products can choose zinc as a protective layer, the protective layer thickness and zinc almost life is proportional to. Where the industrial air pollution in the atmosphere, the corrosion resistance is better than that of cadmium plating galvanized steel zinc coating, on the sea or ocean in the opposite.
Galvanized steel pipe coating has the appearance of a bluish white, the standard electrode potential is -0.76V,soluble in acid, soluble in alkali, is amphoteric metal curved. Zinc in dry air almost does not change, the critical humidity zinc corrosion is greater than 70%, so in the damp air and carbon dioxide and oxygen to form a thin film layer is mainly composed of basic zinc carbonate composition, this membrane has good corrosion inhibition effect, zinc and hydrogen sulfide containing sulfide by reacting zinc sulfide; zinc susceptible the chloride ion etching, the instability in the sea.