Cold galvanized square pipe is galvanized, the amount of zinc is very small, only 10-50g/m2, the corrosion resistance of its own specific galvanized pipe difference. Regular galvanized pipe manufacturers, in order to ensure quality, most do not use electro galvanized (Leng Du). Only those small scale, obsolete equipment of small enterprises using zinc plating, of course, their prices are relatively cheap. At present, the Ministry of construction has been officially below, the elimination of backward technology of cold galvanized pipe, the future is not allowed to use galvanized pipe for water, gas pipe.

Generally speaking, the diameter of the pipe can be divided into outer diameter, inner diameter and nominal diameter. The outer diameter of the pipe for the cold galvanized square pipe is indicated by the letter D, and the diameter and the wall thickness of the outer diameter are added. For example, outer diameter of 108 cold galvanized pipe, wall thickness of 5MM, denoted by D108*5, is also used outside said, such as De63 plastic pipe, such as reinforced concrete pipe, cast iron pipe, galvanized steel pipe, represented by DN, in the design drawings is generally used to represent the nominal diameter, nominal diameter to a standard design and manufacture and maintenance convenience is artificially specified, nominal diameter, tube (or pipe) specification name.

The nominal diameter of the pipe is not equal to its inner diameter and outer diameter. For example: the nominal diameter of 100MM cold galvanized square tube mail 102*5, 108*5 and so on several, 108 for the pipe outside diameter, the wall thickness of the pipe of 5, therefore, the inner diameter of the steel pipe (108*5-5) =98MM. But it is not exactly equal to the difference of two times the wall thickness of the steel pipe. It can be said that the nominal diameter is close to the inner diameter. But it is not equal to the diameter of the diameter of a pipe of the name of the specification, the design drawings in order to use the nominal diameter. The purpose is to determine the nominal diameter of pipe, pipe fittings, valves, flanges, gaskets and other structural dimensions and connection dimensions, nominal diameter DN. If the outer diameter is indicated in the design drawing, the piping specifications shall also be made to indicate the nominal diameter and wall thickness of the pipe.