The nominal diameter is generally used in the design drawings to indicate that the nominal diameter is a standard that is artificially prescribed for the convenience of design, manufacturing and maintenance, and is also a nominal diameter, which is the specification name of the pipe (or pipe fittings). The nominal diameter of the pipe is not equal to its inside and outside diameter, such as:The nominal diameter of 100MM seamless square pipe post 102*5, 108*5 and other several kinds, 108 is the outer diameter of the pipe, 5 indicates the wall thickness of the pipe, therefore, the inner diameter of the square pipe is (108*5-5)=98MM, but it is not completely equal to the square pipe diameter minus twice the difference in wall thickness, it can also be said that the nominal diameter is close to the inner diameter, But not equal to the inner diameter of a pipe diameter specification name, so in the design drawings to use the nominal diameter, the purpose is to determine according to the nominal diameter of the pipe, pipe fittings, valves, flanges, gaskets and other structural size and connection size, the nominal diameter is expressed by the symbol DN, if the outside diameter is expressed in the design drawings, the pipe specification comparison table should also be made. Indicates the nominal diameter and wall thickness of a pipe.
The main difference between galvanized square pipe and welded pipe:welded pipe is divided into spiral seam welding and straight welded square pipe, spiral seam welded square pipe is divided into automatic submerged arc welding pipe and high-frequency welding pipe, and straight welded square pipe is divided into ordinary straight welded steel pipe and stainless welded pipe. Seamless square pipe is divided into hot rolled pipe and cold rolled (pulled) pipe according to the manufacturing method, and its accuracy is divided into ordinary and advanced two kinds. The maximum nominal straight diameter of the cold-rolled (drawn) pipe is 200mm, and the maximum nominal diameter of the hot-rolled pipe is 600mm. There are stainless steel seamless square tubes, stainless steel seamless square tubes are divided into hot rolled, hot extruded stainless steel seamless square tubes and cold rolled (pulled) stainless steel seamless square tubes.
The protective layer type (mainly refers to the inner wall of the pipeline) now has a metal protective layer type and a non-gold protective layer type, and the metal protective layer type is commonly used to have a surface coating protective layer type and a surface pressing protective layer type. The common surface coating protective layer type is galvanized pipe, galvanized pipe also has cold galvanized pipe and hot galvanized pipe, hot galvanized pipe because the protective layer is dense and uniform, strong adhesion and good stability, is still widely used.
2. The role of galvanized steel pipe
Galvanized steel pipe, as the name suggests, is a product made of galvanized steel pipe surface, which is mainly characterized by uniform coating, strong adhesion, long service life and other advantages, and is widely used in industrial production.
In order to improve the corrosion resistance of the steel pipe, the general steel pipe is galvanized. Galvanized steel pipe is divided into hot dip galvanized and electric galvanized two, hot dip galvanized galvanized layer thick, hot dip galvanized steel pipe substrate and molten plating solution composite physical, chemical reaction to form a dense zinc iron alloy layer corrosion resistant structure. The alloy layer is integrated with the pure zinc layer and the steel pipe substrate. Therefore, its corrosion resistance is strong.
Electrogalvanizing cost is low, the surface is not very smooth.
In addition, in order to prevent corrosion, some should be effectively aluminized. Moreover, after galvanized treatment, the strength of the steel pipe will be increased, and it has the performance of resisting damage under static load.
Galvanized steel pipe, in addition to the pipeline pipe for water, gas, oil and other general low pressure fluids, but also used as the petroleum industry, especially the oil well pipe, oil pipeline, chemical coking equipment oil heater, condensing cooler, coal distillation and washing oil exchanger pipe, as well as trestle pipe pile, mine tunnel support frame pipe. The zinc layer of cold galvanized steel pipe is an electric coating, and the zinc layer is separated from the steel pipe substrate. The zinc layer is very thin, the zinc layer is simply attached to the steel pipe substrate, and it is easy to fall off. Therefore, its corrosion resistance is poor. In new homes, it is prohibited to use cold galvanized steel pipes as water supply pipes.
Most of the old houses are used with galvanized pipes, and now the kind of iron pipes used for gas and heating are also galvanized pipes. Galvanized pipes are used as water pipes. After several years of use, a large number of rust and scale are produced in the pipes, and the yellow water flowing out not only contaminizes sanitary ware, but also contains bacteria that breed on the inner wall. In the 1960s and 1970s, the developed countries in the world began to develop new types of pipes and gradually banned galvanized pipes. China's Ministry of Construction and other four ministries and commissions have also issued a document to prohibit galvanized pipes from 2000, at present, the cold water pipes in the new community have rarely used galvanized pipes, and the hot water pipes in some communities use galvanized pipes.