Production and requirement of welded steel pipe

　　Welded steel pipe, also called steel flower welded pipes, is a steel pipe made by welding a steel plate or a steel strip after being crimped. The welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and low equipment investment, but the general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technology, the quality of welded joints has been continuously improved, the variety specifications of welded steel pipes have been increasing, and more and more fields have replaced seamless steel pipe.

　　Welded steel pipes are divided into straight welded pipes and spiral welded pipes in the form of welds. Straight seam welded pipe has simple production process, high production efficiency, low cost and rapid development. The strength of the spiral welded pipe is generally higher than that of the straight welded pipe. It is possible to produce a welded pipe with a larger diameter by using a narrow blank, and it is also possible to produce a welded pipe having a different pipe diameter with a blank of the same width. However, compared with the straight pipe of the same length, the weld length is increased by 30 to 100%, and the production speed is low. Therefore, the smaller diameter welded pipes are mostly straight seam welded, and the large diameter welded pipes are mostly spiral welded.

　　1. Welded steel pipes for low-pressure fluid transportation are also called general welded pipes, commonly known as black pipes. It is a welded steel pipe for conveying general low pressure fluids such as water, gas, air, oil and heating steam and other purposes. The thickness of the steel pipe is divided into ordinary steel pipe and thick steel pipe; the pipe end form is divided into non-threaded steel pipe (light pipe) and threaded steel pipe. The specification of the steel pipe is expressed by the nominal diameter (mm), and the nominal diameter is an approximation of the inner diameter. It is customary to use inches, such as 11/2. The welded steel pipe for low-pressure fluid transportation is mainly used as a raw pipe for galvanized welded steel pipe for low-pressure fluid transportation, in addition to being directly used for conveying fluid.

　　2. Galvanized welded steel pipes for low-pressure fluid transportation are also called galvanized electric welded steel pipes, commonly known as white pipes. It is a hot dip galvanizing (furnace welding or electric welding) steel pipe for conveying water, gas, air, oil and general lower pressure fluids such as heating, steam and warm water. The thickness of the steel pipe is divided into ordinary galvanized steel pipe and thick galvanized steel pipe; the connection end form is divided into non-thread galvanized steel pipe and threaded galvanized steel pipe. The specification of the steel pipe is expressed by the nominal diameter (mm), and the nominal diameter is an approximation of the inner diameter.

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