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Welded and seamless steel pipes

Nov. 28, 2019

1.Welded steel pipe

Welded steel pipes, also known as seam steel pipes, are generally welded from steel plates or steel strips. According to the surface treatment of the pipe, it is divided into galvanized and non-galvanized. The surface is galvanized and white, also called white iron pipe or galvanized steel pipe. Non-galvanized surface is ordinary welded steel pipe, also known as black iron pipe.

Galvanized welded steel pipes are often used for pipelines that require relatively clean transportation media, such as domestic water, purified air, and instrument air. Non-galvanized welded steel pipes can be used for steam, gas, compressed air, and condensed water.

According to user requirements, welded steel pipes can be divided into two types at the factory: one is threaded at the pipe end, and the other is unthreaded at the pipe end. The length of each welded steel pipe with thread at the pipe end is 4-9m, and the length of each pipe without welded steel pipe is 4-12m.Welded steel pipes are classified into thin-walled steel pipes, thickened steel pipes, and ordinary steel pipes according to different wall thicknesses. Ordinary steel pipe is the most used on the process pipeline, and its test pressure is 2.0MPa. The test pressure of the thickened steel pipe is 3.0 MPa.

There are many connection methods for welded steel pipes, including screw connection, flange connection and welding. The flange connection is divided into threaded flange connection and welding flange connection, and the welding method is divided into gas welding and arc welding.

Galvanized Steel Pipe

Galvanized Steel Pipe

2.Seamless steel pipe

Seamless steel pipe is the pipe with the largest amount and most variety in industrial pipes.

Basically divided into two categories: seamless steel pipes for fluid transportation and seamless steel pipes with special characteristics. The former is a steel pipe commonly used in process pipelines, and the latter is a steel pipe for boilers, a cracking furnace pipe, and a heat exchanger steel pipe.

According to the material, it can be divided into: seamless carbon steel pipe, chrome molybdenum seamless steel pipe and stainless, acid-resistant seamless steel pipe.

(1) Commonly used materials for carbon seamless steel pipes are No. 10, No. 20, and 16Mn steel. It is widely used to transport various non-corrosive media to steel, such as steam, oxygen, compressed air, oil and oil and gas.

(2) Low-alloy steel seamless steel pipes are alloy steel pipes containing a certain proportion of alloying elements. Usually divided into two types: one is a low-alloy steel pipe containing manganese, known as ordinary low-alloy steel pipe, such as 16Mn, 15MnV, etc .; the other is a low-alloy steel pipe containing chromium, molybdenum and other elements, called chromium-molybdenum steel pipe. Low-alloy seamless steel pipes are mostly used to transport various high-temperature oil products, oil and gas, and less corrosive salt water, and low-concentration organic acids.

(3) Stainless acid-resistant seamless steel pipes have many varieties according to the different contents of various metals such as chromium, nickel, and titanium, including Cr13, 00Cr17Ni14Mo2, 1Cr18Ni12Mo2Ti, 1Cr18Ni9Ti, and so on. The most used of these steel grades is 1Cr18Ni9Ti. It is used to transport various corrosive media such as nitric acid, acetic acid and urea in chemical production.

(4) The manufacturing material of the high-pressure seamless steel pipe is basically the same as the seamless steel pipe described above, except that the pipe wall is thicker than the low-pressure seamless square steel pipe, and the thickest pipe wall is 40mm. The above high-pressure seamless steel pipes are used in petrochemical plants to transport media such as raw gas, hydrogen nitrogen, synthesis gas, water vapor, and high-pressure condensate.

(5) The low temperature steel pipe is used in the cold area of the introduced project. The material grades are STPL-39 and STPL-46, and the operating temperature can reach -105 ° C. Low temperature steel pipe is divided into two types: seamless steel pipe and seam steel pipe, which are suitable for conveying various non-corrosive low temperature medium pipes. At present, there is no mass production of steel pipes corresponding to this standard in China.