Welded steel pipe is referred to as welded pipe, and the steel pipe is usually welded after the unit and the die are formed by crimping. The welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and less equipment, 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, and the variety specifications of welded steel pipes are increasing, and in more and more fields, especially in In the heat exchange, the spare pipe, the decorative pipe, the medium and low pressure fluid pipe and the like replace the seamless steel pipe.
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 large diameter by using a narrow blank, and it is also possible to produce a welded pipe having a different pipe diameter by using 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.
Generally, the diameter of the pipe can be divided into an outer diameter, an inner diameter, and a nominal diameter. The outer diameter of the tube in which the pipe is a spiral steel pipe is indicated by the letter D, followed by the size and wall thickness of the outer diameter, for example, a seamless steel pipe having an outer diameter of 108.
First, the national standard for welded steel pipe
1. GB/T3091-1993 (galvanized welded steel pipe for low pressure fluid transportation). It is mainly used to transport water, gas, air, oil and heating water or steam, such as general lower pressure fluids and other uses. It stands for material Q235A grade steel.
2. GB/T3092-1993 (galvanized welded steel pipe for low pressure fluid transportation). It is mainly used to transport water, gas, air, oil and heating water or steam, such as general lower pressure fluids and other uses. Its representative material is: Q235A grade steel.
3. GB/T14291-1992 (mineral fluid conveying welded steel pipe). It is mainly used for straight seam welded steel pipes for mine pressure, drainage and shaft discharge. It stands for material Q235A, B grade steel. GB/T14980-1994 (large diameter electric welded steel pipe for low pressure fluid transportation). It is mainly used to transport low pressure fluids such as water, sewage, gas, air, heating steam and other uses. It stands for material Q235A grade steel.
4. GB/T12770-1991 (stainless steel welded steel pipe for mechanical structure). Mainly used in machinery, automobiles, bicycles, furniture, hotel and restaurant decoration and other mechanical parts and structural parts. It represents materials 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, and the like.
Second, welded steel pipe classification
A. Welded pipes can be basically divided into straight seam welded pipes and spiral welded pipes according to the shape of welds:
1. Straight seam welded steel pipe: simple production process, high production efficiency, low cost and rapid development. There are many straight seam welded pipes for general industrial use.
2, spiral welded steel pipe: the strength is generally higher than the straight seam welded pipe, can produce a larger diameter pipe with a narrow blank, can also use the same width of the blank to produce pipes with different diameter; but with the same length of straight pipe Compared with spiral welded steel pipe, the weld length is increased by 30~100%, 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.
B. Welded pipes are divided into the following types according to their purposes:
1. General welded steel pipe: General welded steel pipe is used to transport low pressure fluid. It is made of Q195A, Q215A, Q235A steel. It can also be made of other soft steel which is easy to weld. The steel pipe should be subjected to water pressure, bending, flattening, etc. The quality has certain requirements, usually the delivery length is 4-10m, often requires a fixed length (or multiple feet) delivery. The specification of the welded pipe is expressed by the nominal diameter (mm or inch). The nominal diameter is different from the actual. The welded pipe has the specified wall thickness. Ordinary steel pipe and thick steel pipe. The steel pipe is divided into two types according to the pipe end.
2. Galvanized welded steel pipe: In order to improve the corrosion resistance of the steel pipe, the general steel pipe (black pipe) is galvanized. The galvanized steel pipe is divided into two types: hot-dip galvanizing and electric steel zinc, hot-dip galvanized galvanized layer, electro-galvanized low cost.
3, oxygen-blowing welded steel pipe: used as steel pipe for oxygen blowing, generally with small diameter welded steel pipe, the specifications are made of 3/8 inch-2 inch eight kinds of 08,10,15,20 or Q195-Q235 steel strip For corrosion protection, some for aluminizing treatment.
4, wire casing: is also ordinary carbon steel electric welded steel pipe, used in concrete and various structural distribution projects, commonly used nominal diameter from 13-76mm.
5. Metric welded steel pipe: The specification is in the form of seamless pipe, welded steel pipe with outer diameter * wall thickness and millimeter, using ordinary carbon steel, high quality carbon steel or ordinary low alloy steel for tropical, cold band welding, or It is made by tropical cold welding and then by cold dialing method. Metric welded pipe is divided into general energy and thin wall. It is commonly used as structural parts, such as transmission shafts or conveying fluid. Thin wall is used to produce furniture, lamps, etc., to ensure the strength and bending of steel pipes. test.
6. Roller tube: used for belt conveyor electric welding steel pipe, generally made of Q215, Q235A, B steel and 20 steel, diameter 63.5-219.0mm. For pipe bending, the end face should be perpendicular to the center line, ovality There are certain requirements, generally water pressure and flattening test.
7. Transformer tube: used to manufacture transformer heat pipe and other heat exchangers. It is made of ordinary carbon steel and requires flattening, flaring, bending and hydraulic test. The steel pipe is delivered in fixed length or multiple times, and the steel pipe is bent. Degree has certain requirements.
8. Shaped tube: square tube welded by ordinary carbon-bonded structural steel and 16Mn steel strip, rectangular tube, hat-shaped tube, steel tube for empty rubber steel doors and windows, mainly used as agricultural machinery components, steel window doors, etc.
9, electric welding thin-walled steel pipe: mainly used to make furniture, toys, lamps and so on. In recent years, thin-walled tubes made of stainless steel strips have been widely used, such as high-grade furniture, decoration, and fences.
10. Spiral welded steel pipe: It is made by rolling a low carbon carbon structural steel or a low alloy structural steel strip into a tube blank at a certain angle of a helix (called a forming angle), and then welding the pipe joint, which can be used. A narrow strip produces a large diameter steel tube. Spiral welded steel pipe is mainly used for oil and natural gas transmission pipelines, and its specifications are expressed by outer diameter * wall thickness.
C. According to the shape of the end, it is divided into round welded steel pipe and special-shaped (square, flat, etc.) welded steel pipe.
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