1. Basic knowledge of welded steel pipes
Welded steel pipes refer to steel pipes with seams on the surface that are formed by bending steel strips or steel plates into round, square and other shapes and then welding them. The blanks used for welded steel pipes are steel plates or strip steel. Welded steel pipes have lower costs and higher production efficiency than seamless steel pipes. Welded steel pipes are generally used for circulating cooling water pipes, pressure drainage pipes, and rainwater pipes in factories and high-rise buildings. The difference between welded steel pipes and seamless steel pipes is that seamless steel pipes can withstand stronger pressure.
2. Classification of welded steel pipes
2.1 According to different welding methods, they can be divided into arc welded pipes, high-frequency or low-frequency resistance welded pipes, gas welded pipes, furnace welded pipes, Bondi pipes, etc.
Electric welded steel pipes: used for oil drilling and machinery manufacturing, etc.
Furnace welded pipes: can be used as water and gas pipes, etc., large-diameter straight seam welded pipes are used for high-pressure oil and gas transportation, etc.; spiral welded pipes are used for oil and gas transportation, pipe piles, bridge piers, etc.
2.2 According to the shape of the weld, it can be divided into straight seam welded pipe and spiral welded pipe
Straight seam welded pipe: simple production process, high production efficiency, low cost, and rapid development.
Spiral welded pipe: The strength is generally higher than that of straight seam welded pipe. It can produce welded pipes with larger diameters with narrower billets, and can also produce welded pipes with different diameters with billets of the same width. However, compared with straight seam pipes of the same length, the weld length increases by 30~100%, and the production speed is lower. Therefore, smaller diameter welded pipes mostly use straight seam welding, while large diameter welded pipes mostly use spiral welding.
Spiral seam welded steel pipes are divided into two types: automatic submerged arc welded steel pipes and high frequency welded steel pipes.
a. Spiral seam automatic submerged arc welded steel pipes are divided into Class A pipes and Class B pipes according to the pressure of the conveying medium. Class A pipes are generally welded with ordinary carbon steel Q235, Q235F and ordinary low-alloy structural steel 16Mn, and Class B pipes are welded with Q235, Q235F, Q195 and other steel materials, and are used as low-pressure fluid delivery pipes.
b. Spiral seam high-frequency welded steel pipes Spiral seam high-frequency welded steel pipes, there is no unified product standard, and are generally made of ordinary carbon steel Q235, Q235F and other steel materials.
2.3 According to the use, it is divided into general welded pipes, galvanized welded pipes, oxygen-blown welded pipes, wire casings, metric welded pipes, roller pipes, deep well pump pipes, automobile pipes, transformer pipes, electric welded thin-walled pipes, electric welded special-shaped pipes and spiral welded pipes.
3. Common specifications of welded steel pipes
Nominal diameter: DN15 DN20 DN25 DN32 DN40 DN50 DN65 DN80 DN100 DN150 DN200 DN250 DN300 DN350 DN400 DN500 DN600 DN700 DN800 DN900 DN1000 DN1200
4. Applicable specifications, standards and connection methods
1) DN≤80mm threaded connection;
2) DN≥100mm welding or flange connection "Welded Steel Pipe for Low-pressure Fluid Transportation" GB/T3091-2008
5. Factors affecting the price of welded steel pipes
Price ranking of brand (material): Q345>Q295>Q275>Q255B>Q255A>Q235B>Q235A>Q215>Q195;
Outer diameter and wall thickness: As the outer diameter and wall thickness of stainless steel pipes increase, the price increases;
Well-known brands: Huaqi, Junjia, Tangshan Jinghua, Zhenhong
Other factors: Variety and welding method will affect the price difference, such as ordinary carbon welded steel pipes, alloy steel welded steel pipes;
Meter weight formula: (outer diameter-wall thickness)×wall thickness×0.02466=kg/m;
