Types of production of welded steel pipes

Welded steel tube

Also called welded pipe, it is cut into narrow steel strips from steel strips, and then wrapped into tubes by cold working with molds. A special welder then welds a pipe seam. The outer weld seams are polished brightly. The internal burrs of ordinary welded pipes are not punched. Only precision welded pipes have internal burrs.

Anti-corrosion points: Welded steel pipe refers to a steel pipe with seams on the surface that is welded after bending and deforming a steel strip or steel plate into a round, square, etc. shape. According to different welding methods, it can be divided into arc welded pipes, high frequency or low frequency resistance welded pipes, gas welded pipes, furnace welded pipes, Bondi pipes, etc. According to the shape of the weld, it can be divided into straight seam welded pipe and spiral welded pipe. Electric welded steel pipes are used in oil drilling, machinery and manufacturing industries, etc. Furnace welded pipes can be used as water 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. Welded steel pipes have lower cost and higher production efficiency than seamless steel pipes.

Longitudinal welded pipe

It is made of steel plate or steel strip after bending and then welding. Welded pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of welds. ERW pipes and LSAW pipes are straight seam welded pipes

General welded pipe

Generally, welded pipes are used to transport low-pressure fluids. Made of Q195A, Q215A, Q235A steel. It can also be manufactured from other mild steels that are easy to weld. Steel pipes are subject to water pressure, bending, flattening and other tests, and have certain requirements for surface quality. Usually, the delivery length is 4-10m, and delivery is often required to be fixed length (or double length). The specification of the welded pipe is represented by the nominal diameter (mm or inch). The nominal diameter is different from the actual one. The welded pipe has two types of ordinary steel pipe and thickened steel pipe according to the specified wall thickness. The steel pipe is divided into two types: threaded and unthreaded according to the pipe end form.

There is no need for electric welding machines and high-frequency resistance straight seam welding pipes with wires, and there is no need to make cross-ground wires, no need to paint, and the complicated construction procedures such as traditional fusion welding and wire sleeves are omitted. Just connect the straight pipe joint to the pipe, the threaded pipe joint to the theoretical weight of the round steel pipe and the junction box, and use a special tool to tighten (twist off) the screw after positioning. Fasten with the lock nut at the high-frequency resistance seam welding of the junction box. The pipe bender can be used to bend the corresponding arc on site at the corner of the pipeline.

Technology of Longitudinal Welded Pipe

 The steel pipe dimension is usually specified as follows: the nominal diameter of the welded pipe is 6~150mm, the nominal wall thickness is 2.0~6.0mm, and the length of the welded pipe is usually 4~10 meters. The surface quality of the steel pipe should be smooth, and defects such as folding, cracks, delamination, and lap welding are not allowed. The surface of the steel pipe is allowed to have minor defects such as scratches, scratches, weld misalignment, burns and scars that do not exceed the negative deviation of the wall thickness. The thickening of the wall thickness and the presence of inner seam weld bars are allowed at the weld.

quality inspection

Welded steel pipes should be subjected to mechanical performance test, flattening test and flaring test, and must meet the requirements of the standard. The steel pipe should be able to withstand a certain internal pressure, and if necessary, carry out a 2.5Mpa pressure test to keep it leak-free for one minute. The method of eddy current flaw detection is allowed to replace the hydrostatic test. The eddy current flaw detection method is to fix the probe on the frame, keep a distance of 3~5mm between the flaw detection and the weld seam, and conduct a comprehensive scan of the weld seam by the rapid movement of the steel pipe. The flaw detection signal is automatically processed and sorted by the eddy current flaw detector. To achieve the purpose of flaw detection. The welded pipe after the flaw detection is cut off according to the specified length with a flying saw, and it is rolled off the assembly line through the turning frame. Both ends of the steel pipe should be chamfered with flat ends, printed with marks, and the finished pipes are packed in hexagonal bundles before leaving the factory.

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