According to GB3092 "Welded Steel Pipe for Low Pressure Fluid Transport" standard, the nominal diameter of welded pipe is 6-150 mm, the nominal wall thickness is 2.0-6.0 mm, and the length of welded pipe is usually 4-10 meters. It can be manufactured according to fixed or multiple length. The surface quality of steel pipes should be smooth and no defects such as folding, cracking, delamination and lap welding should be allowed. Slight defects such as scratches, scratches, weld dislocation, burns and scars are allowed on the surface of steel pipes. Thickening of weld wall and existence of internal weld reinforcement are allowed.
Welded steel pipes shall be tested for mechanical properties, flattening and flaring, and shall meet the requirements specified in the standards. The steel pipe should be able to withstand certain internal pressure. If necessary, 2.5 Mpa pressure test should be carried out to keep the pipe free of leakage for one minute. Eddy current testing is allowed to replace hydraulic testing. Eddy current testing shall be carried out according to GB7735 "Inspection Method for Eddy Current Inspection of Steel Tubes". The eddy current testing method is to fix the probe on the frame, keep the distance of 3-5 mm between the detection and the weld, scan the weld comprehensively by the rapid movement of the steel pipe, and process and sort the detection signal automatically by the eddy current flaw detector, so as to achieve the purpose of flaw detection. It is a steel pipe made of steel plate or strip welded after curling and forming. Welded steel pipe has the advantages of simple production process, high production efficiency, many varieties and specifications, and less equipment, but its general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of high-quality strip rolling production and the progress of welding and inspection technology, the quality of weld seam has been continuously improved, the variety and specification of welded steel pipe has been increasing, and seamless steel pipe has been replaced in more and more fields. Welded steel pipe is divided into straight welded pipe and spiral welded pipe according to the form of weld. Longitudinal welded pipe has the advantages of simple production process, high production efficiency, low cost and rapid development. The strength of spiral welded pipe is generally higher than that of straight welded pipe. The welded pipe with bigger diameter can be produced with narrower blank, and the welded pipe with different diameter can also be produced with the same width blank. However, compared with the straight seam pipe of the same length, the length of the weld increases by 30-100%, and the production speed is lower.
The welded pipe after flaw detection is cut off by flying saw in accordance with the specified length and is off-line through the overturning frame. The ends of the steel pipe should be flat-headed and chamfered, printed and marked, and the finished pipe should be packed in hexagonal bundles before it is discharged.
