Three production processes of welded pipes

Steel pipes are generally divided into seamless steel pipes and welded steel pipes according to the production method. This time we mainly introduce welded steel pipes, that is, seamed steel pipes. The production is to bend the tube blanks (steel plates and steel strips) into the required cross-sections by various forming methods. Compared with seamless steel pipe welded pipe, it has high product precision, especially high wall thickness precision, simple main equipment, small footprint, The characteristics of continuous operation and flexible production in production, welded pipes should be divided into three categories: spiral submerged arc welded pipes (SSAW), double-sided submerged arc welded pipes with straight seams (LSAW), and electric resistance welded pipes (ERW).

1. Spiral steel pipe (SSAW)

The raw materials of the spiral steel pipe (SSAW) are strip coil, welding wire and flux. Before forming, the strip undergoes leveling, trimming, planing, surface cleaning and conveying and pre-bending treatment. The welding gap control device is used to ensure that the welding gap meets the welding requirements It is required to strictly control the pipe diameter, misalignment and weld gap. After cutting into a single steel pipe, the first three pipes of each batch must undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion state and surface of the weld. After the quality and non-destructive inspection to ensure that the pipe making process is qualified, it can be officially put into production.

2. Straight seam submerged arc welded pipe (LSAW)

Generally speaking, the straight seam submerged arc welded pipe (LSAW) is made of steel plate. After different forming processes, the welded pipe is formed by double-sided submerged arc welding and post-weld expansion. The forming method of the straight seam submerged arc welded pipe is UO (UOE). , RB (RBE), JCO (JCOE), etc.

UOE straight seam submerged arc welded pipe forming process:

There are mainly three forming processes in the UOE LSAW steel pipe forming process: steel plate pre-bending, U forming and O forming. Each process uses a special forming press to complete the steel plate edge pre-bending, U forming and O forming in turn. Three processes, the steel plate is deformed into a circular tube, the JCOE straight seam submerged arc welded pipe forming process: after multiple stamping on the JCO forming machine, first half of the steel plate is pressed into a J shape, and then the other half of the steel plate is pressed into a J shape shape, forming a C shape, pressurized from the middle to form an open “O” shape tube blank.

Comparison of JCO and UO molding methods:

JCO forming is progressive pressure forming, which changes the forming process of steel pipe from two steps of UO forming to multi-step. During the forming process, the steel plate is uniformly deformed, the residual stress is small, and the surface is not scratched. There is greater flexibility in the size and specification range of the wall thickness, which can produce both large-volume products and small-batch products, not only large-diameter high-strength thick-walled steel pipes, but also small-diameter large-walled steel pipes, especially In the production of high-quality thick-walled pipes, especially the production of small and medium-diameter thick-walled pipes, it has incomparable advantages over other processes, and can meet more requirements of users for steel pipe specifications. UO forming adopts U and O pressure forming twice, which is characterized by It has large capacity and high output. Generally, the annual output can reach 300,000 to 1,000,000 tons, which is suitable for mass production of single specification.

3. Straight seam high frequency welded pipe (ERW)

Straight seam high-frequency welded pipe (ERW) is formed by using the skin effect and proximity effect of high-frequency current to heat and melt the edge of the tube blank after the hot-rolled coil is formed by a forming machine, and then pressure-welded under the action of the extrusion roller.