What is ERW steel pipe?
ERW steel pipe (resistance welded steel pipe) uses the skin effect and proximity effect of high-frequency current to heat and melt the edges of the hot-rolled coil formed by the forming machine, and then weld the pressing and extrusion rollers under pressure to achieve production.
Electric resistance welded steel pipes are divided into two forms: AC welded steel pipes and DC welded steel pipes. AC welding is divided into low frequency welding, medium frequency welding, super medium frequency welding and high frequency welding according to frequency. High-frequency welding is mainly used for the production of thin-walled steel pipes or ordinary-walled steel pipes. High-frequency welding is divided into contact welding and induction welding. Small diameter steel pipes generally use DC welding.
Therefore, in summary, high-frequency welded pipes belong to ERW welded pipes, which are a type of ERW welded pipes produced using high-frequency welding processes. ERW straight seam welded pipe is a steel pipe with advanced product performance, leading quality and relatively economical performance in the field of oil and gas storage and transportation.
What is submerged arc welded steel pipe?
SAW steel pipe (submerged arc welded steel pipe) can be divided into straight seam submerged arc welded steel pipe (LSAW steel pipe) and spiral submerged arc welded steel pipe (SSAW steel pipe). SAW is a manufacturing process that utilizes submerged arc welding of steel, which produces a high current density that prevents the flux layer from quickly losing heat and concentrating it in the weld area. A commonly used standard is API 5L.
Submerged arc welded pipes have the characteristics of high weld quality, high production efficiency, and smoke-free arc ignition. Submerged arc welded pipes are widely used in pressure vessels, pipeline manufacturing, construction beams, low-pressure fluids, and steel structure projects.
Carbon steel welded pipes can be divided into three types according to the forming method of the weld: longitudinal submerged arc welded steel pipes, spiral welded steel pipes, and high-frequency straight seam welded steel pipes (resistance welded steel pipes). During the manufacturing process, we can see that ERW steel pipes and SAW steel pipes (LSAW, SSAW) have completely different forming and welding methods.
1) ERW steel pipe manufacturing method
During the ERW steel pipe welding process, two electrodes, usually made of copper, are used to apply pressure and electric current. The electrodes are disk-shaped and rotate as material passes between them. This allows the electrode to maintain constant contact with the material for long periods of continuous welding.
Due to the different pipe forming, welding and process processes of ERW steel pipes and SAW steel pipes, there are some differences in performance between the two steel pipes:
1. Surface quality.
Although both SAW steel pipes and ERW steel pipes have welds, the welds of ERW steel pipes are flat and smooth, which is better than SAW (LSAW, SSAW) steel pipes. In most submerged arc welded pipes, the main weld reinforcement is internal and external.
2. ERW steel pipes have fewer types of weld defects than SAW steel pipes.
Due to the deposition of solvent in submerged arc welding, more defects will be produced in addition to volume defects. The only defects found in straight seam welded steel pipes are straight welds and linear welds, which are easy to inspect. Defects are easily noticed, and ultrasonic reflection from the surface makes detection easier.
3. The residual stress ratio of ERW steel pipe is lower than that of SAW steel pipe.
ERW steel pipes have lower residual stress than SAW steel pipes. Since the ERW welded pipe is relatively fully deformed during the deformation process, coupled with the oblate ellipse, elliptical vertical changes and shrinkage in subsequent sizing, the residual stress of the ERW steel pipe becomes smaller. Physical testing shows that after ERW welded pipes of the same specifications and materials are cut along the axial direction, the displacements of the axial and transverse cuts are smaller than those of SAW welded pipes.
