ERW pipe (Electric Resistance Welded Steel Pipe) uses the skin effect and proximity effect of high-frequency current to heat and melt the edge of the pipe blank after the hot rolled coil is formed by a forming machine, and presses it under the action of a squeeze roller Welding to achieve production. ERW has the characteristics of high efficiency, low cost, material saving and easy automation, it is widely used in aviation, aerospace,energy, electronics, automotive, light industry and other industrial sectors, is an important link in the welding process.
SAW Welded Pipe vs ERW Welded Pipe
In the manufacturing process, we can see SAW welded pipes (LSAW, SSAW) and ERW welded pipes have completely different forming and welding methods
1) SAW welded steel pipe manufacturing process:
In the single-seam SAW welded steel pipe, submerged arc welding process is used for welding.In this method,a welding arc is submerged in welding flux. A continuous solid filler wire is input from the outside. The pipe is double-welded, first is inside and then welding from the outside.
In the case of double seam SAW welded steel pipe, the first two halves are connected by tack welding, which is called fit-up. Double seam saw steel pipe has two opposite weld seam. Both seams are welded from inside and outside of the pipe.
In a spiral SAW welded pipe, steel plate from the de-coiler is formed in a spiral loop. This spiral loop is then welded from inside and outside of the pipe.Because of the method of manufacture, a wide variety of diameters can be produced. SSAW welded pipes are used for low-pressure services.
Whereas LSAW welded pipes are used for medium to high-pressure services. SSAW welded pipes are less costly compared to LSAW welded pipe.
2) ERW welded steel pipe manufacturing method:
When ERW welded steel pipe welding process, two electrodes, usually made from copper, are used to apply pressure and current. The electrodes are disc shaped and rotate as the material passes between them. This allows the electrodes to stay in constant contact with the material to make long continuous welds.
As ERW welded steel pipe and SAW welded steel pipe in the pipe during forming,welding and process is different,so that two kinds of steel pipe in the performance there are some differences:
1. The surface quality.
Though both SAW pipes and ERW welded pipes all have weld seam.The welding seam of ERW pipe is flat,smooth and better than SAW (LSAW,SSAW) pipes.In most of the SAW pipes, it is mainly about the weld reinforcement internally and externally.
2.ERW welded steel pipe weld defect types is less than the SAW welded steel pipe.
Because of the solvent deposited in SAW, in addition to volume defects it results in more defects.The defects found in ERW welded steel pipes are only straight welds and wire-line and are easy to inspect. The defects can be noticed easily and the ultrasonic reflection on the surface makes it easier to detect.
3. The residual stress ratio in ERW is lower than SAW welded pipes.
ERW welded steel pipe related to SAW welded steel pipe in residual stress ratio is low. Since ERW welded pipe deformation in the deformation process more fully, coupled subsequent sizing flat oval,elliptical vertical changes and necking, making ERW welded pipe residual stress becomes smaller. Physical testing showed that the same specifications, the same material ERW welded pipe after incision along the axis, the axial and transverse incisions smaller displacement than the SAW welded pipe.
4.The overall performance.
Although the overall performance of both ERW welded pipe and SAW welded pipe are the same,when the pipe becomes defective,the steel scrap and welding can be done on ERW welded pipe,while it is not the same in case of SAW, which would result in cracking or corrosion.So ERW welded pipe are more durable than SAW welded pipe.
Spiral welding (SSAW steel pipe)–this is also a type of submerged arc welding with a spiral weld.