The difference between ERW steel pipe and SSAW steel pipe

Posted by zora li on December 2nd, 2022

Raw material difference

1. The raw materials used for ERW pipes are hot-rolled coils produced by regular large factories, and the chemical composition and physical properties are relatively stable.
2. Most of the raw materials used in the spiral pipe factory are inferior hot-rolled strip steel, with unstable chemical composition and physical properties, and many internal defects and impurities.

Differences in production process
1. ERW straight seam electric resistance welded steel pipe is a hot-rolled coil formed by continuous rolling. The edge of the coil is melted by high-frequency current skin effect and proximity effect, and pressure-welded under the action of current. Squeeze roller force. Therefore, the residual stress of ERW straight seam electric resistance welded steel pipe is small, and the residual stress is further released and reduced through weld heat treatment, sizing, straightening, hydraulic pressure and other processes. Practice has proved that the residual stress of ERW straight seam electric resistance welded steel pipe will not affect the steel pipe during storage and use. Without any welding wire, the physical properties and chemical composition of the weld are exactly the same as those of the plate. The quality of ERW straight seam electric resistance welded steel pipe depends on the quality of the plate.

2. The steel plates used for SSAW steel pipes are welded together through the spiral rotation of the unit. The spiral rotation of the steel plates makes the geometric force more complicated, and some even reach the yield limit of the steel plates. There is a large residual stress after SSAW forming, and the residual stress is tensile stress. After the steel pipe bears the internal pressure, the pipe wall also produces hoop tensile stress, which superimposes and weakens the bearing capacity of the steel pipe. It is even less safe to use. The steel plates are welded together by welding wires containing chemical components, and it is easy to generate air bubbles and hot cracks in the welds during the welding process. The physical properties and chemical composition of the weld and the base metal are significantly different. The connection between the weld and the base metal is prone to large stress concentration. During the welding process, the thermal influence is large and the hardness is high.

Purchasing costs are different
Large-scale steel pipe factories in petroleum and petrochemical systems produce SSAW, and their advantages are mainly concentrated in the manufacture of large-diameter steel pipes, and the manufacturing cost is relatively low. However, the manufacturing cost of small and medium diameter (4114mm~(355.6mm) steel pipes is relatively high, which is 8%~15% higher than that of ERW steel pipes on average. Large spiral steel pipe factories often do not produce small and medium diameter spiral steel pipes, and procurement is difficult. There are many manufacturers of small and medium diameter ERW steel pipes , Easy to purchase.

Geometry
1. The geometric dimension accuracy of ERW steel pipe is high; while the geometric dimension accuracy of SSAW is low, and it is difficult to connect the girth weld on site.
2. The welding coefficient of ERW steel pipe is 100%; the weld coefficient of spiral welded pipe is 130%-200%. The length of SSAW welds is much longer than that of ERW steel pipes, and the incidence of defects also increases simultaneously.
3. The internal weld reinforcement of ERW steel pipe is basically close to zero, invisible to the naked eye; the internal and external surfaces of SSAW must have an excess height of about 0.3mm (this is determined by the production process). The weld reinforcement is too high, so that there is a gap between the steel pipe anti-corrosion layer (3PE) and the pipe body, which greatly reduces the corrosion resistance of the steel pipe.
4. Due to the high welding seam height of SSAW, it will cause great disturbance to the high-speed fluid conveyed, increase the flow resistance and reduce the pipeline conveying efficiency. The inner wall of ERW steel pipe is smooth, so this problem does not exist.