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Comparison of ERW Steel Tube and SSAW Steel Tube

Raw material difference
1. The raw materials used in ERW steel 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 tube factory are low-grade hot-rolled strip steel, the chemical composition and physical properties are not stable, and there are many internal defects and impurities.

Production process difference
1. ERW straight seam electric resistance welded steel pipe is a hot-rolled coil formed by continuous roll forming, using high-frequency current skin effect and proximity effect to thermally melt the edge of the coil, and perform pressure welding under the action of the extrusion 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 welding seam heat treatment, sizing, straightening, water pressure and other processes. Practice has proved that the residual stress of ERW straight seam electric resistance welded steel pipe does not affect the steel pipe during storage and use. Without any welding wire, the physical properties and chemical composition of the welding seam 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 sheet.

2. The steel plates for SSAW steel pipes are welded together by the spiral rotation of the unit, and the steel plates are spirally rotated to make the geometric stress more complex, and some even reach the yield limit of the steel plate. After the SSAW is formed, there is a large residual stress, and the residual stress is tensile stress.After the steel pipe is subjected to internal pressure, the pipe wall also produces hoop tensile stress, which superimposes and weakens the bearing capacity of the steel pipe. It is more unsafe to use. The steel plates are welded together by welding wires containing chemical components, and bubbles and hot cracks in the weld bead are easily generated during the welding process. The physical properties and chemical composition of the weld and the base metal are significantly different. It is very easy to generate a great concentration of stress at the connection between the weld and the base metal. During the welding process, the thermal influence is large and the hardness is high.



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

Geometry
1. The geometrical dimensional accuracy of ERW steel pipe is high; while the geometrical dimensional accuracy of SSAW is low, which makes it difficult to connect the girth weld on site.
2. The weld coefficient of ERW steel pipe is 100%; the weld coefficient of spiral welded pipe is 130%-200%. The length of SSAW weld is much longer than that of ERW steel pipe, and the incidence of defects also increases simultaneously.
3. The excess height of the inner weld of the ERW steel pipe is basically close to zero and invisible to the naked eye; the inner and outer surfaces of the SSAW must have an excess height of about 0.3 mm (this is determined by the production process). The excess height of the weld is so high 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 excess height of the weld seam in SSAW, there will be great disturbance to the high-speed fluid being transported, increasing the flow resistance and reducing the efficiency of pipeline transportation. The inner wall of ERW steel pipe is smooth, so this problem does not exist.

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