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.
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.