Both straight seam resistance welded steel pipes (ERW) and spiral submerged arc welded steel pipes (SSAW) can better meet the requirements of oil and gas pipelines. For medium-diameter (Ф630mm) steel pipes, ERW steel pipes are mostly used abroad. Spiral submerged arc welded pipes are generally only used for low-pressure fluid transmission, civil buildings, structures and piling pipes.
Due to the different forming, welding and process of ERW steel pipe and spiral submerged arc welded pipe in the pipe manufacturing process, there is a certain difference in performance between the two steel pipes.
(1) The surface quality of ERW steel pipe is better than that of spiral submerged arc welded pipe. The surface of ERW steel pipe is smooth, flat and beautiful. Spiral submerged arc welded pipe has high internal and external weld seams.
(2) The welding seam of ERW steel pipe is shorter than that of spiral submerged arc welded pipe. The welding seam of ERW steel pipe is as long as the length of steel pipe, and the welding seam of spiral submerged arc welded pipe is generally 1.4-1.7 times the length of steel pipe. The longer the weld, the higher the chance of welding defects.
(3) In the standard, the geometrical requirements for ERW steel pipes and spiral submerged arc welded pipes are basically the same, but in terms of physical objects, ERW steel pipes have sizing and straightening processes. Therefore, the geometric dimensions are higher than that of spiral submerged arc welded pipes.
(4) There are fewer types of weld defects in ERW steel pipes than in spiral submerged arc welded pipes. Spiral submerged arc welded pipes are welded by welding. There are many types of defects. In addition to volume defects, there are line subsidence. The ERW steel pipe weld has only line defects, and the weld is straight. It is easy to trace during the inspection process, and the defect is at the maximum reflection. Once there is a defect, the ultrasonic reflection is strong and easy to detect.
(5) The residual stress of ERW steel pipe is lower than that of spiral submerged arc welded pipe.
Because the ERW steel pipe is relatively deformed during the deformation process, and the subsequent sizing and ellipse sizing changes and shrinkage, the residual stress of the ERW steel pipe becomes smaller. Physical inspection shows that after the ERW steel pipe of the same specification and the same material is cut along the axis, the axial and lateral notch displacement is smaller than that of the spiral submerged arc welded pipe.
(6) The overall performance of ERW steel pipes is consistent. When defects occur in steel pipes, the steel pipes are discarded and repair welding is not allowed. Spiral submerged arc welding pipes allow repair welding, but the performance of repair welding is not consistent with the overall performance of steel pipes, and stress corrosion cracking is prone to occur at repair welding. Experiments have proved that the stress corrosion fatigue life of ERW steel pipes is longer than that of spiral submerged arc welded pipes.
(7) The quality of ERW steel pipe coating is higher than that of spiral submerged arc welded pipe.
ERW production units have large investment, many processes, and relatively high processing costs for steel pipes. Because ERW steel pipes are not repaired, butted pipes are not allowed, and the relative yield is low. Therefore, the direct price of ERW steel pipe is about 300 yuan / T higher than that of spiral submerged arc welded steel pipe. From the overall cost analysis of pipeline construction, it does not increase. First, the quality of ERW steel pipes is good and the service life is long; second, the surface quality of ERW steel pipes is good, the coating is uniform, which saves a lot of coating materials, and the corrosion resistance of the steel pipes is low; High efficiency, in addition to reducing construction costs.
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