In recent years, there has been a trend in the world to replace high-cost seamless steel pipes
with high-quality welded pipes. This is mainly due to the continuous breakthrough in the production technology of welded pipes, which is reflected in the following aspects:
(1) Advances in desulfurization technology have reduced the sulfur content of steel and improved the welding quality of steel pipes.
(2) The application of vacuum degassing technology improves the purity of the tube blank strip, reduces inclusions, and improves the quality of the weld.
(3) Due to the addition of special elements such as V, Ti, and Nb, the carbon equivalent is lowered, and the toughness and strength of the steel pipe are improved.
(4) The development of hot rolling technology has improved the dimensional accuracy of the strip and thus reduced the dimensional deviation of the welded pipe.
(5) Improvement of quality inspection methods, such as ultrasonic non-destructive testing, hydraulic testing machines and other equipment, to ensure the quality of the final product.
Steel pipes selected by petrochemical enterprises generally use seamless steel pipes for fluid transportation because they have to withstand certain pressures. In 1996, during the “National Ninth Five-Year Plan” key construction project “Maoming 300,000 t ethylene project”, the “Mushui Product Oil Pipeline Relocation Project” and the “Second Maoshui Product Oil Pipeline Project” long-distance transmission process part required 325mm× 8mm, 168mm × 7mm, 219mm × 7mm steel pipe, mainly used for the transportation of gasoline, diesel, kerosene, etc.
China's erw steel pipe
industry started in the 1950s and started late. The production process and technology are quite different from those in developed countries. Most of the enterprises have incomplete process and equipment, lack of necessary testing methods, and use short-band and narrow-band materials with poor quality as raw materials, resulting in small diameter of the welded pipe products, low pressure bearing capacity, unreasonable product structure, and 80% of the welded pipe production. It can be used as a low-pressure fluid conveying water gas pipe, and the proportion of various special pipes is low. This low level of welded pipe equipment and technical level makes the quality of the product unguaranteed. Therefore, long-term use of expensive seamless steel pipes such as pipeline pipes, oil casings and oil pipes causes huge waste.
Some technical performances of erw steel pipe are better than seamless steel pipes, but the price is much lower than that of seamless steel pipes, but it has not been widely used in the petrochemical industry. The main reasons are:
(1) The traditional concept that has been formed for a long time. When selecting materials, designers mainly consider whether the material is reliable and rarely consider the cost of materials. Therefore, it is not possible to boldly use erw steel pipes.
(2) The investment system of petrochemical enterprise construction projects restricts the initiative to select erw steel pipes and reduce costs. Investors mainly consider the project's project establishment, funding sources, construction progress and other factors, and less demand for designers to reduce material costs.
(3) China's straight seam electric resistance welded steel pipe developed late, and it is not yet possible to produce large diameter straight seam welded pipe larger than 508mm, thus objectively restricting the wide use of erw steel pipe.