Application of large-diameter seamless steel pipes

https://www.baowi-steel.com/newsdetail/schedule-40-pipes-thickness--weight-chart.htmlWhether the selection and use of welding rods are appropriate directly affects the chemical composition and performance of the weld, and is a very important part of the preparation work for welding large-diameter seamless steel pipes. To select a suitable welding rod, many factors must be considered comprehensively, and sometimes experimental verification is required before the final determination. The aspects that need to be considered are the performance requirements of the weld metal, the shape, rigidity and weld position of the welding rod, the crack resistance of the weld metal, the operation process, the equipment and construction conditions, and the economic rationality.

Heat treatment of large-diameter seamless steel pipe large forgings Large forgings are mainly forged directly from steel ingots. Therefore, the influence of smelting, ingot casting, forging and other processes on the internal quality of the castings must be considered during heat treatment. As long as the influencing factors are: uneven chemical composition and the presence of various smelting defects; coarse and very uneven grains; more gas and impurities; larger forging stress and heat treatment stress. The purpose of heat treatment after forging of large forgings is to prevent white spots and hydrogen embrittlement, improve the internal structure of forgings, eliminate forging stress, reduce hardness and improve cutting performance, so that it can obtain good mechanical properties or prepare for subsequent heat treatment.

Forging of large-diameter seamless steel pipes belongs to the casting of large forgings. The difference between large-diameter seamless steel pipes and welded pipes is mainly the different forming processes. Ordinary steel pipes, such as tap water pipes, are generally welded by bending flat plates, and you can find a weld on them; those with thicker diameters are generally spiral welds. Seamless steel pipes are generally formed by pressing molten steel through annular slits and then stretching and other processing processes, so there is no weld. In terms of performance, especially the pressure bearing capacity is greatly improved compared to ordinary steel pipes, so it is often used in high-pressure equipment. Such as pipeline connections of hydraulic equipment. The weld part of ordinary steel pipes is its weak link, and the quality of the weld is also the main factor affecting its overall performance. People who have lived in the north generally have experienced water pipes or heating pipes being frozen and burst in winter, and the places that burst are generally welds. Welded pipes are not seamless steel pipes. Seamless steel pipe production process The seamlessness of steel pipes is mainly achieved through tension reduction, which is a continuous rolling process of hollow parent material without mandrel. Under the premise of ensuring the welding quality of the parent pipe, the tension reduction process of welded pipes is to heat the welded pipe as a whole to above 950 degrees Celsius, and then roll it into finished pipes of various outer diameters and wall thicknesses through a tension reducer (a total of 24 passes of the tension reducer). The hot-rolled steel pipes produced by this process are essentially different from ordinary high-frequency welded pipes. After heating in a heating furnace, the metallographic structure and mechanical properties of the weld and the parent can be completely consistent. In addition, large-diameter seamless steel pipes are rolled and automatically controlled through multiple passes of tension reducers, making the dimensional accuracy of the steel pipe (especially the roundness and wall thickness accuracy of the pipe body) better than similar seamless pipes.

The fluid pipes and boiler pipes produced in developed countries in the world have been widely used in the seamless process of welded pipes. With the development of society, the situation that domestic hot-rolled welded pipes gradually replace seamless pipes has been formed. The difference between seamless steel pipes and large-diameter seamless steel pipes can be seen from several aspects. First, welded pipes are generally fixed in length, and are generally 6 meters, 9 meters or 12 meters. There are very few seamless steel pipes in fixed lengths, because the factory price of fixed lengths is very high. Second, you can look at the cross-section of the pipe head. If there is rust, wipe it clean. If you look carefully, you will find the welding area. Third, if you pickle it, it will be the most obvious. The quality of the pretreatment of the steel pipe after the coating of the plastic coating directly affects the adhesion of the coating. The surface pretreatment quality of large-diameter plastic-coated steel pipes should meet the Sa2? level requirements specified in the GB/T8923 standard. According to different needs, it can be coated with plastic coatings of various properties such as polyvinyl chloride, polyethylene, epoxy resin, etc. It has good adhesion and strong corrosion resistance. It can resist strong acid, strong alkali and other chemical corrosion. It is non-toxic, rust-proof, wear-resistant, impact-resistant and permeable. The surface of the pipeline is smooth and does not adhere to any substance. It can reduce the resistance during transportation, improve the flow rate and transportation efficiency, and reduce the pressure loss during transportation. There is no solvent in the coating, and no exudable substances, so it will not pollute the medium being transported, thereby ensuring the purity and hygiene of the fluid. It can be used alternately in hot and cold cycles in the range of -40℃ to +80℃, without aging or cracking, so it can be used in harsh environments such as cold areas. The anchor pattern is light 50μm-75μm. The steel pipe with surface pretreatment should be coated within 6h, and it should be re-treated after 6h. Large-diameter seamless steel pipes have large elastic deformation. Improper operation during construction can easily cause large-diameter steel pipes to have large vertical deformation and even instability, seriously affecting the use function.
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