Application of Large Diameter Seamless Steel Tube

Whether welding rods are properly selected and used directly affects the chemical composition and performance of the welds, and is an important part of welding preparation for large-diameter seamless steel tubes. Selecting the right electrode requires comprehensive consideration of many factors. Sometimes it needs to be tested and verified before it can be finalized. The aspects that need to be considered are as follows: the performance requirements of the weld metal, the shape, rigidity and position of the weld, the crack resistance of the weld metal, the workability, equipment and construction conditions, and economic rationality.

Large-diameter seamless steel tube large-scale forgings for heat treatment of large forgings is mainly directly from the steel ingot forging, so the heat treatment must consider the smelting, ingot, forging and other processes on the internal quality of the casting, as long as the influencing factors are: chemical composition is not uniform The existence of various smelting defects; grain coarse and very uneven; more gas and impurities; greater forging stress and heat treatment stress. The purpose of heat treatment after forging of large-size forgings is to prevent white spots and hydrogen embrittlement, improve the internal structure of the forgings, eliminate forging stress, lower the hardness, improve the cutting performance, obtain good mechanical properties, or prepare the structure for the subsequent heat treatment.

The forging of large diameter seamless steel tubes belongs to the casting of large forgings. The difference between large-caliber seamless steel tubes and welded tubes is mainly the difference in the molding process. Ordinary steel pipes, such as tap water pipes, are generally welded by bending a flat sheet material. You can find a weld on the top; a thicker one is generally a spiral weld. The seamless steel pipe is generally formed by the molten steel in a molten state being accumulated in a ring-shaped slit and then processed by a drawing process. Thus, there is no weld seam. In terms of performance, especially the pressure capacity is greatly improved than ordinary steel pipe, so it is often used in high-pressure equipment. Such as hydraulic equipment, such as pipeline connections. The weld part of the ordinary steel pipe is its weak link, and the weld quality is also the main factor affecting its overall performance. People who have lived in the north have generally had the experience of tapping water pipes or heating pipes in the winter. The places where the explosions occur are generally welded seams. Welded pipes are not seamless steel pipes. Seamless steel pipe production process The seamless steel pipe is mainly achieved through tension reduction. The tension reducing process is a continuous rolling process in which the hollow base metal does not have a mandrel. On the premise of guaranteeing the quality of the welding of the mother tube, the tension reducing process of the welded pipe is to heat the whole of the welded pipe to 950 degrees Celsius or more, and then to a variety of outer diameters and walls by a tension reducer (a total of 24 passes of the stretch reducer). Thick finished pipe, using this process of hot-rolled steel pipe and ordinary high-frequency welded pipe are essentially different through the heating furnace heating the weld and the parent metallographic structure and mechanical properties can be completely consistent, in addition, large diameter no Steel pipe through multiple passes of tension reducer rolling and automatic control makes the pipe's dimensional accuracy (especially the pipe roundness and wall thickness accuracy) better than similar seamless pipe.

Fluid tubes and boiler tubes produced in developed countries in the world have adopted a large number of welded tube seamless processes. With the development of society, the domestic hot rolled welded tubes have gradually replaced the seamless tube. The difference between seamless steel tubes and large-diameter seamless steel tubes can be seen from several aspects. First, the welded tubes are generally fixed-size, and are generally 6 meters, 9 meters or 12 meters. The length of the seamless steel pipe is very small, because the factory price increase is very large. The second can be seen from the cross section of the tube head. If there is rust, wipe it clean. If you look closely, you will find the welding area. Third, if pickling, it is most obvious. After the material coating is applied, the quality of pretreatment in the steel pipe indirectly affects the adhesion of the coating. With regard to the large-caliber plastic-coated steel pipe, the amount of surface pretreatment should reach the SA2 defined in the GB/T8923 standard. Grade to provide. Can be coated according to different needs of PVC, polyethylene, epoxy resin and other various properties of plastic coating, good adhesion, strong corrosion resistance, resistant to strong acids, alkalis and other chemical corrosion, non-toxic, Non-corrosion, wear resistance, impact resistance, strong penetration resistance, smooth surface of the pipeline, no adhesion of any substance, can reduce the resistance during transportation, increase the flow rate and transmission efficiency, and reduce the transmission pressure loss. There is no solvent in the coating, no bleed out material, so it will not contaminate the conveyed medium, so as to ensure the purity and sanitation of the fluid. It can be used alternately in the range of -40°C to +80°C, no aging, no Cracks can be used in harsh environments and other harsh environments. The lightness of the anchor pattern reaches 50μm? 75μm. Surface pretreatment work of the steel pipe should be plasticized in 6h, after 6h of power should be renewed. Large-caliber seamless steel tubes have large elastic deformation. Improper operation in construction can easily cause large vertical deformation of large-diameter steel tubes and instability, which seriously affects the function of use.