Stainless steel pipe is a kind of hollow long round steel, which is widely used in industrial transportation pipelines such as petroleum, chemical, medical, food, light industry, mechanical instrumentation and mechanical structural components. In addition, when the bending and torsional strength are the same, the weight is light, so it is also widely used in the manufacture of mechanical parts and engineering structures. Also used to produce a variety of conventional weapons, barrels, shells and so on.
The seamless tube is manufactured by punching a hole in a stainless steel billet at a temperature of 2200 °F, at which the tool steel is softened and spirally formed from the hole by punching and drawing. Thus, the wall thickness of the pipe is uneven and the eccentricity is high. Thus astm allows the wall thickness difference of the seamless pipe to be larger than the wall thickness difference of the seamed pipe. The seamed tubes are made from precision cold rolled sheets (4-5 feet per roll width). These cold rolled sheets typically have a maximum wall thickness difference of 0.002 inches. The steel plate is cut to a width of πd, where d is the outer diameter of the pipe. The tolerance of the wall thickness of the seamed tube is small and the wall thickness of the entire circumference is very uniform.
2, welding performance
There are generally differences in the chemical composition of the seamed tube and the seamless tube. The steel components that produce seamless pipes are only the basic requirements for reaching astm. Steels with seams contain chemical components suitable for welding. For example, silicon, sulfur, manganese, oxygen, and a certain ratio of elements such as triangular ferrite can produce a weld melt that is easy to transfer heat during the welding process to weld the entire weld. Steel pipes lacking the above chemical components, such as seamless pipes, have various unstable factors during the welding process, and are not easily welded and cannot be welded.
3, grain size
The grain size of the metal is related to the heat treatment temperature and the time to maintain the same temperature. The annealed stainless steel pipe and the seamless stainless steel pipe have the same grain size. If the seam is treated with minimal cold treatment, the grain size of the weld is smaller than the grain size of the metal being welded. Otherwise, the grain size is the same.
4, pipeline strength
The strength of the pipe depends on the alloy composition, so the seamless stainless steel pipe and the seamed stainless steel pipe containing the same alloy and the same heat treatment have the same strength in nature.
After the tensile test and the three-dimensional vibration test, the tear of the seamed stainless steel tube occurs almost everywhere away from the welded or heated area. This is because the weld has less impurities and a slightly higher nitrogen content, so the weld is stronger than other parts. However, ASME (American Society of Mechanical Engineers) believes that seamed stainless steel pipes can only withstand 85% of the permit pressure, mainly due to the collection of data earlier than the improved welding equipment used today.
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