The difference between sewn stainless steel pipes and seamless stainless steel pipes
seamless stainless steel tube
The manufacturing process of seamless stainless steel pipes is to punch a hole in the stainless steel billet at a certain temperature. The stainless steel becomes soft and spiral shaped from the hole through stamping and drawing, resulting in uneven wall thickness and high eccentricity of the pipeline.
Seamed stainless steel pipe
Seamed stainless steel pipes are made from precise cold-rolled sheets (each roll has a width of 4-5 feet).
These cold-rolled plates usually have a maximum wall thickness difference of 0.002 inches, and the steel plate is cut into a width of π d, where d is the outer diameter of the pipe. The tolerance for the wall thickness of the seamless stainless steel pipe is very small, and the wall thickness of the entire circumference is very uniform.
The difference between the two
1. Bending and Elongation: The elongation of the welded joint can be verified through the following tests specified by ASTM: bending 45 °, then bending to 90 °, and then flattening along the weld seam; Then turn the stainless steel seam tube and repeat the above steps to make the inner diameter of the weld bend to 180 °.
The standard for weld quality to pass is that no tearing or intergranular separation is allowed under magnification of 40 times. The bending radius of the pipeline is controlled by the composition of the alloy, and the minimum bending radius is generally 2d.
The ideal welding condition is that the weld seam is in a neutral or compressed state. Moreover, pipes should be annealed to reduce their hardness and improve their bending performance.
2. Corrosion resistance: The quality of corrosion resistance also depends on the composition of the alloy.
The corrosion resistance of seamless stainless steel pipes with the same chemical composition and fully heat treated seamless stainless steel pipes is consistent.
The supplementary testing provided by ASTM proves that the corrosion resistance of the welded joint is equivalent to or better than that of the metal being welded. In an acidic chloride environment, the corrosion at the welded joints of partially heat-treated welded steel pipes will accelerate, but this is only necessary for corrosion testing, and the actual environment is not so harsh.
3. Grain size: The grain size of a metal is related to the heat treatment temperature and the time it is maintained at the same temperature. The grain size of annealed and seamless stainless steel pipes is the same.
If the welded pipe is subjected to minimum cold treatment, the grain size of the weld seam will be smaller than that of the welded metal. Otherwise, the grain size will be the same.
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