Stainless steel pipe is a long hollow round steel, which is widely used in petroleum, chemical, medical, food, light industry, machinery and instrumentation, and other industrial pipelines and mechanical structural parts. Besides, when the bending and torsion strength is the same, the weight is lighter, so it is also widely used in the manufacture of mechanical parts and engineering structures. It is also often used to produce various conventional weapons, barrels, and shells.

1. Concentricity
The manufacturing process of seamless pipes is to punch a hole in a stainless steel billet at a temperature of 2200°f. At this high temperature, the tool steel becomes soft and spirally formed from the hole after punching and drawing. In this way, the wall thickness of the pipeline is uneven and the eccentricity is high. Therefore, ASTM allows the wall thickness difference of seamless pipes to be greater than that of seamed pipes. The slotted pipe is made of a precise cold-rolled sheet (with a width of 4-5 feet per coil). These cold-rolled sheets usually 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 slit pipe is very small, and the wall thickness is very uniform throughout the circumference.

2. Welding
Generally, there is a certain difference in chemical composition between seamed pipes and seamless pipes. The steel composition for producing seamless pipes is only the basic requirement of ASTM. The steel used to produce seamed pipes contains chemical components suitable for welding. For example, the mixing of elements such as silicon, sulfur, manganese, oxygen, and triangular ferrite in a certain proportion can produce a weld melt that is easy to transfer heat during the welding process, so that the entire weld can be penetrated. Steel pipes lacking the above chemical composition, such as seamless pipes, will produce various unstable factors during the welding process and are not easy to weld firmly and incompletely.

3. Grain sizes
The grain size of the metal is related to the heat treatment temperature and the time to maintain the same temperature. The grain size of the annealed slit stainless steel tube and seamless stainless steel tube is the same. If the seam pipe adopts minimum cold treatment, the grain size of the weld is smaller than the grain size of the welded metal, otherwise, the grain size is the same.