site logo

What are the differences between stainless steel welded pipe and seamless steel pipe?

What are the differences between stainless steel welded pipe and seamless steel pipe?

Time:2022-03-17 Source:China Wuxi JiaNuo Special Steel Co.

———————————————————————————————————————————

Stainless steel pipe is a kind of hollow long round steel, mainly widely used in petroleum, chemical, medical, food, light industry, mechanical instrumentation and other industrial transmission pipelines and mechanical structural components. In addition, 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. Also commonly used for the production of various conventional weapons, gun barrels, shells, etc. IMG_20200106_090049

1、Concentricity

The manufacturing process of stainless steel seamless steel pipe is to punch a hole in the stainless steel billet at a temperature of 2200 °f. At this high temperature, the tool steel becomes soft and spirally formed out of the hole by stamping and drawing. This gives the pipe an uneven wall thickness and high eccentricity. As a result, astm allows a larger wall thickness difference for seamless pipes than for seamed pipes. Seamed pipe is made from precision cold rolled sheets (4-5 feet wide per roll). These cold rolled sheets typically have a maximum wall thickness difference of 0.002 inches. The plates are cut to a width of πd, where d is the outside diameter of the pipe. Seamed pipe has very small tolerances in wall thickness and is very uniform throughout its circumference.

2、Welding performance

There are some differences in the chemical composition of seamed and seamless pipes in general. The steel composition for the production of seamless pipe is just to meet the basic requirements of astm. While the production of seamless steel contains chemical composition suitable for welding. For example, silicon, sulfur, manganese, oxygen and delta ferrite and other elements in a certain proportion of the mixture can be produced in the welding process, an easy to transfer heat welding melt to make the entire weld weld through. Lack of the above chemical composition of the steel pipe, such as seamless pipe, in the welding process will produce a variety of instability, not easy to weld and weld impermeable.

3、Grain size

Grain size of the metal and heat treatment temperature and maintain the same temperature time. Annealed stainless steel pipe and seamless stainless steel pipe grain size the same. If the seamed pipe with 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.

4、Pipe strength

Pipe strength depends on the alloy composition, thus containing the same alloy and the same heat treatment of seamless stainless steel pipe and seamed stainless steel pipe is essentially the same strength.

After the tensile test and three-dimensional vibration test, the tearing of the seamed stainless steel pipe almost always occurs away from the welding point or the heated area. This is because the weld is less impurities and slightly higher nitrogen content, so the strength of the weld is better than other parts. However, ASME believes that the seamed stainless steel pipe can only withstand 85% of the allowable pressure, mainly due to data collection before the improved welding equipment used today.