Comparison between stainless steel welded tube and stainless steel seamless tube

There are two common forms of stainless steel pipes, welded stainless steel pipes and seamless steel pipes. Their differences can be clearly distinguished from the areas of performance, price, and application. Let's take a closer look at these differences.

Tube concentricity

The production process of the seamless steel pipe is to punch a stainless steel billet out of a hole at a temperature of 2200 °F. At such a high temperature, the tool steel is softened and spirally formed from the hole by punching and drawing. However, this tends to result in uneven wall thickness and high eccentricity. Therefore, it can be accepted that the wall thickness difference of the seamless steel pipe is larger than the wall thickness difference of the seamed pipe. 

The welded tube is made of precision cold rolled stainless steel. These cold rolled Stainless steel sheets typically have a wall thickness difference of up to 0.002 inches. The stainless 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 pipe is small, and the wall thickness of the entire wall of the pipe wall is average.

Grain size of Stainless steel tube
The grain size and heat treatment temperature of the stainless steel material are related to the holding time. The annealed Stainless steel tube and the seamless Stainless steel tube have the same grain size. If the seamed steel pipe is treated with minimum cold treatment, the grain size of the weld bead will be smaller than the grain size of the metal to be welded.

Pipe strength of stainless steel pipe
The pipe strength of the stainless steel pipe is affected by the alloy composition of the steel, and the strength of the same alloy composition and the seamless heat-treated stainless steel pipe and the slotted stainless steel pipe are the same.
Through the tensile test and the three-dimensional vibration test, the tear of the seamed Stainless steel tube occurs substantially at a location away from the welded or heated area. This is because the weld has less impurities and a slightly higher nitrogen content, so the strength of the weld is better than other parts.

Corrosion resistance of stainless steel pipe
The quality of corrosion resistance is also affected by the composition of the alloy. The corrosion resistance of a seamless Stainless steel tube of similar chemical composition and a fully heat treated slotted Stainless steel tube is the same. Tests have shown that the corrosion resistance of the weld is equivalent or better than the metal being welded. In the case of an acid chloride, corrosion at the weld of a seamed steel pipe that is not completely heat treated is accelerated.

Stainless steel tube price
The price of seamed stainless steel pipes is generally only about 50% of stainless steel seamless pipes.

Wall thickness and diameter
Thin-walled Stainless steel tubes having a small thickness and a small diameter of a Stainless steel tube are preferably produced by welding, and thick-walled tubes having a large thickness and a large diameter are preferably formed by a stamping method.

Finally, the quality of the slotted Stainless steel tube is better than that of the seamless Stainless steel tube. Since the slotted Stainless steel tube is made of precision cold-rolled stainless steel plate that has been tested, any defects will only be in the weld area. 

The seamless tube is stamped from a stainless steel blank by punching, resulting in a lot of tearing in the extruded tube wall. Scientific tests have shown that the defective rate of stainless steel pipes with seams is generally lower than the defective rate of seamless stainless steel pipes. And the defects of the stainless steel pipe are more easily detected.