How to Distinguish Stainless Steel Welded Pipes from Stainless Steel Seamless Pipes

Untreated stainless steel welded pipes and seamless pipes are easy to distinguish, but seamless treated stainless steel welded pipes may be difficult to distinguish with the naked eye, so how do we distinguish stainless steel welded pipes from stainless steel seamless pipes?

Differences in production processes

Stainless steel welded pipe: Steel plates or strips are welded after being crimped by the unit and die. The welding methods are divided into straight seam welded pipes and spiral welded pipes, and the more common ones are straight seam welded pipes.

Stainless steel seamless pipe: The outer skin is cut off from round steel, and hot-rolled and perforated after centering to reach the required size.

Different concentricity: The seamless pipe manufacturing process is carried out at 2200 degrees. Holes are formed by punching in stainless steel billets. Under the action of this high temperature, the tool steel will soften and then come out of the hole in a spiral shape. The wall thickness of this pipe is not uniform at all, and the eccentricity is relatively high. Stainless steel welded pipes are made of precision cold-rolled plates. The wall thickness difference of these cold-rolled plates is generally around 0.002 inches, so the wall thickness difference is very small, and the wall thickness of the entire pipe is very uniform.

Appearance

Stainless steel welded pipe: high precision, uniform wall thickness, high brightness inside and outside the pipe (the brightness of the steel pipe surface is determined by the surface grade of the steel plate), can be arbitrarily scaled; can be made into thin-walled pipe.

Seamless pipe: low precision, uneven wall thickness, low brightness inside and outside the pipe, high cost of cutting to length, pitting and black spots inside and outside the pipe are not easy to remove. Usually the wall is thicker.

The difference between stainless steel seamless pipe and stainless steel welded pipe also includes corrosion resistance. The quality of corrosion resistance also depends on the composition of the alloy. Seamless pipes with the same chemical composition have the same corrosion resistance as heat-treated stainless steel welded pipes. The welded parts of seamed steel pipes that have not been fully heat-treated are easily corroded.

Performance

The corrosion resistance, pressure resistance and high temperature resistance of seamless pipes are much higher than those of stainless steel welded pipes. With the improvement of the production process of stainless steel welded pipes, the mechanical properties and mechanical properties are gradually approaching those of seamless pipes, and welded pipes can replace seamless pipes in some aspects.

In general, the chemical composition of stainless steel welded pipes and seamless pipes is somewhat different. The steel composition of seamless pipes just meets the basic requirements, while stainless steel welded pipes contain chemical compositions suitable for welding, such as silicon, sulfur, manganese, oxygen and delta ferrite. If these elements are missing, the welding process will be very difficult.

Price

The production process of stainless steel seamless pipes is more complicated and the price is more expensive than welded pipes.

Uses

Stainless steel welded pipes are often used as decorative pipes, support pipes, and product pipes. They have average pressure-bearing performance and are mainly used to transport water, oil, gas, air, and generally low-pressure fluids such as hot water or steam.

Stainless steel seamless pipes: Pipes used for transporting fluids in engineering and large equipment, and can also be used for high-temperature and high-pressure fluid transport mains and pipelines in power plants and nuclear power plant boilers.

In fact, if the two are compared together, the seamed steel pipe has more advantages than the seamless steel pipe. Since the seamed steel pipe has passed a series of tests and is made of cold-rolled plates, all the disadvantages are limited to welding. The seamless steel pipe is stamped from stainless steel billets, so the tube wall will be torn during the kneading process. Moreover, through testing, the defective pass rate of the seamed steel pipe is mostly lower than that of the seamless steel pipe, and it can be found under ultrasonic testing that the background noise of the seamless steel pipe is relatively large, so it is difficult to find defects. The seamed steel pipe is just the opposite, and it is easier to find faults.