Ask about the differences between welded pipes and seamless pipes!
Thread Content
Colleagues, I have a question for you: what is the difference between seamless pipes and welded pipes? I work in the field of heat exchangers. Nowadays, for stainless steel cylinders with a diameter of less than 426, seamless tubes are generally used. However, the body of a seamless tube is twice as expensive as that of a welded tube, and our prices are always higher than those of other manufacturers. I would like to know what the disadvantages are of using welded tubes instead of seamless tubes? Also, what are the disadvantages of using welded pipes instead of heat exchange tubes?
Welded pipes are formed by welding, and thus have welds; seamless pipes, on the other hand, are drawn out and have no welds. Since pressure vessels and heat exchange tubes are subject to pressure, welded pipes cannot be used.
It can be seen that you work with shell and tube heat exchangers. The inner tubes of such heat exchangers have a small diameter, require a large amount of tubes, and must have a smooth inner surface; moreover, they operate under pressure, so welded tubes are generally not used.
That can’t be right! When the diameter of our tube is greater than 426, there are no seamless steel tubes available; welded tubes have to be used instead. Can’t the welded heat exchange tubes be used either? Welded pipes can also withstand pressure, right!
GB150 does not specify any standards for welded pipes; therefore, pressure-bearing components such as cylinders cannot be made from welded pipes.
Apart from the differences in processing methods, I’m not sure what the big difference between welded pipes and seamless pipes is. It seems that pressure vessels generally do not use welded pipes; instead, manufacturers are required to weld the pipes from sheet metal themselves, with subsequent testing to ensure they meet the standards. As for welding and testing, pressure vessel manufacturing is well-known, right?
The manufacturing quality of welded steel pipes produced domestically is still not high; at present, only carbon steel welded steel pipes can meet the requirements for use in low-pressure water and gas pipelines. However, stainless steel welded pipes are already widely used in heat exchangers and piping abroad.
If it is a stainless steel heat exchange tube, welded tubes can be used; the requirements for welded tubes are specified in the appendix to GB151. As for the cylinder, in my opinion it depends on the specific operating conditions
Seamless steel pipes are formed in one step during rolling. Welded steel pipes are formed by rolling followed by welding, and there are generally spiral welding and straight welding. Considering pressure-related issues, our factory chooses seamless pipes, which also offer better performance.
But in many cases, the operating conditions of the customers are excellent! Oil-water heat exchange. The pressure is all below 10 Bar! Customers just want low prices! So I would like to ask about the application conditions of welded pipes!
The use of welded pipes is generally not recommended in China. In fact, if their quality is good, they can be used in many applications; however, due to various quality issues encountered there, it is advised that welded pipes not be used for components that are subject to significant pressure.
The maximum allowable pressure for standard welded pipes is generally 1.0 Mpa; they cannot be used at pressures higher than this. They can still be utilized if there are no requirements specific to pressure vessels. However, it seems that welded pipes cannot be used in the design of pressure vessels, so steel plates or seamless tubes are typically used for such designs. You can calculate on your own which option is more cost-effective.
GB12771 welded pipes can be used as heat exchange tubes; those permitted under GB151 can also be used
Regarding the selection of materials for the shell and heat exchange tubes in heat exchanger manufacturing, detailed regulations on this are provided in both the standards for heat exchanger manufacturing and acceptance, as well as those for pressure vessel manufacturing and acceptance.