Differences Between Seamless and Welded Steel Pipes

Definition of Seamless Pipe and Welded Pipe

Seamless pipe refers to steel pipes without seams, created through perforation and rolling of a steel bar's center.  Welded pipe is a type of steel pipe with welding seams, where steel plates are rolled into a cylindrical shape, welded, and then processed through drawing and other methods to create a steel pipe with less obvious weld seams.

Manufacturing Methods of Seamless Pipe and Welded Pipe

The representative manufacturing method for seamless pipes is called the "Mannesmann process," which involves heating the steel billet to a high temperature, compressing it from the outer perimeter while utilizing a tool called a "piercing mandrel" to perforate the center, forming it into a pipe.  This manufacturing method is suitable for mass production, capable of producing large-diameter steel pipes, and is suitable for making thick-walled steel pipes. The feature is that due to the lack of seams, it can maintain the original properties of the material. However, from the perspective of the manufacturing method, size accuracy is not very good.

In the welded pipe manufacturing method, materials are not used in billet form but as steel strips (coils). For example, welded pipes using resistance welding involve continuously pulling out steel strips using an uncoiler, forming them into a cylindrical shape.  Using a large current, the joint area of the cylinder is heated to a high temperature and strongly welded through resistance welding. As the welding utilizes the material's own structure, no welding wire is used. Finally, the welding bead (raised join seam) is removed.  After cooling, it undergoes straightening and drawing processes. The feature of this method is that it is suitable for smaller batch production, dimensions can be flexibly set, and the size accuracy is high.  

Distinguishing Uses of Steel Pipes

Piping steel pipes refer to steel pipes used for the purpose of transmitting fluids (such as gases or liquids) inside pipelines.  The outside diameter is referred to as A, and the wall thickness is set by standard numbers. Pipes for pipelines referred to by the wall thickness standard number are quite common (e.g., gas pipes and water pipes), and standard dimensions beyond the norm are hardly used.  In pipes set by wall thickness standards, the pipe material set by actual diameter (millimeters, inches) is referred to as "Tube" rather than "Pipe" (for example, hydraulic pipes and air conditioning pipes). Likewise, general non-standard size pipes are not used.

Structural steel pipes vary in pipe types and circulation depending on their use in construction or mechanical parts. Pipes used in construction also have standard sizes like those used for piping.  There are many types of steel pipes used for mechanical parts, so selection should be made carefully based on the specific use and required quality.

Choosing Steel Pipes When selecting steel pipes, standard size steel pipes have a large circulation volume, offering a wide range of suppliers, generally resulting in quick delivery and cheaper prices.  When selecting non-standard size steel pipes, although there may be variations based on different sizes, choosing welded pipes with smaller production batches and a higher degree of flexibility in size selection could be a beneficial choice.