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Differences in manufacturing process of Seamless Pipes and Welded Pipes

by globalseamless

How is a Seamless Steel Pipe Made?

Seamless steel pipe manufacture is from a round and robust piece of steel known as a billet. The billet has to be heated first, then stretched and finally pushed or rolled over a frame or form until the pipe is hollow. Seamless steel pipes (ASTM and API 5L) adopt their shape by passing through a perforated tube.At this point, the seamless steel pipe forms through the following process:

  • Hot rolled
  • Cold rolled
  • Cold draw

A hot rolled seamless steel pipe manufacture is from forging billet, perforating, rolling, and shaping. The tubing is manufactured through an industrial extrusion process and is used to manufacture thick-walled seamless steel pipes and large diameter pipes.

On the other hand, cold drawn seamless steel pipes use the cold-drawn technology, which is suitable for pipes that are of small diameter and thin-walled since they have a lower material strength. It is also useful when the goal is to manufacture a stunning pipe with a smooth internal surface. During the extrusion process, the seamless steel pipes can only roll using a low alloy structure, carbon structural steel, or an alloy structure.

Some seamless steel pipes often harden during the manufacturing process; in such cases, the manufacturer will not use heat treatment methods.


  • Heavy and thick-walled
  • Has no welds
  • Corrosion resistance
  • Better ovality (roundness)
  • Durable
  • Better pressure capacity
  • No fusion metals used
  • No tests required for weld integrity

Different Applications of Rectangular Mild Steel Pipes

MS ERW Square & Rectangular Pipes are also called, Rectangular Hollow Section (RHS) or Square Hollow Sections (SHS). These are used for general engineering and structural purposes. The process of manufacturing is by ERW (Electric Resistance Welded). However, in some cases Square & Rectangular Seamless Pipes may also be used.

In the world of infrastructure, mild steel (MS) pipes have an important place. MS rectangular pipes are pipes made from steel, which has a carbon content of less than 0.25%. There are different grades of mild steel depending upon the carbon content present in the steel. Other elements may be added to this steel for enhancing its corrosion resistance, wear resistance and tensile strength. The high level of weldability and machinability of this type of steel makes it highly suitable for a range of applications including piping and tubing. Global Seamless Tubes and pipes are leading seamless manufacturer in India.


  • Shorter in length because of manufacturing difficulties
  • Size restriction with a nominal size of 24 inches or less
  • Costly
  • The extrusion process makes it rough
  • Inconsistent wall thickness


  • It can be manufactured in longer lengths
  • Less costly
  • No size restriction
  • Smoother surfaces
  • Readily available
  • Shorter delivery time
  • Thinner walls
  • Lighter in weight
  • Tighter tolerance
  • Consistency in wall thickness


  • Welds are prone to corrosion
  • It can only withstand 20% less weight
  • Must be tested before use
  • Poor ovality

Cold working, applied to both inside and outside surfaces, improves surface finish, increases tensile properties, improves machinability in many grades and results in more precise dimensions. Outside diameter and wall thickness tolerance are improved by approximately 50 percent.

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