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An ERW pipe is used to transport oil, natural gas and other vapor-liquid objects as it can meet the pressure level requirements to transport each of these substances. It is widely used around the world as a transportation pipe for various materials. These pipes are steel pipes made from steel coils and are one of the important uses of steel coils.
According to IS 1239 (Part 1) steel tubes/pipes are manufactured through one of the following processes:
- Hot finished seamless (HFS)
- Cold finished seamless (CDS)
- Hot finished welded (HFW)
- Electric resistance welded or high frequency induction welded (ERW or HFIW)
This article talks about the ERW process that results in an Electric Resistance Welded pipe or ERW pipe.
What is an ERW pipe?
A steel coil is put through the ERW process while making it into a steel pipe is called an ERW pipe. The full form of ERW pipe is Electric Resistance Welding pipe. Electric resistance welding (ERW) is a welding process where metal parts are permanently joined by heating them with an electric current, melting the metal at the points of joining. It is widely used to manufacture steel pipes and to assemble bodies for automobiles.
ERW pipe meaning – Steel pipes made by longitudinally welding steel coils/plates using the ERW process is called an ERW pipe.
How is ERW pipe manufactured?
ERW steel pipes are made using low-frequency or high-frequency resistance. They are round pipes welded from steel coils/steel plates. Steel coils are curved in the shape of a tube and joined using the ERW process to make ERW pipes. The ERW pipe manufacturing process is explained below.
Step 1: A long strip of steel coil is fed into a machine referred to as the forming line
Step 2: The forming line curves the edges of steel coil into the shape of a hollow tube
Step 3: The edges of the steel coil is made into welding seams by passing it through the extrusion roller
Step 4: The welding seams are then joined using a combination of heat and pressure (This is referred to as the ERW process which is explained below)
Step 4: A nominal amount of heat is applied to the welding seams
Step 5: A simultaneous circumferential pressure is applied to the welding seams
Step 6: Heat and pressure weld the seams together resulting in the ERW pipe
As explained under the manufacturing process, once the steel coil is curved the edges of the coil are exposed to electric current which generates heat upon contacting the surface of the edges. The electric current generates heat to the point where one edge can form a bond. Simultaneously, the edges are exposed to pressure which melts and squeezes them together.
The ERW pipe production line can produce longitudinal welded cylindrical pipes, rectangular pipes, square pipes, steel sheet piles and other products.
Benefits of ERW pipes
Unlike ordinary welded pipes, ERW pipes are formed by melting the base material of the steel coil. Therefore, its mechanical strength is better than that of ordinary welded pipe or pipes welded using submerged arc welding.
Let us have a look at the characteristics of an ERW pipe:
- High production efficiency
- Corrosion resistant
- Material saving
- Easy automation
Uses and applications
ERW pipes are mainly used for transportation of various materials. ERW pipes are used in energy, electronics, aviation, aerospace, automobile, and other industrial sectors.
- Water supply and drainage systems
- Structural support columns
- Oil and gas pipelines
- Drilling casings
- Automobile exhaust systems
- Automobile suspension components
- Irrigation systems
Sizes and specifications
ERW pipe sizes are usually customised by most manufacturers. Have a look at a sample of how manufacturers write ERW pipe specification and size in their catalogue:
Permanent Steel Manufacuring Co Ltd – ERW pipe
Wall thickness: 1.65-20mm
Length: 3-12m, or according to customer’s requirement
End: Plain end, beveled end, treaded
Have a look at the IS 1239 for a full list of ERW pipe specifications that are allowed in India.
ERW pipes vs seamless pipes
These are the main differences between ERW pipes and seamless pipes:
- ERW pipe is manufactured by forming metal into a tube and then welding it longitudinally across its length. Seamless pipe is manufactured pressing down the metal to the required length.
- ERW pipe features a welded joint in its cross-section, while seamless pipe does not have any joint throughout its length.
- Seamless pipes have a longer manufacturing process compared to ERW pipes.
- Seamless pipes are more expensive than ERW pipes.
- ERW pipe is manufactured from strips/coils while seamless pipe is manufactured from solid round billets.
- The working pressure capacity of a seamless pipe is 20% higher compared to the working pressure capacity of an ERW pipe.
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