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ERW (Electric Resistance Welded) and seamless pipes are two different types of steel pipes commonly used in various applications. Here are the main differences between ERW and seamless pipes:

1. Manufacturing Process:
   • ERW Pipes: ERW pipes are manufactured by rolling metal sheets into a cylindrical shape and then welding the edges together using electric resistance. This process involves the application of heat and pressure to create the weld.
   • Seamless Pipes: Seamless pipes are manufactured through a process called extrusion or rotary piercing. In this process, a solid steel billet is heated and forced through a piercing rod to create a hollow tube. It does not involve any welding or joining of edges.
2. Welding Seam:
   • ERW Pipes: ERW pipes have a welded seam along their length, where the edges of the metal sheets are joined together. The welding seam may be visible on the surface of the pipe.
   • Seamless Pipes: Seamless pipes do not have any welding seam. They are continuous in structure from one end to the other, providing a smoother internal surface.
3. Strength and Pressure Resistance:
   • ERW Pipes: ERW pipes are generally considered suitable for low to medium pressure applications. The welding process may create a slight reduction in the overall strength of the pipe at the welded seam.
   • Seamless Pipes: Seamless pipes are known for their higher strength and pressure resistance. The absence of welding seams eliminates potential weak points, making them suitable for high-pressure and critical applications.
4. Wall Thickness and Diameter Range:
   • ERW Pipes: ERW pipes are available in a wider range of sizes and wall thicknesses compared to seamless pipes. They are commonly used for smaller diameter pipes, typically up to 24 inches.
   • Seamless Pipes: Seamless pipes are available in a limited range of sizes and wall thicknesses, primarily used for larger diameter pipes exceeding 24 inches.
5. Cost:
   • ERW Pipes: ERW pipes are generally more cost-effective compared to seamless pipes. The manufacturing process is simpler and less expensive, making them a preferred choice for non-critical applications.
   • Seamless Pipes: Seamless pipes are typically more expensive due to the complex manufacturing process and the higher quality standards required for critical applications.

In summary, ERW pipes are made by welding metal sheets together, have a visible welded seam, and are suitable for low to medium pressure applications. On the other hand, seamless pipes are manufactured without any welding seam, have higher strength and pressure resistance, and are commonly used in high-pressure and critical applications.