The primary difference between ERW (Electric Resistance Welded) and seamless stainless steel pipes lies in their manufacturing processes and structural characteristics. Seamless stainless steel pipes are made by extruding a solid billet of steel to create a pipe with no weld seam, which gives them uniform strength and makes them suitable for high-pressure and high-temperature applications. ERW pipes, on the other hand, are made by rolling a sheet of stainless steel and welding the seam longitudinally using electric resistance welding. While ERW pipes are generally more cost-effective and have a smooth surface, they may not be as strong or reliable as seamless pipes under extreme pressure or temperature conditions. The choice between the two depends on the application's requirements for strength, durability, and budget.

Seamless stainless steel pipes are made through a process that involves piercing and extrusion. The process begins with a solid cylindrical piece of stainless steel, called a billet. The billet is heated to a high temperature and then pierced through the center using a rotary piercing mill to create a hollow tube. This initial hollow tube is then elongated and formed into a seamless pipe by stretching or extruding it over a mandrel or using a series of rollers to achieve the desired diameter and wall thickness. The pipe is then further processed, including heat treatment, to improve its mechanical properties, and is cut to the required length and subjected to quality inspections to ensure it meets the necessary standards. The result is a strong, seamless stainless steel pipe with no welded joints.

Seamless pipes can be made from a variety of materials depending on the application and performance requirements. Common materials include carbon steel, stainless steel, alloy steel, and in some cases, non-ferrous metals like copper, nickel, and titanium. Stainless steel seamless pipes, for instance, are typically made from grades such as 304, 316, 321, and duplex stainless steels like 2205. These materials are chosen for their specific properties, such as strength, corrosion resistance, or heat resistance, making seamless pipes suitable for demanding environments in industries like oil and gas, petrochemicals, power generation, and more.