The main difference between seamless and ERW pipes is that seamless pipes are manufactured without welds or joints, while ERW pipes have a longitudinal seam formed by electric induction welding or electric resistance welding without the addition of filler metal. The edges to be welded are mechanically pressed together, and the heat for welding is generated by the resistance of the electric current.
Heat Treatment
Seamless pipes: are supplied from hot-worked steel or, if necessary, by cold working the hot-worked product to produce the desired shape, size and properties. The welds of electric-welded pipes are heat treated after welding to a minimum temperature of 1,000°F or processed so that no untempered martensite remains.
Electric-welded pipes: This erw difference is usually eliminated if heat treated by a quenching and tempering process, which is mandatory for some API 5CT grades.
Outer diameter tolerance
ERW steel pipe: cold bending is adopted, and the sizing is completed by 0.6% diameter reduction. The process temperature is basically constant at room temperature, so the outer diameter control is accurate and the fluctuation range is small, which is conducive to eliminating black buckles;
Seamless steel pipe: hot rolling forming process is adopted, and the sizing is completed at about 8000C. The raw material composition, cooling conditions and cooling state of the rolls of the steel pipe have a great influence on its outer diameter, so the outer diameter control is difficult to be accurate and the fluctuation range is large.
Wall thickness tolerance
ERW steel pipe: hot-rolled strip coil is used as raw material, and the thickness tolerance of modern hot rolling can be controlled within 0.05mm. Seamless steel pipe is produced by round steel perforation, and the wall thickness deviation is large. The subsequent hot rolling can partially eliminate the uneven wall thickness, but the most advanced unit can only be controlled within +5~10%t, corresponding to a steel pipe with a thickness of 8.94mm.
Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.
Performance
Seamless pipe: It is superior to welded pipe in corrosion resistance, pressure bearing, high temperature resistance and other properties, and is usually used in special environments such as high pressure resistance and high temperature resistance.
ERW pipe: Electric resistance welded pipe has the characteristics of high production efficiency, low cost, material saving, and easy automation. Although the mechanical strength is better, it is not as good as seamless pipe.
ERW tube
