Electric resistance welding (ERW) pipes are manufactured by continuously roll-forming hot coil material into a pipe shape, and butt-welding the weld seam after heating/melting the coil edges using the Joule heat generated by passing a high frequency current through the edges. At the seam of the ERW butt weld (hereinafter, seam), the welding beads on the pipe inside and outside surfaces are removed by online, full-length grinding, followed by seam heat treatment to improve the weld microstructure.
After ERW linepipes are cut to the specified length, product pass through the quality assurance process, which includes hydrostatic testing, ultrasonic testing of the seam and pipe body, inspections of external appearance and dimensions, etc.
In general, ERW pipes have the following advantages.
(1) Because hot coils are used as the starting material, thin wall thickness pipe can be manufactured, and its thickness accuracy is good and the pipe has a smooth surface which is free of roughness, pits, etc.
(2) The pipemaking process is characterized by high productivity and high dimensional accuracy. As a result, lower costs can be expected in the pipe-laying process due to reduction of the work load in girth welding to join pipes, etc.
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