Manufacture/Inspection and Advantages of ERW Line Pipe

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.

Knowledge of ERW Line Pipe

With the rapid development of economy and the continuous improvement of the energy demand, the pipeline as the oil and gas resources has developed in recent years. A number of medium-caliber ERW line pipe unit was completed and put into operation. ERW line pipe has been widely used in the oil and gas field gathering pipelines, oil and gas Spur. This article will focus on the circumferential residual stress on the impact of ERW line pipe manufacturing process and final product quality and control aspects of the problem.

ERW pipe forming process can be divided into two phases: the first stage of

deformation; the second stage for reducing distortion. In both phases, the steel pipe inner layer is always affected by the circumferential compressive stress and compressive deformation. The outer layer of fine molding of the bending process by weeks to the tensile stress and extension deformation: in the fine shaping and sizing process. Steel outer layer of compressive stress and compressive deformation. And ERW pipes of different specifications, the outer layer of the final strain differences. This shows that the ERW pipe inner and outer layers in the pipe circumferential strain is inconsistent. Stress state and stress the size of change.

Common problems in manufacturing process of ERW line pipe:
(1) ERW line pipe manufacturing process will bend uneven deformation of the pipe week up there is a large residual stress, so take the necessary measures to reduce the negative impact of residual stress on the ERW line pipe manufacturing process.
(2) the study and control of ERW line pipe residual stress should not be confined to the detection and analysis of the residual stress of the final product, required to pipe forming process of ERW pipeline analysis, taken from the perspective of process control measures to reduce ERW pipeline the residual stress of the pipe, reduce the adverse effects of residual stress may cause the quality of ERW line pipe.
(3) Sizing is mainly to ensure the pipe diameter to meet the requirements, the hydrostatic test is to ensure that the density of steel pipe, but for the ERW pipeline in terms of pipe, Is also an important process to reduce the circumferential residual stress.