Quality assessment process for ERW steel pipes

The quality assessment process of ERW steel pipes includes online non-destructive testing, metallographic structure inspection, flattening and flaring destructive tests, and hydraulic tests. The detailed steps of the assessment process are as follows.

Online Non-Destructive Testing

The flaw detection station's detection arm is rotated along the straight seam welded pipe production line. Through a camera, the weld position is monitored, and the operating rod is used to adjust the probe's position so that the weld aligns with the laser. The parameters are saved, and the steel strip coil number is entered through the DATASERVR and DACQ computers. The flaw detection interface displays waveforms, which are observed to ensure they do not exceed the alarm line. If the waveform does exceed the alarm line, it triggers an alarm. The thickness measurement information is compared to determine whether the signal indicates a defect or interference. A visual inspection of the pipe is conducted, and if necessary, the machine is stopped, and the welding parameters are readjusted.

Metallographic Inspection

(1) Weld Metallographic Microstructure: After heat treatment, the weld is examined to ensure that the coarse structure in the heat-affected zone has been completely refined, that it is consistent with the base metal's structure, and that no inclusions are present at the weld fusion line. A high-quality weld will have no inclusions, no micro-cracks, and a well-defined structure.

(2) Metal Streamline Shape: During high-frequency welding, the proximity effect and skin effect cause the strip steel edges to enter a molten or semi-molten state. Under the squeeze roller's pressure, the weld metal flows in and out, causing the base metal streamlines on both sides of the weld to rise, forming a pinch angle known as the streamline angleα. This angle should generally be between 40°and 70°to be considered qualified; if it falls outside this range, the welding process parameters must be adjusted.

Destructive Testing

(1) Flattening Test: A 100mm section of the welded pipe is cut and placed under a hydraulic press, with the weld seam positioned perpendicular to the pressing direction. The hydraulic press is slowly activated to compress the pipe to 3/4 of its diameter. The weld is inspected for cracks. If no cracks are found, the weld is deemed qualified. If cracks are present, the welding process parameters must be adjusted.

(2) Expansion Test: Another 100mm section of the welded pipe is cut and placed on a cone-shaped top core, which is then placed under a hydraulic press. The press is slowly activated to expand the pipe until it reaches an 8% expansion. The weld is inspected for cracks. If no cracks are found, the weld is qualified. If cracks are present, adjustments to the welding process parameters are necessary.

Hydraulic Test

For the hydraulic test, both ends of the welded pipe are sealed with flange clamps, and the pipe body is filled with water. Pressure is gradually applied until it reaches the standard-required level. After stabilizing the pressure for a set period, the weld seam is visually inspected for leaks. If no leaks are detected, the weld is qualified. If leaks are present, the welding process parameters must be adjusted. The hydraulic test, which ensures no leaks at the weld, is the final step in the quality inspection of welded pipes.