Quality assessment process for ERW pipes

The quality assessment process for ERW pipes involves a series of inspections and tests to ensure their reliability and structural integrity. This article will introduce these procedures in detail.

1. Online Non-Destructive Testing

The detection arm of the flaw detection station in the straight seam welded pipe production line is rotated, allowing the weld position to be observed through a camera. The probe's position is adjusted using an operating rod so that the weld aligns with the laser, and the parameters are saved. The steel strip coil number is entered via DATASERVR and DACQ computers. On the flaw detection interface, the waveform display is monitored. When the waveform exceeds the alarm line, the thickness measurement information is checked to determine if it is a defect wave or interference wave signal. A visual inspection of the pipe is conducted to verify if the waveform exceeds the alarm line. If the waveform does exceed the alarm line, an alarm is triggered, prompting an immediate stop of the machine and readjustment of the welding parameters.

2. Metallographic Inspection

(1) Metallographic Microstructure of the Weld

After heat treatment of the weld, the inspection ensures that the coarse structure in the heat-affected zone is completely eliminated and is consistent with the base metal structure, free of inclusions in the weld fusion line. A weld that shows no inclusions, no micro-cracks, and a clear organizational structure indicates good quality.

(2) Metal Streamline Shape

During high-frequency welding, the proximity and skin effects cause the strip steel edge to be in a molten or semi-melted state. Under the pressure of the squeeze roller, the weld metal flows and the base metal streamlines on both sides of the weld rise, forming a streamline angle (α). This angle, usually between 40°and 70°, indicates qualified welding. If it falls outside this range, the welding process parameters need adjustment.

3. Destructive Testing

(1) Flattening Test

A 100mm section of welded pipe is cut and placed under a hydraulic press with the weld seam perpendicular to the pressing direction. The hydraulic press is activated, and the pipe is slowly pressed down to 3/4 of its diameter. The seam is then inspected for cracks. A lack of cracks signifies qualified welding, whereas the presence of cracks necessitates adjustments to the welding process parameters.

(2) Expansion Test

A 100mm section of welded pipe is placed on a cone-shaped top core and then positioned under a hydraulic press. The press is activated, and the pipe is expanded to 8%. The weld seam is inspected for cracks. No cracks indicate qualified welding; cracks indicate a need for welding process adjustments.

4. Hydraulic Test

For the hydraulic test, both ends of the welded pipe are sealed using flange clamps after welding the flange. The pipe body is filled with water, and pressure is gradually applied to meet relevant standards. Once stabilized, the pipe body is visually inspected for leaks at the weld seams. Absence of leaks confirms qualified welding, while leaks necessitate process adjustments. This test is the final step in ensuring the quality of welded pipes.