Quality assessment process of ERW steel pipes

ERW Steel Pipe (Electric Resistance Welded Pipe) is a type of straight seam welded pipe produced using the electric resistance welding process. It is primarily used to transport vapor and liquid substances, such as oil and natural gas, and is suitable for both high and low-pressure applications. ERW steel pipes play a crucial role in the global transportation pipeline sector due to their versatility and performance in various environmental conditions.

The key distinction between ERW steel pipes and seamless steel pipes is that ERW pipes feature a weld seam, which is critical to the pipe’s overall quality and performance.

ERW Pipeline Assessment Process:

1. Non-Destructive Testing (NDT)

Non-destructive testing is crucial for assessing the integrity of ERW steel pipes without damaging them. In the ERW pipe production process, the inspection station's detection arm is rotated into the pipeline line, and the weld's position is monitored through a camera. The front and rear positions of the probe are adjusted to align the weld with a laser. Key steps include:

Inputting the steel coil number via DATASERVR and DACQ computers to monitor the pipe’s characteristics.

Observing the waveform display on the flaw detection interface, which highlights any abnormal signals.

If the waveform exceeds the alarm threshold, a comparison is made with thickness measurement data to determine whether the signal is due to a defect or interference.

Visual inspections are conducted to confirm whether the waveform exceeds the acceptable limits. An alarm sounds if there are discrepancies, prompting a pause in the machine's operation and an adjustment of the welding parameters.

Surface non-destructive testing is carried out in accordance with industry standards, typically focusing on:

Quality inspection of the outer surface of pipe materials.

Detection of surface defects in important butt welds, fillet welds, socket welds, and tee branch bridge welds.

Surface defects after bending are also inspected.

Inspection of bevel angles in welded joints, especially those with a tendency to undergo material quenching.

For non-austenitic stainless steel pipes, inspection is mandatory if the design temperature is below -29°C.

Rooting inspection is specified for double-sided welds post-rooting.

Defects in repair parts after oxyacetylene flame cutting are detected for tubes prone to hardening.

2. Destructive Testing

Destructive testing is employed to evaluate the mechanical strength and structural integrity of the ERW steel pipe. This process involves testing the welded seams under controlled, destructive conditions to ensure the quality of the finished product:

- Flattening Test:
A 100mm section of the welded pipe is cut and placed under a hydraulic press, with the weld seam perpendicular to the direction of pressure. The hydraulic press applies oil pressure slowly to flatten the pipe until it is compressed to 3/4 of its diameter. The weld is inspected for cracks; if no cracks are found, the weld is considered sound. If cracks appear, the welding process parameters are adjusted accordingly.

- Expansion Test:
Another 100mm section of welded pipe is cut and placed on a conical top core under the hydraulic press. The press is then activated, gradually applying pressure to expand the pipe. The pipe should expand by 8% without the weld breaking. If the weld fails, the machine is stopped, and the welding parameters are adjusted to ensure proper performance in future productions.