ERW (Electric Resistance Welded) steel pipes are made from steel coils or steel plates and the weld seam runs parallel to the pipe. They are commonly applied to transport oil, natural gas and other vapor-liquid objects, and can meet various requirements of high and low pressure. This article will introduce in detail the quality evaluation process of ERW steel pipes. Read on to learn more.
1. Online non-destructive testing
The detection arm of the rotating flaw detection station is placed on the straight seam welded pipe production line. The position of the weld is observed through the camera, and the front and rear position of the probe is adjusted with the operating rod to make the weld coincide with the laser, and the parameters are saved. Enter the number of steel strip coils via DATASERVR and DACQ computers. Observe the waveform display on the flaw detection interface. When the waveform exceeds the alarm line, compare the thickness measurement information to determine whether it is a defective wave or an interference wave signal, and visually inspect the pipeline to see whether the waveform exceeds the alarm line. If the waveform exceeds the alarm line, an alarm will sound. Stop the machine in time and readjust the welding parameters.
2. Metallographic inspection
(1) Weld metallographic structure. It is generally required to determine whether the coarse structure of the heat-affected zone has been completely eliminated after heat treatment of the weld, whether it is basically consistent with the structure of the base metal, and whether there is an inclusion fusion line in the weld. Generally speaking, the weld seam has no inclusions, no micro-cracks, and a clear organizational structure, indicating that the weld seam is grid-shaped.
(2) Metal streamlined shape. In high-frequency welding, the proximity effect and skin effect keep the edge of the strip in a molten and semi-molten state. Under the pressure of the squeeze roller, the weld metal flows in and out, and the base metal on both sides of the weld rises to form clamping. This angle is called the streamline angle α. Generally, it is judged as qualified when the weld is between 40° and 70°. If it exceeds this range, the welding process parameters need to be adjusted in time.
3. Destructive testing
(1) Flattening test. Cut about 100mm of welded pipe and place it under the hydraulic press. The position of the weld seam is perpendicular to the pressing direction of the hydraulic press. Start the hydraulic pressure and slowly press down on the welded pipe until it reaches 3/4 of the diameter. Check the welds for cracks. If there are no cracks, weld the grid; if there are cracks, adjust the welding process parameters in time.
(2) Expansion test. Cut about 100mm of welded pipe and place it on the conical top core; place the conical top core under the hydraulic press, start the oil pressure, and slowly press down the welded pipe. When expanding to 8%, check the weld for cracks. If there are no cracks, weld the grid; if there are cracks, adjust the welding process parameters in time.
4. Hydraulic pressure test
During the hydraulic pressure test, after welding the flange, first seal both ends of the welded pipe with flange clamps, then fill the pipe body with water, and gradually pressurize it to the pressure required by the relevant standards. After a certain period of time, visually inspect the welding condition of the pipe body. Are there any leaks at the seams? If there is no leakage, weld the grid; if there is leakage, adjust the welding process parameters in time. During the hydrostatic test, there was no leakage at the weld and the weld was fused. This is also the last step in the quality inspection of welded pipes.
