Inspection Method of Weld Defects of ERW Steel Pipe

With the continuous increase in the delivery pressure and steel grade of oil and gas pipelines, the requirements of ERW steel pipes for oil and gas transportation are also increasing. The number of ERW steel pipes used in submarine pipelines is relatively large, such as some oilfield group development projects and natural gas development projects. ERW steel pipe is formed by continuous roll forming of hot-rolled coils, which uses the skin effect and proximity effect of high-frequency current to generate resistance heat at the edges of the coils and cause metal melting. Pressure welding is performed under the action of squeeze rollers. Its characteristics: high welding speed, because the current energy is highly concentrated in the welding zone, the heating speed is extremely fast, so the welding speed is very high, the welding speed is generally between 10 m / min and 45 m / min; the heat affected zone is small, because the welding speed is high , The workpiece has a strong self-cooling effect, so not only is the heat affected zone small, but it is not easy to oxidize, and it can obtain a better structure and performance welds with high dimensional accuracy. Therefore, the quality of ERW steel pipe welds will become its main control target.

Piezoelectric ultrasonic testing methods are usually used to detect ERW steel pipe weld defects. Due to the characteristics of ERW steel pipe welding and forming, defects that are at a certain angle to the surface of the steel pipe (hook cracks, unfused, not fully penetrated, etc.) are easy to detect. Defects perpendicular to the surface of the steel pipe (such as cold welding, gray spots, under-welding, etc.) are difficult to detect.

In recent years, research on electromagnetic ultrasonic testing has been conducted at home and abroad. Compared with conventional piezoelectric wafer ultrasonic testing, electromagnetic ultrasonic testing can achieve the advantages of non-contact testing, high temperature monitoring, and automated testing. high sensitivity. However, how to use electromagnetic ultrasonic testing is not involved in the relevant domestic and foreign standards for electromagnetic ultrasonic testing (such as GB / T20935.1 ^ 3-2007, ASTM E1774-96, ASTM E1962-2004 and ASTM E1816-2007, etc.) The content of quantitative detection of weld defects of ERW steel pipes.