What are the inspection methods for ERW pipe

　　There are many methods for nondestructive testing of ERW pipe. Ultrasonic, eddy current or magnetic flux leakage testing are commonly used for ERW pipe. Eddy current testing is suitable for surface defects and near surface defects of metal materials; Magnetic flux leakage testing is used for surface defects and internal defects with a certain depth. Ultrasonic flaw detection can find long and thin defects, and can correctly find and determine the position of incomplete penetration at the top of the weld, hidden cracks and extended cracks in the heat affected zone of the weld center. Through non-destructive testing, the incomplete penetration, incomplete melting, slag inclusion, bubbles, shrinkage cracks, and the horizontal and vertical strip and delamination on the inner and outer surfaces of ERW pipe were detected.

　　There are two levels of NDT. The first level is in the sizing section, that is, on-line NDT, which is used to monitor the weld quality; The second level is the non-destructive testing of the finished steel pipe, which requires the testing of the whole pipe to ensure the product quality.

　　The ERW pipe has the characteristics of more precise geometric dimension, better quality of weld and inner and outer surface, uniform wall thickness and so on. Therefore, in the production of ERW pipe, there are the following requirements for ERW pipe forming unit and its supporting equipment:

　　1. High rigidity, high strength forming and sizing machine base: in order to reduce the strong plastic deformation of ERW pipe unit in the maximum load operation, make the total accumulated error of each machine base, reduce the elastic deformation, so as to improve the dimensional accuracy of ERW pipe. Therefore, it is necessary to improve the rigidity, strength and machining accuracy of the frame, flat roller shaft, bearing seat, screwdown and upper machinery. In the equipment selection, the heavy-duty ERW pipe unit and its supporting facilities should be selected.

　　2. Add 2 ~ 3 molding machine bases: in order to reduce elastic deformation, the processing channel is increased correspondingly. Generally, the number of forming deformation passes of ERW pipe unit is 2-3 times more than that of ordinary ERW pipe unit, so the number of forming frame is 2-3 times more.

　　3. In order to ensure the alignment of each stand on the rolling center line of the unit, the base shaft should be made in the center, and the positioning dimensions on both sides and the intermediate sleeve should be accurate. The unit should have accurate positioning datum. In the position of the horizontal line, the uphill line or horizontal straight line should be formed according to the process requirements to ensure that there is no curve fluctuation. Therefore, it is required that the frame should be equipped with press up and press down machinery to facilitate adjustment.

　　The strength, toughness, wear resistance, surface finish, dimensional accuracy and hardness of the roll die are required to be high, and the hardness should be uniform.

　　5. The ERW pipe unit shall be equipped with lubricant circulation device to cool and lubricate the roll, so as to reduce the deformation of the roll, the stress on the upper surface of the steel strip, prevent surface scratch and reduce micro cracks.