In the manufacturing process of precision welded steel pipes, various defects can generally be found during production through flattening, flaring or hydraulic tests. However, there are also some defects (especially internal defects) hard to be found and judged by visual inspection, but they may appear during use or later during the cold working process. Therefore, it is very necessary to establish non-destructive tests on the production line to detect product defects in time.
Non-destructive testing method of steel pipe:
There are many methods for non-destructive testing of steel pipes. The commonly used welding methods for precision steel pipes or precision steel tubes are ultrasonic, eddy current or magnetic flux leakage testing. Eddy current testing is suitable for the detection of surface defects and defects located near the surface of metal materials; magnetic flux leakage testing is used for surface defects and internal defects of a certain depth. Ultrasonic flaw detection can find slender defects. With ultrasonic flaw detection, incomplete penetration of the top of the weld, latent cracks and cracks extending in the heat-affected zone in the center of the weld can be correctly detected and determined. Through non-destructive testing, the pipes being welded are inspected to see if there are incomplete penetration, unmelted, slag inclusion, bubbles, shrinkage cracks, horizontal and vertical stripes and delamination on their inner and outer surfaces.
The non-destructive inspection is dividied into two steps. The first step is the sizing section, that is, on-line inspection, which is used to monitor the quality of the welding; the second step is the non-destructive testing of the finished steel pipe, which requires the entire pipe to be tested to ensure product quality.
Requirements on the supporting equipment of precision welded steel pipes:
The geometric dimensions of precision welded steel pipes are more precise than those of ordinary welded steel pipes, and the quality of welding as well as the internal and external surfaces is both good, and the wall thickness is uniform. Therefore, in the production of precision welded steel pipes, the pipe welding machine and its supporting equipment should meet the following requirements:
1. Adding 2 to 3 pipe welding machines: In order to reduce elastic deformation, the number of processing flow should be increased accordingly. Generally, the number of the pipe forming and deformation processing flows of the precision pipe welding machine are increased by 2 to 3 compared with that of ordinary welding machine, so the number of the machine needs to be increased by 2 to 3.
2. The roll mold should meet the strict requirements for strength, toughness, wear resistance, surface finish, dimensional accuracy, and hardness, and the hardness must be uniform.
3. The pipe welding machine should be equipped with a lubricant circulation device to cool and lubricate the roll to reduce the deformation of the steel strip on the roll and the upper surface stress, so that to prevent surface scratches and reduce micro-cracks.