After receiving the task of flaw detection, the first thing is to understand the technical requirements of the drawings for welding quality. Ultrasound is used in full penetration weld flaw detector. Its flaw detection ratio is calculated by the percentage of each weld length, and it is not less than 200 mm. For locally inspected welds, if there is an impermissible defect, the inspection length should be increased at the extension of both ends of the defect. The increase length should not be less than 10% of the length of the weld, and it should not be less than 200 mm. When there are still impermissible defects, 100% flaw detection should be carried out for the weld. Secondly, when using the weld flaw detector, the timing of flaw detection should be clear. Carbon structural steel should be tested after the weld cooling to the ambient temperature and low alloy structural steel can be tested 24 hours after the completion of welding. In addition, the thickness of base metal, joint type and groove type of the workpiece to be measured should be known in use. Generally, the base metal thickness of weld flaw detector is between 8 and 16 mm. The groove type includes I type, single V type and X type. The preparatory work before flaw detection can be carried out only after making clear the above.
Before each flaw detection operation, the comprehensive performance of the instrument and the panel curve must be calibrated by using standard test blocks to ensure the accuracy of the flaw detection results.
1. Surface repair: Splash, oxide scale, pit and rust on the welded surface should be removed, and the smoothness is generally less than 4. The repairing width of flaw detection surface on both sides of weld is generally greater than or equal to 2K T+50mm (K: probe K value, T: workpiece thickness).
2. Viscosity, fluidity and adhesion should be taken into account when selecting coupling agent. It has to be corrosion-free, easy to clean and economical to the workpiece surface. Based on the above factors, paste was chosen as coupling agent.
3. Because of the thinner base metal thickness, the detection direction is carried out on one side and two sides.
4. Because the thickness of the plate is less than 20 mm, the horizontal positioning method is used to adjust the scanning speed of the instrument.
5. Rough flaw detection and fine flaw detection are used in flaw detection operation.
6. Record the detection results, such as finding internal defects and evaluating them.