How to inspect the welding quality of elbow fittings

2020-09-27 14:31:30   

1. Appearance inspection of elbow fittings: generally, visual inspection is the main method. Through the appearance inspection, it is found that the weld appearance defects of welded elbow pipe fittings are detected by 5-20 times magnifying glass sometimes. Such as undercut, porosity, weld bead, surface crack, slag inclusion, welding penetration, etc. The overall dimension of weld can also be measured by weld detector or template.

 

2. NDT for elbow fittings: check the defects such as slag inclusion, air hole and crack in the weld. X-ray inspection is the use of X-ray to take photos of the weld, according to the negative image to determine whether there are defects in the weld, the number and type of defects. At present, X-ray testing, ultrasonic testing and magnetic testing are widely used. Then according to the product technical requirements, determine whether the weld is qualified. At this point, the reflected wave appears on the screen. By comparing and identifying these reflected waves and normal waves, the size and location of defects can be determined. Ultrasonic testing is much simpler than X-ray testing, so it has been widely used. However, ultrasonic testing can only be judged by operating experience and cannot leave the basis of inspection. When the ultrasonic beam is transmitted to the metal air interface, it will refract and pass through the weld. If there is a defect in the weld, the ultrasonic beam will be reflected on the probe and bear. Magnetic inspection can also be used for internal defects and very small cracks not deep from the weld surface.

 

3. Mechanical property test of elbow fittings: nondestructive testing can find inherent defects of weld, but it can not explain the mechanical properties of metal in heat affected zone of weld. Sometimes tensile, impact and bending tests are needed for welded joints. These experiments were done on a board. The test plate should be welded with the longitudinal seam of the cylinder to ensure the same construction conditions. Then the mechanical properties of the test plate were tested. In practical production, only the welding joint of new steel grade is tested in this respect.

 

4. Hydrostatic test and pneumatic test of elbow fittings: for the pressure vessels that need to be sealed, hydrostatic test and pneumatic test are required to check the sealing and pressure bearing capacity of welds. The method is to inject the container into the working pressure of the water or 1.25-1.5 times the working pressure of the gas (most of the air) for a period of time, then investigate the pressure drop in the container, and investigate whether there is any leakage phenomenon, so as to determine whether the weld is qualified.