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Four quality inspection aspects of elbow welding
Apr 26, 2018

The elbow must be inspected at the welded joint, which is also an important measure to ensure the welding quality. When the elbow is finished, the weld is tested according to the technical requirements of the product. If the defect is not in conformity with the technical requirements, it should be repaired in time (if the serious unqualified can not be repaired directly). The common inspection of welding quality includes three aspects: appearance inspection, NDT and mechanical performance test. These three are complementary to each other, among which NDT is the main one.

 

1, appearance check: generally observe with the naked eye, sometimes observe with 5-20 times magnifying glass. Through appearance inspection, the weld surface defects such as undercut, welding bead, surface crack, air hole, slag inclusion and welding wear can be found. The size of the weld can also be measured by the solder joint detector or the template.

 

2. NDT: detect defects such as slag, blowholes and cracks hidden inside the weld. At present, the most commonly used are X ray inspection, ultrasonic testing and magnetic flaw detection. X ray inspection is the use of X ray for weld photography, according to the film image to determine whether there are defects, defects and types. And then assess whether the welds are qualified according to the technical requirements of the products. The basic principle of ultrasonic flaw detection is shown in the following chart. The ultrasonic beam is transmitted from the hair to the metal. When the ultrasonic beam reaches the interface between the metal and the air, it is refracted and passed through the weld. If there are defects in the weld, the ultrasonic beam will be reflected to the probe and be accepted, then the reflection wave will appear on the screen. According to the comparison and identification of these reflected waves with normal waves, the size and location of the defects can be determined. Ultrasonic detection is much more convenient than X photography, so it is widely used. However, ultrasonic testing is often based on operational experience and can not leave a basis for inspection. Magnetic flaw detection can also be used for internal defects and tiny cracks on the surface of the weld.

 

3, hydraulic test and pressure test: for pressurized containers requiring sealing, pressure tests and / or air pressure tests should be carried out to check the sealing and pressure capacity of the weld. The method is to inject water with 1.25-1.5 times working pressure into the container or the gas equal to the working pressure (most of the air), stay for a certain time, then observe the pressure drop in the container, and observe the leakage phenomenon in the outside, according to whether these welds are qualified.

 

4, the mechanical performance test of the elbow: nondestructive flaw detection can discover the internal defects of the weld, but can not explain the mechanical properties of the metal in the weld heat affected zone, so sometimes the welding joint should be tested with tension, impact, bending and so on. These tests are done by the test board. The test plate is preferably welded with the longitudinal joint of the cylinder to ensure consistent construction conditions. The test plate is then tested on mechanical properties. In actual production, the welding joint of new steel is usually tested in this aspect.

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