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Common Inspection Methods for Welding Quality of Elbows

Sep. 12, 2020

The elbow must be inspected at the welded joint, which is also an important measure to ensure the quality of welding. Any defect that does not meet the allowable technical requirements must be repaired in time (such as serious unqualified and can not be repaired directly discarded). After the elbow is welded, the weld shall be inspected according to the technical requirements of the product. The common inspections of welding quality include visual inspection, non-destructive testing and mechanical performance test. These three are complementary to each other, and non-destructive testing is the main one.

1. Visual inspection of elbows: Generally, visual inspection is the main method. Through visual inspection, the surface defects of welded elbows can be found, sometimes with a magnifying glass of 5-20 times. Such as undercuts, pores, weld bumps, surface cracks, slag inclusions and weld penetration. The overall dimensions of the weld can also be measured with a weld joint detector or a sample plate.

30°Alloy Steel Elbow

2. Non-destructive inspection of elbows: inspection of slag inclusions, pores, cracks and other defects hidden in the weld. X-ray inspection is the use of X-rays to take pictures of welds, and judge whether there are internal defects, the number and type of defects according to the negative image. At present, the most common use is X-ray inspection, as well as ultrasonic inspection and magnetic inspection. Then according to the technical requirements of the product, the weld is qualified. At this time, reflected waves appeared on the phosphor screen. Based on the comparison and identification of these reflected waves with normal waves, the size and location of the defect can be determined. Ultrasonic flaw detection is much simpler than X-ray photography, so it is widely used. However, ultrasonic flaw detection can only be judged based on operating experience, and no basis for inspection can be left. The ultrasonic beam is emitted by the probe and transmitted to the metal. When the ultrasonic beam reaches the metal-air interface, it is refracted and passes through the weld. If there is a defect in the weld, the ultrasonic beam will be reflected to the probe and be accepted. For internal defects that are not deep from the weld surface and extremely small cracks on the surface, magnetic inspection can also be used.

3. Mechanical performance test of elbow: Non-destructive testing can find the inherent defects of the weld, but it cannot explain the mechanical properties of the metal in the heat-affected zone of the weld. Therefore, tensile, impact, and bending tests are sometimes performed on the welded joint. These tests are completed by test panels. The test board used is best welded together with the longitudinal seam of the cylinder to ensure consistent construction conditions. Then the test panel is tested for mechanical properties. In actual production, generally only welded joints of new steel grades are tested in this respect.

4. Elbow water pressure test and air pressure test: For pressure vessels that require tightness, water pressure test and/or air pressure test must be carried out to check the tightness and pressure bearing capacity of the weld. The method is to inject 1.25-1.5 times the working pressure of clean water or gas equal to the working pressure (mostly air) into the container, stay for a certain period of time, then observe the pressure drop in the container, and observe whether there is any leakage from the outside According to these, the welding seam can be qualified.

The above information is provided pipe elbow supplier.

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