The wall thickness of the elbow pipe fittings is uneven, and the uneven wall thickness of the pipe fittings mainly occurs in the most deformed part of the pipe fittings. For example, the wall thickness of the back of the elbow is thinner than that of other parts, and the wall thickness of the nozzle and the pipe body is different. The relevant national standards stipulate. The maximum wall thickness reduction of pipe fittings should not exceed 12.5% of its nominal thickness, but it was found in field measurements that some wall thickness reductions reached 20-30%. For the inspection of such problems, it is often difficult to find them with general measuring tools such as calipers. At this time, only ultrasonic thickness gauges can be used to measure them. The problem of hardness exceeding the standard is mainly due to the problem of the heat treatment process after forming. The solution is to use the correct heat treatment process to perform another heat treatment. This problem can generally be resolved.
The production of elbow pipe fittings requires the operator to have high technology and rich experience and to determine whether the detected defects belong to cracks or other defects, so as not to miss or misjudgment. At present, the appearance size, hardness, thickness, magnetic particle testing (MT) and ultrasonic testing (UT) of the pipe fittings are often inspected before leaving the factory. Judging from the inspection of the incoming pipe fittings, the most frequent problems are magnetic particle testing and ultrasonic testing. test. It has relatively high requirements for testing equipment, especially for probes. For many parts with large deformation (such as the two shoulders of the tee) and pipe fittings with a diameter below DNS0mm, it is easy to test with domestic straight probes commonly used by most inspectors. Occurrence of missed detection, or even untestable through on-site practice. For the above difficulties, it is better to use the double crystal probe with a diameter of less than 10mm and use the crossing oblique entry method.
The defects caused by the material of the elbow and the processing process are the most harmful to the safety of the device, and it is more troublesome to check. There are many and complicated factors that cause defects. It includes defects in the material itself, manufacturing process problems and defects caused by incorrect heat treatment processes. The inspection of pipe fittings before delivery and after arrival plays an important role in the last process to ensure the quality of pipe fittings. Especially for pipe fittings that withstand high temperature, high pressure and flammable and highly toxic media, the inspection process is particularly important. For magnetic particle testing, manufacturers mostly use the yoke method (carbon steel pipe fittings). However, due to the limitation of equipment, this method is mostly limited to the outer surface of the pipe fittings, and most problems occur on the inner wall of the pipe fittings. For the cracks that often appear in this part, especially the cracks on the inner wall of small-diameter pipe fittings, the magnetic rod method should be used. Or eddy current method for inspection Ultrasonic flaw detection inspection is an inspection item that has high requirements for equipment and technology.
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