Issues with non-destructive testing of high-pressure steam A335P91 pipes
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For high-pressure superheated steam pipes made of A335P91 (508×32.54), in accordance with clause 6.3.3 b of the \"Code for Welding Techniques in Thermal Power Plants\" DL/T869-2012 (for pipes and welded components with a thickness greater than 20 mm, either radiographic testing or ultrasonic testing may be selected), heat treatment is carried out after the entire weld seam has been welded continuously. After heat treatment, TOFD and MT testing are employed. However, the design indicates that TOFD has a near-surface blind zone, which may lead to missed detection of defects; therefore, TOFD cannot be used alone as a detection technique. Since TOFD and UT complement each other to some extent, the recommended approach is 100% TOFD + 100% UT + 100% MT. I would like to ask for suggestions on how to develop a testing plan to ensure welding quality Thank you!
The design of a non-destructive testing plan to ensure welding quality requires taking into account many factors, including material type, welding method, equipment availability, operator skills, etc. Regarding the high-pressure steam A335P91 pipes you mentioned, I can provide some general suggestions. 1. **Comprehensive application of various non-destructive testing methods**: As you mentioned, TOFD (Time of Flight Diffraction), UT (Ultrasonic Testing), and MT (Magnetic Particle Testing) each have their own advantages and limitations. TOFD is suitable for detecting defects inside welds, but it has a near-surface blind zone ； UT can detect surface and near-surface defects, but it may be less sensitive to internal defects than TOFD ； MT is mainly used to detect open defects in surface and near-surface magnetic materials. Therefore, combining these three methods can improve detection efficiency and accuracy. 2. **Consider visual evaluation of welds**: Even after non-destructive testing, visual evaluation of the welds should also be considered. Although this may not provide information on internal defects, it can help determine the overall quality of the weld, such as whether there are cracks, holes, or other visible defects. 3. **Conduct regular inspections and maintenance**: Non-destructive testing should not be carried out only once after welding is completed. To ensure the durability of welding quality, regular inspections and maintenance should be carried out. This can help identify and fix any issues that may arise over time. 4. **Use experienced operators**: Non-destructive testing requires specialized skills and experience. Using experienced operators can improve the accuracy and efficiency of detection. 5. **Tracking and recording inspection results**: Recording and tracking inspection results helps analyze trends in welding quality, enabling timely identification and resolution of issues. Finally, it is recommended that you seek advice from a professional non-destructive testing company, as they can provide the most suitable testing solution based on your specific circumstances. .
Chromomolybdenum steel has a tendency to develop delayed cracking, making it difficult to weld. The process conditions involved are also quite stringent. For qualified and competent welders, the pass rate on the first attempt should be 98%. 100% radiography should be carried out during the processing process, and since TOFD, MT, and UT are not expensive and require little time, it is recommended to use all of them. After heat treatment, a 100% hardness inspection of the area around the weld is also required. It is worthwhile to conduct various tests on this type of important steel. Avoiding a single major accident makes all the cost worthwhile.