On the assessment of stress
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When performing stress analysis calculations, the assessment of stress levels is crucial. I compare stress analysis to taking X-rays in a hospital; it works in the same way. To diagnose a patient, X-rays are taken first, and then those images are shown to the doctor, who uses them to determine the condition and prescribe appropriate treatment. Taking X-rays is important, but the doctor who analyzes those images is even more crucial. If the X-rays are taken incorrectly, it can lead to misdiagnosis by the doctor. When we conduct analytical calculations, it is not only necessary to ensure accuracy in the computations, but also to present the results accurately; moreover, the evaluations must be correct. What should be done is an evaluation based on primary stress, yet instead a secondary stress evaluation is used. The result may seem acceptable, but it poses significant safety risks. Many parts of a machine require stress evaluation, and the criteria for evaluating each part are different. On top of that, we have to deal with countless machines. Some people might say that modern limit load analysis can avoid the problem of distinguishing between primary and secondary stresses; it’s feasible for simple devices, but it’s more difficult to apply to complex designs – such as intricate heat exchangers or complex reaction vessels. It’s not easy to conduct a limit load analysis in such cases. Therefore, although the stress classification method has many shortcomings, it has managed to remain in use over the years, and there is indeed a reason for its existence. We still like it very much and continue to appreciate it. . . Some people say that the standards specify stress classifications for many different parts – do you really believe that? Standards cannot be trusted entirely either; after all, they are created by humans. Standards can be relied on, but one should not depend on them completely. Here are a few examples for everyone to study; without understanding these, one cannot be considered an excellent analysis and design professional, let alone a master-level expert! 1. Stress assessment of bolts 2. Stress assessment of flanges 3. Stress assessment at the flange-tube connection 4. How to apply bolt preload? 5. How does a hydrostatic test enable stress assessment of drilled nozzles? 6. ASME VIII Div. 2 secondary stress assessment 7. Assessment of ratchets 8. Stress assessment of stainless steel reaction vessels 9. Stress assessment of elliptical heads 10. Assessment of ultimate load analysis 11. Assessment of elastoplastic analysis 12. Assessment of openings in flat covers 13. Assessment of flange sealing 14. Assessment of wall thickness of high-pressure cylinders. . . . . . . . . . . . For us, every piece of equipment is new, and we need to treat it with care. Only by understanding its essence can we eliminate potential problems. Many people have spent years doing stress analysis, yet they still fail to see everything clearly, let alone understand the meaning of the standards. What’s needed here is a sense of fate and dedication; let’s take our time, there’s no need to rush!
Regarding the assessment of stress, I agree with you; it is a very important task that requires a high level of professionalism and a meticulous attitude. For each device, we need to conduct in-depth analysis and evaluation from various aspects to identify potential security risks and ensure its safe and stable operation. The stress assessment for each component has its own particularities; we need to select an appropriate assessment method based on the characteristics of the equipment and its actual operating conditions. For stress assessment of components such as bolts, flanges, and vessel joints, many factors need to be considered, such as material properties, operating temperature, and the method of applying preload. We need to conduct a detailed analysis of these factors in order to arrive at an accurate assessment. For stress assessment under standards such as ASME VIII Division 2, it is also necessary to have a thorough understanding of the principles and underlying rationale behind them; we cannot rely on them blindly. Only in this way can we identify the most suitable assessment method for practical use. For evaluating methods such as ultimate load analysis and elastoplastic analysis, we also need to make choices based on the actual conditions of the equipment, with the safety of the equipment being the top priority at all times. In this process, we need to have a spirit of exploration, as well as a passion and dedication to our profession; only in this way can we move further along the path of stress assessment and become excellent stress assessors. So, let’s work together to do this job better. .