The role of non-destructive testing for pressure vessels

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To ensure product quality, non-destructive testing techniques are employed to detect internal defects that are invisible to the naked eye； When inspecting the surface quality of test pieces, non-destructive testing methods can detect many tiny defects that are difficult to see with the naked eye. Due to the wide range of applications of non-destructive testing techniques in defect detection, their high sensitivity, and the reliability of their test results, they are widely used in the in-process inspection and final quality inspection of pressure-bearing special equipment as well as other products. Another advantage of applying non-destructive testing techniques is the ability to conduct 100% inspection. As is well known, with destructive testing, the test specimen is destroyed at the same time as the testing is completed; therefore, destructive testing can only be used for sampling inspections. Unlike destructive testing, non-destructive testing allows the inspection process to be carried out without damaging the specimen; therefore, it enables 100% inspection of products or inspection of each individual item. Many important materials, structures, or products must be guaranteed to be flawless, and only by using non-destructive testing methods can effective quality assurance be provided. To ensure safe use, even pressure-bearing special equipment whose design and manufacturing meet all regulatory requirements can still suffer damage after being in use for a period of time. This is due to harsh operating conditions that cause changes in the equipment’s condition, such as material creep resulting from high temperatures and stress ； Fluctuations in temperature and pressure generate alternating stresses, causing fatigue at the stress concentration points of the equipment ； Due to corrosion causing the wall thickness to thin or material degradation, etc. The aforementioned factors may cause the minor defects that already existed in the equipment and were permitted by the manufacturing specifications to expand and crack, or may lead to the emergence of various new defects in areas of the equipment that originally had no defects, ultimately resulting in equipment failure. To ensure safe use, boilers, pressure vessels, and pressure pipelines in service must be inspected regularly to detect defects promptly and prevent accidents. Non-destructive testing is the main component of these regular inspections and the most effective method for identifying defects. In addition to boilers, pressure vessels, and pressure pipelines, non-destructive testing methods are also frequently used for the periodic inspection of other important equipment, components, and parts in use. Improving manufacturing processes: In product production, in order to determine whether the manufacturing process is appropriate, it is necessary to conduct process tests in advance. In process testing, non-destructive testing is frequently performed on the process samples, and the manufacturing process is improved based on the test results to ultimately determine the ideal manufacturing process. Reducing production costs: Conducting non-destructive testing during the product manufacturing process is often seen as increasing inspection costs, thereby raising manufacturing expenses. However, if non-destructive testing is carried out properly at the appropriate stages of the manufacturing process, it helps to prevent waste in subsequent steps, reduces the need for rework, lowers the defect rate, and thus reduces manufacturing costs. For example, in thick plate welding, if non-destructive testing is conducted only after the welding is complete and defects exceeding the limits are detected, requiring repair, it will take a lot of time or the repairs may be very difficult to carry out. Therefore, a non-destructive testing can be carried out halfway through welding; once it is confirmed that there are no defects exceeding the allowable limits, welding can continue. Although this increases the cost of non-destructive testing, the overall manufacturing cost is reduced. For example, when mechanically processing castings, it is sometimes not allowed for defects such as inclusions, pores, and cracks to appear on the surface after machining. In such cases, non-destructive testing is carried out on the areas to be processed before machining; any defective areas are then left untreated, which reduces the rate of defective products and saves processing time.