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Basic concepts: There are no comprehensive regulations and standards; since such regulations and standards must apply to all pressure vessels and take universality into account, only the most basic requirements can be established. For many special cases, the regulations only require inspectors to select some specific testing methods based on the particular circumstances. Therefore, it is required that inspectors not only be able to skillfully use regulations and standards to inspect pressure vessels, but also have a deeper understanding of pressure vessels with complex structures and operating conditions. Inspectors must understand the structural characteristics of the pressure vessels under inspection, as well as their impact on the inspection of those vessels and their safe use ； It is necessary to understand the material properties of pressure vessels as well as those of the medium they contain. It is important to know how well the materials suit the operating conditions of the vessels, and what effects the working medium has on the vessel materials. It is also essential to be aware of the defects that may arise in pressure vessels during use, as well as the key factors that affect their safe operation. For example, in hydrogenation reactors, structural features such as thick walls, weld overlays, or composite linings make it very difficult to carry out non-destructive testing ； It is prone to hydrogen corrosion during use, which causes defects such as bulging, peeling, and cracking in the container ； Its main material also has the characteristic of temper brittleness, which requires that the wall temperature be kept from dropping too low during pressure increase. Inspectors must select inspection methods, develop inspection plans, and carry out inspections in a targeted manner based on these characteristics. Targeted inspection requires inspectors to take into account the characteristics of the containers, ensuring that any defects that are difficult to detect during use do not pose a risk to the safe operation of the containers due to missed inspections. After the inspection, recommendations for proper use can also be provided to users, so as to prevent damage to the containers resulting from incorrect handling. Inspectors should be able to select inspection methods and formulate inspection plans based on the usage characteristics of pressure vessels. The basis for targeted inspection is the failure of pressure vessels; that is, the inspection procedures are determined based on the relevant failure mechanisms and failure probabilities of pressure vessels. Targeted testing is not contradictory to regulations; it is merely an effective supplement to them. Technical factors: The basis for targeted testing is failure, and the failure modes of pressure vessels should be considered first. The failure modes of pressure vessels can be classified into 9 categories: 1. Thinning ； 2. Size variation ； 3. Failure at the connection point ； 4. Cracking of the container body ； 5. Bubbling ； 6. Micropores, microgaps ； 7. Changes in microstructure ； 8. Changes in material properties ； 9. Formation of the anode. Inspectors should be able to, based on the specific characteristics of the pressure vessel under inspection, identify the possible failure modes for that vessel among these 9 types of failure modes, and devise more effective inspection plans for those potential failure modes. If inspectors conduct targeted inspections on pressure vessels, in addition to being familiar with and mastering relevant regulations and standards, they must also have knowledge in the following areas. (1) Material selection and properties for pressure vessels In the design of pressure vessels, there are certain rules governing the choice of materials. Inspectors should be familiar with the knowledge related to selecting common materials for pressure vessels, understand why a particular material is used, and be aware of the behaviors such materials exhibit during normal operation as well as during startup and shutdown processes. For example, CrMo steel or stainless steel should be chosen under hydrogen-resistant conditions; austenitic stainless steel cannot be used in environments with chloride ions; the carbon content of stainless steel selected for intergranular corrosion environments should be controlled, etc. (2) Structural characteristics and strength calculation of pressure vessels. Pressure vessel inspectors should be familiar with the structural characteristics of the vessels under inspection as well as the methods for assessing their strength; these are among the key factors affecting the safety of pressure vessels. Almost all types of pressure vessels and their main pressure-bearing components have corresponding standards for strength calculation. Understanding and mastering these calculation standards is one of the essential basic skills for targeted testing. (3) Working principles of various types of pressure vessels. There are a great many types of pressure vessels, and it is impossible for an inspector to fully understand and master the working principles of all of them in the course of their entire career. However, when conducting targeted inspections, inspectors must make an effort to understand the working principle of the vessel under inspection. While understanding its working principle, it is also necessary to be aware of the properties of the medium contained in the pressure vessel and their impact on the material used for its construction, the operating procedures, the factors that affect operating pressure and temperature, as well as the measures taken by users to ensure the safe operation of the pressure vessel and its safety accessories. (4) Welding technology for pressure vessels: Almost all pressure vessels rely on welding. Inspectors who conduct targeted inspections should be familiar with the common welding structures, welding methods, and welding materials used in pressure vessels, so as to make accurate judgments regarding any defects identified during inspections. And making the correct judgment of defects is one of the key factors for inspectors to provide an accurate assessment of the safety condition of pressure vessels. For example, determine whether the defect is a porosity, slag inclusions, lack of penetration or lack of fusion, or cracks. At the same time, it is also essential for inspectors to be able to determine whether cracks were caused during manufacturing or during use. (5) Heat treatment of pressure vessels and the microstructure of their materials. The heat treatment state of pressure vessels, as well as the microstructure of their materials under service conditions, play a very important role in ensuring their safe operation. Inspectors should be aware of the appropriate microstructural state of the vessel materials, as well as their heat treatment status and the purposes of such heat treatment, in order to determine whether the microstructural state of the vessel materials is normal. When there are structural defects in the container or when the structural state of its material changes after it has been repaired, it is important to know what methods can be used to restore it. (6) Corrosion prevention techniques for pressure vessels: It is also knowledge that inspectors should possess, such as what types of media have a corrosive effect on pressure vessel materials, and what preventive measures can be taken against such corrosion mechanisms. In particular, this includes information on common stress-corrosion inducing media, as well as stress-corrosion sensitive materials and their microstructures. (7) Various non-destructive testing techniques. Non-destructive testing techniques are one of the fundamental methods for inspecting pressure vessels, and every inspector should understand and be proficient in them. Without a good grasp of these techniques, it is difficult for inspectors to develop accurate and effective inspection plans. In addition to mastering conventional non-destructive testing methods, inspectors should also be familiar with specialized testing techniques such as ultrasonic testing and acoustic emission testing for multi-layer welded joints. (8) Failure analysis techniques for pressure vessels. Failure analysis techniques for pressure vessels are effective means of ensuring their safe operation; they are a comprehensive technique based on many fundamental technologies. Its target audience are devices that have already encountered problems; by analyzing the causes of these failures, it identifies measures to prevent such failures. (9) Defect safety assessment and fracture mechanics of pressure vessels. The safety assessment of pressure vessels is an advanced technique within the field of technologies related to such vessels; it is applied to pressure vessels with defects, and it is particularly important for large-scale critical equipment in large enterprises.