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1. How are pressure vessel categories, types, and pressure grades classified? I. Methods for classifying pressure vessels: II. Classification by pressure level: The design pressure (p) of pressure vessels is divided into four pressure levels: low pressure, medium pressure, high pressure, and ultra-high pressure: (1) Low pressure (code L), 0.1MPa ≤ p < 1.6MPa ； (2) Medium pressure (code M), 1.61MPa≤p＜10.0MPa ； (3) High pressure (code H), 10.0MPa≤p＜100.0 ； (4) Ultra-high pressure (code U), p≥100.0MPa. III. Classification of pressure vessel types: 2. How is the minimum thickness after head forming determined? Answer: The minimum forming thickness of the head shall not be less than the nominal thickness minus the negative deviation of the steel plate, and this value should be indicated in the transition area of the head. 3. Under what conditions do the Regulations on Safety Technical Inspection of Pressure Vessels stipulate that the weld joints between the nozzles and the vessel shell should adopt a fully penetrative design? Answer: The full penetration design shall be adopted in any of the following situations: 1. Pressure vessels whose medium is flammable or extremely or highly toxic. 2. Pressure vessels subjected to pressure testing. 3. Third category of pressure vessels. 4. Low-temperature pressure vessels. 5. Pressure vessels designed according to fatigue criteria. 6. Pressure vessels directly heated by flames. 7. Mobile pressure vessels. 4. According to the provisions of the \"Regulations on Safety Supervision of Pressure Vessels,\" what information must at least be indicated on the design diagram of a pressure vessel? Answer: (1) The name and category of the pressure vessel. ⑵ Design conditions and supplementary conditions under specific circumstances. ⑶ Material grade and material requirements of the main stressed components. ⑷ Main characteristic parameters. ⑸ Manufacturing requirements. ⑹ Heat treatment requirements. ⑺ Corrosion protection requirements. ⑻ Non-destructive testing requirements. ⑼ Requirements for voltage withstand testing and airtightness testing. ⑽ Specifications of safety accessories and special ordering requirements. ⑾ Location of the pressure vessel nameplate. ⑿ Requirements for packaging, transportation, on-site welding, and installation. ⒀ Special requirements. 5. What conditions should be considered when selecting the corrosion margin when designing pressure vessels, as specified in the \"Regulations on Safety Technical Inspection of Pressure Vessels\"? Answer: When designing pressure vessels, sufficient corrosion margin should be provided. The corrosion margin should be determined based on the expected service life of the pressure vessel and the corrosion rate of the material by the medium, taking into account as well the erosion and wear caused by the flow of the medium on the pressure vessel or its pressure-bearing components. When performing structural design, the impact of local corrosion should also be taken into account to meet the safety requirements for pressure vessels. To prevent safety issues arising from the operation of pressure vessels beyond their designed lifespan, the design agency should generally indicate the designed service life of the pressure vessel in the design drawings. 6. What is the purpose of GB150 classifying weld joints into categories A, B, C, and D based on the location of the weld joint, the structural types of the two components it connects, and the stress levels? Answer: The purpose is to establish different requirements specifically for aspects such as misalignment, heat treatment, non-destructive testing, and weld dimensions. 7. How is the grade of forgings determined? What grade should be selected for carbon steel and low-alloy steel forgings with a nominal thickness greater than 300 mm? Answer: The grade of forgings is determined in accordance with the technical requirements specified in NB/T 47008 \"Forgings of carbon steel and alloy steel for pressure-bearing equipment\"; for carbon steel and low-alloy steel forgings with a nominal thickness greater than 300 mm, Grade III or Grade IV should be selected. 8. How are the design pressure and design temperature of a pattern determined? 10. How should the type of first flange sealing surface be selected for flange-connected pressure vessels? What are the characteristics of flange sealing surfaces in various forms? 11. Why is it necessary to install a ground plate? Answer: In applications where protection against lightning strikes and static electricity is required, the containers (equipment) should be equipped with static grounding measures. To achieve anti-static effects, an electrostatic ground plate structure should be installed. The ground plate is made of stainless steel and features two holes, one for joint welding and the other for securing wires. For container equipment with a diameter of ≥2.5 m or a volume of ≥50 m3, there should be two or more grounding points (ground plates), which should be arranged evenly along the perimeter of the equipment. 12. Which pressure vessels should undergo overall stress-relief heat treatment in a furnace? Answer: High-pressure vessels, medium-pressure reaction vessels and storage vessels, horizontal storage tanks for storing mixed liquefied petroleum gas, and mobile pressure vessels should undergo stress-relief heat treatment carried out in a furnace. 13. How should the allowable stress value of Q345R steel plates at the design temperature be determined? Answer: According to Table 1 in Annex I of Document No. 2010 (Quality Inspection Special Letter) 86, for carbon steel and low-alloy steel plates, the stress value must be selected directly based on the plate thickness range and temperature range, or via interpolation. 14. How are the container categories for multi-chamber containers classified? How should the design and manufacturing technical requirements be established? Answer: Multi-chamber pressure vessels (such as the tube side and shell side of heat exchangers, the drum and heat exchange chamber of waste heat boilers, jacketed vessels, etc.) are classified according to the category of the highest-pressure chamber; however, design and manufacturing technical requirements shall be specified separately for each pressure chamber based on its own category. 15. What are the principles for considering the corrosion margin of the main components in shell-and-tube heat exchangers? 16. After the tube holes in the tube sheet are machined, why does GB151 stipulate that the inspection of these tube holes should be carried out at the end of the tube sheet where drilling has been done? Answer: Inspecting the tube holes from the end of the tube sheet where drilling is completed allows for controlling the deviation in the width of the hole bridges, takes into account the influence of the tube sheet thickness on drilling, and also facilitates inspection and measurement. It is more reasonable than the method in JB/T1147-1973, which only restricts the hole center deviation without considering the influence of the tube sheet thickness. 17. What is the scope of application for combining expansion welding? Answer: In the following situations, the connection between the tube sheet and the heat exchange tubes should be made by expansion welding: 1. In applications where high sealing performance is required ； 2. Applications subjected to vibration or fatigue loads. 3. Cases with intergranular corrosion ； 4. Cases where a composite tube sheet is used. 18. Why is it required to specify the design service life of pressure vessels in the design drawings? Answer: To prevent safety issues arising from the operation of pressure vessels beyond their designed service life, the design agency should generally indicate the designed service life of the pressure vessel on the design drawings. The design service life of pressure vessels is not necessarily equal to their actual useful life. Indicating the design service life is merely a reminder to users that once a vessel exceeds this period, its safety margin decreases, as does its safety rating. At this point, necessary guardianship measures should be put in place and the inspection cycle shortened.