【2026 Knowledge Expansion】Why pressure-bearing components such as pump casings and compressor housings are not governed by the design methods specified in GB/T150, nor by the safety supervision regulations outlined in TSG21?

Looking again at item (4) of Chapter 1, “Scope of Application,” in TSG 21‑2016 \"Regulations on Safety Technical Inspection of Fixed Pressure Vessels,\" the wording is almost identical: pressure vessels that are integral to or serve as components in mechanical equipment that moves rotatably or reciprocally (such as pump casings, compressor housings, turbine casings, hydraulic cylinders, papermaking rolls, etc.).

By comparing the two provisions, it can be concluded that pressure-bearing components such as pump casings and compressor housings are not governed by the design methods specified in GB/T150, nor by the safety supervision regulations set out in TSG21. However, in field work, it is possible that someone used the 150 standard to verify the wall thickness of the pump casing, or required that the compressor housing be registered as a pressure vessel—both of these actions represent typical misapplications of standards.

Question 1: Why are pressure-bearing components such as pump casings and compressor housings, which are indeed subject to pressure, \"excluded\" by 150/TSG21? In fact, the nature of the load is completely different. The design logic of the GB/T 150 series of standards assumes that internal/external pressure is the primary loading factor; the overall strength is calculated based on film stress, with only secondary loads such as those resulting from openings, flanges, and supports being taken into account. This approach is suitable for stationary pressure-bearing equipment.

For components such as pump casings, compressor cylinders, and hydraulic cylinders, the primary load is not merely internal pressure; the stress conditions are much more complex: 1. In the case of centrifugal pump casings, the rotation of the impeller creates a centrifugal force field, resulting in continuous pressure fluctuations within the flow channels. The casing must withstand a combination of pressure forces, vibrations caused by rotor imbalance, and thermal shocks. Given the frequent start-up and shutdown cycles of such equipment, the risk of fatigue-related failure is extremely high. 2. Reciprocating compressor cylinder: The reciprocating motion of the piston causes periodic fluctuations in gas pressure. The cylinder is subjected over time to alternating internal pressures, lateral forces from the piston, and inertial loads transmitted by the connecting rods; these alternating stresses are the main cause of failure. 3. Hydraulic cylinder: The piston rod moves back and forth, and the cylinder barrel is subjected to thermal-mechanical coupled loads resulting from internal pressure, bending moments exerted by the piston rod, and seal wear; the stress conditions involved are well beyond those encountered in static loading situations.

That is, GB/T1 50 applies to containers that are under \"static pressure,\" with failure modes including static strength, creep, and uniform corrosion； Components such as pumps, compressors, and hydraulic cylinders are subjected to pressure while in motion, and their failure modes mainly include fatigue, wear, and rotor dynamics failures. Their design systems and verification logic are completely different; such components fall under the jurisdiction of their respective machine-specific standards and are not covered by the 150 standard. Similarly, the TSG21 supervision regulations apply primarily to fixed and stationary pressure-bearing equipment. Rotating/reciprocating pressure-bearing components are classified under other categories in the catalog of special equipment or according to the standards for their respective machine products, and are not included in the supervision system for pressure vessel records. For more information, please read: [Knowledge Expansion 2026] GB/T150 and TSG21 do not apply to pressure-bearing components such as pump casings and compressor housings; however, this does not mean that such components can be designed arbitrarily without any regulatory constraints.

The following are the main revisions to GB150-2024 \"Pressure Vessels\", for reference.