Pressure Vessels
This domain tests the scope definition, the medium-group/category logic that drives every downstream requirement, safety accessories, and the periodic inspection cycle tied to 安全状况等级.
Scope
A pressure vessel is a fixed or transportable container of gas, liquefied gas, or liquid at or above its standard boiling point, with maximum working pressure ≥0.1 MPa gauge, volume ≥30 L, and internal diameter (or maximum internal boundary dimension for non-circular sections) ≥150 mm.
Medium group and category
Group 1 media: extremely or highly hazardous toxic media, explosive media, liquefied gases. Group 2: everything else. Category (Ⅰ, Ⅱ, Ⅲ) follows from medium group, design pressure and volume. Category drives design requirements, NDT proportions, and inspection interval - this is the single most examined link.
Safety accessories
Safety valves, bursting discs, bursting caps, fusible plugs, emergency shut-off devices, pressure gauges, level gauges, temperature instruments. Where a safety valve alone cannot guarantee isolation of hazardous media, a bursting disc may be fitted in series with a tell-tale.
Periodic inspection
- Annual check performed by the user.
- Comprehensive inspection: first one within 3 years of commissioning; thereafter, safety condition grade 1 or 2 - generally every 6 years; grade 3 - 3 to 6 years; grade 4 - monitored service with interval set by the inspection body; grade 5 - scrapped.
- Pressure test generally at 1.25 times design pressure, with the medium and temperature controlled.
Worked example
A Group 2 vessel, design pressure 1.6 MPa, volume 5 m³, was graded 3 at its comprehensive inspection in 2021. Reasoning: grade 3 sets a 3–6 year interval; 2025 is within the band but the interval must be justified from corrosion rate and remaining life, not defaulted to 6 years. Check whether a pressure test is due within the interval, verify safety-valve calibration, and confirm the annual checks were recorded. A grade 3 defaulted to a 6-year cycle without justification is an exam trap.
Traps that cost marks
Conflating 30 L volume with 150 mm diameter (both apply); treating annual check as an inspection-body duty; assuming every vessel gets 6 years regardless of grade.