Pressure vessel service life regulations

Code for Management of Service Life of Pressure Vessels

Pressure vessels are special equipment that carries gases or liquids and withstands a certain pressure. Their service life management must follow the principles of scientific evaluation and standardized maintenance to ensure the safe operation of the equipment. The following are management guidelines based on industry practices and technical standards:

1. Design life and legal inspection cycle

1. Design life definition
   The design life of pressure vessels is usually 10-20 years, which is comprehensively determined by the design unit based on material properties, corrosion rate, fatigue strength and other parameters. For example, the design life of carbon steel containers under normal operating conditions is about 15 years, and the design life of stainless steel containers can be extended to 20 years due to their better corrosion resistance.

2. Legal inspection requirements
   According to the “Safety Technical Supervision Regulations for Fixed Pressure Vessels”, equipment needs to be supervised and inspected regularly:

• Comprehensive inspection cycle: 3-6 years/time (determined based on safety status level)
• Withstand pressure test cycle: The maximum period shall not exceed 9 years (only after passing the comprehensive inspection)

2. Key factors affecting service life

1. medium corrosiveness

• Corrosive media (such as acid, alkali, and salt solutions) will accelerate the thickness of the container wall, and life needs to be extended by upgrading materials or increasing corrosion margins. For example, in a chloride ion environment, the annual corrosion rate of ordinary carbon steel can reach 0.3 mm, while the corrosion rate of stainless steel can be controlled within 0.01 mm.

2. Volatility of operating conditions

• Frequent pressure and temperature fluctuations can lead to metal fatigue. Experimental data show that after the number of pressure cycles exceeds 10, the probability of fatigue crack initiation in the container increases significantly.

3. Maintenance quality

• Maintenance measures such as regular internal and external inspections, wall thickness measurements, and safety accessory calibration can extend the service life of the equipment. For example, magnetic particle testing is carried out every two years, and more than 90% of surface cracks can be discovered in advance.

3. Service life evaluation and life extension management

1. periodic evaluation mechanism

• Risk assessment is carried out every 3 years, with key inspections:
  • Wall thickness reduction (remaining wall thickness ≥ 90% of the design wall thickness)
  • Weld quality (no excessive defects are displayed)
  • Support settlement (verticality deviation ≤H/1000)

2. Extension approval process

• After reaching the design life, if you need to continue using it, you need to entrust a professional organization to:
  • Re-inspection of material properties (tensile strength, impact toughness)
  • Residual life prediction (based on fracture mechanics analysis)
  • Safety factor calculation (not less than 1.5 times the original design value)

4. Scrap disposal standards

When one of the following circumstances occurs, use should be stopped immediately and scrapped:

1. Wall thickness corrosion exceeds the design wall thickness by 30%
2. Presence of penetrating cracks or deformation exceeding 1% of container diameter
3. Safety attachment fails and cannot be repaired
4. The assessed remaining life is less than 1 inspection cycle

5. Enterprise implementation suggestions

1. Establish equipment files to record full life cycle data such as design parameters, inspection reports, and maintenance records.
2. Formulate an annual inspection plan, giving priority to the use of advanced non-destructive testing technologies such as acoustic emission testing and phased array ultrasound.
3. For equipment close to the design life, a 20% inspection period is reserved as a buffer period to avoid the risk of sudden shutdown.
4. Carry out special training for operators, focusing on the emergency response process for abnormal conditions such as overpressure, overheating, and leaks.

conclusion
The safe operation of pressure vessels must be based on scientific management, and economic operation under the premise of controllable risks is achieved through design life control, statutory inspection execution, and intelligent monitoring technology application. Enterprises should establish a full-cycle management system of “prevention-monitoring-evaluation-disposal” to ensure that equipment can maximize its value on the premise of safety and compliance.