Regulations on service life of pressure vessel

Management specification for service life of pressure vessel

as a special equipment that carries gas or liquid and bears a certain pressure, the service life management of pressure vessels should follow the principles of scientific evaluation and standardized maintenance to ensure the safe operation of the equipment. The following management guidelines are based on industry practices and technical standards:

1. design life and legal inspection cycle

1. design Life Definition
   the design life of the pressure vessel is usually 10-20 years, which is determined by the design unit according to the parameters such as material performance, corrosion rate and fatigue strength. For example, the design life of carbon steel containers under normal working conditions is about 15 years, and the design life of stainless steel containers can be extended to 20 years due to better corrosion resistance.

2. Statutory Inspection Requirements
   according to the Safety and Technical Supervision Regulations for Stationary Pressure Vessels, the equipment shall be subject to regular supervision and inspection:

• comprehensive inspection cycle: 3-6 years/time (determined according to safety level)
• withstand voltage test period: the longest shall not exceed 9 years (only after the comprehensive inspection)

2. the key factors affecting the service life

1. corrosivity of medium

• corrosive media (such as acid, alkali, salt solution) will accelerate the thinning of the wall thickness of the container, and it is necessary to upgrade the material or increase the corrosion allowance to extend the life. For example, the annual corrosion rate of ordinary carbon steel can reach 0. 3mm the corrosion rate of stainless steel can be controlled within 0.01mm.

2. Fluctuations in operating conditions

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

3. Maintenance Quality

• regular internal and external inspection, wall thickness measurement, safety accessories calibration and other maintenance measures can extend the service life of the equipment. For example, magnetic particle testing every 2 years can find more than 90% of surface cracks in advance.

3. Service Life Assessment and Life Extension Management

1. periodic evaluation mechanism

• carry out a risk assessment every 3 years, focusing on:
  • wall thickness reduction (residual wall thickness ≥ 90% of design wall thickness)
  • weld quality (no over-standard defect display)
  • support settlement (verticality deviation ≤ H/1000)

2. life Extension Approval Process

• after reaching the design life, if you need to continue to use, you need to entrust professional institutions:
  • re-inspection of material properties (tensile strength, impact toughness)
  • residual life prediction (based on fracture mechanics analysis)
  • safety factor accounting (not less than 1.5 times the original design value)

disposal standard for 4. scrapping

when one of the following situations occurs, it should be stopped immediately and scrapped:

1. wall thickness corrosion exceeds design wall thickness by 30%
2. there are penetrating cracks or the deformation exceeds 1% of the vessel diameter.
3. Safety attachment fails and cannot be repaired
4. the estimated remaining life is less than 1 inspection cycle.

Implementation recommendations for 5. enterprises

1. establish equipment files, record design parameters, inspection reports, maintenance records and other life cycle data.
2. Make annual inspection plan, give priority to the use of acoustic emission testing, phased array ultrasound and other advanced non-destructive testing technology.
3. For equipment close to the design life, 20% of the inspection cycle is reserved as a buffer period to avoid the risk of sudden shutdown.
4. Carry out special training for operators, focusing on emergency handling procedures for abnormal conditions such as overpressure, overtemperature and leakage.

Conclusion
the safe operation of pressure vessels should be based on scientific management, and the economic operation under the premise of risk control can be realized through the design life control, the implementation of statutory inspection and the application of intelligent monitoring technology. Enterprises should establish a full-cycle management system of “prevention-monitoring-evaluation-disposal” to ensure that the equipment plays the maximum value under the premise of safety and compliance.