How to evaluate the maintenance effect of pressure vessels?

1. Equipment operation status
1. Stability of operating parameters
Pressure: Observe the fluctuation of pressure of pressure vessels during normal operation. If the maintenance effect is good, the pressure should be stable within the specified operating range with minimal fluctuation. For example, for a container with a design pressure of 1.0MPa, the pressure should be maintained between 0.9 and 1.0MPa during stable operation, and the fluctuation range should not exceed ±0.05MPa.
Temperature: Similarly, the temperature should also be maintained within a reasonable range. For reaction vessels with specific temperature requirements, such as a chemical reaction that requires the temperature to be controlled at 150-160°C, effective maintenance should ensure that the temperature fluctuation does not exceed ±5°C. Stable temperature helps to ensure the normal progress of the reaction, and also reflects that the heat exchange system, insulation layer, etc. of the container are properly maintained.
Liquid level (for storage containers): The liquid level should be accurately controlled within the design liquid level range. For large oil storage tanks, the deviation of the liquid level should not exceed the upper and lower limits of the specified safe liquid level, which indicates that the liquid level monitoring device, inlet and outlet valves, etc. are well maintained and there is no leakage or misoperation.
2. Equipment availability
Calculate the availability of the pressure vessel, that is, the ratio of the actual operating time of the equipment to the planned operating time. If the maintenance is effective, the equipment availability should be high, for example, more than 95%. This means that the equipment is less downtime due to failure or maintenance and can meet production needs. The increase in availability indicates that maintenance measures help reduce sudden equipment failures and extend the normal operation cycle of the equipment.
2. Equipment integrity
1. Appearance inspection results
Check whether there is new corrosion, wear, deformation or cracks on the outer surface of the container. If the surface of the container remains good after maintenance and no new defects appear, it means that the maintenance work such as anti-corrosion measures (such as painting, coating protection) and anti-wear measures (such as lubrication, reasonable operating procedures) is effective. For example, after a period of operation, the paint on the surface of the container is still intact, and no rust or corrosion pits are found, which is a manifestation of successful anti-corrosion maintenance.
Check whether the logo and nameplate of the container are clear and complete. Clear markings help operators to correctly identify equipment and also reflect the overall attention paid to the equipment during maintenance.
2. Internal inspection results (if feasible)
Check the internal conditions of the container through endoscopes or internal inspections. If no new corrosion, scaling, loose or damaged parts are found inside, it means that the internal cleaning, anti-corrosion, tightening and other maintenance work have achieved the expected results. For example, for heat exchangers, there is no scaling on the surface of the internal heat exchange tubes, indicating that regular cleaning and water quality management are effective.
Check whether the internal support structure, baffles and other components are firm. Their integrity helps to maintain the structural stability of the container and prevent abnormal vibration or deformation during operation.
III. Safety performance
1. Effectiveness of safety devices
Safety valve: Check whether the safety valve can accurately open and return to the seat at the specified pressure. For example, a safety valve with a set opening pressure of 1.2MPa should be reliably opened when the pressure reaches 1.2MPa in actual tests, and should be able to return to the seat normally when the pressure drops to about 1.1MPa, indicating that the safety valve functions normally after maintenance (such as calibration, cleaning, etc.). Bursting disc: Check whether the bursting disc is intact, without premature rupture or corrosion, deformation, etc. The normal state of the bursting disc ensures that the pressure can be released in time under overpressure conditions to protect the safety of the container.
Pressure gauge and thermometer: The readings of the calibrated pressure gauge and thermometer should be accurate. For example, when comparing the pressure gauge with the standard pressure gauge, the error should be within the allowable range (such as ±0.5%). Accurate pressure and temperature measurement helps operators to correctly judge the operating status of the container.
2. Leakage detection results
Check whether there is leakage in the container and its connection parts through various leak detection methods (such as airtightness test, soap bubble detection, helium leak detection, etc.). If no leakage is detected after maintenance, it means that the maintenance work related to sealing, such as seal replacement and flange tightening, has achieved results. Especially for containers containing toxic, flammable and explosive media, no leakage is the key to ensuring safety.
IV. Implementation of maintenance work
1. Compliance with maintenance plan
Check whether various maintenance work is performed in accordance with the pre-established maintenance plan. Check the maintenance records to ensure that each prescribed maintenance item (such as monthly safety device inspection, annual non-destructive testing, etc.) is completed on time and as required. High compliance indicates that the maintenance work is organized and managed in an orderly manner, which helps to ensure the continuity of maintenance results.
2. Completeness and accuracy of maintenance records
Maintenance records should record in detail the date, content, problems found, measures taken, and signatures of maintenance personnel for each maintenance. Complete and accurate records help trace the maintenance history of the equipment, analyze the failure trend of the equipment, and also reflect the standardization of maintenance work. For example, when recording the results of non-destructive testing, the inspection location, the inspection method used, and the inspection results (such as whether defects are found, the type and size of defects, etc.) should be clearly stated to provide a basis for subsequent evaluation and decision-making.
V. Cost-benefit analysis
1. Maintenance cost
Statistics of direct costs incurred during maintenance, including parts replacement costs, maintenance labor costs, inspection costs, and consumables such as lubricants and seals. If the maintenance effect is good, the maintenance cost should be at a reasonable level while ensuring the safe and stable operation of the equipment. For example, compared with enterprises or equipment of the same type and size, the maintenance cost should not be too high.
2. Production Benefits
Evaluate the impact of pressure vessel maintenance on production benefits. Due to the stable operation of the equipment, interruptions in the production process are reduced, product quality is stable, and output is guaranteed. For example, after effective maintenance of a reaction vessel in chemical production, the reaction can continue to proceed stably, the product qualification rate is improved, and the output also meets the design requirements, which shows that maintenance has brought positive production benefits.
By comprehensively evaluating the above multiple aspects, the effect of pressure vessel maintenance can be comprehensively and accurately judged, and the maintenance strategy can be further optimized based on the evaluation results to improve the safety, reliability and economy of the equipment.