Discussion on pressurizing heat exchangers

Temperature changes do affect the results of pressure testing on heat exchangers; the temperature difference between day and night leads to pressure variations, which is a normal physical phenomenon. If the change in pressure is mainly due to temperature fluctuations, and the pressure remains within the specified allowable range, it can generally be assumed that there is no leakage issue with the heat exchanger. As for having \"sufficient time\" to check for any leaks, it is generally recommended to observe for at least 30 minutes to 1 hour in order to determine whether there is a continuous drop in pressure or any obvious signs of leaks. If the operating specifications do not specify this, the appropriate inspection interval can be determined based on practical operational experience and the conditions of the equipment. At the same time, you can consult relevant equipment manufacturers or industry experts for more specific guidance. .

It will take half an hour on our end, and the Special Inspection Institute also approves it

Normally, according to the procedure, you should maintain the pressure at the test pressure for at least half an hour, and then reduce it to the design pressure and hold it there for a sufficient amount of time; as long as there are no leaks or unusual noises, that’s acceptable. The fact that you decide to maintain the pressure for 24 hours shows great caution on your part. There is currently no evidence suggesting that excessive pressure fluctuations are caused by large temperature differences; this is merely a personal speculation. According to standards, the wall temperature and water temperature should be kept similar to each other, and under normal circumstances, there should not be significant temperature differences if the system is in operation for just over half an hour.

The sequence for pressure testing heat exchangers shall comply with the requirements of GB/T151-2014: 1. Shell side → Tube side: a. Fixed tube sheet type； b. U-tube type ； 2. Pipe end → Tube side → Shell side: a. Floating head type ； 3. Pipe end → Shell side + Tube side ； a. Differential pressure design ； Other types of heat exchangers depend on design requirements.

The pressure is maintained at the test level for 30 minutes to ensure no drop in pressure, which essentially rules out major leaks. \"Sufficient time\" is a flexible criterion that depends on factors such as conditions and the personnel involved; for example, during a sunny day, an inspector with good eyesight may need less time for the inspection, while at night, when lighting is poor, an inspector with mild myopia who does not wear glasses may require more time. In my opinion, this timing is entirely in the hands of the inspectors; it is necessary to provide them with sufficient time for inspection and grant them the authority to do so. At the same time, once the inspectors confirm that something is compliant, they can release the pressure, but they must also assume corresponding responsibilities. The \"sufficient time\" at our company is usually between 10 and 30 minutes; for smaller containers, it’s about 10 minutes. Larger containers or heat exchanger tube sheet joints require more time, but it’s still generally within 30 minutes.

Maintaining pressure for half an hour is intended to allow any minor leaks to become visible to the naked eye; a lack of pressure drop after half an hour under pressure should not be used as evidence of no leaks.

Our leaders were too cautious; it was somewhat unnecessary, and they even had the manufacturer conduct another inspection. As a result, there was no leakage in the equipment