Leakage test of pipelines

Inspect the piping system, including equipment connected to the piping system, for leaks. Generally, air or inert gas is used as the medium, and it is carried out under the design pressure. It is tested with the foaming agent, ammonia, helium and other methods specified in the design document. If no leakage points appear to be found, it is qualified.

1. Pipeline system testing (1) Main types of piping system testing 1. Pressure test: Using liquid or gas as the test medium, the pipeline system is gradually pressurized to reach the specified test pressure to check the strength and tightness of the pipeline system. 2． Vacuum degree test: Evacuate the pipeline system to form a negative pressure inside the pipeline system, and check the tightness of the pipeline system based on the pressurization rate of the pipeline system within the specified time. 3． Leakage test: Using gas as the test medium, under the design pressure, use foaming agents, color developers, gas molecule sensors or other specialized means to check leakage points in the pipeline system. 4． Irrigation test: Use clean water as the test medium to fill the non-pressure pipeline system with water to the specified height to test the tightness of the pipeline system. 5. ball test: Pass a ball with a diameter not less than 2/3 of the diameter of the drainage pipe through the pipe to check the smoothness of the pipe (2) Conditions that must be met for the pipe system test 1. The pipeline installation projects within the test scope have all been completed according to the design drawings, except for painting and insulation that have not been completed, and the installation quality complies with relevant regulations. 2． For parts requiring heat treatment and non-destructive testing, the results are all qualified. 3． The expansion joints on the pipeline are equipped with temporary restraint devices, and the pipeline has been reinforced according to the test requirements. 4． The pressure gauges used for testing have been calibrated during the weekly inspection period, and their accuracy meets the specified requirements. There should be no less than two pressure gauges. 5. Isolation measures have been taken between the pipeline system to be tested and the pipeline system not to be tested. If a blind plate is used for isolation, the location where the blind plate is installed should be clearly marked and recorded. 6． The safety valve, blasting plate and instrument components on the pipeline to be tested have been removed or isolated, and all intermediate valves should be opened. 7. For pipelines transporting highly toxic fluids and pipelines with a design pressure greater than or equal to 10MPa, the relevant information has been reviewed by the construction unit before the pressure test. 8. The trial protocol has been approved and a technical briefing has been conducted. (3) Key points for pressure test implementation 1. Hydraulic test implementation requirements (1) The test pressures of pipeline systems of different types or immovable materials (such as carbon steel, non-ferrous metals, cast iron, jacketed pipes, etc.) should be implemented in accordance with the corresponding construction and acceptance specifications. (2) When pipelines and equipment are tested as a system, when the test pressure of the pipeline is equal to or less than the test pressure of the equipment, the test should be carried out according to the test pressure of the pipeline ； When the pipeline test pressure is greater than the test pressure of the equipment, and the test pressure of the equipment is not less than 1.15 times the design pressure of the pipeline, the test can be carried out according to the test pressure of the equipment with the consent of the construction unit. (3) The hydraulic test should slowly increase the pressure. After reaching the test pressure, stabilize it for 10 minutes. Then reduce the test pressure to the design pressure and stop the pressure for 30 minutes. If the pressure does not drop and there is no leakage, it is qualified. (4) The hydraulic pressure test of the water supply pipeline system, fire protection system and outdoor water supply pipeline network system in civil buildings must meet the design requirements. When not specified in the design, the test pressure is 1% of the working pressure. 5 times, but not less than 0. 6MPa。 The test methods and qualification requirements shall be implemented according to the specifications of the pipe materials. (5) The pressure test requirements, test methods and qualification requirements for hot water supply systems, various heating systems and outdoor heating pipes in civil buildings should be implemented in accordance with the requirements of the "Construction Quality Acceptance Code for Building Water Supply, Drainage and Heating Engineering". 2． Key points for the implementation of pressure tests (air pressure) using gas as medium (1) The test pressure of steel pipes and non-ferrous metal pipes withstanding internal pressure should be 1.15 times the design pressure, and the test pressure of vacuum pipelines should be 0.2MPa. (2) When the design pressure of the pipeline is greater than 0.6MPa, it must be stipulated in the design document or approved by the construction unit before gas can be used for pressure testing. (3) Before the test, a pre-test must be conducted with air with a pressure of 0.2MPa. During the air pressure test, the pressure should be gradually and slowly increased. When the pressure rises to 50% of the test pressure, the system should be inspected. If no abnormalities or leaks are found, continue to increase the pressure step by step by 10% of the test pressure, and stabilize the pressure for 3 minutes at each level. After the pressure rises to the test pressure, the pressure is reduced to the design pressure. The foaming agent is deemed to be qualified if there is no leakage. (4) During the test, it is strictly forbidden to make the test temperature close to the brittle transition temperature of the metal. (4) Implementation requirements for vacuum degree test 1. After the vacuum system passes the air pressure test, it should also conduct a 24-hour vacuum degree test in accordance with the design documents. 2． For the vacuum degree test, the pipeline system is evacuated according to the requirements of the design document. After reaching the vacuum degree specified in the design, the system is shut down. The system pressurization rate after 24 hours should not be greater than 5%. (5) Leakage test implementation requirements 1. Pipelines transporting highly toxic fluids, toxic fluids, and flammable fluids must undergo leakage tests. 2． The leakage test should be carried out after the pressure test is passed. 3． The test medium should be air, and the test pressure is the design pressure. 4． The leakage test should focus on inspecting valve stuffing boxes, flange or threaded connections, vent valves, exhaust valves, drain valves, etc. The foaming agent is deemed to be qualified if there is no leakage. (6) Implementation requirements for irrigation test 1. Covered or buried indoor drainage pipes must be filled with water before being concealed. The water filling height should not be lower than the upper edge of the sanitary appliances on the subsurface or the height of the house floor. 2． Inspection method: Fill the water until it is full for 15 minutes, then fill it and observe it for 5 minutes after the water level drops. If the liquid level does not drop and there is no leakage at the interface of the indoor drainage pipe, it is considered qualified. 3． Test in sections according to outdoor drainage inspection wells. The test water head should be increased by 1m from the top of the upstream pipe of the test section, and the time should be no less than 30 minutes. If there is no leakage at the pipe interface, it is qualified. (7) The drainage risers and horizontal main pipes in the ball-passing test room shall be subjected to a ball-passing test after installation. The diameter of the ball-passing ball shall not be less than 2/3 of the diameter of the drainage pipe. Successful passing shall be regarded as qualified. 2. Purge and Cleaning of Pipelines (1) General Provisions 1. After the pipeline system passes the hydraulic test and before the gas leakage test, the pipeline system should be purged and cleaned (purge). 2． The purging method should be determined based on the usage requirements of the pipeline, the working medium and the degree of dirt on the inner surface of the pipeline. 3． Duct system purging. The plan should include: Purge procedures, purge methods, purge media, and layout of purge equipment ； Operation control method of pressure, flow rate and flow rate of purging medium ； Inspection methods and qualification standards ； Safety technical measures and other precautions. 4． Preparation before purging piping system: (1) The orifice plate, nozzle, filter screen, regulating valve, check valve spool, valves on the pipeline, sleeve expansion joint, corrugation repair device, etc. should be removed and replaced with short pipes, and reset after passing the purge. For valves that do not need to dismantle the valve core, lift the valve core to make it fully open. ； Equipment and pipelines that are not allowed to be purged should be equipped with temporary blind plates to isolate them from the purging system. (2) Check the firmness of pipe supports and hangers and reinforce them if necessary. (3) The purging medium inlet pipeline should have sensitive and reliable pressure gauges and control valves. 5. Precautions for purging the pipeline system (1) Purge drains should be set up in front of equipment, valves, and instrument parts. Purge drains should also be set up in pipe sections that are difficult to purge, sharp turns, emptying, and backwashing. When purging, measures should be taken to prevent dirt from the pipeline from entering the equipment or dirt from the equipment from entering the pipeline. The purged emissions must not pollute the environment and are strictly prohibited from being discharged anywhere. (2) Purge in the order of main pipe → branch pipe → drainage pipe ； When purging the main pipe, the branch pipe valve should be closed ； The branch pipes should be started in sequence from the first branch pipe in the forward direction of the medium. (3) The purging medium should ensure sufficient flow and pressure. The purging pressure should not exceed the design pressure of the pipeline system, and the purging speed should not be lower than the working flow rate. (4) After the pipeline blowing is qualified, other operations that affect the cleaning inside the pipeline shall not be carried out except for the prescribed inspections. After the pipeline system has passed the purge and before final sealing, the construction unit shall jointly inspect and confirm with relevant units, and fill in the "Pipeline System Purge and Cleaning Record" in accordance with regulations. (2) Requirements for pipeline purging and cleaning methods 1. Water flushing (1) Clean water should be used for flushing pipelines. When flushing austenitic stainless steel pipelines, the chloride ion content in the water should not exceed 25×10ˉ6 (25ppm). (2) Water flushing should be carried out continuously. The water color and transparency of the discharge outlet should be consistent with the visual inspection of the inlet water to be qualified. (3) When the pipeline is not in operation temporarily after being flushed with water, the water should be drained and dried in time. 2． Air purging (1) Air purging should use the large compressor of the production device, or use the large container in the device to store gas for intermittent purging. The purge pressure shall not exceed the design pressure of the container and pipeline, and the flow rate shall not be less than 20m/s. (2) When purging oil-free pipelines, the gas must not contain oil. (3) During the air purging process, when there is no smoke and dust in the exhaust, a wooden target plate with white cloth or white paint should be installed at the exhaust port for inspection. If there is no rust, dust, moisture or other debris on the target plate within 5 minutes, it should be qualified. 3． Steam purging (1) Steam piping system should be purged with steam. If air purging of non-steam pipelines cannot meet the cleanliness requirements, and the structure of the pipeline system can withstand the influence of high temperature and thermal expansion factors, steam purging can be used instead with the consent of the design unit. (2) Steam purging should be carried out in the order of heating → cooling → reheating, and the method of purging one pipe at a time and taking turns to purge should be adopted. Use large flow steam to purge, warm the pipes, drain water in time, and check the thermal displacement of the pipes before purging. 4． Oil cleaning (1) For the lubrication, sealing and control oil pipeline systems of mechanical equipment, oil cleaning should be carried out after the equipment and pipelines have been purged and pickled and before the system is commissioned. Stainless steel pipes should be steam blown and then oil cleaned. (2) Oil cleaning should be carried out by oil circulation. During the circulation process, the oil temperature should be raised and lowered 2 to 3 times in the range of 40 to 70°C every 8 hours, and the filter element should be cleaned or replaced in time.

The current specifications require a leakage test, which is different from the original leakage volume test. The leakage test uses air and is tested under the design pressure. If there is no leakage or pressure reduction, it is qualified. This test is based on the pipeline system and does not require the connection of process equipment. It is implemented by the construction unit. Usually before starting the vehicle, the owner also needs to conduct the entire process system. For system airtightness testing, this requirement is more stringent and must generally be maintained for more than 24 hours to ensure no leakage and no pressure drop. On-site, in order to ensure smooth system airtightness, the leakage test requirements for important systems are usually stricter, and the pressure must be maintained for 24 hours without leakage.

In addition to using air for leak testing, the pressure must be maintained for one day. If the pressure does not change much after one day, then it is OK. This is how our company's leak testing works.

7.5.5 Pipelines transporting highly toxic fluids, toxic fluids, and flammable fluids must undergo leakage tests. The leakage test shall be carried out in accordance with the following provisions: 7.5.5.1 The leakage test should be carried out after the pressure test is passed. The test medium should be air. 7.5.5.2 The leakage test pressure should be the design pressure. 7.5.5.3 The leakage test can be carried out in conjunction with the commissioning work. 7.5.5.4 The leakage test should focus on inspecting valve stuffing boxes, flange or threaded connections, vent valves, exhaust valves, drain valves, etc. The foaming agent is deemed to be qualified if there is no leakage. 7.5.5.5 Pipes that have passed the air pressure test and have not been disassembled after the test do not need to undergo the leakage test. 7.5.6 After the vacuum system passes the pressure test, it should also undergo a 24-hour vacuum degree test in accordance with the design documents. The pressure increase rate should not be greater than 5%. 7.5.7 When the design document stipulates that the leakage test shall be carried out with halogen, helium, ammonia or other methods, it shall be carried out in accordance with the corresponding technical regulations.

That is to first bring the pressure to the design pressure of the pipeline. After maintaining the pressure for one day, check whether the pressure gauge has dropped. If it has not dropped, it means that the pipeline pressure test has passed!

Generally, the leakage volume in 24 hours is <2%

I don’t have much contact with LPG, so the pressure test requirements are quite strict. For us, the wellhead natural gas pressure test is only a hydraulic test, and then a 7kg gas seal. The new regulations require airtightness to be 1.1 times the operating pressure and maintain pressure for 6 hours, and the time requirements are not based on standard specifications.