Sealing Tests and Cleaning of Carbon Steel Pipes for Ships
2.2 Sealing tests of piping systems
1) Testing equipment
For the same pressure test pipeline, at least two pressure gauges or recorders that have been calibrated within 6 months must be prepared, and a calibration certificate is required. The measuring range of the pressure gauges and recorders shall be twice or close to the test pressure. If the pressure test lasts more than 4 hours or the ambient temperature changes in a large range, it is necessary to record the changes in the pressure in the pipe and the ambient temperature.
2) Inspection before pressure tests
Before the pressure test, it is necessary to confirm that the required flaw detection ratio has been done for the welding seams of the pressure test system. All joints including welded joints and connections parts shall be exposed during the test. The piping should be fixed wells, preferably permanently. During the pressure test of the piping system, the equipment shall be isolated by blind plates or valves. If a valve is used for isolation, it must be ensured that the valve used can meet the test pressure. When testing the water pressure and filling the system with water, a vent should be provided at a high position. When purging is performed at the end of the test, the low point should be provided with a discharge port. Before the pressure test, remove or isolate all safety valves, expansion joints, transmission instruments and other devices, and all outlets will be blocked with plugs or blind flanges. Replace removed components with bulkheads or short pipes with flanges on both ends. If the pressure of the valve is higher than the test pressure, it is not necessary to remove the valve. However, all valves including ball valves, butterfly valves and gate valves should be fully opened during the test to ensure that the valve core doesn’t bear force and the pipeline has connectivity.
When the pipeline that is subjected to the pressure test is tested with gas, the gas must be free of oil and impurities, because the airtight test may cause dangerous situations. During the entire test stage, a safe area for pressure test isolation should be set up; the warning tape should be set up, and a special person should be arranged for guardianship. Each system to be tested for airtightness should be as small as possible. For this purpose, a large system should be divided into many small parts for testing sealing. When the pipeline that is subjected to pressure tests is tested with drinking water or fresh water, it must be ensured that it does not contain suspended solid particles which may block the pipe. For fresh water used for testing stainless steel pipes, the content of chloride should not exceed 50 ppm and a water quality test report should be provided.
3) Pressure tests
Begin the leak test with a pressure of 0.5 bar or 7.25 psi (1 bar equals 100 kPa and 1 psi equals 6.895 kPa) and check all connections for leaks. When the pressure is stable, gradually increase it to 50% of the specified pressure and keep it for 10 minutes to balance the stress and deformation. Afterward, the pressure shall be gradually increased by 10% of the specified test pressure, and the pressure shall be stabilized for 10 minutes each time to balance the stress and deformation until the specified test pressure is reached, which shall be maintained for at least 30 minutes. Check whether there is any leakage at the pipe joints and flanges. If there is a leakage point during the test, mark it and repair it after the pressure is released. After the repair, the pressure test must be done again.
2.3 Cleaning of piping systems
1) Preparation before cleaning
Before cleaning, it is necessary to select a suitable connection point; set a crossunder pipe on the system, and connect the system completely through the crossunder pipe to ensure that the cleaning liquid is in a closed circuit and a single system which only has one outlet and one inlet. If only one inlet and outlet cannot be guaranteed, the equipment system needs to be changed to a subsystem with only one inlet and outlet for cleaning. The selected cleaning pump should include a bypass valve to adjust the flow rate or pressure, and the rated flow rate of the pump is greater than the flow rate of the liquid during system use. A variable precision oil return magnetic filter with a globe valve and no bypass valve should be selected for the filter. The cleaning medium is the working medium of the system, or the cleaning medium recommended by the equipment manufacturer. It should be compatible with the working medium of the system, easy to clean and corrosion-resistant.
2) Cleaning of gas of the piping system
Blow the pre-cleaned piping system with clean and dry compressed air, and at the same time tap the pipe joints and corners with a rubber hammer to remove impurities such as welding slags attached to the pipe until no iron filings are blown out. Then put a sponge column matching the pipe diameter into the inlet of the piping system, and use compressed air to push the sponge column to blow out from the outlet. Repeat the above steps until the surface of the blown sponge column is free of impurities.
3) Cleaning of the liquid of the piping system
When cleaning is conducted, the flow rate of the liquid is controlled at 10 to 12m/s; a filter with 77 to 109μm should be selected, and then gradually increase until it reaches the requirement of accuracy required. After the cleaning starts, the time for the first two dismantlings and inspection of the filter should not be too long. It is recommended to perform the first dismantling and inspection at about 10 minutes. When the dismantling and inspection are performed for the third time, the time can be extended, with the longest time of 1 hour. When the filter screen’s accuracy reaches the manufacturer’s requirement, the cleanliness of the filter screen is similar for three consecutive times, and the cleaning can be temporarily considered qualified. At this time, according to the requirements, take a sample of the liquid washed in series before the filter. Mark it; seal and store it. Sent it to the testing center for testing.
2.4 Heat insulation wrapping of the piping system
To reduce energy loss and prevent the physical state change of the medium in the pipe with the outside world due to heat exchange, the surface of part of the pipe system needs to be wrapped with cotton for heat insulation. This work should be carried out under the condition that the accessories have been restored after the series washing of the piping system is completed. The thermal insulation structure is generally divided into a thermal insulation layer and a protective layer. When the thermal insulation layer is laid, the joints should be sealed well; the filling should be even, and the binding should be firm. For piping systems with multiple layers of heat insulation, the longitudinal and circumferential joints must be staggered from the previous layer. For the longitudinal welding seams at the two adjacent ends of the semi-tubular heat insulation layer, the longitudinal welding seams need to be staggered, and an 18 galvanized annealed steel wire is bundled at an interval of 200 mm. The wire used for tying is to be taut, cut off the excess wire ends, and the wire ends are bent inside the insulation. The protective layer is generally glass fiber cloth. If necessary, it can be painted twice. After the protective layer is constructed, tightness and firmness must be ensured, and the appearance should be neat and beautiful. The exposed pipelines outdoors and in cabins where personnel frequently visit shall be covered with stainless steel sheets of 0.5 mm on the glass fiber cloth. The longitudinal and circumferential joint layout of the iron sheet should be as waterproof as possible and conducive to drainage, with a minimum overlap of 50 mm, and the iron sheet should be fastened with rivets at intervals of 200 to 250 mm according to the actual location on site.
1) Testing equipment
For the same pressure test pipeline, at least two pressure gauges or recorders that have been calibrated within 6 months must be prepared, and a calibration certificate is required. The measuring range of the pressure gauges and recorders shall be twice or close to the test pressure. If the pressure test lasts more than 4 hours or the ambient temperature changes in a large range, it is necessary to record the changes in the pressure in the pipe and the ambient temperature.
2) Inspection before pressure tests
Before the pressure test, it is necessary to confirm that the required flaw detection ratio has been done for the welding seams of the pressure test system. All joints including welded joints and connections parts shall be exposed during the test. The piping should be fixed wells, preferably permanently. During the pressure test of the piping system, the equipment shall be isolated by blind plates or valves. If a valve is used for isolation, it must be ensured that the valve used can meet the test pressure. When testing the water pressure and filling the system with water, a vent should be provided at a high position. When purging is performed at the end of the test, the low point should be provided with a discharge port. Before the pressure test, remove or isolate all safety valves, expansion joints, transmission instruments and other devices, and all outlets will be blocked with plugs or blind flanges. Replace removed components with bulkheads or short pipes with flanges on both ends. If the pressure of the valve is higher than the test pressure, it is not necessary to remove the valve. However, all valves including ball valves, butterfly valves and gate valves should be fully opened during the test to ensure that the valve core doesn’t bear force and the pipeline has connectivity.
When the pipeline that is subjected to the pressure test is tested with gas, the gas must be free of oil and impurities, because the airtight test may cause dangerous situations. During the entire test stage, a safe area for pressure test isolation should be set up; the warning tape should be set up, and a special person should be arranged for guardianship. Each system to be tested for airtightness should be as small as possible. For this purpose, a large system should be divided into many small parts for testing sealing. When the pipeline that is subjected to pressure tests is tested with drinking water or fresh water, it must be ensured that it does not contain suspended solid particles which may block the pipe. For fresh water used for testing stainless steel pipes, the content of chloride should not exceed 50 ppm and a water quality test report should be provided.
3) Pressure tests
Begin the leak test with a pressure of 0.5 bar or 7.25 psi (1 bar equals 100 kPa and 1 psi equals 6.895 kPa) and check all connections for leaks. When the pressure is stable, gradually increase it to 50% of the specified pressure and keep it for 10 minutes to balance the stress and deformation. Afterward, the pressure shall be gradually increased by 10% of the specified test pressure, and the pressure shall be stabilized for 10 minutes each time to balance the stress and deformation until the specified test pressure is reached, which shall be maintained for at least 30 minutes. Check whether there is any leakage at the pipe joints and flanges. If there is a leakage point during the test, mark it and repair it after the pressure is released. After the repair, the pressure test must be done again.
2.3 Cleaning of piping systems
1) Preparation before cleaning
Before cleaning, it is necessary to select a suitable connection point; set a crossunder pipe on the system, and connect the system completely through the crossunder pipe to ensure that the cleaning liquid is in a closed circuit and a single system which only has one outlet and one inlet. If only one inlet and outlet cannot be guaranteed, the equipment system needs to be changed to a subsystem with only one inlet and outlet for cleaning. The selected cleaning pump should include a bypass valve to adjust the flow rate or pressure, and the rated flow rate of the pump is greater than the flow rate of the liquid during system use. A variable precision oil return magnetic filter with a globe valve and no bypass valve should be selected for the filter. The cleaning medium is the working medium of the system, or the cleaning medium recommended by the equipment manufacturer. It should be compatible with the working medium of the system, easy to clean and corrosion-resistant.
2) Cleaning of gas of the piping system
Blow the pre-cleaned piping system with clean and dry compressed air, and at the same time tap the pipe joints and corners with a rubber hammer to remove impurities such as welding slags attached to the pipe until no iron filings are blown out. Then put a sponge column matching the pipe diameter into the inlet of the piping system, and use compressed air to push the sponge column to blow out from the outlet. Repeat the above steps until the surface of the blown sponge column is free of impurities.
3) Cleaning of the liquid of the piping system
When cleaning is conducted, the flow rate of the liquid is controlled at 10 to 12m/s; a filter with 77 to 109μm should be selected, and then gradually increase until it reaches the requirement of accuracy required. After the cleaning starts, the time for the first two dismantlings and inspection of the filter should not be too long. It is recommended to perform the first dismantling and inspection at about 10 minutes. When the dismantling and inspection are performed for the third time, the time can be extended, with the longest time of 1 hour. When the filter screen’s accuracy reaches the manufacturer’s requirement, the cleanliness of the filter screen is similar for three consecutive times, and the cleaning can be temporarily considered qualified. At this time, according to the requirements, take a sample of the liquid washed in series before the filter. Mark it; seal and store it. Sent it to the testing center for testing.
2.4 Heat insulation wrapping of the piping system
To reduce energy loss and prevent the physical state change of the medium in the pipe with the outside world due to heat exchange, the surface of part of the pipe system needs to be wrapped with cotton for heat insulation. This work should be carried out under the condition that the accessories have been restored after the series washing of the piping system is completed. The thermal insulation structure is generally divided into a thermal insulation layer and a protective layer. When the thermal insulation layer is laid, the joints should be sealed well; the filling should be even, and the binding should be firm. For piping systems with multiple layers of heat insulation, the longitudinal and circumferential joints must be staggered from the previous layer. For the longitudinal welding seams at the two adjacent ends of the semi-tubular heat insulation layer, the longitudinal welding seams need to be staggered, and an 18 galvanized annealed steel wire is bundled at an interval of 200 mm. The wire used for tying is to be taut, cut off the excess wire ends, and the wire ends are bent inside the insulation. The protective layer is generally glass fiber cloth. If necessary, it can be painted twice. After the protective layer is constructed, tightness and firmness must be ensured, and the appearance should be neat and beautiful. The exposed pipelines outdoors and in cabins where personnel frequently visit shall be covered with stainless steel sheets of 0.5 mm on the glass fiber cloth. The longitudinal and circumferential joint layout of the iron sheet should be as waterproof as possible and conducive to drainage, with a minimum overlap of 50 mm, and the iron sheet should be fastened with rivets at intervals of 200 to 250 mm according to the actual location on site.
