Seek the doc version of TSG Z0004-2007 – Basic Requirements for Quality Assurance Systems for the Manufacturing, Installation, Modification, and Maintenance of Special Equipment

Pressure Test Control Procedure 1 General Provisions 1.1 To standardize the pressure testing procedures for pressure vessels (hereinafter referred to as “vessels”) and ensure the quality of such tests, the Quality Inspection Department has established and implemented the \"Process Guidelines for Pressure Vessel Hydrostatic and Integrity Tests\". 1.2 This procedure applies to the pressure testing of all pressure vessels in the company. 2. Preparations and inspections before testing: 2.1 Before the pressure test, the engineer responsible for the pressure test shall recheck the circumferential membrane stress values of the container shell in accordance with the following requirements to determine whether they meet the specified standards. 2.1.1 During the hydraulic test, the value shall not exceed the product of 90% of the material’s yield strength at the test temperature and the welding joint factor of the cylinder. 2.1.2 During the pressure test, the value shall not exceed the product of 80% of the material’s yield strength at the test temperature and the welding joint factor of the cylinder. 2.1.3 When verifying the pressure test pressure, the wall thickness taken into account should deduct the additional wall thickness; for hydraulic tests, the pressure applied should also include the static pressure of the liquid column. For shell-and-tube heat exchangers where the shell side pressure is lower than the tube side pressure, no corrosion allowance need to be deducted. 2.2 Before the pressure test, all inspection tasks related to the container must have been completed, and permission from the inspector is required before proceeding, including visual inspections, geometric dimensions, the position of the pipe openings, and various gauges. 2.3 Containers that have undergone overall heat treatment must be heat-treated prior to the pressure test. 2.4 Pressure testing must be carried out using two pressure gauges with the same range and that have been calibrated; the range of these pressure gauges should be approximately twice the test pressure, but it should not be less than 1.5 times nor more than 3 times the test pressure ； For pressure gauges, the accuracy requirement is not less than grade 2.5 for Class 1 vessels, and not less than grade 1.5 for Class 2 and Class 3 vessels ； The pressure gauge shall have a diameter of not less than 100 mm, and shall be installed at a position on the top of the container under test that is convenient for observation. 2.5 Pressure testing requires a dedicated site along with safe and reliable protective facilities; fences are generally used for isolation, and this arrangement must be approved by the inspector. During the pressure testing process, unauthorized personnel who are not involved in the testing shall not enter the testing area. 2.6 The piping for pressure testing must be unobstructed; valves and pressure pumps should be installed properly, with good sealing and smooth operation. 2.7 Before the pressure test, all fastening screws at the connection points of the container must be fully installed and securely tightened. 2.8 Containers shall be placed in accordance with the specifications provided in the drawings or process documents. Where no placement method is specified, they should be arranged reasonably based on the principles of facilitating pressure testing, ensuring safety and reliability, and preventing deformation. Attention should be paid to using padding materials to support them and avoiding welds so as to facilitate inspection. 2.9 For containers equipped with perforated reinforcement rings, compressed air at a pressure of 0.4–0.5 Mpa should be introduced before the pressure test to check for any air leaks in the welds; the pressure test can only be carried out once this check is successful. The signal holes must remain intact. 3. Hydrostatic testing 3.1 The testing medium is generally clean water. For containers made of carbon steel, 16MnR, and normalized 15MnVR, the water temperature must be at least 5°C; for containers made of other low-alloy steels, it must be at least 15°C. When performing hydrostatic testing on austenitic stainless steel containers, it is necessary to strictly control the chloride ion concentration in the water to no more than 25 mg/L. 3.2 After the container is filled with water, any gas remaining inside it must be removed. The surface of the container should remain dry; it can only be slowly raised to the design pressure once the wall temperature of the container is close to the temperature of the liquid ； After confirming there are no leaks, continue to increase the pressure to the specified test pressure and hold it at that level for 30 minutes. Then reduce the pressure to 80% of the specified test pressure and maintain it at that level for a sufficient duration (usually not less than 30 minutes) for inspection. The pressure must remain constant during the inspection; continuous pressure application cannot be used to maintain this pressure. During the pressure testing process, bolts must not be tightened under pressure, nor any external force applied to the components under stress. 3.3 During the pressure testing of the container, if defects such as weld leaks are detected, the testing must be stopped; the pressure should be released before any repairs are carried out. It is strictly prohibited to carry out welding or grinding work while under pressure. After the repairs are completed, a new pressure test must be conducted until satisfactory results are achieved. 3.4 Heat exchanger pressure test 3.4.1 For fixed-plate and U-tube heat exchangers, the shell side should be pressurized first, while the pipe joints are inspected; only after this is successful can the tube side be pressurized. 3.4.2 For floating-head heat exchangers and kettle-type reboilers, it is necessary to first perform pressure testing on the pipe ends using specialized pressure testing tools; only after this is successful can pressure testing be carried out separately on the tube side and the shell side. 3.4.3 For heat exchangers designed based on pressure difference, first perform joint pressure testing using the maximum test pressure difference specified in the drawings; once this is successful, carry out pressure testing for the tube side and shell side according to the test pressures and procedures specified in the drawings. 3.4.4 When the test pressure of the tube side is higher than that of the shell side, the joint testing shall be carried out in accordance with the specifications in the drawings, or by a method agreed upon by both the supplier and the purchaser. 3.4.5 For overlapping heat exchangers, the pressure testing of the joints can be carried out on each unit individually; when the tubeside and shellside of the various heat exchangers are connected to each other, the pressure testing is performed after the overlapping assembly is completed. 3.5 A vessel after a hydraulic test is considered qualified if it meets the following conditions: 3.5.1 No leakage. 3.5.2 No visible deformation. 3.5.3 No abnormal noises were heard during the test. 3.5.4 No cracks were detected on the surface of materials whose specified minimum tensile strength is 540 Mpa or higher, as determined by non-destructive testing. 3.5.5 After the test is successful, the water residue inside the container should be removed and dried. 4. Pneumatic testing 4.1 Pneumatic testing shall be accompanied by reliable safety measures, such as iron fencing and isolation of the testing area. Inspection and supervision can only be carried out by the Quality Control Department. 4.2 The gas used in the tests is dry and clean air, nitrogen, or other inert gases; the company generally uses air or nitrogen. 4.3 For carbon steel and low-alloy steel containers, the temperature of the medium during testing must not be lower than 15°C; for containers made of other types of steel, the testing temperature shall be in accordance with the specifications given in the drawings. 4.4 During the test, the pressure should first be increased slowly to 10% of the specified test pressure, held at that level for 5–10 minutes, after which a preliminary inspection of all welds and joint areas should be carried out. If there is no leakage, the pressure can be increased further to 50% of the specified test pressure. If no abnormal phenomena occur, the pressure is then increased in stages to 10% of the specified test pressure, until reaching the test pressure, after which it is held at that level for 30 minutes. Subsequently, the pressure is reduced to 87% of the specified test pressure, and it is held at this level for a sufficient period of time for inspection; the pressure must remain constant during this inspection period. Continuous pressure application shall not be used to maintain the test pressure constant. 4.5 It is strictly prohibited to tighten bolts under pressure during the testing process; if there is a leak, pressure must be released, the issue repaired, and testing resumed thereafter. 4.6 During the testing process, if the container makes no abnormal noises, shows no air leaks when inspected with soapy water, dishwashing liquid, or other leak detection fluids, and exhibits no visible deformation, it is considered qualified. 5. Airtightness test 5.1 The safety measures for the medium used in the airtightness test shall be the same as those for the pressure test ； For the temperature of the test gas, containers made of carbon steel and low-alloy steel must be at a temperature of not less than 5°C; pressure vessels made of other materials shall comply with the specifications given in the design drawings. 5.2 The container may undergo a airtightness test only after passing the hydraulic test. The test pressure is specified in the drawings; during the test, the pressure is increased gradually. Once the specified test pressure is reached, the pressure is maintained for a sufficient length of time (usually not less than 30 minutes) to conduct a leak check on all welded joints and their connection points (soapy water or dishwashing liquid is generally applied to the outer surface of the welds). For small containers, they can be submerged in water for inspection. If any leaks are detected, the pressure is reduced, the defects are repaired, and then hydraulic and airtightness tests are conducted again. 5.3 During the pressure retention inspection, it is considered qualified if there is no air leakage and no visible deformation. 6. Reporting on Inspection and Testing 6.1 During hydraulic testing, pneumatic testing, and airtightness testing of containers, the entire testing process must be carried out under the supervision of an on-site inspection officer. 6.2 For containers that pass the tests, a pressure test report shall be issued promptly, to be signed and approved by the engineer responsible for the pressure testing as well as by the on-site inspection officer; the test report shall be stored together with the product documentation. 7. Relevant and Referenced Documents 7.1 “Measurement and Equipment Control Procedures” 7.2 “Process Control Procedures” 7.3 “Quality Inspection Control Procedures” 7.4 “Code for Pressure Vessel Hydrostatic and Integrity Tests” 8. Quality Records Used 8.1 “Pressure Test Report”