Hydraulic test

Refer to Clause 8.6 of GB50235-2010 for detailed specifications: the hydraulic test pressure, pneumatic test pressure, and leakage test pressure are all equal to the design pressure. Pipes carrying extremely hazardous and highly hazardous materials, as well as flammable materials, must undergo leakage tests. It seems that most of our chemical materials require leakage testing!

Reply to 1# zhenzhenzwc: Actually, you’ve already answered it yourself – one is a strength test and the other is a tightness test; their purposes are different.

Before a chemical processing unit is put into operation or after a major maintenance session, pressure tests must be carried out in accordance with regulations; these tests include strength tests and integrity tests. Through pressure testing, it is possible to verify whether containers and pipelines meet the required pressure resistance, tightness, quality of joints or connections, welding quality, and degree of sealing, thereby allowing for the timely detection of any issues in the materials or during the manufacturing process. 1. Strength tests include hydraulic testing and pneumatic testing. To prevent accidents during pressure testing, hydraulic testing is commonly used, and the medium for hydraulic testing is usually clean water. When conducting hydrostatic tests on austenitic stainless steel vessels and piping systems, it is necessary to strictly control the chloride ion content in water to <25 mg/L. 2. The tightness test primarily checks the sealing performance of all connection points in the container and pipeline systems (including welds, rivet joints, and detachable connections), to ensure that the container and pipeline systems remain airtight under operating pressure. Note: 1. To ensure the safety of the airtightness test for containers and piping systems, the airtightness test should be carried out after the hydrostatic test is successful. 2. Hydrostatic testing is generally used for strength tests, while airtightness testing is used to check tightness. Under what circumstances was the stringent hydraulic test mentioned by the original poster proposed? It can be discussed further.

One is the voltage withstand test, whose main purpose is to determine whether the equipment materials are of satisfactory quality； One is the high-pressure sealing test (with liquid as the test medium), which is primarily used to determine whether the equipment’s sealing performance is satisfactory. GB/T13927-2008 can be referred to

Reply to 3# zero229: I think that during the strength test, what is actually being done is a sealing test. If there is no leakage when pressure is applied in the strength test, then there shouldn’t be any leakage, right? I’m not sure where my misunderstanding lies; please give me some guidance!

In my opinion, the purpose of the strength test is to verify the system’s capacity to withstand overloads, while the sealing test is intended to check the sealing quality of the entire system; the two should not be used interchangeably. The strength test takes a short time, namely 30 minutes, while the sealing test usually lasts 24 hours.

　1. General requirements 　After the piping installation is completed, a pressure test on the piping system shall be carried out in accordance with the design requirements. Based on the purpose of the test, they can be classified into strength tests to evaluate the mechanical properties of the pipes, tightness tests to assess the quality of pipe connections, vacuum tests to check the vacuum retention capacity of the piping system, and leakage tests conducted for fire safety reasons. Except for vacuum pipeline systems and pipeline systems with fire protection requirements, most pipelines are only subjected to strength tests and tightness tests. For the strength and tightness tests of piping systems, hydrostatic testing is generally used; if hydrostatic testing cannot be employed due to design considerations or other reasons, pneumatic testing can be used instead. 　　(1) The pressure test shall comply with the following provisions: 1) The liquid shall be used as the testing medium for the pressure test. When the design pressure of the pipeline is less than or equal to 0.6 MPa, gas can also be used as the testing medium, but effective safety measures must be taken. Gas pressure testing is strictly prohibited for brittle materials. 　　2) When the site conditions do not permit the use of liquids or gases for pressure testing, with the consent of the project owner, the following methods may be used as alternatives: A. All welds (including those on attachments) shall be inspected using the liquid penetration method or the magnetic particle method ； 　　B. The butt welds are inspected using 100% radiography. 　　3) When conducting pressure tests, a no-entry zone should be established, and unauthorized personnel must not enter. 　　4) No repairs shall be made on the pipeline after the pressure test is completed. 　　5) The construction unit shall participate in the pressure test; once the test is successful, it shall, together with the construction unit, fill out the pressure test record for the pipeline system in accordance with the relevant specifications. 　　(2) Conditions to be met prior to the pressure test: 1) The pipeline installation work within the scope of the test, excluding painting and insulation, has been fully completed in accordance with the design drawings, and the installation quality meets relevant regulations. 　　2) Temporary restraining devices have been installed on the expansion joints of the pipeline. 　　3) The pressure gauges used for testing have been calibrated and are within their weekly inspection period; their accuracy must be at least 1.5 grade. The full scale value of the gauges should be 1.5 to 2 times the pressure being measured, and there must be no fewer than 2 such gauges. 　　4) The liquids or gases that meet the pressure test requirements are already available. 　　5) The pipeline has been fixed as required by the test. 　　6) For pipelines transporting highly toxic fluids and pipelines with a design pressure of 10 MPa or higher, prior to the pressure test, the following documents have been rechecked by the project owner: A. Quality certificates of the pipeline components ； 　　B、Inspection or testing records of pipeline components ； 　　C、Pipe processing records ； 　　D、Welding inspection and heat treatment records ； 　　E. Documents for design modifications and material substitutions. 　　7) The test pipeline and unrelated systems have been separated using blind flanges or other measures. 　　8) The safety valves, rupture discs, and instrumentation components on the test pipeline have been removed or isolated. 　　9) The test plan has been approved, and the technical details have been communicated. 　　2. Procedures, steps, and methods for hydrostatic testing The procedures, steps, and methods for hydrostatic testing are as follows: 1) Connection. Connect the pressure testing equipment to the pipeline system to be tested; install various valves and pressure gauges for pressure testing within the system, place a vent valve at the highest point of the system, and install a drain valve at the lowest point. 　　2) Irrigation. Open the vent valve at the highest point of the system, close the drain valve at the lowest point, and fill the system with water. Pure water should be used for pressure testing. When testing austenitic stainless steel pipes or pipes connected to such pipes or equipment, the chloride content in the water must not exceed 25×10-6 (ppm). Once the exhaust valve is continuously draining water outward, close the release valve. 　　3) Inspection. After the system has been filled with water, do not rush to increase the pressure; instead, first check for any signs of leakage in the system. 　　4) Voltage boosting. The water filling check shows no abnormalities, so pressure can be increased. This should be done using a manual pressure testing pump (or an electric pressure testing pump). The pressure increase must be slow and steady; first raise the pressure to half of the test pressure, then conduct a thorough inspection of the piping system. If any issues are found, the pressure must be reduced before repairs are carried out – repairs under pressure are strictly prohibited. If there are no abnormalities, continue to increase the pressure. When it reaches 3/4 of the test pressure, conduct another thorough inspection; if nothing is abnormal, then proceed to raise the pressure to the test level. Generally, this is done in 2 to 3 steps. 　　5) Hold pressure. Once the pressure reaches the test pressure, it is maintained for 10 minutes; then the pressure is reduced to the design value, and the system is left at this pressure for 30 minutes. Success is deemed achieved if there is no drop in pressure and no leaks. 　　6) Operations after pressure testing: After the pressure testing is completed, the blind flanges and expansion joint restraint devices should be removed promptly, and any water accumulated in the system should be drained. 　　3. Precautions for hydrostatic testing 1) Before the test, when filling the system with water, all air from the system must be removed. 　　2) During testing, the ambient temperature should not be lower than 5°C; when it is below 5°C, anti-freezing measures must be taken. 　　3) During testing, the test temperature should be measured; it is strictly prohibited for the material’s test temperature to approach the brittle transition temperature. 　　4) The test pressure for above-ground steel pipes and non-ferrous metal pipes subjected to internal pressure shall be 1.5 times the design pressure; the test pressure for buried steel pipes shall also be 1.5 times the design pressure, and must not be less than 0.4 MPa. 　　5) When the pipes and equipment are subjected to pressure testing as a single system, if the test pressure for the pipes is equal to or less than that of the equipment, the testing shall be carried out at the pressure specified for the pipes. If the test pressure for the pipes is higher than that of the equipment, and the test pressure for the equipment is not less than 1.15 times the design pressure of the pipes, then, with the consent of the project owner, the testing can be conducted at the pressure specified for the equipment. 　　6) When the design temperature of the pipeline is higher than the test temperature, the test pressure shall be calculated using the following formula: Ps=1.5P〔σ〕1/〔σ〕2 Where Ps is the test pressure (gauge pressure), in MPa ； 　　P – Design pressure (gauge pressure) in MPa ； 　　〔b〕1 – Allowable stress of the pipe material at the test temperature, MPa ； 　　〔b〕2 – Allowable stress of the pipe material at the design temperature, in MPa. 　　When [б]1/[б]2 is greater than 6.5, use 6.5. 　　When Ps generates a stress exceeding the yield strength at the test temperature, the test pressure Ps should be reduced to the maximum pressure at which it does not exceed the yield strength. 　　7) The test pressure for buried cast iron pipes subjected to internal pressure shall be twice the design pressure when the design pressure is less than or equal to 0.5 MPa, and shall be the design pressure plus 0.5 MPa when the design pressure is greater than 0.5 MPa. 　　8) For pipes with a large alignment difference, the static pressure of the test medium should be included in the test pressure. The test pressure for liquid pipelines is based on the pressure at the highest point, but the pressure at the lowest point must not exceed the bearing capacity of the pipeline components. 　　9) For pipes subjected to external pressure, the test pressure shall be 1.5 times the difference between the design internal and external pressures, and shall not be less than 0.2 MPa. 　　10) The test pressure for the inner tube of the jacketed tube shall be determined as the higher of the internal or external design pressure. 　　11) When a leak is detected during the test, it must not be repaired while under pressure; the pressure should be reduced for repairs, and once the defect is eliminated, the test must be conducted again.

One is a strength test, and the other is a sealing test. Taking valves as an example, the strength test checks for any leaks at the housing, valve stem, or middle flange, while the sealing test checks whether there are any issues with the internal seals. The purposes of these tests are completely different, as are the required pressure levels