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Petrochemical plants are manufacturing facilities that primarily use petroleum cracking to produce various fuels and chemical raw materials. The various process media within the device are mostly flammable, explosive, and toxic substances. Therefore, during the construction of petrochemical plants, the installation quality of various process pipelines must be strictly controlled; any leakage is strictly prohibited, as it could lead to serious consequences. During the installation of process pipelines, pressure testing is a very important and essential key step, used to verify the quality of the welds as well as the tightness of the flange connections. This article briefly outlines the preparation, conditions, methods, steps, and safety measures for pipeline pressure testing, to serve as a reference for similar projects. I. Preparatory work before pressure testing 1. Technical preparation: Large petrochemical plants have numerous process pipeline systems with complex layouts; to ensure the smooth progress of pressure testing, thorough technical preparations must be carried out in advance. Before pressure testing, a pressure testing plan should be prepared based on the process flow diagram, the testing procedure should be clarified, and the pressure testing medium, methods, steps, as well as various safety measures for the testing should be determined in accordance with the requirements. 2. Pipeline integrity inspection: The inspection of pipeline integrity is a necessary step prior to pressure testing; systems that have not passed this integrity check shall not undergo pressure testing under any circumstances. The basis for the integrity check is technical documents such as the pipeline system diagram, pipeline plan view, pipeline sectional view, pipeline support diagram, and simplified pipeline pressure testing system diagram. The methods for integrity checking are as follows: first, the construction team conducts its own inspections of the pipelines they have installed, in accordance with the design drawings; second, the construction technicians recheck each pipeline in the pressure testing system individually; third, after all pipelines in the pressure testing system have been verified to be in compliance with the design drawings, an application is submitted to the quality supervision department and the owner for further inspection and quality assessment. The contents of the integrity check are divided into hardware and software parts. Hardware inspection involves checking whether the model, specifications, material, coordinates, elevation of the pipes installed on-site, the flow direction of the valves, the orientation of the handles, as well as the type and position of supports and hangers, as well as the slope, verticality, and levelness of the pipes, all meet the design requirements and regulatory standards ； A comprehensive inspection should also be conducted on the piping welds. This includes checking whether the welding work has been completed, if non-destructive testing has yielded satisfactory results, whether heat-treated welds have undergone the necessary treatment, and whether stainless steel welds have been pickled and passivated. Software inspection involves checking whether the pipeline installation records and welding records are correct and complete, as well as whether all relevant record forms have been approved. 3. Material preparation: Pressure testing is a relatively dangerous task. Therefore, thorough preparation of materials should be carried out before starting this work. It mainly includes the maintenance of pressure testing equipment, safety inspections, and on-site setup ； Calibration, inspection, and installation of various pressure testing instruments and meters ； Installation and layout of temporary pipelines and fittings for pressure testing ； Preparation of materials such as blind flanges, bolts, nuts, gaskets, etc., for pressure testing ； Implementation of isolation measures for equipment, instruments, valves, pipe fittings, safety valves, flow meters, etc ； Tasks such as the supply of materials required for various safety measures during pressure testing and the on-site setup. 4. Personnel organization: Pressure testing is a relatively complex process, and to carry it out successfully, effective organizational and coordination efforts are necessary in terms of personnel. A dedicated pressure testing team should be established to take full responsibility for the pressure testing of pipelines, and effective communication tools should be provided to the testers to ensure that the entire process is carried out in an orderly manner. II. Pressure testing media: Pipeline pressure testing media generally fall into two categories: one is gas, and the other is liquid. Gases commonly used include air, dry oil-free air, and nitrogen. Liquids generally include water, clean water, and pure water. The medium used for pressure testing is generally determined based on the specific requirements of the process pipeline. For pressure testing, using hydraulic pressure is relatively safer than using air pressure. Therefore, if there are no special requirements for the pipeline, water is generally used as the pressure testing medium. According to the requirements of the pipeline system, there are strict regulations regarding the water used for pressure testing. For clean water used in pressure testing, appropriate filters should be installed in the water supply pipes. The requirement for water used to test stainless steel pipes is that the chloride ion content must not exceed 25 ppm. For pipes that have been sandblasted on the inside, testing should be carried out using a water solution containing an appropriate rust inhibitor; this rust inhibitor should not affect the process media used later on. III. Pressure test: The test pressure for pipelines subjected to internal pressure is 1.5 times the design pressure of the pipeline ； When the design temperature of the pipe is higher than the test temperature, the test pressure shall comply with the following formula: Ps=1.5δ1/δ2. If δ1/δ2>6.5, the value 6.5 shall be used ； When Ps generates a stress exceeding the yield strength at the test temperature, the test pressure should be reduced to the highest test pressure at which the pipeline pressure does not exceed the yield strength. The test pressure for the pneumatic test pipeline is 1.15 times the design pressure ； For pipelines undergoing pneumatic testing at pressures exceeding 0.6 MPa, such testing must be carried out only after being specified in the design documents or with the owner’s approval and appropriate safety measures having been taken. Before the hydraulic test, the testing system is first filled with water. An exhaust valve is installed at the highest point of the pipeline to remove any air from it. Pressure gauges are placed at the highest point as well as in locations on the ground where they can be easily observed; the pressure is determined based on the reading of the gauge at the highest point. Then, the pressure is increased gradually. Once the test pressure is reached, the pressure is maintained for 10 minutes. After a thorough inspection, the test is considered successful if there are no leaks and no visible deformation. During the pressure strength test, the pressure should be increased gradually. Once the pressure reaches 50% of the test pressure, and no leaks or abnormalities are detected, the pressure can be increased further in steps of 10% of the test pressure. Each step should be maintained for 3 minutes until the test pressure is reached; after that, the pressure should be held steady for another 10 minutes. Finally, the pressure should be reduced to the design value. The test is considered successful if there are no leaks and no visible deformation. After the pipeline strength test is passed, a gas-tightness test of the pipeline should be conducted. In the airtightness test using a liquid as the medium, after reducing the pressure in the piping system to the level specified in the design documents, a thorough inspection is conducted via direct observation; the system is considered satisfactory if no leaks are detected. For pipelines tested for hydraulic strength using hydraulic pressure and for airtightness using air pressure, these tests should be conducted after the pipelines have been purged successfully. During the testing, the pressure should be increased gradually; inspections should be carried out when the pressure reaches 90% of the test pressure. Only after confirming that there are no leaks or abnormalities can the pressure be increased further. Thereafter, inspections should be performed every 10% increase in test pressure until the target pressure is reached, followed by a comprehensive inspection. The system is considered to pass the test if there are no leaks and no drop in pressure after maintaining the pressure for 30 minutes. For pipelines undergoing a pressure strength test, after the strength test is passed, the test pressure should be directly reduced to the pressure level required for the airtightness test. The pressure is then maintained for 30 minutes; the test is considered successful if there are no leaks and no pressure drop. The inspection is carried out by applying a leak detection fluid to welds, flanges, and seals. IV. Safety Technical Regulations for Pressure Testing Pipeline pressure testing is extremely dangerous; therefore, all necessary safety technical measures must be taken. The length of the hydraulic testing section should generally not exceed 1,000 meters. The temporary reinforcement measures used for testing must be checked to ensure they are safe and reliable, and proper markings should be applied. The test pressure gauges must be within their calibration validity period; their accuracy should be no less than 1.5 grade, and their range should be 1.5 to 2 times the pressure to be measured. There must be at least two pressure gauges in the pressure testing system. When filling a hydraulic test system with water, all air must be purged. This should be done at an ambient temperature above 5°C; otherwise, anti-freezing measures are required. For alloy steel piping systems, the liquid temperature must not be lower than 5°C. During the test, in case of any leakage, repairs must not be carried out under pressure. After the defect is rectified, a re-pressurization test should be conducted. After the pressure test is successful, the pressure should be released promptly; during a liquid pressure test, the liquid inside the pipe must be drained completely in a timely manner. After the system testing is completed, all temporary blind flanges should be removed promptly, and a pressure testing record should be filled out. During the pressure testing process, a warning line must be set up around the test area; unauthorized personnel are not allowed to enter. Operators must follow instructions and must not open or close valves at will.