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I. Installation of safety valves A safety valve must be installed in one of the following 11 situations: 1. An independent pressure system (separated from other systems by a shut-off valve). The system refers to being entirely gas-phase, entirely liquid-phase, or in communication with gas. 2. Overpressure caused by reactor abnormalities. 3. Cases where there is no safety valve at the source of the pressurized material in the container. 4. Vessels and pipelines whose design pressure is lower than the pressure at the source of that pressure. 5. Outlet pipes for positive displacement pumps and compressors. 6. Vessels where overpressure is generated due to the accumulation of non-condensable gases. 7. If a shut-off valve or control valve is installed on the outlet pipeline of the heating furnace, a safety valve should be installed upstream of that valve. 8. Areas of overpressure caused by process accidents, automatic control failures, power supply failures, fire accidents, and utility system failures. 9. The area where the liquid undergoes thermal expansion due to the closed valves at both ends. 10. Steam outlet pipe of the condensing turbine. 11. In some cases, due to leakage in the pump outlet check valve, a safety valve is installed on the pump’s inlet pipeline. Typical methods for installing safety valves: 1. Method 1: Install only one safety valve, without installing shut-off valves before or after it. 2. Method 2: Install only one safety valve, with isolation valves placed before and after it. 3. Method 3: Install only one safety valve, with shut-off valves and bypass valves placed before and after it. 4. Method 4: Install only one safety valve, with a set of rupture discs placed in front of it ； Between the burst disc and the safety valve, a four-way component interface is installed for online calibration. 5. Method 5: Install only one safety valve, with a set of burst discs placed in front of it ； Between the rupture disc and the safety valve, a four-way component interface for online calibration is installed, and a shut-off valve is placed in front of the rupture disc as well as behind the safety valve. 6. Method 6: Install two safety valves simultaneously, and add a shut-off valve in front of and behind each safety valve, so that the valves can serve as backups for one another. Selection of the typical method: 1. The safety valve should be set according to Method 1 in any of the following situations: (1) In operational units where production is intermittent or batch-based, it is possible to meet the requirement of calibration once a year ； (2) To meet the requirement of calibrating the safety valve once a year, when the materials inside the equipment can be emptied. 2. For equipment that needs to operate continuously for more than one year, and for which other measures can ensure that the system does not experience overpressure during the period of safety valve calibration, the safety valve shall be installed according to Method 2. 3. The safety valve shall be set according to Method 3 in one of the following situations: (1) When other measures cannot be used to ensure that the system does not exceed its pressure limit during the safety valve calibration period ； (2) When starting up or shutting down, to discharge material through the relief valve’s bypass valve. 4. The safety valve shall be set according to Method 4 in any of the following situations: (1) when the medium is viscous, corrosive, prone to self-polymerization, or contains solid particles ； (2) Install a safety valve, when a burst disc alone is sufficient to meet the requirements for on-line calibration. 5. In the case of paragraph 4 of this article, and when it is necessary to replace the burst disc online during the equipment’s operating cycle, the safety valve shall be installed in accordance with Method 5. 6. In cases where the requirement of \"at least one verification per year\" cannot be met using the above methods, install parallel standby safety valves in accordance with Method 6, and use lead seals to keep them in one open and one closed state. 7. As required by the system, when two or more safety valves are installed on a discharge source, in order to meet the requirement of \"at least one calibration per year,\" one of the six methods mentioned above should be selected to ensure that the setup meets both functional requirements and economic considerations. 8. The installation of safety valves with special requirements regarding the process shall be carried out in accordance with relevant regulations. II. Selection of safety valves 1. For pressure relief due to the expansion of incompressible liquids, a slightly opening type safety valve is suitable; a fully opening type safety valve can also be used. When a full-opening safety valve is used with a liquid as the medium, its operating behavior becomes that of a slightly-opening type, and the inner diameter of its nozzle should be calculated based on the slightly-opening type. 2. Under normal operating conditions, a spring-loaded safety valve or a pilot-operated safety valve should be selected. 3. Balanced bellows-type safety valves should be used in the following situations: (1) when the back pressure of the safety valve is greater than 10% of its set pressure but less than 30% of it ； (2) When the medium is corrosive, prone to scaling, or prone to coking, it can affect the proper functioning of the safety valve spring ； However, balanced bellows safety valves are not suitable for media such as phenol, wax liquids, heavy petroleum fractions, and materials containing coke dust, nor are they appropriate for use in reciprocating compressors. 4. Pilot-operated safety valves should be used in the following situations: (1) When the back pressure of the safety valve is more than 30% of its set pressure ； (2) Applications requiring particularly good sealing performance from safety valves ； (3) When the medium is toxic or harmful, a non-flowing pilot valve should be used (that is, when the pilot valve opens, it does not discharge the medium outward). 5. Except for safety valves used for water, steam, air, and nitrogen, all safety valves should adopt a closed spring-type design.