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In the safe production of chemicals, pressure vessels that may experience overpressure must be equipped with pressure relief devices; common ones include safety valves and burst discs, and sometimes a combination of both is used. Next, a summary and discussion on the combined usage are presented. I. Advantages and Disadvantages (1) Advantages. The burst disc and safety valve are combined in series, with the burst disc located on the inlet side of the safety valve. First, it can effectively prevent the medium from entering the safety valve, thus avoiding its failure due to high temperatures, corrosion, and other factors. Secondly, when there is internal leakage in the safety valve, the rupture disc acts as a barrier, providing better sealing. Thirdly, the safety valve features a return movement of its valve core after activation, allowing control over the amount of medium discharged. (II) Disadvantages. First, after each overpressure start-up, the rupture disc must be removed and replaced. Secondly, it is difficult to observe the condition of the rupture disc; once internal leakage in the rupture disc causes a decrease in the pressure difference between the front and back, its pressure-relief function is compromised. Third, the selection of the rupture disc based on its compatibility with the medium must be accurate; otherwise, it will not serve as a \"double safety mechanism\". (III) Application restrictions. Metal rupture discs may be corroded in certain corrosive media, while non-metallic rupture discs may have better corrosion resistance, but they might suffer from shortcomings in terms of strength and other aspects. Discussion: With the development of control technologies, it may be possible to pressurize the pipe section between the rupture disc and the safety valve, thereby reducing the pressure difference across the rupture disc and compensating for the weakness in the strength of non-metallic rupture discs. II. Application Scenarios (1) It is used in media environments that are corrosive, highly viscous, or prone to crystallization, in order to prevent crystallization and scaling in the pipes ahead of the safety valve, as well as corrosion, scaling, and crystallization inside the safety valve itself, which could affect its performance. (II) In environments with highly toxic media, the burst disc serves as the first level of sealing, compensating for the tendency of safety valves to leak internally. (III) Prevent material loss resulting from the rupture of the burst disc. (IV) Since it is not allowed to install stop valves between the overpressure relief device and the pressure vessel, sometimes, in order to enable online calibration of the safety valve, a burst disc device can be installed between the safety valve and the pressure vessel. (5) For pressure vessels that contain media with extremely high, high, or moderate toxicity, explosive media, corrosive or viscous media, or valuable media, in order to facilitate the cleaning and replacement of safety valves, it is permissible to install a shut-off valve between the overpressure relief device and the pressure vessel, provided that this is approved by the person in charge of safety management at the using unit and that reliable preventive measures are put in place. However, during the normal operation of the pressure vessel, the shut-off valve must remain fully open (sealed with a lead seal or locked); the structure and diameter of the shut-off valve must not prevent the safe operation of the overpressure relief device. III. Structural requirements: A vent valve, pressure gauge, or other alarm indicator should be installed in the chamber between the blast disc safety device and the safety valve, in order to indicate whether the blast disc is leaking or damaged, and to release the pressure accumulated in the chamber in a timely manner, thereby preventing back pressure from affecting the blasting pressure of the blast disc. IV. Common hidden dangers (1) A stop valve is installed between the safety valve and the pressure vessel, with no seal or locking device in place. Analysis: Although both sealing with lead seals and locking are acceptable according to the standards, lead seals have lower reliability. 1. The function of a lead seal is, first, to indicate that the valve should not be closed casually, and second, to allow it to be detected if someone does close the valve, though it cannot prevent accidental operations. 2. Using a locking mechanism ensures that, once locked, it will not be turned off without permission, at least not due to negligence. However, there is also a problem: whether it can be locked in a timely manner when put into use. If it cannot be locked promptly, it is essentially useless. (II) Pressure relief valves combined with burst discs should be installed in certain situations, but burst discs are not installed in such cases. 1. Generally, the temperature of the pressure relief pipe is lower than that of the equipment it serves; media prone to crystallization can easily crystallize and clog the safety valve and the pipes ahead of it, resulting in the failure of the safety valve to function properly. Installing a burst disc in front of the safety valve helps to keep the safety valve and the pipeline ahead of it unobstructed. Since the burst disc is located close to the equipment it serves, the temperature drop is generally small, and its structure is not prone to crystallization-related blockages. 2. For corrosive media, safety valves often have a shorter service life; by installing a burst disc in front of them, materials resistant to corrosion can be used, providing an additional layer of protection against corrosion and ensuring the reliability of the safety valve. (III) Inadequate pressure monitoring between the burst disc and the safety valve. First, it cannot be monitored without a pressure gauge. Second, there is no exhaust valve; any air leakage between the rupture disc and the safety valve cannot be released. Third, there was poor management, preventing timely inspection to detect air leakage from the rupture disc. V. Precautions: When designing this combination, it is necessary to conduct precise tests on the displacement.