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1 Combined use of safety valves and burst discs 1. The burst disc is installed at the inlet of the safety valve – this is the most common arrangement. Its advantage is that the burst disc separates the safety valve from the process medium at the inlet, preventing leaks in the system. The safety valve is not corroded by the process medium, which can reduce its cost. Once the system overpressures, the rupture disc and safety valve can burst simultaneously to start pressure relief. Once the system pressure returns to normal, the safety valve automatically closes again, **reducing the loss of process media.** 2. The rupture disc is installed at the outlet of the safety valve – this is the most common arrangement. Its advantage is that the rupture disc isolates the safety valve from the common discharge pipeline at the outlet; as a result, the safety valve is not subjected to corrosion by the process medium in that discharge pipeline, nor is it affected by the back pressure in it. 2 Overpressure of Equipment and Selection of Safety Accessories 1. Overpressure of Equipment – Overpressure generally refers to the situation where the maximum operating pressure inside a device exceeds its allowable pressure limit. Equipment overpressure is divided into physical overpressure and chemical overpressure. The pressure values considered in equipment design are all gauge pressures. Physical overpressure occurs when the increase in pressure is not caused by chemical reactions of the medium; only physical changes take place in the medium. Chemical overpressure – an increase in pressure caused by chemical reactions within the medium. (1) Common types of physical overpressure: ① Overpressure resulting from the continuous accumulation of material inside equipment, with no timely removal of that material; ② Overpressure caused by the expansion of material due to heating (fires); ③ Overpressure arising from sudden pressure fluctuations, such as local pressure increases caused by the rapid closing of valves, phenomena like \"water hammer\" or \"steam hammer\". Additionally, at the ends of steam pipes, rapid cooling of the steam creates a local vacuum, leading to rapid flow of steam toward those ends and thus generating shock waves that cause overpressure similar to that of water hammer. (2) Common types of chemical overpressure: ① Overpressure caused by the deflagration of combustible gases (aerosols); ② Overpressure resulting from the combustion and explosion of various organic and inorganic combustible dusts; ③ Overpressure arising from the uncontrolled progression of exothermic chemical reactions. 2. Overpressure relief devices: ① Principle of safe relief: When the equipment experiences overpressure, the safety accessories built into it immediately activate to release the excess pressure, thereby protecting the container. It is required that the amount of medium produced per unit time can be discharged through the outlet at the same rate; the pressure release rate per unit time must be greater than the pressure increase rate, to ensure that the maximum pressure inside the equipment remains below its maximum allowable value. ②The operating principle of overpressure relief devices is divided into two types: overpressure relief and overtemperature relief. Common overpressure relief devices include pressure relief valves and burst discs. Working principle of the rupture disc: When the calibrated burst pressure is reached inside the device, the rupture disc bursts instantly, thereby fully opening the discharge path. Advantages: ① Fast, accurate, reliable operation with no leakage. ②The emission area can be of any size, offering wide applicability (such as in high temperature, high pressure, vacuum, and highly corrosive environments). ③It has prominent advantages such as a simple structure and easy maintenance. Disadvantage: once the channel is opened, it cannot be closed again, resulting in the loss of all the material. 3 Classification and Structural Features of Blowing Disc Devices 1. Classification of Blowing Discs Based on shape, they include positively curved blowing discs (with the concave side under pressure), negatively curved blowing discs (with the convex side under pressure), flat-sheet blowing discs, and graphite blowing discs. Based on the failure mode under stress, rupture discs can be classified into tensile failure type, instability failure type, and bending or shear fracture failure type. Tensile failure-type rupture discs, in which tensile stress exists within the diaphragm, are classified into: standard positive arch type, slotted positive arch type, slotted flat plate type, slitted positive arch type, and slitted flat plate type. Unstable failure-type rupture discs, in which compressive stress exists within the diaphragm; these are classified into: reverse arch with blade type, reverse arch with crocodile tooth type, and reverse arch with groove type. Bent or shear failure-type rupture discs, in which the diaphragm fails due to shear forces; these are mainly those made from a single piece of material, such as rupture discs fabricated from graphite. 2. Common types and codes of rupture discs: (1) Forward-acting rupture discs – Characterized by compression on the concave side and failure due to tension; they can be single-layer or multi-layer, with codes starting with “L”. Classification of positive-dome type rupture discs: Ordinary positive-dome rupture discs, code: LP; Grooved positive-dome rupture discs, code: LC; Slit-type positive-dome rupture discs, code: LF. (2) Reverse-acting rupture discs – The stressed surface is the convex side, which leads to instability and failure; they can be single-layer or multi-layer, and their codes start with “Y”. Classification of reverse-arch shaped rupture discs: Reverse-arch with blade-type rupture disc, code: YD; Reverse-arch with crocodile-tooth type rupture disc, code: YE; Reverse-arch with cross-slot (welded) rupture disc, code: YC (YCH); Reverse-arch with ring-slot type rupture disc, code: YHC (YHCY). (3) Mechanical properties of flat-type rupture discs – They gradually deform and arch under stress, eventually failing due to stretching at the rated pressure. They can be single-layer or multi-layer, and their codes start with “P”. Classification of disc-type rupture discs: Slotted disc-type rupture discs, code: PC; Slit-disc type rupture discs, code: PF. (4) Graphite rupture discs – These rupture discs fail under shear stress. Code: PM 3. Lifespan characteristics of various types of rupture disks. All rupture disks are designed and manufactured based on their ultimate lifespan; there is no safety factor, and they will burst instantly once the specified burst pressure is reached. Its safe service life mainly depends on the product shape, stress characteristics, and the ratio of the maximum operating pressure to the minimum burst pressure—the operating ratio. To ensure the long-term use of burst discs, the international standard ISO4126-6 \"Application, selection and installation of bursting disc safety devices\" specifies the maximum allowable operating rates for various types of burst discs, as follows: ① Ordinary positive-dome burst discs – maximum operating rate ≤ 0.7 times; ② Positive-dome burst discs with grooves or slits – maximum operating rate ≤ 0.8 times; ③ Various negative-dome burst discs (with grooves, blades, etc.) – maximum operating rate ≤ 0.9 times; ④ Flat-plate burst discs – maximum operating rate ≤ 0.5 times; ⑤ Graphite burst discs – maximum operating rate ≤ 0.8 times. 4. Characteristics of burst disc usage: ① Characteristics of ordinary positive-dome burst discs (LP): The burst pressure is determined by the material thickness and the discharge diameter, and it is limited by the thickness and diameter of the diaphragm; such discs are generally suitable for applications involving high pressures. The maximum allowable operating pressure must not exceed 0.7 times the minimum burst pressure. Debris will be generated during blasting; it cannot be used in flammable, explosive environments or in situations where debris is not allowed (such as when connected in series with a safety valve), and its fatigue resistance is generally average. Insufficient clamping force at the periphery can lead to loosening and detachment there, resulting in a decrease in blasting pressure. Generally, minor damage does not significantly affect the blasting pressure. Suitable for gas and liquid media. ② Characteristics of the positive arch slotted rupture disc (LC): The rupture pressure is primarily determined by the depth of the slots, and it is more difficult to manufacture. The maximum operating pressure that a rupture disc can withstand must not exceed 0.8 times the minimum rupture pressure. The blasting cracks along the weakening groove without producing fragments; it has no requirements regarding the application environment and exhibits good fatigue resistance. Insufficient clamping force at the periphery can lead to loosening and detachment there, resulting in a decrease in blasting pressure and the generation of debris. As long as minor damage does not occur at the grooves, the blasting pressure will not change significantly. Suitable for gas and liquid media. ③ Positive arch slotted rupture disc (LF): The bursting pressure is primarily determined by the pore spacing; it is easy to manufacture and is generally used in low-pressure applications. It must be ensured that the maximum allowable working pressure does not exceed 0.8 times the minimum burst pressure. Very small fragments may be generated during blasting, but through proper structural design, it is possible to eliminate fragment formation, with generally good fatigue resistance. Insufficient clamping force at the periphery can lead to loosening and detachment there, resulting in a decrease in blasting pressure. If the damage does not occur at the short bridge, it will not cause a significant change in the blasting pressure. These types are generally used in gas-phase applications. 1. Characteristics of reverse-arched blade-type (YD) and reverse-arched crocodile-tooth type (YE) blast discs: The blasting pressure is primarily determined by the thickness of the disc and the height of its arch; the YE type is usually used in situations where the pressure is low. The maximum allowable operating pressure shall not exceed 0.9 times the minimum burst pressure. During bursting, the diaphragm flips and strikes against blades or other sharp elements, resulting in rupture without the generation of fragments; it also exhibits excellent fatigue resistance. After each explosion, the blade of the knife-type gripper must be repaired. Insufficient clamping force or damage to the arch surface of the blast disc can lead to a significant reduction in the blasting pressure; in severe cases, this can prevent the release valve from opening. Special care should be taken during installation. Applicable only to gas phase 2. Characteristics of reverse-arch cross-slot type (YC) and reverse-arch cross-slot welded type (YCH) rupture discs: The maximum operating pressure must not exceed 0.9 times the minimum rupture pressure. Rupture occurs along the weakened slots, resulting in four fragments; there are no debris. They exhibit excellent fatigue resistance. For the welded-type rupture discs, complete leaklessness can be achieved. Insufficient clamping force or damage to the dome of the rupture disc can lead to a significant reduction in the rupture pressure; in severe cases, this can prevent the release valve from opening. Special care should be taken during installation. Applicable only to the gas phase. 3. Characteristics of the reverse-arch grooved rupture disc (YHC/YHCY): The maximum operating pressure must not exceed 0.9 times the minimum rupture pressure; rupture occurs along the weakening grooves, with no fragments generated, and it exhibits good fatigue resistance. Insufficient clamping force or damage to the dome of the rupture disc can lead to a significant reduction in the rupture pressure; in severe cases, this can prevent the release valve from opening. Special care should be taken during installation. Suitable for gas and liquid phases. 4. Flat slotted rupture discs (PC): ① Characteristics of flat slotted (PC) rupture discs: The rupture pressure is primarily determined by the depth of the slots; they are difficult to manufacture, especially for low-pressure, small-diameter applications. The maximum operating pressure for slotted flat plates generally does not exceed 0.5 times the minimum burst pressure. The blasting occurs along the weakening groove without generating fragments; there are no specific requirements regarding the application environment, but its fatigue resistance is poor. The clamping force around it is insufficient, which can lead to loosening and detachment in that area, resulting in a decrease in blasting pressure and the formation of fragments. As long as minor damage does not occur at the grooves, the blasting pressure will not change significantly. Suitable for gas and liquid media. 5. Plate-slotted rupture discs (PF) ② Characteristics of plate-slotted type (PF): Generally, the maximum operating pressure shall not exceed 0.5 times the minimum rupture pressure. Very small fragments may be generated during blasting, but through proper structural design, it is possible to achieve zero fragmentation, even though fatigue resistance is lower. Insufficient clamping force at the periphery can lead to loosening and detachment there, resulting in a decrease in blasting pressure. As long as minor damage does not occur at the bridges between stop holes, the blasting pressure will not change significantly. Generally used in gas-phase applications, graphite rupture discs must have a maximum operating pressure that does not exceed 0.8 times the minimum rupture pressure; they produce fragments upon rupture and have poor fatigue resistance. It has good resistance to corrosion by various media, but cannot be used in strongly oxidizing acids. It is suitable for gas and liquid phases. 4 Naming rules for rupture discs: Type code, caliber, designed burst pressure, designed burst temperature. For example: YC100-1.0-100. The model YC indicates a designed burst pressure of 1.0 MPa and a designed burst temperature of 100°C; this means that the rupture disc’s designed burst pressure at 100°C is 1.0 MPa.