Classification and use of blast discs

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1. Classification of rupture discs: Based on their shape, they are divided into positively curved rupture discs (with the concave side under pressure), negatively curved rupture discs (with the convex side under pressure), flat rupture discs, and graphite rupture discs. Based on the failure mode under stress, rupture disks can be classified into tension 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: plain 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; they 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 mainly refer to rupture discs made from a single piece of material, such as those made of 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 convex surface is under compression, leading to instability and failure; they can be single-layer or multi-layer, with codes starting 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-groove (welded) rupture disc, code: YC (YCH); Reverse-arch with ring-groove 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 bursting pressure is reached. Its safe service life primarily 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 ISO 4126-6, “Application, selection and installation of bursting disc safety devices,” specifies the maximum allowable operating rates for various types of burst discs, as follows: ① Plain positive-dome burst discs – maximum operating rate ≤ 0.7 times; ② Grooved or slotted positive-dome burst discs – maximum operating rate ≤ 0.8 times; ③ Various negative-dome burst discs (with grooves, knives, etc.) – maximum operating rate ≤ 0.9 times; ④ Flat 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 plain positive-dome burst discs (LP): The bursting pressure is determined by the thickness of the material and the discharge diameter, and it is limited by the thickness and diameter of the diaphragm; such discs are generally suitable for applications with high pressures. The maximum allowable operating pressure must not exceed 0.7 times the minimum burst pressure. Shrapnel will be generated during detonation; it cannot be used in flammable, explosive environments or in situations where shrapnel 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 Positive arch slotted rupture disc (LC): The burst pressure is primarily determined by the depth of the slot, 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 hole spacing; it is easy to manufacture and is generally used in low-pressure applications. It must be ensured that the maximum allowable operating pressure does not exceed 0.8 times the minimum burst pressure. Very small fragments may be generated during blasting, but through proper structural design, fragment-free operation can be achieved, 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 hits the blade 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 dome surface of the blast disc can lead to a significant reduction in the blasting pressure, and in severe cases, it may prevent the release valve from opening. Special care should be taken during installation. Applicable only to gas phase 2. Characteristics of reverse-arch cross-groove type (YC) and reverse-arch cross-groove welded type (YCH) blast discs: The maximum operating pressure must not exceed 0.9 times the minimum burst pressure. The burst occurs along the weakened grooves, resulting in four fragments; there are no debris, and the fatigue resistance is very high. For the welded-type blast 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. It has poor fatigue resistance, and insufficient clamping force at the periphery can lead to loosening and detachment there, 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 should 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 eliminate fragment generation, 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 disks have a maximum operating pressure that must 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 is YC; the designed burst pressure is 1.0 MPa, and the designed burst temperature is 100°C. This indicates that the rupture disc’s designed burst pressure at 100°C is 1.0 MPa.