1 Combined application of safety valve and bursting disc
1. The bursting disc is installed at the entrance of the safety valve — the most common advantage of this setting is that the bursting disc will isolate the safety valve and the imported process medium, and the system has no leakage. Safety valves are not corroded by process media, which can reduce the cost of safety valves. Once the system overpressures, the bursting disc and the relief valve can simultaneously burst and begin relieving pressure. When the system pressure returns to normal, the safety valve can be automatically closed, greatly reducing the loss of the medium.
2. The bursting disc is installed at the outlet of the safety valve. The most common advantage of this setting is that the bursting disc will isolate the safety valve from the public release pipeline at the outlet.
2 Equipment overpressure and selection of safety accessories
1. Equipment overpressure
Overpressure – generally refers to the maximum working pressure in the equipment exceeds the allowable pressure of the equipment. Equipment overpressure is divided into physical overpressure and chemical overpressure
The pressure in the equipment design is gauge pressure
Physical overpressure – The increase in pressure is not caused by a chemical reaction in the medium where only a physical change occurs. Chemical overpressure – A rise in pressure caused by a chemical reaction in the medium
(1) Common types of physical overpressure
① Overpressure caused by material accumulation in the equipment and can not be discharged in time;
② Overpressure caused by material expansion caused by heat (fire);
③Overpressure caused by instantaneous pressure pulsation; local pressure rise caused by sudden and rapid closing of the valve, such as “water hammer” and “steam hammer”; in addition to the end of the steam pipe, steam cooling quickly, local vacuum formation, resulting in rapid steam flow to the end. A shock is formed, causing an overpressure similar to the “water hammer” effect.
(2) Common types of chemical overpressure
① Deflation of combustible gas (aerosol) causes overpressure
② all kinds of organic and inorganic combustible dust combustion and explosion causes overpressure
③ exothermic chemical reaction control causes overpressure
2. Overpressure relief device
① Safe release principle
Equipment overpressure, the equipment on the safety accessories immediately action, the overpressure media will be released in time to protect the container. It is required to achieve how much media is generated per unit time, and the release port can also be discharged within a unit time. The pressure relief rate per unit time is greater than the pressure boost rate, and the maximum pressure in the equipment is less than the maximum allowable pressure of the equipment.
② Overpressure relief device
The operation principle is divided into two kinds: overpressure relief and overtemperature relief
Common overpressure relief device: pressure relief valve and bursting disc.
Working principle of bursting disc
When the calibration bursting pressure is reached in the equipment, the bursting disc will burst instantaneously and the release channel will be completely opened.
Advantages:
① Sensitive, accurate, reliable, no leakage.
② The size of the emission area is not limited, and the suitable surface is wide (such as high temperature, high pressure, true space, strong corrosion, etc.).
③ Simple structure, convenient maintenance and other prominent characteristics of the shortcomings: the channel can not be closed after opening, all the material loss.
3 Classification and structural characteristics of bursting disc
1. Classification of bursting disc
The shape of the bursting disc can be divided into positive arch bursting disc (concave compression), anti-arch bursting disc (convex compression), flat plate bursting disc and graphite bursting disc.
The mechanical failure of the bursting disc can be divided into tensile failure type, unstable failure type and bending or shearing failure type. The tensile destructive bursting disc, with tensile stress in the diaphragm, can be divided into: arch ordinary type, arch groove type, plate groove type, arch slit type and plate slit type. The instability breakage type bursting disc, the compression stress in the diaphragm, can be divided into: reverse arch belt knife type, reverse arch alligator tooth type, reverse arch belt groove bending or shear failure bursting disc, diaphragm shear failure: mainly refers to the whole material processing, such as graphite made of bursting disc.
2. Common types and codes of burst discs
(1) Mechanical characteristics of forward-acting bursting disc — concave compression, tensile damage, can be single layer or multi-layer, code with “L” beginning. Classification of positive arch bursting disc: positive arch ordinary type bursting disc, code: LP positive arch groove type bursting disc, code: LC positive arch slotted bursting disc, code: LF
(2) reverse-acting mechanical characteristics – convex compression, instability damage, can be single layer or multi-layer, code with “Y” beginning. Classification of reverse arch bursting disc: Reverse arch with knife type bursting disc, code: YD reverse arch alligator tooth type bursting disc, code: YE reverse arch cross groove type (welded) bursting disc, code: YC (YCH) reverse arch ring groove type bursting disc, code: YHC (YHCY)
(3) Stress characteristics of flat shaped bursting disc — gradually deformation and arch after stress to reach the rated pressure tensile failure, can be single-layer, multi-layer, code with “P” beginning. Classification of flat plate bursting disc: flat plate with groove type bursting disc, code: PC flat plate slit type bursting disc, code: PF (4) Graphite bursting disc Mechanical characteristics of the bursting disc – damaged by shear action. Code name: PM
3. various types of burst disc life characteristics
All the bursting discs are designed and manufactured according to the ultimate life, without safety coefficient. When the specified bursting pressure is reached, it will burst instantly. Its safety life mainly depends on the shape of the product, the stress characteristics and the ratio of maximum operating pressure to minimum bursting pressure – operation rate. In order to ensure the long-term use of bursting discs, ISO4126-6 international standard Application, selection and Installation of bursting disc safety devices specifies the maximum allowable operation rate of bursting discs of various forms. The rules are as follows:
① Normal arch bursting disc — maximum operation rate ≤0.7 times
② positive arch groove and positive arch slit bursting disc — maximum operation rate ≤0.8 times
③ all kinds of reverse arch bursting disc (with groove, with knife, etc.) — maximum operation rate ≤0.9 times
④ Flat shaped bursting disc — maximum operation rate ≤0.5 times
⑤ graphite bursting disc — maximum operation rate ≤0.8 times
4. Use characteristics of bursting disc
① Characteristics of arch normal type bursting disc (LP)
The bursting pressure is determined by the thickness of the material and the discharge diameter, and is limited by the thickness and diameter of the diaphragm. The maximum working pressure shall not exceed 0.7 times of the minimum burst pressure. Blasting will produce debris, can not be used for flammable and explosive or not allowed to have debris occasions (such as in series with the safety valve), fatigue resistance. The lack of clamping force around the perimeter is easy to cause the surrounding loose and fall off, resulting in the reduction of blasting pressure. Generally minor damage will not significantly affect the burst pressure. Suitable for gas and liquid media
② The characteristic bursting pressure of groove type bursting disc (LC)
In straight arch belt is mainly determined by groove depth, which is difficult to manufacture. The maximum working pressure of the bursting disc shall not exceed 0.8 times of the minimum bursting pressure. Blasting along the weakened groove split, no debris, no requirements for the use of the occasion, good fatigue resistance. The lack of clamping force around the perimeter is easy to cause the perimeter to loosen and fall off, resulting in the reduction of blasting pressure and debris. As long as minor damage does not occur in the groove, the burst pressure will not change significantly. Suitable for gas and liquid media
③ The bursting pressure of straight arch slit type bursting disc (LF) is mainly determined by the hole spacing, which is convenient to manufacture and generally used in low pressure occasions. Make sure that the maximum working pressure cannot exceed 0.8 times of the minimum burst pressure. Small fragments may be produced during blasting, but through reasonable structural design, no fragments can be produced and fatigue resistance is normal. The lack of clamping force around the perimeter is easy to cause the surrounding loose and fall off, resulting in the reduction of blasting pressure. If the damage does not occur at the short bridge, it will not cause significant change in the burst pressure
1. The bursting pressure of YD and YE bursting disc is mainly determined by the thickness of the blank and the height of the arch. YE type is usually used for low pressure. When the maximum working pressure is not more than 0.9 times of the minimum blasting pressure, the diaphragm will overturn and impact on the blade or other sharp structures and break, no debris will be generated, and the fatigue resistance is very good. After each blasting of the knife gripper, the knife must be repaired for insufficient clamping force or damage to the arch surface of the bursting disc, which will lead to significant reduction of the bursting pressure, and serious results in the failure to open the release port. Special care should be taken during installation. It only works in the gas phase
2. The maximum working pressure of backarch cross groove type (YC) and backarch cross groove welded (YCH) bursting disc cannot be more than 0.9 times of the minimum bursting pressure. The blasting along the weakened groove is broken into four valves, no debris, very good fatigue resistance, and no leakage of welded bursting disc can be completely. Insufficient clamping force or damage to the arch surface of the bursting disc will lead to significant reduction of the bursting pressure, and serious damage will cause the release port can not be opened. Special care should be taken during installation. It only works in the gas phase
3. The maximum working pressure of reverse arch ring groove bursting disc (YHC/YHCY) is not more than 0.9 times of the minimum bursting pressure. It is broken along the weakened groove with no debris and good fatigue resistance. Insufficient clamping force or damage to the arch surface of the bursting disc will lead to significant reduction of the bursting pressure, and serious damage will cause the release port can not be opened. Special care should be taken during installation. Suitable for gas and liquid phase
4, flat plate groove type (PC) characteristics of the burst pressure is mainly determined by the groove depth, manufacturing is difficult, especially difficult for low pressure small diameter manufacturing. The maximum working pressure of flat plate with groove is generally not more than 0.5 times of the minimum burst pressure. Blasting along the weakened groove crack, no debris, no requirements for the use of the occasion, poor fatigue resistance is insufficient surrounding clamping force, easy to lead to the surrounding loose off, resulting in the reduction of blasting pressure, debris. As long as minor damage does not occur in the groove, the burst pressure will not change significantly. Suitable for gas and liquid media
5, flat plate slit burst disc (PF) ② Flat plate slit type (PF) characteristics
Generally, the maximum working pressure cannot exceed 0.5 times of the minimum burst pressure. Small fragments may be generated during blasting, but no fragments can be generated through reasonable structural design, and the fatigue is poor. The lack of clamping force around the perimeter is easy to cause the surrounding loose and fall off, resulting in the reduction of blasting pressure. As long as minor damage does not occur at the bridge between holes, the blasting pressure will not change significantly. Generally used in the gas phase
Graphite bursting disc
The maximum working pressure can not exceed 0.8 times of the minimum blasting pressure, blasting debris, poor fatigue resistance. It has good corrosion resistance to various media, but can not be used for strong oxidizing acid suitable for gas and liquid phase
4 Rules for naming bursting discs
Type code diameter — design bursting pressure — design bursting temperature, such as YC100-1.0-100 model YC, design bursting pressure 1.0MPa, design bursting temperature 100℃ indicates that the design bursting pressure of the bursting disc at 100℃ is 1.0MPa.
Post time: Dec-02-2022