An Overview of Pressure Relief Devices for Pressure Vessel

 
In industrial production, pressure vessels and pipeline systems often face the risk of excessive pressure, which may lead to equipment failure or even explosions. To ensure the safe operation of pressure vessel and prevent accidents, pressure relief devices have been developed. These devices effectively control and discharge excessive pressure gas, ensuring that the system operates within a safe range. This article will introduce several common types of pressure relief devices to help readers better understand and choose suitable safety protection equipment.

Valve-Type Safety Pressure Relief Devices

 
Valve-type safety pressure relief devices, commonly known as safety valves, are common equipment used to protect pressure vessels or pipeline systems from excessive pressure. They automatically open to discharge excessive gas, thereby reducing the pressure within the system. The main advantages include:
 
Automatic closing function: The safety valve can automatically close when the pressure inside the container drops to the normal range, preventing the complete discharge of gas due to excessive pressure. This not only reduces resource waste but also avoids production interruptions.
Reusability: The design of the safety valve allows for multiple uses, and installation and adjustment are relatively simple, facilitating maintenance.
 
Despite these advantages, safety valves also have some disadvantages:
 
Insufficient sealing performance: Even under normal working pressure, the safety valve may experience slight leakage. Long-term use may lead to further degradation of sealing performance.
Reaction lag: Due to the inertia of components such as springs, there is a lag in the opening of the safety valve, resulting in a slower pressure relief response. This lag may be particularly prominent in applications with high-frequency pressure fluctuations.
Medium contamination issues: For gases containing solid particles or pollutants, the interior of the safety valve may become blocked, or the valve disc may become stuck, affecting its normal operation.
 
Safety valves are suitable for cleaner media, such as air and steam, but are not suitable for media with strong toxicity or that may cause violent chemical reactions.

Rupture-Type Pressure Relief Devices

 
Burst discs and burst caps are two common forms of rupture-type pressure relief devices. They achieve pressure relief by the rupture of the bursting element under high pressure. The specific features are as follows:
 
Burst disc: Mainly used for medium and low-pressure containers. Burst discs have good sealing performance and do not leak under normal working conditions. They have a fast rupture speed and can quickly respond to situations of excessive pressure. The advantages also include being unaffected by oil and other impurities in the medium. However, once ruptured, the burst disc cannot be reused, and the equipment must be stopped for operation. In addition, burst discs are prone to fatigue failure when long-term under high stress, so they need to be replaced regularly.
 
Burst cap: Usually used for ultra-high pressure containers, with functions similar to burst discs. It also has good sealing performance and a fast response speed, but also has the same issues of being non-reusable and potentially failing due to fatigue.
 
Rupture-type pressure relief devices are suitable for chemical reaction containers with sharp pressure increases or media containing highly toxic substances, but are not suitable for liquefied gas storage tanks or containers with large pressure fluctuations.

Melting-Type Pressure Relief Devices

 
Melting-type pressure relief devices are commonly known as fusible plugs. A fusible plug is a pressure relief device that uses the melting of a low-melting-point alloy at high temperatures to discharge gas. The main advantages include:
 
Simple structure: The structure of the fusible plug is simple, easy to replace, and has a low maintenance cost.
Temperature control: The melting temperature of the alloy is more accurate in controlling the pressure relief action and can be set at a specific pressure value.
 
However, fusible plugs also have some shortcomings:
 
Single use: Once triggered, the alloy of the fusible plug will melt, and the device can no longer be used. The equipment must be stopped for operation to replace a new fusible plug.
Small discharge area: Due to the strength limit of the fusible alloy, the discharge area of the device is relatively small and may not be effective enough in high-flow applications.
Potential failure: The fusible alloy may fall off or melt under pressure or other factors, leading to a failure in the pressure relief action and even causing accidents.
 
Fusible plugs are suitable for situations where the pressure inside the container increases sharply but are not suitable for liquefied gas storage tanks or equipment prone to liquid leakage.

Combined Pressure Relief Devices

 
Combined pressure relief devices use different types of pressure relief devices (such as safety valves with burst discs or fusible plugs) in combination to achieve better protection effects. Common combinations include the following.
 
Safety valve and burst disc combination: This combination structure has the advantages of both, preventing leakage when the safety valve is used alone and restoring the use of the container after discharging excessive pressure. The burst disc can be set on the inlet or outlet side of the safety valve, with the former protecting the safety valve from corrosion or blockage, and the latter preventing the burst disc from being affected by gas pressure. The combined device requires that the rupture of the burst disc does not interfere with the normal operation of the safety valve, and a check device is set between the burst disc and the safety valve to prevent pressure from affecting the normal operation of the burst disc.
 
Safety valve and fusible plug combination: This combination also plays the advantages of both, with the safety valve handling low-pressure leaks and the fusible plug responding to sharp increases in pressure.
 
Combined pressure relief devices are suitable for containers with corrosive liquefied gases or highly toxic and rare gases, but due to the lag of the safety valve, they are not suitable for containers with extremely fast pressure rise rates.

Other Safety Devices

 
In addition to pressure relief devices, pressure vessels should also be equipped with other types of safety devices to ensure the safe operation of the equipment.
 
Interlocking devices: Including interlocking switches and linkage valves, and other control mechanisms, are used to prevent operational errors. These devices ensure that the equipment remains in a normal state during operation, avoiding safety accidents caused by misoperation.
 
Alarm devices: Such as pressure alarms, temperature monitors, etc., they can issue audible or other obvious alarm signals when the container has unsafe factors, reminding operators to deal with potential dangerous situations in time.
 
Measurement devices: Automatically display process parameters related to safety, such as pressure gauges, thermometers, and level meters. These devices help monitor the operation of the equipment, provide real-time data support, and ensure that the container operates within a safe range.
 
In industrial production, ensuring the safe operation of pressure vessels and pipeline systems is crucial. Through a detailed analysis of various pressure relief devices, including valve-type safety pressure relief devices, burst discs, fusible plugs, and combined devices, we can choose the most suitable safety protection plan. Reasonable configuration of these devices, combined with interlocking, alarm, and measurement systems, not only effectively controls and discharges excessive pressure to ensure the safe operation of equipment but also prevents potential accident risks, thereby ensuring the stability and safety of the production process.