A bursting disc (also known as a rupture disc) is a non-reclosing pressure relief device designed to protect equipment, vessels, or systems from over-pressure or vacuum conditions. When the pressure exceeds a predetermined limit, the disc bursts open, allowing the excess pressure to safely escape and preventing damage or catastrophic failure.
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Typical Over-pressure Scenarios
- Blocked discharge - The system continues to feed the vessel while the outlet is partially or totally blocked due to personnel error, valve failure, actuator failure.
- Fire Case – a pressure vessel / pipe is exposed to a fire causing its contents to expand. A liquid could flash into a vapour causing a significant increase in pressure.
- Thermal expansion – a pipe or vessel is filled with a liquid that is locked in by valves being closed. As the pipe / vessel slowly heats up in the sun. This can cause really high hydraulic forces as the liquid is not compressible.
- Runaway reaction – in some systems there is a possibility of a thermal runaway reaction causing a sudden increase in pressure.
- Tube rupture in heat exchangers - If a tube ruptures in a heat exchanger, it creates a massive overpressure because, under pressure, the fl uids will evaporate rapidly when exposed to atmosphere.
How a Bursting Disc Works
When the system pressure exceeds the discs rated burst pressure, the disc ruptures along its engineered weak points. This sudden release of pressure prevents damage to equipment and reduces the risk of injury or explosions. The burst pressure is carefully calibrated during manufacturing and can range from a few psi to several thousand psi, depending on application requirements.
Summary of Bursting Disc Types
- Forward-Acting (Tension Loaded) Discs - These discs are domed and rupture when pressure pulls the metal outward. They are simple and cost-effective but sensitive to fatigue.
- Reverse Buckling Discs - These are installed with the dome facing the pressure source. When pressure reaches a set point, the disc inverts and bursts. They offer better resistance to cycling and are suitable for higher pressure applications.
- Graphite and Composite Discs - Made from layered materials, these are chemically resistant and often used in corrosive environments.
- Vacuum Support Discs - Designed to protect systems from both overpressure and vacuum conditions.
Advantages of Bursting Discs
- Fast-acting relief - Reacts faster than many mechanical valves.
- No mechanical parts - Less prone to failure and requires minimal maintenance.
- Leak-tight seal - Prevents emissions or contamination.
- Versatile - Compatible with a wide range of gases, liquids, and temperatures.
- Cost-effective - Especially in applications where a one-time pressure event is expected.
Rupture Disc Holders
Most discs are relatively thin pieces of metal and hence require a holder.
Safety Valve or Bursting Disc or Both??
Safety valves and bursting discs are installed to protect equipment and life in an over-pressure situation.
A safety valve is classified as a reclosing safety device. Bursting discs are classified as a non-reclosing safety device as once it bursts it must be replaced.
If only one type is to be used, it is more common for them to be safety valves as it allows for continued operation of the process, even when spurious over-pressures occur.
It two types are to be used, then the safety valve(s) are usually the primary protection device with a bursting disc as a secondary backup device (belt and braces).
For corrosive or hazardous mediums, bursting discs are sometimes installed just before the inlet of the safety valve (the upstream side), where it provides a pressure and chemical seal, reducing the risk of corrosion to the safety valve and emission leakage.
Advantages of Rupture Discs Used in Combination with Safety Relief Valves
- Zero Process Leakage to Atmosphere
- Valve Life is Extended
- A Less Expensive Valve Material Can Be Used
- Depending on the disc type, the valves can be tested in place
Further information on Forward-Acting and Reverse Acting Bursting Discs
A forward-acting bursting disc (also called a tension-loaded or conventional rupture disc) is used primarily for overpressure protection in systems where pressure relief is critical. It is often chosen because:
- Cost-Effective Design: Forward-acting discs are generally less expensive to manufacture compared to reverse-acting ones, making them a good choice for less demanding applications.
- Simple and Reliable: These discs are mechanically simple and rupture in a predictable way once the pressure exceeds the specified limit, offering high reliability in static systems.
- Low Burst Pressure Tolerance: They can be designed for lower burst pressures compared to reverse-acting discs, which is helpful in low-pressure applications.
- Clean Burst: They provide a clean, full opening upon activation, which is ideal for quick and complete pressure relief without fragmentation (especially if scored or designed with precision).
- Corrosive or Toxic Media Isolation: Since the disc typically has a solid, unbroken face until rupture, it can act as a barrier against corrosive or toxic materials, protecting downstream equipment.
Comparison between forward-acting and reverse-acting discs
| Feature | Forward-Acting Disc | Reverse-Acting Disc |
|---|
| Operation Principle | Bursts under tensile stress (pulled apart) | Buckles under compressive stress before bursting |
| Pressure Range | Better for low to moderate pressures | Designed for higher pressures |
| Cost | Generally lower cost | Typically more expensive |
| Fragmentation | May produce fragments unless scored or reinforced | Usually non-fragmenting due to controlled buckling |
| Vacuum Resistance | Typically needs support (vacuum support) | Naturally handles vacuum conditions without extra support |
| Back Pressure Sensitivity | More sensitive to back pressure | Less sensitive to back pressure |
| Flow Opening | Often provides a clean, full opening | May need knife blades or scoring to ensure full opening |
| Durability | Less fatigue-resistant under cycling conditions | More durable in pressure cycling applications |
| Applications | Simpler systems, where cost is a concern and pressure is relatively stable | High-pressure or cycling systems, often in more demanding environments |
In summary:
- Choose forward-acting when cost, simplicity, and low pressure are key.
- Choose reverse-acting for durability, safety in high-pressure or cycling systems, and applications requiring vacuum compatibility.
Key Features of Graphite Rupture Discs:
A graphite rupture disc is a type of forward-acting bursting disc made from resin-impregnated graphite, commonly used in corrosive environments.
| Feature | Description |
|---|
| Material | Made from layers of graphite bonded with resin, offering excellent chemical resistance |
| Corrosion Resistance | Ideal for highly corrosive gases or liquids like acids, chlorinated compounds, or aggressive solvents |
| Bursting Accuracy | Reasonably precise, though generally less accurate than metal discs |
| Temperature Tolerance | Good for moderate temperatures (typically up to ~180°C / 356°F depending on design and resin) |
| Fragmentation | May fragment on rupture, so often used where fragmentation isn’t a safety concern |
| Vacuum Support | Often requires a vacuum support if used in vacuum or back-pressure conditions |
| Cost | Generally affordable, especially in corrosive service where exotic metal discs would be costly |
| Standards | Often used in systems conforming to ASME, PED, or ISO standards for pressure relief devices |
Typical Applications:
- Chemical processing plants
- Chlorine gas systems
- Sulfuric or hydrochloric acid systems
- Storage tanks or pipelines with corrosive contents
Limitations:
- Brittle material: vulnerable to damage during installation or from mechanical shock
- Lower pressure ranges compared to metal discs
- Shorter service life under cycling or extreme temperatures
For any bursting disc enquiries, please contact us on +44 (0)1482 601030 or email sales@flowstar.co.uk.