What Is a Rupture Disc?
A rupture disc (also called a bursting disc) is a non-reclosing pressure relief device that protects vessels, piping, and equipment from overpressure by bursting at a predetermined differential pressure. Once the disc ruptures, the full bore of the device opens instantly, providing rapid depressurization. Rupture discs are used as primary relief devices or installed upstream of pressure relief valves to isolate the valve from corrosive or fouling process fluids.
How Rupture Discs Work
The disc is a thin, precision-manufactured metal membrane clamped between two flanges in a holder assembly. When the upstream pressure reaches the disc’s rated burst pressure, the membrane fails along engineered score lines or reverses and fragments in a controlled pattern, opening the full flow area. Unlike a safety valve, a rupture disc cannot reseat; it must be replaced after activation.
Types of Rupture Discs
| Type | Mechanism | Advantages | Limitations |
|---|---|---|---|
| Forward-acting (tension-loaded) | Dome-shaped disc bursts when pressure exceeds tensile strength | Simple design, low cost | Fatigue from pressure cycling |
| Reverse-acting (compression-loaded) | Disc reverses under overpressure, knife blades open petals | Excellent fatigue life, tight burst tolerance (+/- 2%) | Higher cost, requires knife blades |
| Scored forward-acting | Laser-scored lines control opening pattern | Predictable fragmentation, no knife blades | Slightly reduced fatigue life |
| Graphite/composite | Non-metallic disc for corrosive service | Chemical resistance, low burst pressures | Limited temperature range |
| Sanitary | Polished disc for food/pharma applications | Clean, no dead legs | Not for high-pressure service |
Key Specifications
| Parameter | Typical Range |
|---|---|
| Burst pressure | 0.1 to 1,000+ bar |
| Burst tolerance | +/- 2% to +/- 5% of rated burst pressure |
| Sizes | 1/2 in to 60 in |
| Disc materials | Inconel, Monel, Hastelloy, 316 SS, nickel, graphite |
| Holder materials | Carbon steel, stainless steel, alloy steel |
| Temperature | -270 to 700 deg C |
| Design standards | ASME Section VIII Div. 1, API 520/521, EN ISO 4126-2 |
| Certification | Each lot tested; burst pressure certified per ASME UG-127 |
Rupture Disc vs Safety Valve
A rupture disc opens faster (milliseconds) than a safety valve and provides full-bore relief, making it the preferred choice for rapid-pressure-rise scenarios such as runaway reactions. However, it is a single-use device. Many facilities combine both: the rupture disc sits upstream of the safety valve, protecting the valve seat from corrosion and fouling while allowing the valve to handle minor overpressure events without disc replacement.
Proper sizing follows API 520 Part I for required orifice area and ASME Section VIII for burst pressure selection relative to the vessel’s maximum allowable working pressure (MAWP). The relief system must also comply with downstream pipe inspection and testing requirements.
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