Rupture Disc (Bursting Disc)
Valves / Relief ValveA rupture disc (bursting disc) is a non-reclosing pressure relief device consisting of a thin metal disc designed to burst at a specified pressure, providing overpressure protection as a primary or secondary relief device where rapid, full-bore discharge is required and reclosing is not needed.
Working Principle
The rupture disc is a precision-manufactured thin metal membrane held between two flanges or a holder. When system pressure reaches the rated burst pressure, the disc ruptures, providing an instantaneous full-bore opening for pressure relief. Unlike a safety valve, the rupture disc does not reclose — once it bursts, flow continues until the system is depressurized and the disc is replaced. The burst pressure is determined by disc material, thickness, diameter, and manufacturing tolerance. Rupture discs can be forward-acting (bulged toward the outlet, burst by tensile stress) or reverse-acting (bulged toward the inlet, burst by compression/buckling). Reverse-acting discs can be scored to provide a clean, predictable opening pattern.
Key Components
Disc (thin metal membrane), holder (flanges or bolted assembly), outlet piping, tell-tale indicator (optional, for disc rupture detection).
Types & Variants
| Type | Key Feature | Typical Use |
|---|---|---|
| Forward-acting tension disc | Bulged toward outlet, tensile failure | General overpressure protection |
| Reverse-acting compression disc | Bulged toward inlet, scored pattern | Low burst pressure, cycling service |
| Composite disc | Multi-layer for corrosion resistance | Corrosive service |
| Graphite disc | Graphite membrane, non-metallic | Highly corrosive service |
Common Materials
Disc: 316SS, Inconel 600/625, Monel 400, Nickel 200, Hastelloy C-276, tantalum, or graphite depending on corrosion requirements. Holder: carbon steel, 316SS, or alloy. Gaskets: PTFE or spiral wound per flange service.
Applicable Standards
- API 520 Part I (sizing and selection, reference)
- API 526 (reference)
- ISO 4126-2 (rupture disc devices)
- ASME Section VIII Div.1 UG-127 (non-reclosing pressure relief devices)
- CGA S-1.1 (pressure relief device standards)
Industrial Applications
- Secondary overpressure protection behind a safety valve (in series)
- Primary protection for reactors and vessels where instantaneous full-bore relief is needed
- Explosion venting for dust collectors and silos
- Vessel isolation where reclosing is not required
- Corrosive service where safety valve seats would be attacked
- Emergency venting of storage tanks
Advantages & Disadvantages
Advantages
- Instantaneous full-bore opening — fastest possible pressure relief
- No moving parts — virtually maintenance-free until burst
- 100% tight until burst (no simmer or leakage)
- Available in any material for any corrosive service
- Can be installed upstream of a safety valve to protect the valve from corrosive media
Disadvantages
- Non-reclosing — once burst, the system loses containment until the disc is replaced
- Manufacturing tolerance on burst pressure (typically +/-5%)
- Cannot be tested without destroying the disc
- Replacement requires system shutdown and depressurization
- Improper installation (reversed, damaged, wrong orientation) causes premature or delayed burst
Selection Guide
- When installing a rupture disc upstream of a safety valve, install a tell-tale pressure gauge between them to detect disc leakage
- Reverse-acting scored discs provide more predictable burst pressure and lower manufacturing tolerances than forward-acting discs
- Never install a rupture disc backwards — a forward-acting disc installed in reverse will burst at the wrong pressure
- Replace rupture discs at the manufacturer's recommended interval, even if they have not burst — material creep causes burst pressure to drift
- Size the disc per API 520 or ISO 4126-2 with the appropriate flow coefficient (Kd)
Practical Tips
- A rupture disc upstream of a safety valve is the standard combination for corrosive gas service — the disc protects the valve seat from corrosion, and the valve provides reclosing capability. A tell-tale between them detects disc failure before the valve is exposed
- Manufacturing lot consistency is critical — always order spare discs from the same lot as the originals to ensure consistent burst pressure. Different lots can vary by the full manufacturing tolerance
FAQ
When should I use a rupture disc instead of a safety valve?
Use a rupture disc when: (1) instantaneous full-bore discharge is required, (2) the service is too corrosive for a safety valve, (3) the process cannot tolerate any leakage (reclosing is not needed), or (4) as a secondary device in series with a safety valve for dual protection.
Can a rupture disc be tested without destroying it?
No. The burst test is destructive by nature. However, manufacturers provide certified burst pressure test data for each lot. Visual inspection can detect corrosion or mechanical damage but cannot verify burst pressure. Order discs from the same lot and rely on the manufacturer's lot certification.