Quick estimate: gas service
Required flow area and disc size for a gas discharging to atmosphere.
Assumes: API 520 Part I coefficient-of-discharge method, Kd = 0.62, 10 % overpressure, ideal gas (Z = 1), discharge to atmosphere, critical flow.
What the full rupture disc calculator does
- Gas, steam and liquid relief with back pressure, compressibility, steam superheat and viscosity corrections.
- Two directions: find the required area from a flow, or find the rated capacity of a disc you already have.
- 10 %, 16 % and 21 % overpressure for single devices, multiple devices and fire cases.
- Disc recommendation from the Flammer range (forward-acting, reverse-buckling, sanitary and graphite types) with the reasons for the choice.
- A live installation drawing that changes with your inputs, and a two-page datasheet you can print or save as PDF.
- Excel import to size a whole list of discs in one upload.
How rupture disc sizing works
A rupture disc is sized so that, once it has burst, the opening passes the required relief flow without the vessel pressure rising above the limit set by the design code. For a gas in critical flow, API 520 Part I gives the required area as:
where W is the mass flow, C a constant that depends on the gas, Kd the discharge coefficient, P1 the absolute relieving pressure, T the absolute temperature, Z the compressibility factor and M the molecular weight. The disc chosen is the next standard size whose flow area is at least A. The guide Rupture disc sizing to API 520 walks through every step with numbers.
Inputs you will need
| Input | Gas | Steam | Liquid |
|---|---|---|---|
| Burst pressure and back pressure | Yes | Yes | Yes |
| Required flow (or the disc area, to find capacity) | Yes | Yes | Yes |
| Relieving temperature | Yes | For superheat | No |
| Molecular weight, k and Z | Yes (auto-filled from the gas list) | No | No |
| Specific gravity | No | No | Yes |
Common questions
Which standards does the rupture disc calculator follow?
API RP 520 Part I, ASME Section VIII Division 1 and ISO 4126-6. You choose the design code and the tool applies its overpressure rules and reports against it.
What information do I need to size a rupture disc?
The burst pressure, the relieving temperature, the fluid (gas, steam or liquid) and the flow the disc must pass. For a gas the tool also needs the molecular weight and the ratio of specific heats, which it fills in when you pick the gas from the list.
What discharge coefficient is used?
Kd = 0.62 for gas and steam and 0.65 for liquid by default, as used in the coefficient-of-discharge method. You can enter a certified value for a specific disc.
Is the quick estimate enough to order a disc?
No. It covers one common case: a gas discharging to atmosphere at 10 % overpressure. Back pressure, steam, liquids, fire cases and the choice of disc model are handled in the full tool, and the final selection should be confirmed with Flammer.