Rupture disc sizing calculator

No, we deliberately do not publish an online calculator. A calculator can only work with the inputs it receives, and the most important decisions lie outside it. We prefer to review the inputs with you and turn them into a real disc and holder specification. You can use the request form below this page to send us your data. If you have already used a calculator, send the result along with the assumptions. We will check them against the disc types and holders available from STRIKO. That gives you a result that can actually be ordered. It also gives you documentation for your design file.

The core inputs are the medium and its phase, the required relief rate, the set pressure and the allowable overpressure. The relieving temperature is needed as well, because it affects the fluid properties and the disc. Back pressure on the outlet side has to be included. For a gas, the molecular weight, ratio of specific heats and compressibility are required. For a liquid, density and viscosity matter. For longer relief lines, the geometry of the inlet and outlet piping is also needed. Without these inputs the result is only a rough estimate. We ask for the same data when you send us a request.

A calculator usually treats the disc as an isolated nozzle with an exact set pressure. In reality the burst pressure has a tolerance and is specified at a temperature. The disc also sits in a relief path with its own flow resistance. The chosen disc type may change the operating ratio and therefore the burst pressure. The final nominal size has to fit a standard DIN or ANSI connection. Each of these steps can move the final size away from the first estimate. That is normal and not a sign that the calculator was wrong. It simply shows that sizing continues after the first number appears.

The relief rate comes from a relief study of the process, not from the disc or the pipe. That study looks at scenarios such as blocked outlets, cooling failure, external fire and runaway reactions. Each scenario gives its own relief load. The governing scenario sets the rate used for sizing. In reactive or flashing systems, the relief may be two-phase, which needs a specialised assessment. If the relief rate is estimated rather than calculated, every result that follows is uncertain. The plant owner and its engineers are responsible for defining the scenarios. We can support that work with product data and in HAZOP and safety studies.

A rupture disc responds to the pressure difference across it. Back pressure on the outlet side therefore raises the process pressure needed to burst the disc. It also reduces the pressure difference available to drive the flow. Superimposed back pressure from a header is present before the disc opens. Built-up back pressure develops once the medium starts to flow. A calculator that ignores both can overestimate capacity and underestimate the opening pressure. For discs discharging into shared systems, this effect can be significant. Always include the expected back pressure in the inputs you send us.

Most simple calculators are designed for single-phase gas or liquid flow. Two-phase relief from reactive systems, flashing liquids or foaming media behaves very differently. It can require a much larger flow area than a gas-only calculation suggests. Dedicated methods and process safety software are normally used for these cases. The results of that work then become the basis for disc selection. Using a single-phase calculator for a two-phase case is one of the more serious sizing errors. If your case may be two-phase, mention it clearly in your request. We will then ask for the study results rather than a single relief rate.

We first check whether the inputs are complete and consistent. Where data are missing, we ask targeted questions instead of making assumptions. Then we look at the disc type that suits your operating ratio, medium and pressure profile. Next we select a material and a holder that fit the temperature and the connection. The flow resistance of the chosen disc and holder is used to check the sizing basis again. Finally we prepare a proposal with the relevant documentation. Holder documentation includes material certificates to EN 10204 3.1, pressure calculations and inspection reports. You then have a specification you can review and approve.

For a like-for-like replacement with a confirmed design basis, the original specification is usually the best reference. A new calculation is only needed when the process, the medium or the equipment has changed. The existing tag data, the burst pressure, the temperature and the holder type are the starting point. Many older plants have made process changes without updating the relief basis. In that case a quick check with a calculator can reveal whether the old disc still fits. If the result differs from the installed size, the relief study should be reviewed. We can help identify which data need to be updated. Send us the existing tag data and we will take it from there.