Where and how are rupture discs used?

Rupture discs are used on pressurized equipment and systems as pressure relieving devices (PRD)

A rupture disc is a non-reclosing, non-mechanical pressure relief device (PRD) used to protect vessels, piping, and other systems from excessive pressure and/or vacuum. Rupture discs are highly reliable because there are no moving parts. They activate in milliseconds, much faster than safety valves or other types of PRD, and they can be made cost-effectively from higher alloys than other PRDs due to their lower weight.

Rupture discs are suitable for use as a single PRD, in systems designed with multiple PRDs, and in fire condition applications. Rupture discs are never to be used on power boilers or other fired vessels as described in ASME section I. They are suitable for applications on all other non-fired vessels as described in ASME Section XIII.

How are rupture discs used?

Rupture discs may be used as the only source of pressure relief or in combination with another PRD. To comply with the ASME Boiler and Pressure Vessel Code, the maximum burst pressure allowed for the discs in each instance is different:

• For rupture discs used as the sole or primary source of pressure relief, it is required that the marked burst pressure not exceed the maximum allowable working pressure (MAWP) of the vessel that is protected.
• For rupture discs installed in parallel to another PRD, the burst pressure must not exceed 105% of the MAWP.
• In a fire condition with a single rupture disc, the burst pressure shall not exceed 110% of the MAWP.
• In a fire condition with rupture discs installed in parallel, the burst pressure shall not exceed 116% of the MAWP.

Rupture discs are often installed in series with a Pressure Relief Valve (PRV). In these types of applications, the devices are considered ‘close coupled’, which limits shock loading on the relief valve during activation.

What factors affect how a rupture disc performs?

Rupture discs are known for their reliability, however, as they are precisely calibrated pressure relief devices, several factors will affect when and how they burst. These include temperature, fluid media and disc installation:

Temperature

Rupture discs are known for their reliability, however as temperature-sensitive devices, changes in temperature will affect their bursting point. In general, a rupture disc’s burst pressure will decrease as temperatures increase. By the same principle, a rupture disc’s burst pressure will increase as temperatures decrease. Due to this characteristic, a designer must make careful consideration of the relieving temperature when selecting and specifying a rupture disc.

Fluid media

Rupture discs can be specified for use in nearly any fluid regime. The type of fluid media in a process will affect the opening characteristics of a rupture disc at the time of bursting, so we recommend seeking specialist advice to ensure the rupture disc you are using is correctly specified for your media.

Installation‍

There are also a few installation factors that will affect a rupture disc’s performance:

• Installing a rupture disc that is damaged can decrease or increase the pressure at which it will burst. Care should always be taken in handling and installing rupture discs to avoid this concern.
• Installing a rupture disc the wrong way round can also decrease or increase the pressure at which it will burst. Care should be taken to follow the rupture disc installation instructions and to ensure installation in the correct orientation.
• Some rupture disc designs can be sensitive to uneven torque of companion flanges or forces applied by misaligned piping. This can cause unplanned failure of a rupture disc in service.

 When selecting a rupture disc, we would always recommend working with an engineer from a specialist pressure safety company such as OsecoElfab. This is to verify correct selection, and ensure safety and compliance.