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Rupture Discs 101.
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/ How it works
A rupture disc has exactly one job: to open when it matters.
It protects vessels and systems against harmful overpressure or vacuum. When the nominal pressure is reached, the bursting element ruptures within milliseconds, the medium escapes and the system is relieved. Try it yourself.
Drag the slider to the right. The disc domes as the pressure rises – and opens at nominal pressure.
/ 18 questions, 18 answers
The questions we are asked most often.
From the definition to the applicable standards: the essentials of rupture discs, the way our customers need them most often. Use the list on the left to jump straight to a question.
What is a rupture disc?
A rupture disc is a pressure safety device that protects pressurised vessels (e.g. gas cylinders) or systems (e.g. pumps) against harmful overpressure or vacuum. It does so by opening the bursting element in a defined manner within milliseconds once a critical pressure condition is reached. The enclosed medium (gas or liquid) escapes through the opening created, relieving the system immediately.
Is a rupture disc always a disc?
The term “rupture disc” is a common umbrella term for bursting elements of various designs, such as discs, caps, domes or pre-bulged membranes. Even when the bursting element is installed in a holder or housing (screw-in solution, plug), the term “rupture disc” is frequently used.
What is the "nominal pressure" of a rupture disc?
The “nominal pressure” of a rupture disc is its specified response or burst pressure, i.e. the pressure at which the disc is designed to open. Due to the material, the nominal pressure is always stated with a tolerance, e.g. ± 10 %. This creates a corridor within which the rupture disc must open as intended.
What determines the burst pressure of a rupture disc?
The burst pressure of a rupture disc depends on the following factors:
- Material
- Material properties
- Material thickness
- Diameter of the opening
- Burst geometry
- Temperature
What are rupture discs made of?
Our rupture discs are made exclusively from corrosion-resistant materials such as stainless steel, nickel, nickel-based alloys (e.g. Inconel or Hastelloy), tantalum, or in combination with corrosion-resistant plastics such as FEP and PTFE.
Why are there so many material types?
The demands placed on bursting elements in practice are diverse. It is not only the required burst pressures that differ. The specific properties of the media to be protected, as well as other factors such as unusual ambient temperatures, create individual requirements that have to be taken into account. The range of materials available to us allows us to respond precisely to these different requirements. In this way an optimal solution and reliable protection can be found for almost every application.
Is the burst pressure of a rupture disc the same at every temperature?
Because of the physical properties of the materials used, the response pressure of a rupture disc changes with temperature. As a rule, the response pressure decreases as the temperature rises. Different materials react differently to temperature changes – nickel versus stainless steel, for example. These differing material properties can be used to advantage when selecting rupture discs.
How loud is a rupture disc when it bursts?
The noise level on bursting depends mainly on the pressure, the medium and the diameter of the opening. The range extends from a quiet “pop” to an extremely loud bang.
What is the difference between a rupture disc and a safety or pressure relief valve?
A safety or pressure relief valve is a protective device that opens automatically when the set pressure is reached and relieves pressure by venting the medium to atmosphere. Once the pressure falls below the set point, the valve closes again automatically. With a rupture disc system, the relief cross-section remains permanently open after activation and the rupture disc has to be replaced. Relief valves are used where recurring overpressure is to be expected (the normal case). Rupture discs, on the other hand, are intended for systems in which overpressure is an unplanned exception that needs to be safeguarded against.
What is a puncture disc and what is a burst foil?
Puncture discs and burst foils differ from rupture discs in their function and purpose.
A puncture disc is a rupture disc that acts as a pressure safety device on the one hand and, on the other, is deliberately opened mechanically (punctured) by the system or by a user in certain situations in order to release the enclosed medium for a defined purpose.
A burst foil, by contrast, is not a pressure safety device. Its only purpose is to enclose a medium in an unpressurised environment (a container). As soon as the system is pressurised as intended, the foil bursts and the medium can escape.
Puncture discs and burst foils are used in foam fire extinguishers, for example. The main chamber of the container holds the extinguishing foam, which is retained by a burst foil. The extinguisher also contains a CO2 cartridge protected by a puncture disc. When the extinguisher is used, this puncture disc is opened by the initial actuation of the extinguisher, the CO2 pressurises the container, the burst foil bursts and the foam can be discharged.
How big are rupture discs and how thick?
The size and thickness of a rupture disc depend on the application. The smallest rupture discs have a diameter of a few millimetres, the largest of more than one metre. The thickness varies between a few micrometres (µm) and several millimetres.
Which pressures can be protected?
Rupture discs from Wehberg Safety can protect pressures between 3 and 7,000 bar.
What has to be considered when protecting hot, toxic or contaminated media?
In the case of hot, toxic or contaminated media, the plant operator must ensure controlled discharge of the medium in the event of bursting, using suitable equipment such as piping and collection vessels. With our Hybrid System® models, Wehberg Safety offers standard solutions for precisely this field of application.
Are there standards and regulations for rupture discs and pressure vessels?
Pressure systems, pressure vessels, safety valves and bursting disc safety devices are subject to technical regulations and rules that are continuously adapted to the state of the art. Important standards and regulations in this field include:
- 2014/68/EU, Pressure Equipment Directive (PED); issued by the European Union
- DIN EN ISO 4126-2, Safety devices for protection against excessive pressure – Part 2: Bursting disc safety devices; issued by ISO/TC 185 “Safety devices for protection against excessive pressure”
- AD 2000, code of practice for the European Pressure Equipment Directive; issued by Verband der TÜV e. V. (VdtÜV), Germany
- CGA S-1.1, Pressure Relief Device Standards; issued by the Compressed Gas Association, USA
Does a rupture disc last forever?
The service life of a rupture disc depends on the loads it is exposed to in practice. A rupture disc that is normally exposed to no pressure, or only to low pressure compared with its nominal pressure, is very durable. Elevated continuous pressure and, above all, pressure cycling lead to material fatigue. Plant operators must therefore define suitable replacement intervals for rupture discs according to the individual conditions, in order to avoid unintended activation below the nominal pressure due to fatigue.
How leak-tight is an installed rupture disc, and how is this ensured?
Rupture discs from Wehberg Safety achieve a helium leak rate of up to 1 x 10-9 mbar l/s. This also applies to screwed, framed and press-fitted versions. Our high-quality test equipment allows us to carry out the corresponding measurements, up to and including 100 % testing, depending on the customer’s requirements.
How is the burst strength of a rupture disc tested?
Burst tests are carried out during the production of rupture discs. Their type and scope are defined in the standards and regulations mentioned above. Depending on the size of an order or batch, a certain number of test pieces must be pressurised and burst using a calibrated test rig.
What are bursting disc safety devices, and what technical requirements do they have to meet?
Safety devices for protection against excessive pressure based on the use of rupture discs are referred to as “bursting disc safety devices” in accordance with DIN EN ISO 4126-2:2019.
A bursting disc safety device must be fitted with a rupture disc whose material is attacked neither by the medium to be protected nor by an industrial atmosphere.
The clamping force on the rupture disc is applied using torque wrenches or torque screwdrivers. The device must be designed so that the rupture disc is seated concentrically, can be clamped plane-parallel and is not damaged in pressure ranges in which it domes. It must also be ensured that the disc clamping cannot work loose.
Bursting disc safety devices must remain leak-tight to atmosphere within the operating temperature range until they respond, and must release the required cross-section when the disc bursts.
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