A rupture disc, also sometimes known as a “bursting disc” or “disc diaphragm,” is a mechanical component that is generally installed as a safety device to prevent damage and injury caused by pressure problems within a machine or other device. It is essentially a metal or synthetic ring that is fitted within the internal chambers of something like a valve or pressurized tube. If and when the pressure becomes more than the device can handle, the disc bursts, or ruptures, effectively halting mechanical activity. In nearly all cases, the disc only has a one-time use; once it ruptures, it can’t be resealed. Replacing it can take some time, but usually saves a lot of money and effort when compared with the damage that often happens when internal pressure gets out of control. A number of different devices use this sort of mechanism, though it tends to be most common in aerospace and aviation, pharmaceutical manufacturing and processed food production, and medical appliances.
Most Common Applications
These sorts of devices are very common in a range of industrial machines, usually in situations where there is a need to regulate forced pressure within a certain chamber or valve. In aerospace, for instance, this happens in fuel chambers and cabin pressure systems for aircraft and vessels headed high into the atmosphere or beyond. They’re also used a lot in boilers and steam pressure tanks, both of which are common in food and drug manufacturing. Certain medical appliances, particularly those that rely on hydraulics, may also use them.
Although most of the machines and appliances in these categories are quite large, the discs tend to be on the smaller side. They’re usually made specifically for the appliance in which they are installed, but are typically placed in the internal parts of valves and other points of distribution.
Shape and Characteristics
The pressurized side of most discs is concave and bowl-like. As pressure builds, the disc experiences tension forces as the material stretches or bulges outward. The original rupture disc was developed in 1931 by BS&B Safety Systems, and was improved and slightly modified into what’s known as the “type B disc” beginning in 1934. The type B disc has been used in hundreds of thousands of applications since that time, and is the prototype for most modern models.
Basic Design Criteria and Manufacturing
The most important design criteria is usually that the disc fail at the specified pressure within the range specified by the manufacturer. Differences in pressure limits are achieved by variations in the material properties, shape, and size of the disc and the mounting system. Additional design criteria may include non-fragmentation of the disc, use for sterile conditions, or biological containment systems that allow the escape of pressure but not any biological or other materials.
Discs destined for service in a nuclear environment, such as a nuclear submarine or power plant, are usually subjected to very strict design requirements. The material properties, particularly the friability, or ease of breakage, may change should the disc be subjected to radiation. As a consequence, devices in these categories should be regularly tested and inspected to ensure their integrity.
In most cases, these sorts of pressure relief safety devices are manufactured as a system. The correct holders must be employed, as well as the correct parts themselves. While the wrong components may physically fit, the tolerances, design strain, or other parameters may sufficiently differ and yield unnecessarily low pressure failures or allow overpressure conditions to continue.
Consequences of Failure
Typically, once a disc fails it cannot be reset and must be replaced instead. This design requirement is based on the reasoning that to maintain safe operations, the cause of the overpressure condition should be found. The equipment involved and the surrounding equipment and structures should also be inspected before reuse.
Specialized Uses
Specialized uses include those designed for tanks in transit, such as by train or truck. The movement of liquid inside the vessel requires the rupture disc to be non-reactive with any of the components within the liquid. Hazardous materials may require a second rupture disc that fails at a higher pressure to contain the material despite the overpressure condition.