What is a rupture disc and what is its primary purpose in a fluid system?
A Rupture Disc is also known as a pressure safety disc, rupture disc, bursting disc, or burst diaphragm, is a pressure relief device that is designed to burst at a predetermined pressure and temperature. It is typically made of a thin metal disc that is clamped in a holder. When the pressure in the system exceeds the burst pressure of the disc, the disc ruptures and releases the pressure.
How does a rupture disc function to provide overpressure protection?
A rupture disc is a non-re-closing pressure relief device that protects a pressure vessel, equipment or process piping system from over-pressurization or potentially damaging vacuum conditions.
What are the main components of a rupture disc and their functions?
A rupture disc device is a non-reclosing pressure relief device that actuates upon differential pressure across the disc. It consists of two main components: the rupture disc holder which provides the pressure boundary and clamps the disc into position, and the rupture disc (the actuating element).
- Rupture disc holder: Also known as a flange assembly, this component holds the rupture disc in place and provides support, alignment, and sealing. It also creates a pressure boundary and clamps the disc into position.
- Rupture disc: Also known as the actuating element, the rupture disc breaks open when pressure builds up, releasing pressure and preventing an explosion. The burst pressure of the rupture disc is determined by the differential pressure across the disc.
What materials are typically used in the construction of rupture discs to ensure reliability and performance?
Standard materials: aluminum, nickel alloy 200, Inconel® alloy 600, Inconel® alloy 625, Monel® alloy 400, niobium, 316L ss, Hastelloy® alloy C-276, tantalum, titanium, Hastelloy® alloy C-22.
- Metals: Carbon steel, stainless steel, aluminum, nickel alloy 200, Inconel alloy 600, Monel alloy 400, 316L ss, Hastelloy alloy C-276, tantalum, titanium, Hastelloy alloy C-22, Inconel alloy 625, and niobium
- Plastics: Can be used in one or more layers
- Graphite: Can be used to make corrosion resistant rupture discs
How do pressure and temperature ratings affect the selection and performance of rupture discs?
Temperature: Rupture discs are sensitive to temperature and their bursting point is affected by changes in temperature. As the temperature increases, the burst pressure of the disc decreases, and as the temperature decreases, the burst pressure increases. The effect varies depending on the material and design of the disc. When manufacturers qualify a disc lot, they use a specified temperature given to them by the customer as the manufacturing specification for the test temperature. If the stable temperature of the disc at the time of rupture is not selected properly, the disc may not burst at its marked burst pressure.
Pressure: When selecting a rupture disc, you can consider the pressure the device must withstand without opening in the opposite direction to normal isolation
What are the primary applications of rupture discs in various industries?
Rupture discs are non-reclosing pressure relief devices that are used in many industries to protect pressure-containing components from overpressure and vacuum. They are often used in industries such as chemical, pharmaceutical, oil and gas, and food and beverage. Here are some of the primary applications of rupture discs in these industries:
- Chemical manufacturing: Rupture discs prevent equipment failure.
- Pharmaceuticals: Rupture discs maintain process integrity, especially in fermenters and bioreactors where cooling systems can fail and cause over-pressurization.
- Oil and gas: Rupture discs help prevent potential disasters.
- Pressure relief valve protection: Rupture discs can be installed upstream of the valve to isolate it from process media and act as a leak-tight seal. They can also be installed on the outlet end of the valve to protect it from atmospheric fluids
How does a rupture disc differ from other types of pressure relief devices, such as safety valves?
Rupture discs and safety valves are both pressure relief devices that are installed in the same place in a process to prevent pressure from building up and causing problems. However, they differ in a few ways:
- Reclosing: Safety valves reseat after the pressure drops, but rupture discs do not.
- Moving parts: Safety valves have moving parts, but rupture discs do not.
- Size: Rupture discs are usually smaller than safety valves.
- Cost: Rupture discs are often more cost-effective than safety valves because they are less complex and require less maintenance.
What are the common causes of rupture disc failures and how can they be prevented?
Abrasive media can wear rupture disc material away, reducing the burst pressure quickly. Placing rupture disc in areas protected from impingement, selecting thicker rupture disc designs and changing rupture disc more frequently will help to prevent premature disc failures.
Due to their very nature, rupture discs are fragile and can easily break if removed to poke the debris from the duct stub. This results from a combination of wrong rupture-disc-selection and poor piping-design. Many process materials are also prone to building up and solidifying on internal surfaces.
This can create a problem for the typical vessel discharge port that may become partially or completely blocked, thereby resulting in potentially higher than expected rupture-disc burst pressures and restricted discharge flow.
There are also specific places and industries where you shouldn’t use rupture discs, such as those that tend to have significant pressure fluctuations. Highly corrosive atmospheres can also significantly damage the materials that the discs are made out
What are the common maintenance and inspection procedures for rupture discs to ensure their functionality?
If a rupture disc is installed to isolate the relief valve from a particularly corrosive process, and the integrity of the rupture disc is known to be good, the interval between inspections may be increased. The rupture disc integrity must be verified via checks for pressure between the rupture disc and relief valve.
Confirm the marked disc set pressure is equal to or less than the vessel MAWP.
Look at the marked disc temperature and confirm it has been specified so that it is the temperature of the disc when it is expected to burst, and not the vessel design temperature.
How can rupture discs be tested to ensure they are working properly and within specifications?
The ASME Code defines 3 methods of acceptance testing for rupture discs. The most common method requires that at least two discs from the lot be burst tested at the specified disc temperature. The results of these tests must fall within the rupture tolerance.
What safety considerations should be taken into account when installing and operating rupture discs?
The discharge piping for relief and safety valves and rupture discs should have a minimum of fittings and bends. There should be minimum loading on the valve, and piping should be used with adequate supports and expansion joints. Suitable drains should be used to prevent liquid accumulation in the piping and valves.
How does the installation position and orientation of a rupture disc impact its performance and effectiveness?
The selection of an appropriate single-use isolation device depends upon more than just the desired burst pressure. An engineer must also determine system requirements for the following:
Maximum Isolation Pressure – The required pressure the device must withstand without opening in the normal direction of isolation. When an engineer determines the pressure and validates a design, consideration must be given to the maximum pressure rise rate, the number of cycles, and the length of time the device may be subject to this pressure.
Maximum Downstream Pressure – The pressure the device must withstand without opening in the direction opposite to normal isolation. When an engineer determines the pressure and validates a design, consideration must be given to the maximum pressure rise rate, the number of cycles, and the length of time the device may be subject to this pressure. Based on the design of the shearing element, the rating for isolation pressure and downstream pressure may be significantly different.
Flow Capacity – The amount of flow that must pass through the device after it is activated or open.