Integrated Rupture Disk Assemblies for OEM Hydraulic & Pneumatic Equipment
For more than 85 years, rupture disks have served as an effective passive safety mechanism to protect against overpressure or potentially damaging vacuum conditions. The disk, which is a one-time-use membrane made of various metals, including exotic alloys, is designed to activate within milliseconds when a pre-determined differential pressure is achieved.
As equipment reliability in operation is essential for its owner, high integrity from the pressure relief technology used to protect low- and high-pressure OEM systems is crucial.
By Jeff Elliott
In an effort to ensure high integrity pressure relief technology, OEMs are increasingly turning to integrated rupture disk assemblies with all components combined by the manufacturer. As opposed to loose rupture disk and holder devices that leave much to chance, these assemblies are being tailored to the application, can be miniaturized, and utilize a wide range of standard and exotic materials. This approach ensures the rupture disk device performs as expected, and ultimately enhance equipment safety, reliability, and longevity while simplifying installation and replacement.
Separate Components Versus Integrated Assemblies
Traditionally, rupture disks are standalone components that are combined with the manufacturer's separate holder device at the point of use. The user’s installation of the application contribute significantly to the function of the rupture disk device. There is a delicate balance between the rupture disk membrane, its supporting holder, and the flanged, threaded, or other fastening arrangement used to locate the safety device on the protected equipment. If installed improperly, the rupture disk may not burst at the expected set pressure. For this reason, an integrated rupture disk assembly is often a more reliable application.
The no assembly required, integrated units are commonly certified as devices that perform at the desired set pressure. Consisting of a rupture disk and the housing, a disk assembly’s one-piece design allows for easier installation and quick removal, when activated. The rupture disk and holder are combined by: welding, bolting, tube stub, adhesive bonding, or crimping, based on the application conditions and leak tightness requirements. It is also custom engineered to work with the user's desired interface for the pressurized equipment. The devices are typically threaded, flanged, or configured for industry specific connections such as: CF/KF/Biotech/VCR couplings.
Integrated assemblies also prevent personnel from utilizing unsafe or jury-rigged solutions to replace an activated rupture disk. The physical characteristics of increasingly miniaturized rupture disks, as small as 1/8”, can make it challenging for personnel to pick up the disk and place it into a separate holder.
Figure 1. Clamped, threaded, torqued application interfaces. OEMs utilize threading and several other connection types to attach the rupture disk assembly to the application.
Hydraulic and Pneumatic Applications Benefit
An integrated assembly is ideal for numerous hydraulic, pneumatic and other low, medium and high-pressure applications including: pumps, piston & bladder accumulators, engines, pressure vessels and piping. For example, the oil and gas industry utilizes rupture disks on triplex pumps for many field applications such as oil extraction and well servicing operations. Triplex pumps are positive-displacement pumps configured with three plungers. Commonly referred to as ‘mud pumps,’ the devices can typically handle a wide range of fluid types, including: corrosive fluids, abrasive fluids, and slurries containing relatively large particulates. The pressures the pump must endure depends on the depth of the drilling hole and the resistance of flushing fluid, as well as the nature of the conveying drilling fluid. Typically, application specific hydraulic operating pressures are in the 5,000 to 20,000 psi range. “A three-plunger pump is continuously cycling, so the disk must be able to withstand high pressures with 1,000,000 pressure cycles or more,” explained Geof Brazier, Managing Director of BS&B Safety Systems Custom Engineered Products Division.
In most industries that depend on hydraulic systems to store energy and smooth out pulsations, standard system components, like accumulators, require rupture disks. By definition, accumulators hold hydraulic fluid under pressure. If the pressure spikes too high, there is a risk that without a rupture disk the system, or even accumulator, could experience a catastrophic failure.
Both medical devices and fire rescue breathing equipment also depend on integrated application specific rupture disk solutions for critical life safety reliability. Medical devices in particular must often be very compact and low profile. In aerospace, tailoring integrated rupture disk applications for use with lightweight, compact materials, like titanium and aluminum, is also important, since it takes more energy to get heavier vehicles off the ground.
Figure 2. BS&S miniature rupture disk technology. The physical characteristics of increasingly miniaturized rupture disks as small as 1/8” can make it challenging for personnel to pick up a disk and place it into a separate holder.
Integrated Assemblies – Rupture Disk Design
According to Brazier, the most important design considerations for rupture disk devices are: having the correct operating pressure, knowing the temperature information, and being aware of the expected service life; this is often expressed as the number of cycles the device is expected to endure during its lifetime. Since pressure and cycling varies depending on the application, each requires a specific engineering solution. “Coming up with a good, high reliability, cost-effective, and application specific solution for an OEM involves selecting the right disk technology, the correct interface (weld, screw threads, compression fittings, single machined part) and the right options, as dictated by the codes and standards.” As user material selection can also determine the longevity of rupture disks, the devices can be manufactured from a range of metals and alloys such as: stainless steel, nickel, Monel, Inconel, and Hastelloy.
For some industries, it can be important for rupture disks to have a miniaturized reverse buckling capability in both standard and exotic materials. In almost all cases, ‘reverse buckling’ rupture disks are utilized because they outperform the alternatives with respect to service life. “Where economics is the driver, reverse buckling disks are typically made from materials such as nickel, aluminum, and stainless steel. Where aggressive conditions are required, more exotic materials like Monel, Inconel, Hastelloy, Titanium and even Tantalum can be used,” said Brazier. In almost all cases, 'reverse buckling' rupture disks are utilized because they outperform the alternatives with respect to service life.
Reverse Buckling Disks
In a reverse buckling design, the dome of the rupture disk is inverted toward the pressure source. Burst pressure is accurately controlled by a combination of material properties and the shape of the domed structure. By loading the reverse buckling disk in compression, it can resist operating pressures up to 95% of minimum burst pressure, even under pressure cycling or pulsating conditions. The result is greater longevity, accuracy, and reliability over time.
While the process industry has relied on reverse buckling disks for decades, new advancements in the technology have made it possible for OEMs to obtain miniature disks. With companies, such as BS&B, creating disks with as small as 1/8” burst diameter, more applications can rely on the disks for equipment safety. Small nominal size rupture disks are sensitive to the detailed characteristics of the orifice through which they burst. This requires strict control of normal variations in the disk holder. “With small size pressure relief devices, the influence of every feature of both the rupture disk and its holder is amplified,” explained Brazier. “With the correct design of the holder and the correct rupture disk selection, a user will avoid premature failure.”
Figure 3. Integrated rupture disk assembly. With the availability of integrated, miniaturized rupture disk solutions tailored to the application in a variety of standard and exotic materials, OEMs can significantly enhance equipment safety, compliance, and reliability even in extreme work conditions.
While OEMs have long relied on rupture disks in their hydraulic and pneumatic equipment, high-pressure, high-cycling environments have been particularly challenging. Fortunately, with the availability of integrated, miniaturized rupture disk solutions tailored to the application in a variety of standard and exotic materials, OEMs can significantly enhance equipment safety, compliance, and reliability even in extreme work conditions.
About the Author
Jeff Elliott is a Torrance, California-based technical writer. He has researched and written about industrial technologies and issues for the past 15 years. For more information on this topic, contact BS&B Safety at firstname.lastname@example.org.