7 Reasons Not To Use A Knife-Blade Style Reverse Acting Rupture Disk Design

1. The design relies on razor sharp knife-blades installed in the holder outlet to cut the disk material open upon reversal. Any degradation of the knife-blades can result in reduced or no opening of the disk and limited ability to relieve the over-pressure.
2. When the assembly is installed into the piping, the knife-blades are hidden and cannot be inspected while in service. The potential of unknown corrosion of the knife-blades over-time is high. The reasoning is that modern piping designs do not vent out to the atmosphere but are internally contained, this will result in a build-up of corrosive medium leading to the corrosion of the knife blades.
3. Knife-blade designs require the explosive energy of a compressed fluid to operate correctly. Liquids do not contain this energy and therefore the design CANNOT be used on liquid service.
4. High minimum burst pressures when compared to other reverse acting designs.
5. Fragile especially in lower burst pressure ratings.
6. If damaged, the disk can burst up to 20 times higher than the marked burst pressure.
7. If installed upside-down (which is not uncommon), the disk is placed in tension, resulting in a burst pressure up to 10 times higher than the marked burst pressure.

Widely recognized that the knife blade design is now seen as having many drawbacks which can lead to dangerous situations on plant, rupture disk manufacturers have developed improved designs that address some of the safety concerns.

It’s important to note that Kr is only one element of the sum which produces the full system flow resistance and actually in most cases the disk Kr makes a minor contribution to the overall system flow resistance. Flow resistance is attributed not only to the rupture disk device but any and all pipework components, such as nozzle entrances/exits, tees, elbows, etc.

• Certified for liquid, gas, or two-phase applications
• Does not rely on the companion flange bolts to achieve correct torque load.
• Integral high strength preassembly screws ensure proper loading of the disk improving burst pressure consistency and eliminating unwanted leaks.
• Allows for removal, inspection and replacement of the complete assembly.

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