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Understanding why rupture disks fail can help ensure that they don't
Even with the best process design, the unexpected can happen. Anticipating this, rupture disks are often installed as the last line of defense against the over-pressurization of equipment used for the manufacture, transport and storage of many types of chemicals, petrochemicals, medicines, plastics, powders, food and beverages. When handled and installed properly, rupture disks are a safe and economical means to protect people, equipment and processes.
When they work well, rupture disks can provide safety against catastrophic equipment failure and personal injury from unexpected events, such as explosions, control failures, power outages, runaway reactions, external fires and blocked valves. (For more on general safety issues, see Part 1 of this report, p. 30.) Quite often when a disk does not work as expected, the cause can be extremely frustrating to diagnose because the ruptured disk relieves the pressure condition that caused the rupture, and the disk's energy release can erase clues that can help identify the root cause.
Here we examine the more common causes for disk ruptures, based on our troubleshooting experience. Consideration of these causes can help identify and eliminate potential problems that could lead to a failure.
Rupture disk design
In its simplest form, a rupture disk is nothing more than a formed, thin metal membrane designed to burst at a certain pressure and temperature in order to prevent over-pressurization of the attached vessel. The disks can be machined, scored, or injection molded. Some disks act in tension like a balloon or a hammock, while others have a reverse-buckling design that is compression loaded like an arched bridge.
Regardless of the design, rupture disks cannot be made with an added "safety factor", meaning that a rupture disk designated to burst at 100 psi must burst at 100 psi (within the agreed upon tolerance), and not at 1.5 or 2 times the burst pressure. Because of this exacting burst-pressure designation, a good understanding of the physical issues and the technology surrounding rupture disks is needed to prevent field failures. Variations in rupture-disk designs and holders can also contribute to improper installations that cause failures.
What is a rupture disk failure? Before moving on to troubleshooting, a definition of a rupture disk...