Pressure relief is an essential element of both gaseous and liquid hydrogen storage systems to guard against excessive pressure that could result in catastrophic failure of the system. A burst disk (or rupture disk) is a common pressure-relief device that is designed to break at a predetermined pressure. It is a one-time-use device that is either destroyed or permanently deformed in response to over pressurization and then must be replaced. A burst disk is sometimes used as a backup to a resettable pressure-relief device such as a relief valve.
The majority of the pressure-related safety event records in the H2Incidents.org database involve burst disks. The key lessons learned from these safety events are summarized below. These lessons learned are followed by brief accounts of the 12 burst disk safety event records in the database, with links provided to each record.
Burst disks can provide valuable pressure protection and can be used to meet code requirements. However, care should be taken to properly install them for safe operation. An improperly installed or designed burst disk system can result in a greater risk than the hazard for which it was installed. A significant consideration is that burst disks are non-reclosing, so their rupture will usually lead to the release of the entire system contents. Some of the most serious incidents within the hydrogen industry have been associated with pressure-relief devices. Such devices should only be installed when necessary to prevent a serious overpressure hazard. Burst disks are sometimes required by code, but other times are specifically excluded from installation (e.g., where the premature release of a toxic or flammable gas might be a higher risk than a vessel failure).
Burst disks prematurely failed below their rated pressure. These failures may have been prevented with closer attention to the design and maintenance of the burst disks and their integration into the hydrogen storage and piping systems. Burst disks used in a hydrogen system should be manufactured from a material compatible with hydrogen service and sized and pressure-rated to the system they are protecting. Material selection is important to reduce hydrogen embrittlement failures. Currently there is no specific industry guidance related to burst disk material, however, materials with improved resistance to degradation when exposed to hydrogen should be used. The pressure rating of the burst disk should be sufficiently above the intended hydrogen system operating pressure to prevent premature failure. Since burst pressure is affected by temperature, the expected range of environmental conditions should be considered in the burst disk selection process. In some of the incidents, a recommendation was made to eliminate burst disks from the system and instead rely on other relief devices (e.g., spring-activated pressure-relief devices that close after the pressure is reduced below the set relieving pressure).
Burst disk failed to protect from over pressurization or activated at a higher pressure than the design pressure. The burst disk must be rated and installed correctly for its application. In one case, multiple burst disks were installed in a holder where only one was supposed to be used. Since a burst disk is activated by differential pressure, back pressure against the burst disk discharge will cause it to burst at a higher pressure than intended.
Burst disk vent piping failed to maintain integrity. Some of the vent systems were not adequately restrained and could not accommodate the expected maximum flow and pressure conditions after a burst disk ruptured. Some involved failures from multiple pressure-relief events. Vent system piping must be adequately secured to withstand the high thrust loading from burst disk ruptures.
Burst disk vent stack discharge was inadequate and/or poorly located. It is recommended that a hazard analysis be performed to assure that all effluent vent operations are discharged to a safe location that is remote from people and property, since discharge fires are common. Particular attention should be paid to avoiding water intrusion into the vent piping, including protection from water sprays during emergency response situations. In one incident, water freezing on a burst disk surface caused it to fail. The ideal vent stack would discharge outside, high above the ground, and far away from personnel and surrounding equipment, and it would be protected from water intrusion.
Burst disk and associated vent system maintenance and inspection were inadequate. Burst disks have finite lifetimes, and routine replacement should be planned. Since burst disks are susceptible to failure from cyclic loading, systems with higher cyclic loading frequencies should consider higher replacement frequencies. Frequent inspection of the hydrogen system would likely have prevented some failures, since deteriorated or missing components, especially those exposed to weather conditions, were found in post-incident inspections.
Burst disks frequently fail during fill operations. Some tube trailer incidents had burst disk failures during filling operations. Operators should always be attentive to the fill operation and make sure that it takes place in a safe location. Personnel near the fill operation should be informed, and suspension of nearby activities during the fill is recommended.
Twelve applicable burst-disk incidents from the H2Incidents.org database are highlighted below in chronological order of occurrence date, from the earliest to the most recent.
A burst disk ruptured as designed during a liquid hydrogen transfer from a hydrogen delivery vehicle when an over-pressurization occurred due to an operator error. The lessons learned are 1) that a burst disk that is properly designed into a hydrogen system will provide protection from over-pressurization, and 2) that refueling operations must be conducted carefully by attentive operators.
For unspecified reasons, a burst disk on a large liquid hydrogen tank blew and exhausted cold gaseous hydrogen through the vent stack. Firefighters responding to the hydrogen release sprayed water on the tank and vent stack. Since the vent stack was open, some water entered and froze, plugging the stack and sealing off the only hydrogen pressure-relief exit path. In time, the tank warmed, became over-pressurized, and ruptured. In this case, the burst disk may have functioned properly as designed, but the vent stack design and the emergency response actions did not allow the vent stack to function. The lessons learned are 1) to post signage indicating that no water is to be sprayed on the vent stack, and 2) to install a backup pressure-relief vent stack in case the main vent stack fails.
A plugged outlet line on a continuous-feed autoclave system caused an over-pressurization, which resulted in the burst disk performing its function and discharging the autoclave contents, including hydrogen gas, through the vent pipe. The vent pipe exhausted the hydrogen gas mixture into the autoclave cell, where it ignited in a fireball and then ignited nearby combustibles. The hydrogen gas and the autoclave system were turned off immediately, but fire continued to burn in the autoclave cell. The fire heated a small compressed gas cylinder (lecture bottle) until it exploded with enough force to cause an estimated $55,000 in facility structural damage and burns to one employee. One lesson learned is that a thorough hazard analysis should be performed prior to system operation to determine how to safely discharge the effluent from a burst disk failure.
This incident involved a CO2 cylinder that failed catastrophically from over-pressurization. The CO2 system failure created a projectile that physically damaged a nearby hydrogen storage unit, causing a fire. Post-event review found three burst disks in the disk holder where there should have been only one. An important lesson learned is that burst disks should be properly installed.
While being filled with hydrogen, a small gas cylinder was over-pressurized due to a faulty pressure transducer and failed catastrophically. The fill system had a burst disk that failed to protect the cylinder because it was rated at too high a pressure. The key lesson learned is that a burst disk should be rated properly for the components that it is designed to protect.
A hydrogen explosion occurred at a plant, damaging a wall adjacent to the hydrogen storage assembly. The investigation revealed that the explosion was the consequence of the failure of a burst disk at a pressure much lower than its rating. The burst disk was damaged by water entering the vent line, freezing, and expanding against the burst disk.
A malfunctioning valve at the discharge of a hydrogen compressor caused the pressure in the piping between the hydrogen bottle and the compressor to exceed the maximum allowed pressure. The associated burst disk ruptured as designed to relieve pressure and sent hydrogen through the vent piping, where it ignited at the vent tube exit. After a short time, the hydrogen fire self-extinguished without further incident. The key lesson learned was that the vent stack design should be re-evaluated. The vent stack design was reviewed, and as an additional safety measure to protect nearby people and property, the vent stack height was extended.
