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).
Setting: Hydrogen Delivery Vehicle/Tube Trailer
Description: 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.
Lessons Learned: The lessons learned are:
Setting: Chemical Plant
Description: 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.
Lessons Learned:
Setting: Laboratory
Description: A 2000-psia-rated gas cylinder (nominal size 10"x1 1/2") was being filled with hydrogen to a target pressure of 1500 psia. The cylinder suffered a failure at an indicated pressure of 1500 psia during filling. Investigation of the failure subsequently revealed that a faulty digital readout had allowed the cylinder to be over-pressurized. There were no safety consequences due to the failure and no damage to the facility or equipment. The cylinder was being filled in a test vault that was specially designed for the high-pressure burst testing of pressure vessels and components. While no over-pressure cylinders were released from the laboratory for use, this incident is being reported to address the potential and subsequent lessons learned...
Lessons Learned: This occurrence underscores the importance of completing a hazard analysis for each different process. Non-safety-related systems or equipment may be used for purposes other than their primary purpose so long as potential hazards are identified and engineering and administrative controls are applied to eliminate or minimize them...
Setting: Laboratory
Description: A fire occurred in a continuous-feed autoclave system (fixed-catalyst-bed tubular reactor) when the rupture disc released, discharging hot oil, oil distillates, and hydrogen gas out a vent pipe into the autoclave cell. The flammable mixture was discharged directly into the cell because there was no system in place to catch or remotely exhaust the autoclave contents...
Lessons Learned: The reactor outlet line was plugged with viscous oil, which resulted in over-pressurization of the system. If the plug had been in the feed line, the rupture disc on the reactor would never have been over-pressurized. If the staff had added a second rupture disc near the pump outlet to relieve pressure before the reactor rupture disc, with a check valve in between the two, the release might have been avoided. This design change was incorporated into the system rebuild. The fixed-catalyst-bed tubular reactor system should have been reviewed and approved by health and safety, facilities engineering, or building management staff...
Setting: Power Plant
Description: 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.
Lessons Learned: An important lesson learned is that burst disks should be properly installed.
Setting: Power Plant
Description: No description given.
Lessons Learned: The uncontrolled release of hydrogen occurred as a result of the rupture of the No. 6 hydrogen storage tube’s burst disc. This disc failed in response to being overloaded by mechanical stresses developed as water expanded and formed ice while in direct contact with the burst disc. It was the degraded condition of the vent cap (defective equipment) that enabled water to access the burst disc.
As a corrective action, eliminate burst discs from hydrogen storage assembly. Redesign venting system for the pressure relief valves to prevent or inhibit moisture build up and allow moisture drainage.
The investigation uncovered two instances where the supplier was in possession of information ("safety data") that, if successfully conveyed to plant management and subsequently acted upon, would have prevented or reduced the chance of occurrence of the subject incident. Specifically, the hydrogen supplier found ice in a vent pipe, and was aware that the vent caps were cracked (recall the cracks were painted). Had a requirement existed for this information to be communicated to the plant, then plant management would have had the opportunity to evaluate and potentially influence the supplier's maintenance and operations program.As a corrective action, contract documents for the hydrogen and nitrogen supplies will be modified to stipulate the following:
Suppliers of potentially hazardous equipment will provide plant management, for acceptance purposes, with written documentation describing the supplier’s preventive maintenance program.
The supplier shall provide the plant representative with a copy of a preventive maintenance report upon the completion of each PM check performed by the supplier. The supplier shall expeditiously rectify any identified deficiency.
Plant management will recommend to the Manager of Corporate Safety and Health that the above contract document modifications are implemented corporate wide.
Setting: Compressor Room, Hydrogen Storage/Use Facility
Description: No description given.
Lessons Learned: The following corrective actions have been taken:
Setting: Hydrogen Delivery Vehicle/Tube Trailer, Power Plant
Description: A premature burst disk failure was the likely cause of an explosion that occurred while a hydrogen delivery vehicle was unloading compressed hydrogen gas used to cool the steam generators at a power plant. The burst disk had been repaired by the vendor six months earlier.
Lessons Learned: One key lesson learned is to consider the use of spring-style pressure-relief valves instead of burst disks.
Setting: Commercial Facility
Description: An outside liquid hydrogen storage vessel slowly heated over time, causing an over-pressurization that was relieved by a burst disk rupturing with a loud noise. The vessel vented the hydrogen contents to the associated vent stack as designed without further incident.
Lessons Learned: Hydrogen safety training should be provided to local emergency responders, liquid hydrogen installations should be inspected by facility personnel on a frequent basis, industrial gas companies that design, install, and maintain liquid hydrogen installations should follow the guidelines set in the Compressed Gas Association (CGA) publications, and burst disks are highly sensitive to any form of back pressure.
Setting: Hydrogen Delivery Vehicle/Tube Trailer
Description: 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.
Lessons Learned: The lessons learned are:
Setting: Government Facility, Hydrogen Delivery Vehicle/Tube Trailer, Hydrogen Storage/Use Facility
Description: No description given.
Lessons Learned:
Setting: Government Facility, Hydrogen Delivery Vehicle/Tube Trailer
Description: Two burst disks associated with two tubes on a hydrogen tube trailer failed prematurely while being filled, releasing hydrogen to the associated vent line. After the first burst disk failure occurred, the vent line was not sufficiently attached to take the thrust force from the hydrogen release and bent outward violently, damaging some adjacent vent system components. When the damaged portion of the tube bank was isolated, filling operations resumed with the unaffected portion of the tube bank until the second burst disk failed. The investigation determined that the failed burst disks were fabricated from nickel, a material not recommended for hydrogen service. Although the vent line was procured from a commercial source, it was not of sufficient strength to contain the hydrogen gas pressure relief. Subsequently, corrective action was taken to increase the vent line diameter and to add bracing.
Lessons Learned: Lessons learned include making sure that the burst disk material is suitable for hydrogen service, and that vent system components are properly sized and secured to take the thrust pressure from burst disk activations.
Setting: Hydrogen Delivery Vehicle/Tube Trailer, Hydrogen Storage/Use Facility
Description: A burst disk associated with a tube on a hydrogen tube trailer failed below design pressure during a fill operation and vented hydrogen through a vent tube. The hydrogen ignited at the vent tube exit. The emergency responders cooled the tube trailer with water and closed the isolation valves to extinguish the fire without further incident. A mechanic working under the tube trailer was slightly injured when the loud noise from the burst disk rupture caused him to bump into the trailer several times while quickly exiting the area.
Lessons Learned: Specific response drills/exercises need to be conducted yearly. In this case, all safety systems worked as they should and outside emergency responders were not needed.
Performing other tasks while filling hydrogen tube trailers, such as mechanic work, should be avoided. Most premature failures of hydrogen tube trailer PRD burst discs occur during the fill process.
Grounding, as was done in the incident, should always be done during hydrogen filling. However, even when the fill vessel is grounded, it is not unusual for a hydrogen release to immediately ignite.
The facility safety deluge water system should be checked periodically for coverage. In this case, a water cannon was a little off target from the last time it was operated and has now be repositioned and stabilized to ensure that it does not move in the future.
Emergency responders assumed that adjacent tube trailers were heating up from single-cylinder vent flare as a 300°F (149°C) reading was obtained with a thermal device. This slightly delayed the closing of the cylinder isolation valves on the tube trailer. After-incident investigation found no paint discolored or burnt, so the temperature taken by the emergency responders was likely near the flaming vent discharge point.
Securing hydrogen fill valve(s) at the back of the tube trailer was not dependent on the temperature at the vent stack, as this area was covered by deluge nozzles and located 40 feet (12.2 meters) away from the vent stack.
Media involvement and resulting speculation can portray a situation as being much worse than it actually is.
Some of the key lessons learned from these safety events are summarized below.
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).
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.
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.
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 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
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.
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