Fire on a valve of a hydrogen pipe network

At a chemical processing plant, a release of pressurised hydrogen gas resulted in an explosion and fire injuring lightly three workers and causing damage to plant.
The incident occurred during the recommissioning of equipment after routine scheduled maintenance.
The release was caused by the failure of a butterfly valve under a hydrogen of approximately 2000 kPa (20 bar), due probably to wrongly installed bearing during the maintenance.
The event had the potential to cause a more significant adverse effect.

The INITIATING CAUSE was the release of hydrogen caused by the failure of a valve.
The bearing bush bolts of the butterfly valve may not have been correctly installed at the time of overhaul resulting in separation of valve bearing bush.

The local authorities identified the following key issues:
(1) High pressure valves must be quality checked for correct assembly post maintenance overhauls.
(2) Effective systems and processes that ensure quality assurance must be used for the overhaul and testing of the valves to prevent failure of such valves.
(3) The maintenance of the equipment involved in hydrogen usage must comply with Original Equipment Manufacturer (OEM) specifications.

The ROOT CAUSE may then be identified in shortcomings in the execution of the maintenance. Nevertheless, a component may lay in material defects.

bearing ,valve

Event happed at the re-start of operations after scheduled maintenance

Three injured workers: two were recommissioning the equipment, and a third was a store worker approximately at 40 m from the location of the release. The injured workers did not require hospitalisation.

The local authorities issued the following recommendations. All Site Senior Executives should:
(1) Remember that hydrogen is considerably more hazardous than liquid petroleum gas (LPG), as it possesses a wider explosives range, and the ignition energy is approximately 13 times lower than that of the LPG. Further, the low viscosity and small size of a hydrogen molecule create the potential for gradual dispersion through the atomic matrix of solid metal, such as pipework, leading to additional challenges in containing hydrogen.
(2) Employ highly sensitive and specialised detection method, as detecting hydrogen gas leaks can present difficulties, particularly due to its tendency to disperse rapidly.
(3) Refer to OEM specifications to ensure work methods and testing procedures are suitable for application, when working on a hydrogen equipment.
(4) Ensure suitable trained personnel are engaged in maintenance and quality assurance.

[Note of HIAD Validator: it is unclear if these recommendations were triggered by safety-shortcoming findings specific to this event, or if they are general recommendations issued in all cases]