A technician accidentally loosened critical bolts holding a fitting to the top of an H2 tank, which caused a large hydrogen leak in the dewar. The fitting contained various instruments, and upon loosening the third bolt, H2 gas exited through an opening in the seal. The Viton or neoprene O-ring was blown out of its groove and was immediately frozen, making it impossible to reseal the fitting cover. The area was evacuated, the dewar was vented and the gasket was replaced. The ullage space was not purged with helium gas during the gasket replacement, which may have been responsible for small leaks which developed during the transfer.
The fitting containing the instruments was mounted on a flange, which was in turn secured to another flange. Long bolts and short bolts were used to retain the components. The bolt heads were identical and not identified, hence leading to the error in loosening the wrong bolts. The leaks that occurred after the gasket was replaced were probably due to moisture condensation on related vent valve components.
- Hydrogen Storage Equipment
Proper bolt identification can prevent similar occurrences in the future. This can be achieved by simply painting the critical bolt heads a certain color (or by purchasing bolts with painted bolt heads). An explanation form should then be clearly posted, which indicates which bolts are critical, and which aren't. This information should then be disseminated to all of the relevant technicians.