Leak from a valve in a HRS

A leak occurred at the compression unit of the refuelling station.
The employees had just initiated the normal procedure of starting up the hydrogen production equipment, and opened the three shut-off valves, one for each of the three storage vessels. At this point, the gas leak detection system located above the valve unit room detected a hydrogen concentration of 1 vol% or more and issued a high-level alarm.
This triggered the activation of the safety devices which automatically shut down the hydrogen production equipment and cutting off the power supply to the compressed hydrogen station.
The leak location was identified on one of the three a shut-off valve.

The INITIATING CAUSE of the leak was the deterioration of a rubber o-ring.

The investigation revealed that the hydrogen was leaking from the O-ring used in the maintenance plug of the shutoff valve. The O-ring was degraded due to the high temperature of the hydrogen passing through the shutoff valve, 40°C higher than the outside temperature.
(1) The O-ring used in the maintenance plug of the shutoff valve was an O-ring developed for low-temperature, high-pressure hydrogen, intended for pre-cooling. The high-temperature side was designed to withstand temperatures of 85°C or less.
(2) Tests revealed that when the O-ring is exposed to high-pressure hydrogen at room temperature for a long period of time, the plasticizer components added to the ring are released, causing the ring to lose its elasticity and not return to its original shape.
(3) Similar hydrogen leaks had occurred at nearly 20 other hydrogen filling stations, and the O-ring was a regular replacement item, but this information was not communicated to the hydrogen filling station installers and operators. As a result, it is believed that continued use of the ring led to the hydrogen leak.

The ROOT CAUSE was a material design shortcoming, related to the wrong choice of the material of the O-ring for the operative vonitions of the valve.

O-ring, shut-off valve

The HRS was starting the hydrogen production, according to a standard procedure.

DESCRIPTION OF THE FACILITY
The HRS was a 70MPa refuelling station with a high-pressure gas production capacity: 29.9m3/day. A non-further specified hydrogen generator was connected in parallel to three storage vessels via shut-off valves. Three additonal shut-off valves, one for each of the three vessels,were located between the vessels and the dispenser.
Although the scheme provided by the KHK reprot does not show a compressor, it coudkl be assumed that a comressor was isnalled betwee nthe production unit and the valve (unless the the production unit was able to deliver high-pressure hydrogen to the vessels).

This is case at the border between a minor incident and a near miss. The safety systems in place worked as designed with no consequence to human or installation, except the time lost during the shut-down and the neeed to change the design.

This is a case at the border between a minor incident and a near miss. The safety systems in place worked as designed with no consequence to human or installation, except the time lost during the shut-down and the investigation.
In the period when this event occurred, many high-pressure gas equipment used at hydrogen refuelling stations were newly developed and had little performance and failure track record. This applies as well to consumables such as O-rings. Therefore, it was (an still is) critical that hydrogen station operators, installation engineers and high-pressure gas equipment manufacturers establish a system for sharing information about mishaps and other problems.

The O-rings at the leaking points and in six shutoff valves of the same specifications were replaced with other O-rings that have a proven track record of mass production and durability. There were no leaks from the shutoff valves after the O-ring replacement.

The manufacturer of the shut-off valves was instructed to promptly inform the operator if any parts were subject to replacement/modification in the future.

The collection of information on the parts subjected to (frequent) replacement was ongoing, according to which corrective action will be undertaken.