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Incident report: vent stack flame on world's first LH2 carrier
An incorrectly fitted solenoid valve on liquified hydrogen (LH2) carrier Suiso Frontier caused a brief flare from a gas combustion unit vent stack on the vessel’s maiden voyage, according to an Australian Transport Safety Bureau (ATSB) report
The Australian government safety body’s incident report on Suiso Frontier’s maiden voyage said a worker on board the ship saw a yellow gas flame "briefly propagate from the gas combustion unit’s (GCU) vent stack on the ship’s deck. There was no subsequent fire or explosion, and no injuries or damage were reported".
The 116-m LH2-carrying vessel was docked at Australia’s Port of Hastings, Victoria when the incident occurred on 20 January 2022, according to the report. The vessel had loaded additional LH2 on board the day prior to the incident.
The ATSB report found the GCU’s air fan discharge damper actuators – which regulate the flow of air into the GCU – "were fitted with direct current electrical solenoid valves, which were incompatible with the 230-V alternating current supply from the GCU control system".
Because venting cargo is restricted, a gas combustion unit offers a means of controlling tank pressure and temperature when the boil-off gas poses safety risks beyond the tank’s design conditions.
“During roughly 400 hours of service prior to the occurrence, the solenoid valves were subjected to conditions for which they were not designed,” ATSB chief commissioner Angus Mitchell said in his findings.
The liquified hydrogen cargo on board the vessel, which was built as a prototype to trial and assess transporting LH2 by sea, is highly flammable. As US space agency NASA discussed in reviewing its early trials of the fuel for its missions, "even small amounts of liquid hydrogen can be explosive when combined with air, and only a small amount of energy is required to ignite it. Both its explosiveness and the extremely low temperatures involved make handling it safely a challenge".
The report said that in addition to the incorrect solenoid valve being fitted, the ATSB found the gas combustion unit was not equipped to detect the failure of the valve, nor the subsequent closing of the damper.
“When one of these solenoid valves failed, the fan discharge damper it was operating closed. Consequently, the temperature of the gas combustion unit increased, eventually resulting in the discharge of flame from the unit’s vent stack. Automated safety controls intended to detect a malfunction to prevent such an incident were not effective,” Mr Mitchell said.
In response to the incident, the manufacturer of the gas combustion unit, Saacke, fitted limit switches on each air fan discharge damper to monitor damper position and programmed the system’s control logic to stop the unit if a fault is detected.
“The ATSB’s investigation highlights the importance of ensuring automated shipboard operating systems are equipped with safety controls to prevent hazardous consequences in the event of a malfunction,” Mr Mitchell said.
“The incident also shows the importance of stringent manufacturer quality controls to ensure correct system components are specified and fitted to equipment.”
Earlier this week, UK design and engineering consultancy Houlder conducted a fuel and propulsion feasibility study and concept structural design work on a 20,000-m3 liquid hydrogen carrier for oil major Shell’s International Trading and Shipping Co.
Shell supported the development of Suiso Frontier by Kawasaki Heavy Industries through Japan’s CO2-free Hydrogen Energy Supply-Chain Research Association.
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