N2 Enters the High Pressure Tank
[NOTE: The system involved in this neear miss are not completely clear]The system involved appears to consist in an electrolyzer, a compressor and high pressure tanks, used to refuel hydrogen buses. A nitrogen line used for purging was apparently left open so that N2 was flowing into the hydrogen tank svia the compressor.Because only oxygen is monitored, and not nitrogen, the mishap was discovered only on high nitrogen consumption and anomalous system pressures.
Event Date
November 30, 2012
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
Valve not properly closed after rinsing the lines with N2 and H2.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
flowmeter, tank
Storage/Process Medium
Location Type
Location description
Unknown
Operational Condition
Pre-event Summary
The technician was called because of a leaking flow meter on an electrolyzer (empty of hydrogen).The technician rinsed the lines with N2 and H2, operating the valves manually. After rinsing with N2 he forgot to close the valve. Production was started without errors.The next day the service team noticed that the N2 consumption was too high. The technician thought that the N2 safety valve was reacting too early. So he reduced the N2 pressure to 8 bar (normal N2 consumption).After two days, the onsite technician noticed that the safety valve was faulty. To replace it, the electrolyzer has to be rinsed in N2. Firstly the valve was not right but the technician managed to fix it.Tuesday: High pressure tanks were rinsed. After refueling the first fuel bus it looks OK. But once the second bus had been refueled the N2 level was higher than the H2 level.Wednesday: technicians cleaned tanks to a pressure of 5 bars Thursday: technicians clean tanks twice (load with 70 - 100 bars and clean until 5 bars) Friday: technician cleans tanks, installs a new trailer. Tests refueling and checks the vehicles.
Environmental Damage
70000
Currency
Lessons Learned
Lessons Learned
Unknown
Event Nature
Emergency Action
Rinsing the tanks with N2.
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Report provided but confidential