ITEM
FAILURE
POSSIBLE CAUSES
SYMPTOMS
EFFECTS
END EFFECT
COMPENSA-
TIING
CRITIC-
ALITY
ACTIONS
MODES
MEASURES
F C
20.01 Loss of all valve operations Control or power failure No change in valve indication  Loss of ballasting capability Limited or no operational activities Valves may be manually operated or possibly operated from the board at the 21 ft level 1 5 Carry out immediate repairs
20.02 Reduction of operating capability Sticking valve, seal failure Slow response, unwanted slow filling or emptying of tanks Slow operation  Incorrect tanks being filled or emptied The manual block valve in the system limits such effects 4 2 Empty affected tanks and repair valve
20.03 Unintended opening and closing of valves, including inverse response Control system malfunction Valve position indicator Movement of water in or out of incorrect tanks or possibly between tanks  Unintended list or trim with reduction or loss  of stability Manual valve in system reduces effects. 5 1 Repair system immediately
Stop pumps, shut down system manually. Cease operations

FMEAs and FMECAs


Failure Mode and Effect Analysis (FMEA) and Failure Mode, Effect and Criticality Analysis (FMECA) can be used to determine the effectiveness of systems on offshore units. Typically they can be used to ensure that there are no major failings in ballast systems or mooring systems.

Using a ballast system as an example, each part of the system would be analysed, identifying the various means by which the sub-system could fail, and what the results of such a failure would be. This process extends from the main engines to the individual valves in the pipework. In relation to main engines, for instance, such an analysis would determine whether the system could be made safe at any time on main power failure, and what the frequency and consequence might be.

Frequencies are based on failures per million hours, and typically one failure per million hours would be a very low failure rate, 20 failures per million hours an acceptable failure rate and 200 failures per million hours a high failure rate. Consequence definitions may range from the lowest level, There would be no identified adverse effects resulting from the failure, to the highest level "The failure could completely prevent the ballasting operation, immediate action to ensure the safety of life required".