Changing a historic operational paradigm allowed important reductions in platform shutdowns and productivity increase.
A large offshore platform in the Scottish North Sea had suffered chronic non-planned shutdowns, caused by frequent failures in the cooling system, induced by severe vibrations
The problem had affected the installation since start up, and over twelve years in operation it was interpreted as a piping resonance problem, which would be too expensive to correct.
The reliability team decided to use Ai-Relia-BDt to explore possible contributing factors to the problem.
Process data of six months of operation, stored in the DCS, were provided for the analyses.
Data from other operational functions revealed extreme downtime costs generated by chronic frequent failures of: Pressure Control Valves, Isolation valves, Main heat exchangers, Piping systems .
Ai+Reliability - Root Causes Analysis
These correlations presented robust information to challenge the mechanical resonance paradigm. Further investigation indicated that values of vibration frequencies and amplitudes were very disperse, which is not the case in mechanical resonance.
Further engineering analysis revealed that design flow velocity was high and differential pressure across the main pressure control valve (PCV) was too high, also the testing procedure of fire pumps used to introduce additional flowrates into the system, which increased flow velocity.
These factors combined with water temperature leaving heat exchangers were creating severe cavitation across the PCV.
Correctives to eliminate the root causes included piping modifications to reduce water velocity, process control modifications to reduce operating pressure and changing testing procedure of fire pumps.
Cavitation was a systemic root cause (SRC) affecting many assets in the cooling system. Savings from correcting this problem were calculated in the range of 35 million USD per year.