Subsea production control systems are unique because they operate using electrical power and communications but in an underwater environment. Over time water ingress into an electrical distribution system can cause degradation of system electrical integrity. The objective of this paper is to show how these issues arise, to discuss methods for finding the location of integrity faults, and to give an example of how integrity faults can be located, what action can be taken to effect repairs, and how to mitigate against further recurrence.
Since it is not normally possible to determine the location of subsea electrical faults using visual methods alone, various other methods can be used such as Time Domain Reflectometry (TDR), Insulation Resistance (IR) measurements and branch isolations. In addition to the complexities of determining a fault location subsea, the situation is further complicated by difficulties in gaining access to potential subsea fault locations using divers or Remotely Operated Vehicles (ROVs). This paper will show the fault diagnosis procedures that were employed in determining the location of an electrical fault in a subsea production control system and will also discuss the issues and the procedures used in order to gain access to potential fault locations such as opening hatches and removing protection covers under water.
The results of this work were the safe and successful location and remediation of the subsea electrical fault. The subsea production control system was restored to full operation and there were no HSE incidents during the work. The performance of the system continues to be monitored and analysed for signs of any new degradation.
This paper will present information that will be of benefit to others in the subsea industry who are facing electrical integrity issues in subsea production control systems. The benefits that can be gained are both in terms of testing strategies that can be followed and in potential new technologies that can be deployed.