Electrical Protection From Design to Commissioning for Subsea Electrically Heat Traced Flowline Pipe in Pipe System, The Challenge of Inaccessible Subsea Electrical Assets.

Abstract

Abstract This paper will describe the analysis, optimisation and subsequent implementation of an electrical protection system utilised on a subsea Electrically Heat-Traced Flowline system (EHTF) using conventional topsides power protection equipment deployed in a novel topology. It will also discuss the project-imposed challenge of protecting an electrical subsea system of significant length from only a single feeder protection whilst keeping it simple, sensitive, rapid, and covering 100% of the long heating cable length. The paper will describe the detailed electrical analysis methods deployed, the additional electrical verification carried out and the decision-making processes and drivers choice used during an electrical system design optimisation challenge that was conducted in a short timeframe and planned around operational assets. The close collaboration between contractor, client, vendors and third-party expertise was fundamental to solve successfully the challenges and mitigate the overall risks. Key engineering processes described: Subsea Umbilical Riser and Flowline (SURF)/Topside interface management / interface meetings, design review process, use of interim design reviews, the decision scoring matrix, the go/no go risk assessments, pre-commissioning, commissioning, performance test. The benefits and drawbacks of the different electrical topologies investigated will be reported, specifically the retention of an isolated neutral system. The paper will provide the final chosen protection topology and the results of the individual component testing. A key observation to report being that when technology is new, the need to validate the implementation of it must be included in the initial design. There must be added monitoring even if it’s not thought to be essential at start of a project, even if it’s considered as "sugar coating" a design or adding complexity, there can be huge benefits on new technology deployment. The paper will report on the observed benefits of site integration testing versus individual routine / factory acceptance testing when deploying TRL7 items in novel topologies. The final commissioning results will be reported and an engineer’s view of a journey from concept to final commissioning will be presented. Existing literature is limited on electrical topology on subsea infrastructures and thus this paper enhances the industry knowledge base. The paper describes a novel topside protection system for subsea ground isolated loads. As the subsea industry turns towards electrification, it is essential that lessons are learned. This ensures novel solutions can be deployed provided a correct design verification process. The paper could trigger discussions around a new best practice recommendation about the interface topsides/subsea electrical infrastructures.