Electrical & Optical Double Barrier Qualification and Implementation on FENJA Electrically Trace Heated Pipe-in-Pipe Project
Authors: Le-Naour Frederic , Marret Antoine , MacLeod Kenny , Vivet Romain , Aglen Ida Margaretha 
Published: August 2021

This paper provides an overview of the work completed to design, qualify, manufacture and integrate electrical and optical double barrier penetrators with the Electrically Trace Heated Pipe-in-Pipe (ETH-PiP) as part of the Neptune Energy Fenja Development Project.

Typical subsea penetrator systems in the oil and gas industry, such as pumps, compressors and X-trees are designed to be retrievable, to enable periodic refurbishment as well as providing the option for replacement, if required. However, the ETH-PiP architecture makes retrieval of system components complicated and uneconomical. Both the electrical and optical dual barrier penetrator system designs have to comply with a set of ETH-PiP specific criteria, such as to be maintenance free over a 25 years service life, prevent water ingress to the pipeline, provide pressure containment for operational media (in an unlikely scenario where the inner pipe bursts) and guarantee minimum footprint to allow an optimum integration onto the Pipeline End Termination (PLET) structure. In addition, the electrical system has to comply with a medium voltage rating (i.e. 5.0/8.7kV) to ensure a wide range of possible ETH-PiP architectures. The optical system has to maintain insertion loss below 0.5dB and a back reflection below -45dB to comply with the stringent requirements of distributed temperature monitoring sensor system over long distances.

The qualification program of the electrical dual barrier penetrator system was performed in accordance with IEC 60502-4 and SEPS-SP-1001. A tailor made sequence had to be developed for the optical system, based on guidance from SEAFOM-TSD-01, considering that the system partly falls outside the associated standard application.

The electrical dual barrier penetrator system qualification sequence was developed in two phases; firstly, the electrical transition contacts in the feedthrough chamber were qualified in accordance with IEC 60502-4 and secondly, four electrical double barrier penetrator prototypes were manufactured to allow the completion of the qualification sequence defined as per SEPS-SP-1001. The optical dual barrier penetrator system qualification employed the manufacturing of three prototypes to execute the pre-defined qualification sequence.

Following the individual qualification of the electrical and optical dual barrier penetrator systems, subsequent welding and full-scale assembly trials were performed to ensure that the maximum allowable temperatures within the penetrators would not be exceeded during welding to the PLET, and to proof test the assembly procedure. Electrical verification testing was also undertaken during these trials to verify that the integrity of the penetrators had been maintained during the assembly and that the PLET arrangement did not give rise to any electrical stresses that could result in excessive deterioration of the penetrators.

Integration of the four electrical and two optical dual barrier penetrator systems to the project PLET was completed in Q1 2020, with the actual subsea installation of the first ETH-PiP section including the PLET in Q3 2020.