The Development of a Cable Termination System for Deep Water Applications
Authors: Theobald John , Painter Howard , Barlow Stewart 
Published: October 2008

As offshore developments are pushed into deeper waters, new enabling technologies are required to terminate electrical, optical and hybrid cables. Recent experience has shown that, depending upon cable construction, two failure modes are possible.

Firstly, in many cable terminations, the individual cores of the cables pass from an atmospheric cable breakout chamber into a dielectric fluid-filled pressure-balanced splice chamber. Even supported core elements can collapse into the atmospheric cable breakout when used in deep water applications, resulting in damage to the conductors.

Secondly, many cable terminations have a single sealing element separating the oil or gel-filled volume from the cable and conductor interstices which are, in many cases, atmospheric. If this sealing element is compromised, the resulting venting of the oil can lead to failure of the termination.

A new, key enabling cable termination technology has been developed to extend the operational depth and significantly increase the reliability of cable terminations. This modularized system completely isolates the cable elements from the pressure-balanced splice chamber and ambient environment. This approach to cable termination eliminates cable-dependent design limitations and common mode/single point failures. This paper provides an overview of the current designs and typical failure modes. It then provides a description of the new termination system and the solutions it offers.

Introduction

As oil and gas production projects move into deeper waters, new key enabling technologies are required to terminate electrical, optical and hybrid subsea umbilicals. Two failure modes have been identified using current termination technology in deepwater applications: core element collapse into an atmospheric breakout region and wicking of the compensating fluid from the termination, past a single sealing element, into the interstices of the cable or conductor. Either failure may lead to partial or catastrophic failure of the termination. Each failure mode can be directly linked to the interaction of the cable elements with the pressure-balanced dielectric fluid-filled splice region in the termination.

Both of these failure modes have been encountered in the recent past during the installation phase of ultra-deepwater developments. In each instance, an understanding of the failure mode led to the development of design modifications that were qualified and successfully deployed. The difficult lessons learned from these experiences have resulted in new design considerations and more rigorous qualification procedures during the development of cable specific Field Installable Termination Assemblies (FITAs). These lessons have also been cause to rethink the design philosophy of cable terminations. Ocean Design, Inc. (ODI) has embarked on an ambitious design program to eliminate the limitations of the current technology and increase the reliability of their terminations. The result of this effort is the FACT (Field Assembled Cable Termination) system; a modularized termination system that completely isolates the cable's internal elements from all pressurized fluid interfaces. This paper will detail the common failure modes of the current technology along with the mitigating remedies and preview a new technology for terminating cables for deepwater applications that eliminates known failure modes.