First Deepwater Pipe-in-Pipe Electrical Integrity Method using a Subsea Time Domain Reflectometer
Authors: March David M. , Liney David J. , Wylde Raymond J. 
Published: October 2008

This paper describes the development of a Time Domain Reflectometry (TDR) method applied subsea to verify the insulation integrity of electrically heated flowlines1. The proven TDR method is suited to direct electrical heated flowlines in deepwater remote locations post-installation and during operational life of the flowlines. The paper describes the qualification philosophy, the creation of robust components through testing, the equipment operation and example TDR results. The Time Domain Reflectometer TDR) for this application delivers risk reducing data to the benefit of offshore exploration and production operators where electrical heating pipe-in-pipe flowlines (EHPIP, or referred as EHF) have been employed in subsea developments.

Introduction

Before high voltage is applied to heat an electrical heating ready subsea flowline, it is preferable to confirm the insulation integrity of the annular space. This reduces damage potential to the power delivery equipment and confirms the flowline is 'ready' to accept power and heat-up. The nomenclature for this type of pipe-in-pipe flowline design is Electrical Heating Ready2. This paper presents the design, testing and implementation of time domain reflectometry in a deepwater, subsea environment to establish and maintain a health check of pipe-in-pipe flowlines in a condition of readiness to accept electrical heating.

Pipe-in-pipe flowlines are increasing in popularity for heating by electrification to deliver robust flow assurance methods to subsea developments2,9. The method is designed to maintain production or support recovery of production owing o hydrate blockage or hydrate associated flow restriction. The applications for electrical heating technology are usually remote, in deep water and can occur on flowlines with neither end directly connected to the host infrastructure. During installation, the EHPIP can be simply and periodically checked for electrical integrity as each joint of pipe is welded in the string and deployed. During flowline installation, the application of using surface mounted TDR equipment on the flowline ends and establishing a return signal from the subsea sled bulkhead at a measurable distance is a proven technique. This technique has a high reliability to detect water and debris inadvertently introduced at this early stage of the flowline lifecycle. Once the flowline second end is laid down, the use of non-intrusive testing of the annulus becomes impossible as both flowline ends are subsea. The new subsea TDR integrity testing method described in this paper is used to detect a number of events that could create an electrical short circuit. For example, seawater may leak through the Casing (outside) Pipe due to a buckle or denting impact into the annulus space or condensation may accumulate in the annulus space at a location of localized topographical dip in the flowline route. The subsea TDR integrity checking method is designed to be simple in operation and application deployed by an ROV from a support vessel of opportunity. An annulur space is shown in the typical cross sectional view of a pipe-in-pipe flowline