Pipeline Repair Development in Support of the Oman to India Gas Pipeline
Authors: Abadie Wade , Carlson Warren 
Published: October 2008

This paper provides a summary of development which as been conducted to date for the ultra deep, diverless pipeline repair system for the proposed Oman to India Gas Pipeline. The work has addressed critical development areas involving testing and/or prototype development of tools and procedures required to perform a diverless pipeline repair in water depths of up to 3525 m.

INTRODUCTION

The Oman Oil Company is implementing the Oman to India Gas Pipeline Project whose offshore section is 1139 km long, between Ra's al Jifan in Oman and Rapar Gadhwali in India. The route was selected following an extensive survey conducted in 1994, and reaches a maximum water depth of 3525 m. The principal features of the route are shown in Figure 1.

The extreme water depths and high operating pressure ecessitate use of thick wall pipe and provision of thick wall buckle arrestors. In order to ensure minimal disruption to construction schedules and product delivery, a reliable diverless pipeline system is mandatory for replacing a damaged pipeline section during both the Installation and Operating phases of this pipeline.

There have been several efforts at developing diver less pipeline repair systems (Ref.1 -5). Most have not developed past the engineering phase, due to costs and the down turn of the industry in the mid 1980's. No iver less pipeline repair has been performed, to date.

SELECTED REPAIR SCHEME

The ability to perform a diver less pipeline repair in such extreme depths, during installation or operation, is considered essential. A survey of available repair components and systems showed that there were no systems capable of completing a permanent repair for this pipeline. Special issues other than the depth included the pipe wall thickness, diameter, internal pressure requirement and long-term reliability of the repair.

Because of material strength limits and potential damage scenarios, lifting the pipe to the surface for repair cannot be relied on as part of the repair procedure. For this reason, a replacement spool piece with connectors must be attached to the pipe subsea.

Available subsea connectors rely on slip-locking or forging rocesses to attach to the pipe ends. Neither of these principles were considered reliably acceptable for this thick-wall pipeline. Consequently, the direction taken focused on the use of subsea machining of the pipe ends, to allow a standard collet connector to attach directly to a machined hub. The provision of the heavy wall buckle arrestors fortuitously provides adequate thickness for the machining of the connector hub. A replacement spool piece with pre-attached collet connectors is subsequently lowered to connect with the prepared collet hubs.

Although remote machining is not the only means of completing a repair, it has applicability in several other repair scenarios in terms of pipe facing or preparation for connectors other than collet type. This is particularly true for the several connectors which rely on external slip- Iocking.

The basic pipeline repair system will be modular in concept and comprised of the following components.