Pipeline operators have sought to advance pipeline safety through integrity management programs. However the fundamental feature of the pipeline causing the gradual loss of integrity, its composition of carbon or low alloy steel, is relatively unchanged for the past half century. Flexible steel pipelines can be pulled into existing deteriorating and/or damaged conventional steel oil and gas pipelines as a rehabilitation operation. This pipeline rehabilitation method can renew structural integrity, improve flow characteristics, provide added corrosion resistance to the pipeline system and avoid the environmental/third party damage that exists with other methods of repair.
In recent years, pipeline operators and the United States government have sought to advance pipeline safety through documented integrity management programs that addresses leak detection and in-line inspection. The US Pipeline Safety Improvement Act of 2002 directs the US Office of Pipeline Safety to develop rules requiring pipeline operators to identify and protect segments where pipeline failures would threaten people and property1. However the fundamental feature of the pipeline causing the gradual loss of integrity, its composition of carbon or low alloy steel, is relatively unchanged for the past half century. To slow the effects of corrosion, a rigid steel pipeline requires costly cathodic protection and chemical inhibition systems. The pipeline must be monitored for reduction in wall thickness and the operating pressures reduced accordingly, which in turn causes flow capacity to decline. Once a pipeline is no longer usable, it must be repaired, replaced or abandoned. Traditional methods of excavating pipelines for repair or replacement are becoming less feasible due to: ? Environmental concerns in unusually sensitive areas (USAs)
? Economic and infrastructure impacts in metropolitan high consequence areas (HCAs)
? Difficulty in overcoming regulatory, permitting and other hurdles for installing new
pipelines
The installation of thermoplastic liners into existing pipelines is widely used to seal damaged pipelines and prevent further corrosion from the conveyed fluid, but these liners depend on the structural integrity of the original pipeline, and thus have limited pressure containment capability2. When un-reinforced thermoplastic liners are utilized, the remaining pipeline strength must still conform to ASME B31G3 and/or similar applicable standards.
Alternatively, flexible steel pipelines can be pulled in to repair damaged steel pipelines. For a standard repair, flexible steel pipe with an OD smaller than the ID of the existing pipeline is pulled in, using techniques typical of loose fit liners. The reduction in effective ID of the flowline is generally considered to be offset by the smooth surface of the polymer liner of the flexible steel pipe which has a very low friction factor, and the inherent thermal resistance of the flexible that retains heat better than steel pipes, improving viscosities for multiphase flow. Where equal or greater internal diameter for the flow line is required, pipe bursting and similar techniques are used to effectively open the existing steel pipe diameter and pull-in flexible steel pipes. This replacement typically allows up to 2-inches greater ID in the replacement pipeline than was in the original. In either case, the refurbished pipeline is rated for relatively high pressure, since the flexibles are inherently pressure containing and do not require any type of structural support from the old steel pipeline.
A relatively new development of flexible steel pipe combines traditional flexibl
