The industry's strong desire during a time of uncertain oil price stomore economically exploit marginal oilfields has provided a strong stimulus to the development of associated pipeline technologies. Largely as are sult of pioneering work performed in the 19708, an alternative pipeline technology centered around the use of flexible steel reinforced pipe has been gaining greater prominence. The need for the introduction of a dynamic pipe capability into many subsea or floating production scenaria stems largely from the requirement to accomodate the system's high inertial loads generated as a consequence of connecting fixed subsea hardware to a floating surface facility. Because of flexible pipes properties and composite construction, it provides a structure that can be quickly installed, variably configured and which can adapt to a great range of system motions and environmental loads. Over the past 15 years advances in oil resistant polymers and increases in the chemical resistivity of certain classes of steel have resulted in the construction of new types of flexible pipes capable of transporting ever harsher well fluids at higher temperatures These and other improvements have resulted in greater product reliability and extended service life times.
Flexible steel reinforced pipe was first used in the 1940s to transport aromatics and fuels in support of the Normandy invasion, but only experienced its technical rebirth in the mid-1970s. The oil industry was then looking for a new pipeline construction which could offer greater chemical resistance to transported fluids, could be quickly installed utilizing less costly installation spreads, and which could inherently accomodate seabed undulations. The principal applications were as static seabed riser or flow line connecting adjacent fixed production platforms The "flexibility aspect" the relatively low minimum bend radius (eight to ten times pipe id) when compared to that of rigid steel pipe (up to 500 times id) offered obvious installation benefits. The pipe's ability to deflect without experiencing damage enabled relative large misalignments to be accommodated - At a time when a premium was demanded for the hiring of a dynamically positioned vessel from a relatively limited supply pool greater choice in selecting a simpler installation spread resulted in lower overall pipeline completion costs.
The early uses of flexible pipe were confined to applications where the principal loads were imposed during installation rather than during long-term operation. Operating condition were generally undemanding-pipes typically handled fluids up to 70°C at design pressures up to 200 barg with virtually no differential pressure across the pipe wall being experienced Pig or TFL tool passage was unknown as was the concept of accomodating dynamic loads.
The principal concerns regarding the life time for these early flexible pipe designs were primarily related to the inner polymer liner's ability to resist ageing and degradation as a result of exposure to transported fluids. The secondary concern was its permeability with respect to associated gases.
