Traditionally flexible pipe is utilised to transport production fluids, such as oil and/or gas and/or water, from one location to another. Flexible pipe is particularly useful in connecting a sub-sea location to a sea level location. Flexible pipe is generally formed as an assembly of a pipe body and one or more end fittings. The pipe body is typically formed as a combination of layered materials that form a fluid and pressure-containing conduit. The pipe structure allows large deflections without causing bending stresses and strains that impair the pipe's functionality over its lifetime. The pipe body is generally built up as a structure including metallic and polymer layers.
In many known flexible pipe designs the pipe includes one or more pressure armour layers. The primary load on such layers is formed from radial forces. Pressure armour layers tend to be wound with a large angle in relation to the longitudinal axis of flexible pipe body and often have a specific cross section profile to interlock so as to be able to maintain and absorb radial forces resulting from outer or inner pressure on the pipe. The cross sectional profile of the wound tapes which thus prevent the pipe from collapsing or bursting as a result of pressure are sometimes called pressure-resistant profiles.
In many known flexible pipe designs the pipe includes one or more tensile armour layers. The primary load on such a layer is tension. In high pressure applications, such as in deep water and ultra deep water environments, the tensile armour layer experiences high tension loads from the internal pressure end cap load as well as weight. This can cause failure in the flexible pipe since such conditions are experienced over prolonged periods of time.
Unbonded flexible pipe has been an enabler for deep water (less than 3,300 feet (1,005.84 meters)) and ultra deep water (greater than 3,300 feet) developments for over 15 years. The technology enabled the industry to initially produce in deep water in the early 90's and then to ultra deep waters up to around 6,500 feet (1,981.2 meters) in the late 90's. Water depths greater than 6,500 feet push the envelope where typical free-hanging riser configurations and flexible pipe in general can operate. It is the increasing demand for oil which is causing exploration to occur at greater and greater depths where environmental factors are more extreme. For example in such deep and ultra-deep water environments ocean floor temperature increases the risk of production fluids cooling to a temperature which may lead to pipe blockage. Increased depths also increase the pressure associated with the environment in which the flexible pipe must operate. As a result the need for high levels of performance from the pressure armour and tensile armour layers of the flexible pipe body is increased.
One way to improve the strength and thus performance of armour layers is to make the layers from thicker and stronger and thus more robust materials. For example for pressure armour layers in which the layers are often formed from wound tape with adjacent windings in the layer interlocking, manufacturing the tape from thicker material results in the strength increasing appropriately. However as more material is used the weight of the flexible pipe increases. Ultimately the weight of the flexible pipe can become a limiting factor in using flexible pipe. Additionally manufacturing flexible pipe using thicker and thicker material increases material costs appreciably which is also a disadvantage.