Objectives and problems to be solved: Due to the need to reduce reliance on foreign oil imports and improve trade balance, the EU is faced to challenges of developing new resources recently found in deepwater locations 500 to 3000 m below sea-level. The riser provides a conduit for the transport of hydrocarbons from the seabed to the topside structure. Replacing conventional risers with lightweight composite risers will have a cascading weight reduction effect on the entire facility. The project will develop and validate a prototype riser section including a lifetime prediction tool. In order to reduce production costs new thermoplastic-carbon fibre composite materials will be developed. Description of work: To make the risers cost competitive, new thermoplastic composite pre-prig tape materials will be developed. The thermoplastic winding techniques will be further developed to achieve the quality needed for oil risers. Processing parameters, lay-up, tape specifications will be optimised for riser performance, costs and manufacturing speed. The risers are critical components; hence a lifetime prediction tool will be developed. Expected Results and Exploitation Plans: The main objective is the development and validation of a prototype riser section. The sections will be ca 2 meter long, have 200 mm internal diameter and will be validated for loads representative of 2000 meter water depth, 500 bar internal pressure and well fluid temperature of 160°C. Tests include for chemical environment, fatigue, bending and external and internal pressure. If the project is successful the composite flexible risers will be turned into commercial large-scale production. This alone will create a large market for the newly developed materials. The application of fibres and composites in critical structures like risers will open new markets for these products.
A generic composite riser design methodology was developed. The methodology is valid for both harsh and benign environments and includes all load conditions and load cases, global analyses for extreme response, fatigue analyses and take into account all required ancilliary equipment. This methodology will be used for future composite riser engineering. A qualification catalogue was developed to document the development of the riser and contains reference to documents required for the qualification of a riser segment. The catalogue covers all aspects from design to fabrication, installation and operation and adheres to relevant guidelines, codes and standards. This will be the basis for future composite riser qualifications. A predictive model to analyse the fatigue life of the riser under variable amplitude loading in combination with static stresses at different service temperatures was developed. Fatigue testing was performed on flat plates and tubes and S-N cuAn optimisation of carbon fiber thermoplastic tape was performed.
The result is characterized by very consistent width and thickness dimensions to facilitate accurate lay-down of the tape to obtain void free structures and fully exploit the inherent performance potential of the composite riser body. In addition, the ultra-long length of at least 5000 m of the tape ensures a continuous, uninterrupted, failure-free and hence economic high-volume processing to fabricate the risers structures. The result is augmented by a set of material data to support and facilitate the global and local analysis of the risers according to recognised standards. The line extrusion process development generated results that can be used to control the brittleness of the pipe, from producing pipes that have brittle failure at only fractions of percentage deformation to very ductile pipe that can be completely flattened without cracking. Bonding of the first composite layers to a liner has been determined. From the pipe manufacturing work, a tool to simulate the winding process with thermal gradients and mechanical forces was developed. The numerical models for the physical processes underlying the simulation software are well documented.
Funding SchemeCSC - Cost-sharing contracts