Improved design basis for offshore flexible pipes
The aim of the project was to get better means for predicting the environment (meant as gas composition and amount) in the annulus of a flexible pipe. The single most important parameter for this environment is the amount of gas diffusing from the bore to the annulus through the inner polymer liner.
The purpose of the project is to improve the design basis for offshore flexible pipes by measurement and modelling of diffusion through polymer liners in flexible pipes. There is a lack of knowledge of diffusion through polymer barriers at high temperatures and high pressure in a chemically aggressive environment with simultaneous diffusion of multiple gas components. Data is obtained through measurements which take place under moderate and extreme operating conditions. These data are used for a more reliable modelling of the concentration of gasses in annulus where the metal armouring is placed. This results in a better estimation of corrosion conditions and thus lifetime expectancy of flexible pipes. The calculation model will take into account diffusion through liner, and concentration of methane and carbon dioxide in various operating conditions, including slow and rapid changes at different selection of materials and dimensioning and construction of offshore flexible pipes. A full-scale test will be used to evaluate the calculation models and make necessary adjustments of these in order to ensure correlation of laboratory measurements to full scale operation. Oil companies will be invited to an Advisory Group to secure application of the results, and probably also to initiate activities concerning corrosion fatigue in metal armourin of offshore flexible pipes. Results may be used to correct design of flexible pipes by making a better or more cost-efficient design. A subsequent project might be to study metal armour corrosion within such flexible pipes
The annulus environment is determining for the dimensioning of the armouring layers due to corrosive attack on the steel armouring from gases lik CO2 and i combination with water. Permeation data for methane, CO2 and hydrogen sulphide at pressures between 20 and 600 bars has been generated for HDPE, MDPE, PA11 and PVDF, at relevant temperatures. In addition, solubilitiy has been determined for methane and CO2 at pressures up to 200 bars in the same polymers. A mathematical model for simulation of diffusion of gases in flexible pipes has been developed. The model operates in two dimensions: axial and radial. Two test rigs have been built - one for measuring permeation on cylindrical extruded liners from flexible pipes at a pressure up to 690 bar, and one full scale test rig for measuring of gas permeation in a real flexible pipe. These have been made operational, but have not yet generated data. The project has been presented in a joint industry project on permeation and corrosion in flexible pipes, where it among oil companies and other pipe manufacturers proved to be on the technological edge
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Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Danmarks Tekniske Universitet (DTU) |
