High pressure-high temperature developments are on the rise globally as operators are pushing the current limits by investing in technology for the future, for e.g., Total West Franklin and ConocoPhillips Jasmine Pipeline Bundles. Pipeline Bundles have been designed and installed by Subsea7 for over 35 years globally and have been utilised where fluid transport requirements have made other technical solutions uneconomic. The Pipeline Bundle product has been incrementally developed over the years to the current pressure & temperature record of (604bar and 160°C). The next stage in development is to increase the temperature and pressure range for the product through the use of pre-tensioning. For HP/HT fields pre-tensioned Pipeline Bundles offers a technical and commercial key advantage, they reduce the build-up of unacceptable axial forces, mitigate the need for expansion/cooling spools and hence provide an economic fully integrated HP/HT solution.
This paper outlines the general benefits of Bundles and how mechanical and thermal methods can be used to set the pre-tension in-to the PIP (Pipe in Pipe) and their comparison. If EHTF (Electrical Heat Traced Flowlines) are integrated in the Bundle these might also be used to set the pre-tension and test the electrical heat trace system.
The base case for a comparative study is Total West Franklin which had design pressure of 604bar and 160°C temperature. Pre-tensioning calculations with varying combinations of pressure and temperatures are utilised to assess the impact on design of the Bundle based on the Total West Franklin Bundle. The effects of pressure and temperatures up to 1379bar and 220°C respectively are evaluated during the R&D project using calculations and advanced FEA with Abaqus. The paper will also outline the effect on the HP/HT design of changing the thickness of the production pipe by utilising displacement controlled and limit based design codes in combination with advanced FEA to assess the design, moreover requirements in regards to fracture mechanics are determined.
In regards to HP/HT pre-tensioned pipeline Bundles, the design codes PD-8010 and DNV-OS-FlOl are not developed for Bundles and hence further work in developing an advanced FEA methodology for HP/HT Bundles, which is integrated with these codes would yield further benefit. A thick walled pipe might be beneficial for pressure containment and reduce overall stresses but in combination with higher temperatures also results in amplified compressive loads due to expansion. It can be established from results that a pipe with pre-tensioning and detailed flowline integrity analysis will enable design with higher temperature usage and optimise the pipe thickness.
It is expected that a technically feasible and economically advantageous solution for HP/HT developments will be realised for operators by pre-tensioned Pipeline Bundles.