Heat Transfer in Offshore Pipeline Bundles

A key design parameter for the operation of subsea pipeline systems is the Overall Heat Transfer Coefficient or "U Value". In some cases for bundles with flow lines insulated in a common sleeve, the steady state flow condition "U Value" is not a characteristic parameter since it varies depending on the individual flowline temperatures and corresponding heat fluxes along the length. It is therefore difficult to specify an overall "U Value" coefficient either for the bundle or for each flowline in the bundle. It is, however, possible to use computational fluid dynamics models to evaluate these heat fluxes and effective "U Values" for each pipeline over a short bundle segment given specified flowline temperatures. Prediction of the flowline temperatures is difficult particularly in cases when fluids are flowing in the opposite directions i.e. production lines and gas injection line, but by using a simplified Rockwater in-house thermal analysis model, the temperature inputs to the CFD model of the bundle section can be estimated. FIDAP, a general purpose CFD code based on the finite element method has been used in the present studies. FIDAP works with the 2-D bundle model to predict heat flux under steady state conditions thus verifying the Rockwater mathematical model by calculating convection velocity and temperature contours.