Heat transfer calculations for a buried pipe can affect temperature profile prediction and insight into pressure changes, velocity, phase behavior, wax deposition, and hydrate formation. Improvements to heat transfer calculations may therefore help improve the economic design and operation of the pipe.
This work will evaluate three methods of calculating the ground heat transfer coefficient of a buried pipe under different external pipeline configurations. A traditional equation to calculate the outer heat transfer coefficient, widely used by flow simulation software, proved to have limitations at shallow depths. An adaptation of this equation to overcome the limitation can become inappropriate at greater burial depths. It will be shown that a calculation method published by Zakarian et al [1] is better able to predict the outer heat transfer coefficient over this range of buried pipe configurations.
The sensitivity of the liquid holdup in simulated pipelines to the different heat transfer calculation methods will be presented using a number of case studies with a range of burial depths in both subsea and onshore pipeline configurations. The relative merits of the heat transfer calculation methods and their appropriate use will be discussed for each scenario.
Design of a pipeline system for acceptable performance throughout its lifecycle may rely on an assessment of liquid holdup, hydrate conditions, pressure loss and other process variables under a variety of potential operating conditions. An accurate temperature profile is important to predict the fluid properties and phase behavior at points along a pipe. The temperature profile of a fluid as it moves through a pipe will be affected by the Joule-Thomson effect, velocity change and heat transfer with the surroundings.
In many uninsulated buried pipelines the controlling thermal resistance will be the ground surrounding the pipe. Prediction of the ground resistance using simplified equations is therefore a sensible subject of practical research. In recent years authors have reviewed and improved the level of detail of equations used to model radial heat transfer for buried pipelines [1, 2, 3]. Some authors have validated their approximated equations to results from analytical methods [4] for similar boundary conditions. For the purpose of this study three equations were selected based on their simplicity and wide use in commercial simulators.
