High Temperature Pipeline Design

High temperature operation is an alternative to the use of a diluent to reduce the viscosity of heavy oil or bitumen for pipeline transportation. This paper deals primarily with two fundamental design issues for a hot bitumen (hotbit) pipeline, modeling the restart problem and establishing the maximum practical operating temperature. The concept of flow capacity is introduced to model the transient behavior during restart of a high temperature pipeline filled with a high viscosity fluid that has cooled during a shutdown. The heat lost from a buried high temperature pipeline causes environmental disturbance by elevating the ground temperature near the pipeline. This can alter growing conditions above even an insulated, deeply buried pipeline. Results are presented for a hypothetical case modeled using a thermal simulator developed by one of the authors. Axial thermal loads increasingly constrain the design and operation of a buried pipeline as higher operating temperatures are considered. Strain based design affords the opportunity to design for higher operating temperature than allowable stress based design techniques. With either design method, there is a temperature at which expansion loops are required to partially relieve the thermal stress. As the design temperature increases, there is a point at which an above grade pipeline becomes an attractive option.