Evaluating the Effective Friction Factor and Overall Heat Transfer Coefficient During Unsteady Pipeline Operation

Abstract

This paper presents a method to determine the effective friction factor and overall heat transfer coefficient for a high pressure, natural gas pipeline during fully transient flow conditions. Time varying SCADA (Supervisory Control And Data Acquisition) measurements at the pipeline boundaries (i.e., inlet and outlet) provide boundary conditions for a transient flow model as well as additional information that is utilized to determine these parameters. The resulting friction factor and overall heat transfer coefficient minimize the least-squared difference between the additional SCADA measurements at the pipeline outlet and the corresponding values predicted from the transient flow model. This concept is referred to as parameter estimation. The transient flow model is based on a numerical solution of the one-dimensional, unsteady flow equations (i.e., continuity, momentum and energy) which are discretized using a highly accurate compact finite-difference scheme. The transient flow model and parameter estimation are incorporated into a computer program that is initially tested on a simple pipeline with steady flow conditions. Here, the predicted outlet pressure and temperature, using the estimated friction factor and overall heat transfer coefficient, exactly matches the corresponding prescribed values. Subsequently, a portion of the Foothills Pipe Line Ltd. transmission system in Alberta is considered using time varying SCADA flow measurements. The resulting outlet pressure and temperature from the transient flow model are in good agreement with SCADA measurements at this location.