Comparison of Pressure Decay Models for Liquid Pipelines

Abstract

Abstract This paper presents a comparative study of various models in characterizing the reduction of pressure severity along the length of a given liquid pipeline section. Four models were considered in this study, namely the API RP1176 model, CEPA model, SSI Linear Interpolation model and Pressure Range Linear interpolation model. A total of 132 sets of pressure spectra from TC Energy’s liquid pipelines were collected. Each set includes three pressure spectra, namely one pressure spectrum from a given intermediate valve station and other two pressure spectra from the discharge end of its immediate upstream pump station and the suction end of its immediate downstream pump station. The SSI is used to characterize the severity of a given pressure spectrum. To quantify the uncertainties of the model error associated with the four pressure decay models, the calculated SSI based on the spectrum from the intermediate valve station is compared with the model-predicted SSI at the location of the intermediate valve station based on the SSIs of the upstream discharge and downstream suction pressure spectra. The comparative analyses indicate that the CEPA model is the most accurate and precise model in evaluating the pressure decay along the length of a given pipeline section, and in a descending order followed by Pressure Range Linear Interpolation model, API RP1176 model, and SSI Linear Interpolation model. A fitness-for-service assessment program for liquid pipeline can incorporate the probabilistic characteristics of the model error associated with each of the four models derived based on the 132 sets of pressure data.