Blockage Detection and Characterization in Natural Gas Pipelines by Transient Pressure-Wave Reflection Analysis

Abstract

Summary Pipeline blockage is a major problem in gas production and transportation processes. Safety and economic costs of pipeline blockages are compelling the industry to design innovative means for early detection of partial blockages along pipe systems as a preventive measure. This paper presents a simple numerical model to be used for accurate blockage characterization in natural gas pipelines. The transport phenomenon is modeled with a quasi-1D set of partial differential equations for isothermal natural gas flow in pipes. The variable area formulation maintains the simplicity of a 1D formulation and yet allows for the complex geometries associated with natural gas pipeline blockages. Viscous effects are also included in the formulation of the governing equations, and a cubic equation of state is incorporated into the model to provide the quasi-compositional effect of real gases without the complexities of a fully compositional model. The generalized Newton-Raphson technique is used to solve the piece-wise finite-volume formulation iteratively as an optimization problem with pressure and velocity as perturbed variables. Reflected pressure waves observed at the pipe inlet node were analyzed for blockage characterization. It was observed that viscous losses have no effect on blockage length and location prediction accuracy, but has significant impact on the accuracy of blockage severity predictions.