This paper presents a model for predicting the contaminated mixing volume arising in pipeline batch transfers without physical separators. The proposed technique represents an improvement over the existing methods since it takes into account time-dependent flow rates and accurate concentration-varying axial dispersion coefficients. The governing equation of the model forms a nonlinear boundary-value problem that is solved by a finite element method coupled to the Newton’s method. A comparison among the theoretical predictions of this method, a field test, and other classical procedures show that the proposed method exhibits the best estimate over the whole range of admissible concentrations investigated.

In the oil industry the localization of a leak that occurs in a pipeline is an important piece of information that needs to be obtained before mitigating actions can be taken to remedy the leak effects. In this paper we are particularly interested in testing a leak localization model for two-phase flows based upon the intersection of the hydraulic grade lines emanating from the pipeline ends. This methodology is commonly applied to single-phase-flows. In two-phase flows, the flow-pattern that develops along the entire pipeline upstream and downstream of the leak strongly affects the pressure gradient and has significant influence on the location of the leak. We consider this two-phase flow to be steady and to occur in a nearly horizontal pipeline characterized by the stratified-flow pattern. We also assume that the flow is isothermal with a compressible gas phase and an incompressible liquid phase. The results of the numerical simulations allow the model sensitivity to be studied by changing the leak location, for a given leak magnitude. From this analysis, we may observe how these parameters affect the pressure gradients along the pipeline that develop upstream and downstream of the leak and the model’s ability to predict the leak location.

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Two mechanical models have been presented in this paper for structural failure prediction of piping systems conveying liquids subjected to pressure transients. One model takes into account the axial fluid–structure interaction (FSI) phenomenon between fluid and pipe motion, whereas the other refers to an extension of the well‐known waterhammer formulation. Both models are described by a system of non‐linear hyperbolic equations which are solved by using a numerical procedure based upon the operator splitting technique and Glimm's scheme. To implement Glimm's method, it is presented the solution of a 4×4 Riemann problem with discontinuous coefficients. Numerical predictions of both models are presented and compared, so that the influence of the FSI term on the failure analysis is focused on. © 1998 John Wiley & Sons, Ltd.

This work presents a structural integrity model for piping systems conveying liquids which takes the axial fluid-structure interaction into account. The model is used to numerically investigate the influence of pipe motion on the degradation of the piping when fast transients are generated by valve slam. The resulting mathematical problem is formed by a system of nonlinear partial differential equations which is solved by means of an operator splitting technique, combined with Glimm’s method. Numerical results obtained for an articulated piping system indicate that high piping flexibility may induce a substantial increase in damage growth along the pipes.