Parametric Modeling Studies for Sediment Deposition as Sites for Under-Deposit Corrosion in Oil Transmission Pipelines

Abstract

Transmission heavy crude oil carries water-wetted solid particles. Studies have shown that these particles can accumulate on the pipe floor and cause under-deposit corrosion and that the incidence of accumulation is strongly correlated to locations downstream of overbends. Computational fluid dynamics (CFD) analysis of light and heavy crude oil flows in a representative segment of a real transmission pipeline suggested that the deposition patterns in heavy oil flow are a result of low near-wall velocity, especially downstream of overbends, which prevents the flow from sweeping particles along the pipe floor, not the tendency of particles to fall to the pipe floor. The objective of the present study was to provide information that would help establish mitigation strategies. The present parametric study used the CFD model to predict the decrease in near-wall velocity at the pipe floor downstream of overbends for different pipe diameters and oil flow rates and properties. This information provided the basis for mapping the transition from light oil behavior to heavy oil behavior. The results were condensed to a chart that provides the reduction in near-wall velocity downstream of overbends as a function of the Reynolds number. It indicated a sharp overbend effect as the Reynolds number decreased below 30,000.

Comparison of Mono- to Diphosphate Ester Ratio in Inhibitor Formulations for Mitigation of Under Deposit Corrosion

“…Although studies have been conducted to understand how deposits form in order to mitigate deposit formation [1][2] and to experiment with inhibitor packages to understand the risk and mechanisms involved with inhibition of UDC, 3,7-10 no formal attempt has been made to observe the effects of specific chemical components in an inhibitor package on UDC. The objective of this study was to test individual chemical components used in industrial inhibitor packages against localized UDC.…”

“…Under deposit corrosion (UDC) is a localized corrosion that occurs where sediments, carried through a production or transmission pipeline, have settled in stagnant or low-flow sections of a pipeline and mitigation strategies are ineffective or impractical. Computational fluid dynamics studies [1][2] have recently been conducted to understand mechanisms of solids deposition in order to mitigate deposit formation. Conclusions from these studies confirmed specific conditions related to flow and pipeline geometry reduce the near-wall velocity at the pipe floor, allowing deposits containing a mixture of water, hydrocarbons, microorganisms, and inorganic compounds to form.…”