Explicit spreadsheet method for predicting internal corrosion in two galvanically coupled long pipes

Abstract

Some piping systems used in deep water oil production, including risers and flow lines, or those used for sea water piping, are galvanically coupled. The potential and current distributions in the pipe's axial direction have traditionally been predicted using either an analytical expression assuming linear polarisation kinetics or a numerical modelling using polarisation data or corresponding Tafel equations as the model input. The analytical expressions are invalid when the polarisation behaviour is non-linear, as often is the case. The numerical method may find limited users because many experimentalists, technicians and practicing engineers often are not used to or experienced with it. This paper reports an explicit four-step procedure that requires only the use of a spreadsheet to obtain the potential and current distributions from the polarisation data, and the results are robust. The predicted potential distribution is compared with those obtained from traditional numerical and analytical methods. In addition, a method developed to scale the pipe diameter is reported.