Effects of misaligned pipe-wall working electrodes on electrochemical corrosion rate measurements in pipes

Turbulence models were used to simulate numerically the effect of electrode misalignment on corrosion rate (i(corr)) measurements in turbulent pipe flow. The effect of the mass transfer entry length was considered. Simulations were presented for flow in a pipe 25 mm (0.98 in.) in diameter and with a Reynolds number of 50,000. Protruding and recessed electrodes were considered with misalignments from 0 mu m to 500 mu m. Results showed that, if an electrode of suitable length was chosen (60 mm [2.36 in.] in the present case) and misalignment was < 50 mu m, the error in the polarization resistance measurement for wholly mass transfer-controlled corrosion was < 10% for a flush electrode, with additional 2% and 5% errors for protruding and recessed electrodes, respectively. Determination of the effect for partially mass transfer-controlled i(corr) measurements was illustrated. Interfacial metal ion concentration and pH profiles were determined for mass transfer-controlled partially mass transfer-controlled and charge transfer-controlled corrosion and discussed in terms of their possible effects on film formation.