EFFECTS OF MISALIGNED PIPE-WALL WORKING ELECTRODES ON ELECTROCHEMICALCORROSION RATE MEASUREMENTS IN PIPES

Turbulence models were used to simulate numerically the effect of elec trode misalignment on corrosion rate (i(corr)) measurements in turbule nt pipe flow. The effect of the mass transfer entry length was conside red. 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 recesse d 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 ad ditional 2% and 5% errors for protruding and recessed electrodes, resp ectively. Determination of the effect for partially mass transfer-cont rolled i(corr) measurements was illustrated. Interfacial metal ion con centration and pH profiles were determined for mass transfer-controlle d partially mass transfer-controlled and charge transfer-controlled co rrosion and discussed in terms of their possible effects on film forma tion.