GB1016361A - Improvements in or relating to polarisation resistance measurement and apparatus therefor - Google Patents

Abstract

1,016,361. Electrolytic cell for polarization resistance measurement. IMPERIAL CHEMICAL INDUSTRIES Ltd. June 25, 1964 [July 5,1963], No. 26722/63. Heading G1N. The rate of corrosion of a metal in a corrosive liquid environment, e.g. in chemical plant, boilers, power station plant, pipelines or structural steelwork, is tested by measuring the polarization resistance in a cell comprising a first electrode of said metal, a second electrode and the corrosive liquid environment, the change in potential of the first electrode being measured in comparison with a reference electrode also in contact with the corrosive liquid. The reference electrode 5 Fig. 3 (not shown) is situated in the current dead space within an annular electrode 4 of the metal under test (said first electrode), which preferably has an exposed area of at least ten times the exposed area of the reference electrode, mounted in one end of a sheath 1, e.g. of stainless steel, which may serve as said second electrode. The sheath may be sealed to a high pressure vessel 6, by a P. T. F. E. joint ring 9. The electrodes may be insulated from each other by P. T. F. E. sleeves 7, 8 and an epoxy resin filling 3 or, for high temperature use, the insulation may be entirely P. T. F. E. and water cooling (not shown) may be provided. A table is given of suitable metals for use as the reference electrode with various metals under test. Figs. 1 and 2 (not shown) exemplify other electrode assemblies. Fig. 4 shows a circuit enabling a valve voltmeter to be switched to measure the potential difference between the reference electrode (A) and the first electrode (B) for a given current between the first electrode and said second electrode (C), which current is deduced from the voltage drop across R 2 . The ohmic resistance of the cell may be separated from the polarization resistance by combining AC and DC measurements. The rate of change in potential difference between electrodes A and B with respect to the current between B and C indicates the rate of corrosion of electrode B. The invention may be used to measure continuously and record rates of corrosion and to operate a system for the automatic addition of a corrosion inhibitor as necessary.