Abstract
The criteria section of NACE Recommended Practice RP0169 included the -0.85 volt (V) criterion (copper/copper sulphate electrode) and stipulated that the determination of this voltage is to be made with the cathodic protection (CP) applied as did Revisions RP0169 - 72, RP0169 - 76 and RP0169 - 83. 6,7,8,9 NACE Revision RP0169 - 92 implies that the -0.85 V criterion voltage is to be determined as a "polarized potential"10, and it has become widely accepted that this means the voltage measured "shortly" after the CP has been switched off. Field problems such as the "reported spiking phenomenon", synchronous removal of all CP from the pipeline, interference currents on pipelines, AC currents on coated pipelines, etc., have hampered this measurement technique.1,2,3,4 This paper presents the results of a study conducted with an oscilloscope on coated and bare steel pipe specimens in a laboratory and bare and coated steel pipelines in the field in order to evaluate these problems and the merits of determining the -0.85 V measurement with the CP applied compared to determining it "shortly" after the CP has been switched off.
