It is generally referred to as a steel native potential or a free corrosion potential, although it can also be an instant off-potential, a decayed off-potential, or a rest potential. The values of these potentials can be measured correctly only when there is absence of interference by stray currents or long-line currents.
Nevertheless, if the steel native or rest potentials can be known, the level of cathodic polarization applied on the steel pipe surface for a given off-potential can be evaluated and provides a more direct measure (than an off-potential) on the magnitude of corrosion rate reduction.
The meanings of on- and off-potentials, polarization (decay or growth) and ohmic voltage drop (IR), native and rest potentials are labeled and shown clearly.
Figure 4 shows the native or rest potentials of operating pipelines or installed coupons vs.
The change of [pH.sub.i] from 7.2 to 8.5 produced a slight hyperpolarization of rest potential by about 1 mV.
We are proposing that the reduction of [I.sub.L] with increasing [pH.sub.i] allows the negative slope character of [I.sub.NaP] to destabilize the equilibrium point (rest potential) of the axon at --60 mV, thereby resulting in autonomous activity.
The ionic model that we propose for the spontaneous activity is novel and counterintuitive, in that the effect is attributable to a reduction of inward current, thereby leading to a destabilization of the rest potential by the [I.sub.NaP] component.