NACE RP 169 : The 100 mV criterion in CP

[Hamdy Khalaf]

Can someone explain this method ?

[Marty Thompson]

From the NACE CP-1 student guide...
The 100-mV polarization criterion can be applied by either starting with the known corrosion potential (native or original “off” potential) or the polarized structure potential. Begin by momentarily interrupting the current flow to determine the “instant off” (polarized) potential. With current interrupted, watch the decay of the polarized potential. If the potential drops (becomes more positive) at least 100 mV, the criterion has been met. Likewise, if the “instant off” reading is at least 100mV more negative than the native reading, the criterion has been met.

[Marty Thompson]

From the NACE CP-1 student guide...
The 100-mV polarization criterion can be applied by either starting with the known corrosion potential (native or original “off” potential) or the polarized structure potential. Begin by momentarily interrupting the current flow to determine the “instant off” (polarized) potential. With current interrupted, watch the decay of the polarized potential. If the potential drops (becomes more positive) at least 100 mV, the criterion has been met. Likewise, if the “instant off” reading is at least 100mV more negative than the native reading, the criterion has been met.

[JUANPE]

This criterion requires that when the current is switched off, the instant potential shall be at least 100 mV more negative than the free corrosion potential. This criterion has seen some acceptance with the CP of rebar steel in concrete.

[Hamdy Khalaf]

Many Thanks