Chapter 4 - Criteria for CP Flashcards
3 primary criteria used for cathodic protection of underground or submerged steel or cast iron oiling. *Listed in NACE RP-01-69 1996 edition)
-850mV (CSE) with CP applied
-850mv (CSE) polarized potential
100 mV polarization
Which of the NACE criteria is most widely used for steel or cast iron structures?
-850mv (CSE) with CP applied
What potential is substituted for -850mv (CSE) when there are hot pipelines or where the presence of microbes is confirmed or suspected?
-950mV (CSE)
What is native potential?
potential of structure before CP is applied.
How can damage be avoided from hydrogen generated in the cathodic protection process?
Avoid potentials more negative than -1.05 to -1.1mV (CSE) polarized.
What is polarized potential?
potential across the structure /electrolyte interface that is the sum of the corrosion potential and the cathodic polarization,.
How is a polarized potential measured?
immediately after all current sources have been interrupted.
Describe how to measure the “formation” of cathodic polarization for the 100 mV criteria?
- Measure the native potential
- Apply CP and allow structure to polarize,
- Measure the polarized (instant off) potential
- Find the difference of the native and polarized potentials,
- if greater than 100mV, criteria is met.
Describe how to measure the decay of cathodic polarization for the 100mV criteria?
- Measure the polarized potential (instant off)
- De-energize CP system and allow structure to depolarize
- Measure the depolarized potential
- Dind the difference between the polarized and depolarized potential
- if greater than 100mV, criteria is met.
Which of the following criteria can also be used on metals other than steel?
100 mV polarization
Why should the 100mV polarization criteria not be utilized in areas where inter granular external SCC is suspected?
criteria may place the structure in the range for cracking, which is between the native and -850 mV CSE.
Which cathodic protection criteria require the “side drain” procedure?
Net protective current
Which cathodic protection criteria are used for copper?
100 mV polarization
Which cathodic protection criteria are used for copper if it is electrically connected to steel?
- -850 mV (CSE) with CP applied
2. -850 mV (CSE) polarized potential
Which cathodic protection criteria is most commonly used for well-coated structures but can be cost prohibitive for poorly coated or bare structures?
-850 mV (CSE) with CP applied
According to the text, which 4 criteria should not be utilized in areas of stray current activity?
- E-log-I
- 300 mV shift
- 100 mV polarization
- Net protective current
Which cathodic protection criteria is measured directly after the interruption of all current sources?
-850 mV (CSE) polarized potential
CSE reference electrode uses
best for soil and fresh water environment
SSC/AgAgCl reference electrode
best for salt water and concrete environments
Zinc Reference electrode/ZRE
potential can change as the environment changes
SCE/Saturated calomel electrode
mercury - mercury chloride
laboratory use
SHE/Saturated Hydrogen Reference Electrode
- laboratory use
- determines the potential f other reference electrodes that are better suited for field use
- mother reference of all electrodes
polarization
moving all cathode to electro negative direction
ideal reading
true and accurate reading/real polarized potential
CP concept
- current flows onto structure from external anode, polarize cathode in electronegative (active) anode
- potential difference between anode and cathode is reduced to zero = no corrosion current flow.
IR Drop consideration
- determining the significance of voltage drops by method such as
- measuring/calculating voltage drops
- remaining the historical performance
