AMPP CP4 Specialist flashcards
AMPP CP4 Specialist · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Galvanic anode driving voltage
- The difference between the anode open-circuit potential and the structure polarized potential; it is the electromotive force that drives protective current in a sacrificial system.
- Anode current capacity
- Total charge an anode can deliver over its life, computed from net mass, theoretical capacity, current efficiency, and utilization factor divided by design life.
- Anode resistance formula
- For a vertical rod anode in homogeneous soil, R = (ρ/2πL)[ln(4L/d) − 1], where ρ is soil resistivity, L is length, and d is diameter.
- 100 mV polarization criterion
- A protection criterion requiring at least a 100 mV negative shift of structure potential from its native potential, measured after IR drop is removed.
- Zinc anode limitation
- Zinc anodes can passivate in low-resistivity, high-pH, or sulfate-rich soils, reducing current output; magnesium is preferred in such environments.
- Anode utilization factor
- Fraction of anode mass actually consumed before the anode reaches end of life; typically about 0.5 for slender anodes and 0.85 for compact anodes.
- Sacrificial anode spacing
- Anode placement determined by current distribution needs, coating damage locations, and geometry; spacing controls how evenly protection reaches the structure.
- Seawater protection criterion
- In seawater, -0.80 V versus Ag/AgCl is a common protection criterion for steel, distinct from the -0.85 V versus Cu/CuSO4 soil criterion.
- Impressed current rectifier sizing
- Rectifier DC voltage must exceed circuit resistance times design current plus back-EMF; current rating includes margin for coating degradation and seasonal changes.
- Total circuit resistance
- Sum of anode-to-electrolyte resistance, structure-to-electrolyte resistance, and cable/connection resistance; it sets the rectifier voltage needed for a given current.
- MMO anode
- Mixed metal oxide coated titanium anode used in impressed current systems; low consumption rate and high current density capability make it long-lived.
- Coke breeze backfill
- Carbonaceous backfill around impressed current anodes that lowers anode resistance, extends anode life, and improves current distribution into the electrolyte.
- High-silicon cast iron anode
- Impressed current anode material suited to soil and freshwater; consumption rate and current density limits depend on environment and backfill.
- Coating breakdown factor
- Multiplier applied to coated area current density to account for coating degradation over time; it raises design current as the coating ages.
- Stray current interference
- Current from a CP system or other DC source that enters a nearby metallic structure and discharges elsewhere, causing accelerated corrosion; mitigated by bonds or shielding.
- Graphite anode
- Impressed current anode material with low consumption rate in many soils; requires backfill and careful current density control to avoid damage.
- Rectifier transformer taps
- Adjustable taps on the rectifier transformer that allow output voltage to be set to match actual circuit resistance and seasonal soil resistivity changes.
- Current demand calculation
- Design current equals protected area times current density times coating breakdown factor; coating quality strongly reduces required current and rectifier size.
- Platinum-niobium anode
- Impressed current anode used in seawater and other aggressive environments; the platinum coating provides low consumption and high current density capability.
- Attenuation coefficient
- α = sqrt(r/R), where r is longitudinal resistance per unit length and R is coating leakage resistance to earth per unit length; it controls how potential decays with distance.
- Attenuation equation
- Potential at distance x along a protected structure is E(x) = E0 × exp(−αx), where E0 is the potential at the drain point and α is the attenuation coefficient.
- Longitudinal resistance
- Resistance per unit length of the pipe or structure metal; higher longitudinal resistance increases attenuation and shortens the effective protection distance.
- Coating leakage resistance
- Resistance per unit length between structure and electrolyte through the coating; better coatings give higher R, larger α, and shorter attenuation distance.
- Wenner four-pin method
- Field method for measuring soil resistivity using four equally spaced pins; resistivity = 2πaR, where a is pin spacing and R is measured resistance.
- Polarization definition
- The negative shift of structure potential from its free-corrosion potential toward the protection potential; it measures CP effectiveness rather than current alone.
- IR drop
- Voltage error in potential measurements caused by current flowing through electrolyte resistance; removed by instant-off readings to reveal true polarized potential.
- Current density criterion
- Design current per unit area of protected surface; typical values are 10-25 mA/m² for coated steel in soil, with higher values for bare steel.
- Reference electrode types
- Cu/CuSO4 for soils, Ag/AgCl for seawater, and saturated calomel (SCE) in laboratory work; each has a defined potential offset used to compare readings.
- Ohm's law in CP
- V = I × R; current output equals driving potential divided by total circuit resistance, linking anode resistance, soil resistivity, and rectifier voltage.
- Protection distance
- Distance along a structure over which potential remains at or beyond the protection criterion; governed by attenuation coefficient and drain point potential.
- Coating conductance
- Per-unit-length leakage conductance (1/R) between structure and electrolyte; damaged or bare coating raises conductance and current demand.
- Native potential
- The free-corrosion potential of a structure before CP is applied; it is the baseline from which polarization shift and the 100 mV criterion are measured.