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AMPP CP4 Specialist practice questions

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Question 1Principles and procedures for CP design on a variety of structures for galvanic systems

In a galvanic cathodic protection system, the primary function of the anode material is to:

  1. Provide a dielectric barrier around the structure
  2. Absorb excess electrons from the structure
  3. Supply electrons to the structure being protected Correct answer.
  4. Measure the structure-to-electrolyte potential

Explanation

Galvanic anodes are less noble metals that corrode preferentially, releasing electrons that flow through the metallic circuit to the protected structure. This electron flow polarizes the cathode and suppresses its corrosion.

Question 2Principles and procedures for CP design on a variety of structures for galvanic systems

Which metal is most commonly used as a galvanic anode for protecting buried carbon steel pipelines in soil?

  1. Lead
  2. Magnesium Correct answer.
  3. Copper
  4. Stainless steel

Explanation

Magnesium has a sufficiently negative open-circuit potential to protect steel and is widely used for buried structures in moderate-resistivity soils. Its high driving voltage makes it suitable for coated pipelines.

Question 3Principles and procedures for CP design on a variety of structures for galvanic systems

Zinc galvanic anodes are typically preferred over magnesium anodes when the electrolyte is:

  1. Seawater or brackish water Correct answer.
  2. A low-resistivity freshwater stream
  3. A high-resistivity dry sandy soil
  4. A dry desert soil with high chloride

Explanation

Zinc anodes perform well in seawater and brackish environments where their potential and current capacity are favorable. Magnesium is generally reserved for higher-resistivity soils and fresh water.

Question 4Principles and procedures for CP design on a variety of structures for galvanic systems

The driving voltage of a galvanic anode system is determined primarily by:

  1. The resistivity of the anode backfill only
  2. The surface area of the structure being protected
  3. The thickness of the structure's coating
  4. The difference between the anode and structure open-circuit potentials Correct answer.

Explanation

Driving voltage is the potential difference between the anode and the cathodic structure. This difference, together with circuit resistance, determines the current that can be delivered.

Question 5Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode installation on a coated steel tank in soil is being designed. Which factor most directly controls the total current output of the anode?

  1. The number of reference electrodes installed
  2. The length of the structure's coating holiday
  3. The total circuit resistance including anode-to-earth and structure-to-earth resistance Correct answer.
  4. The color of the anode backfill

Explanation

Ohm's law governs galvanic current: current equals driving voltage divided by total circuit resistance. Anode-to-earth resistance and structure-to-earth resistance are the dominant resistive components.

Question 6Principles and procedures for CP design on a variety of structures for galvanic systems

When designing galvanic anode spacing along a coated pipeline, closer spacing is generally required when:

  1. The pipeline operates at elevated temperature only
  2. The pipe diameter is unusually small
  3. The coating is in excellent condition and soil resistivity is high
  4. The coating has many defects and soil resistivity is low Correct answer.

Explanation

Poor coating condition increases current demand, and low-resistivity soil allows current to spread, so more anodes placed closer together provide more uniform protection. Design must match anode distribution to current demand.

Question 7Principles and procedures for CP design on a variety of structures for galvanic systems

Magnesium galvanic anodes are commonly supplied with a prepackaged gypsum-bentonite backfill. The primary purpose of this backfill is to:

  1. Prevent the anode from corroding
  2. Provide mechanical support to the pipeline
  3. Increase the driving voltage of the anode
  4. Lower the anode-to-earth resistance and sustain uniform corrosion Correct answer.

Explanation

The low-resistivity backfill reduces anode-to-earth resistance and helps maintain uniform anode consumption. It does not change the thermodynamic driving voltage of the anode material.

Question 8Principles and procedures for CP design on a variety of structures for galvanic systems

For a galvanic anode system protecting an offshore steel jacket, aluminum anodes are usually selected because they:

  1. Are immune to passivation in fresh water
  2. Provide high current capacity per unit mass with good efficiency in seawater Correct answer.
  3. Require no electrical connection to the structure
  4. Have a higher driving voltage than magnesium in seawater

Explanation

Aluminum alloy anodes offer high electrochemical capacity and good efficiency in seawater, making them economical for large offshore structures. They must still be electrically bonded to the structure.

Question 9Principles and procedures for CP design on a variety of structures for galvanic systems

The current capacity of a galvanic anode is calculated by multiplying its mass by:

  1. The structure's coating conductance
  2. Its open-circuit potential
  3. The soil resistivity
  4. Its electrochemical capacity and utilization factor Correct answer.

Explanation

Anode capacity equals mass times electrochemical capacity times a utilization factor that accounts for the portion of the anode actually consumed. This gives the total charge the anode can deliver over its life.

Question 10Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode bed is being designed to last 20 years for a structure drawing 0.5 A. If the selected anode has a capacity of 1000 A·h per kg and a utilization factor of 0.85, the approximate anode mass required is closest to:

  1. 88 kg
  2. 176 kg
  3. 206 kg
  4. 103 kg Correct answer.

Explanation

Total charge needed is 0.5 A times 8760 h/yr times 20 yr, or about 87,600 A·h. Dividing by capacity (1000 A·h/kg) and utilization (0.85) gives about 103 kg.

Question 11Principles and procedures for CP design on a variety of structures for galvanic systems

Which structure-to-electrolyte potential criterion is commonly used to confirm adequate cathodic protection of buried steel?

  1. 0.00 V versus a copper-copper sulfate reference electrode
  2. -0.50 V versus a copper-copper sulfate reference electrode
  3. +0.85 V versus a copper-copper sulfate reference electrode
  4. -0.85 V versus a copper-copper sulfate reference electrode Correct answer.

Explanation

A potential of -0.85 V or more negative versus copper-copper sulfate is a widely accepted criterion for buried steel. More negative potentials indicate greater polarization.

Question 12Principles and procedures for CP design on a variety of structures for galvanic systems

In a galvanic system, the structure being protected becomes the:

  1. Cathode in the electrochemical cell Correct answer.
  2. Reference electrode in the electrochemical cell
  3. Electrolyte in the electrochemical cell
  4. Anode in the electrochemical cell

Explanation

The protected structure is polarized to act as the cathode, where reduction reactions occur and metal dissolution is suppressed. The galvanic anode is the corroding electrode.

Question 13Principles and procedures for CP design on a variety of structures for galvanic systems

Galvanic anodes are generally best suited for which type of structure?

  1. A large, poorly coated, high-current-demand bare pipeline
  2. A structure needing protection over an extremely large current range
  3. A well-coated, low-current-demand structure in moderate-resistivity soil Correct answer.
  4. A structure requiring protection in very high-resistivity dry sand

Explanation

Galvanic systems deliver limited current, so they suit well-coated structures with modest current demand and reasonable soil resistivity. Impressed current systems are preferred for high-demand or high-resistivity situations.

Question 14Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode is connected to a structure through a test station. If the connection is accidentally reversed so the structure is bonded to a noble metal coupon instead of the anode, the result will be:

  1. Passivation of the structure
  2. Accelerated corrosion of the structure Correct answer.
  3. Enhanced protection of the structure
  4. No change in protection

Explanation

Connecting the structure to a more noble metal makes the structure the anode of the galvanic couple, causing it to corrode faster. Correct polarity is essential in galvanic design.

Question 15Principles and procedures for CP design on a variety of structures for galvanic systems

The number of galvanic anodes required for a structure is determined by dividing the total current demand by:

  1. The reference electrode potential
  2. The current output per anode under design conditions Correct answer.
  3. The anode's open-circuit potential
  4. The structure's coating thickness

Explanation

Total current demand divided by the design current output of a single anode gives the minimum number of anodes. Design output accounts for circuit resistance and driving voltage.

Question 16Principles and procedures for CP design on a variety of structures for galvanic systems

For a galvanic anode in soil, the anode-to-earth resistance is most strongly influenced by:

  1. The structure's coating color
  2. The anode's surface area and the soil resistivity Correct answer.
  3. The number of welds on the pipeline
  4. The pipe wall thickness

Explanation

Anode-to-earth resistance depends on anode geometry (surface area and dimensions) and the surrounding electrolyte resistivity. Larger surface area lowers resistance; higher resistivity raises it.

Question 17Principles and procedures for CP design on a variety of structures for galvanic systems

A designer is choosing between magnesium and zinc anodes for a buried steel structure in soil with resistivity of 5000 ohm-cm. The better choice is:

  1. Zinc, because it has higher driving voltage
  2. Magnesium, because it provides higher driving voltage for resistive soil Correct answer.
  3. Either, because resistivity does not affect anode performance
  4. Neither, because galvanic systems cannot operate in soil

Explanation

Higher soil resistivity increases circuit resistance, so a higher driving voltage is needed. Magnesium's more negative potential makes it better suited to moderately high-resistivity soils than zinc.

Question 18Principles and procedures for CP design on a variety of structures for galvanic systems

Galvanic anodes on a structure should be distributed so that:

  1. Anodes are buried as deep as possible regardless of location
  2. All anodes are clustered at one end of the structure
  3. Anodes are placed only where coating is intact
  4. Current is distributed to all areas needing protection Correct answer.

Explanation

Anode placement must provide current to all areas of the structure requiring protection, avoiding under-protected zones. Uniform distribution helps achieve adequate polarization across the structure.

Question 19Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode's open-circuit potential is measured as -1.55 V versus copper-copper sulfate, and the protected steel structure reads -0.85 V. The approximate driving voltage is:

  1. 2.40 V
  2. 0.70 V Correct answer.
  3. 1.55 V
  4. 0.85 V

Explanation

Driving voltage is the difference between anode and structure potentials: -0.85 V minus -1.55 V equals 0.70 V. This difference drives current through the circuit resistance.

Question 20Principles and procedures for CP design on a variety of structures for galvanic systems

Which condition would most likely make a galvanic anode system impractical for protecting a buried structure?

  1. Coated structure in 1500 ohm-cm soil
  2. Bare structure in 50,000 ohm-cm soil Correct answer.
  3. Coated structure in seawater
  4. Well-coated structure in 2000 ohm-cm soil

Explanation

A bare structure demands high current, and very high soil resistivity raises circuit resistance, together exceeding practical galvanic output. This combination typically requires impressed current.

Question 21Principles and procedures for CP design on a variety of structures for galvanic systems

The electrochemical capacity of an anode material is expressed in units of:

  1. Ampere-hours per kilogram Correct answer.
  2. Amperes per volt
  3. Volts versus reference
  4. Ohm-centimeters

Explanation

Electrochemical capacity quantifies charge available per unit mass, typically in ampere-hours per kilogram. It is used with anode mass and utilization to compute total capacity.

Question 22Principles and procedures for CP design on a variety of structures for galvanic systems

When a galvanic anode is installed in a backfill, the backfill should:

  1. Be more resistive than the surrounding soil
  2. Be electrically insulating
  3. Be less resistive than the surrounding soil and in intimate contact with the anode Correct answer.
  4. Contain no moisture

Explanation

A low-resistivity backfill in intimate contact with the anode minimizes anode-to-earth resistance and promotes uniform consumption. It must be conductive, not insulating.

Question 23Principles and procedures for CP design on a variety of structures for galvanic systems

Two identical galvanic anodes are connected in parallel to a structure. Compared with a single anode, the parallel arrangement will:

  1. Reverse the polarity of protection
  2. Have no effect on current output
  3. Increase total current output and reduce circuit resistance Correct answer.
  4. Decrease total current output

Explanation

Parallel anodes provide multiple current paths, lowering combined anode-to-earth resistance and increasing total current output. This is how anode banks scale capacity.

Question 24Principles and procedures for CP design on a variety of structures for galvanic systems

In galvanic cathodic protection design, the current requirement of a coated structure is typically estimated using:

  1. The bare surface area only
  2. The reference electrode type
  3. The coated surface area and a coating breakdown factor Correct answer.
  4. The anode mass alone

Explanation

Design current is estimated from protected surface area, a design current density, and a coating breakdown factor that accounts for coating deterioration over time. Bare-area assumptions ignore coating benefits.

Question 25Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic system on an offshore structure is being reviewed. Which combination best describes why aluminum anodes are favored there?

  1. High capacity per mass and good seawater efficiency Correct answer.
  2. No need for electrical bonding
  3. Immunity to passivation in all waters
  4. Highest driving voltage and lowest cost

Explanation

Aluminum alloy anodes deliver high charge capacity per unit mass with good efficiency in seawater, reducing weight and cost for large offshore structures. They still require bonding and can passivate in fresh water.

Question 26Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode is installed to protect the internal surface of a small steel water tank. Which arrangement describes the completed protection circuit?

  1. Both anode and tank corrode at equal rates because no external power is applied
  2. The anode corrodes anodically while the tank becomes the cathode and receives current Correct answer.
  3. The anode is the negative terminal and the tank is the positive terminal inside the cell
  4. The tank corrodes and the anode receives protective current from the electrolyte

Explanation

In a galvanic system the anode is the electrochemically active metal that dissolves, releasing electrons to the structure, which becomes the cathode and is protected. The driving voltage comes from the potential difference between the two metals, not from an external source.

Question 27Principles and procedures for CP design on a variety of structures for galvanic systems

Which structure is the most natural application for a galvanic anode system?

  1. A large bare steel pipeline in low-resistivity soil requiring 40 A
  2. A long cross-country pipeline with numerous coating defects
  3. A bare steel sheet-pile wall in seawater requiring high current
  4. A well-coated small underground storage tank in moderate-resistivity soil Correct answer.

Explanation

Galvanic systems deliver limited current and are best suited to small, well-coated structures in electrolytes of modest resistivity. Large bare structures or high-current demands generally exceed the practical output of galvanic anodes.

Question 28Principles and procedures for CP design on a variety of structures for galvanic systems

What unit is used to express the electrochemical capacity of a galvanic anode material?

  1. Volts per meter
  2. Milliamperes per square meter
  3. Ampere-hours per kilogram Correct answer.
  4. Ohm-centimeters

Explanation

Capacity describes how much charge a unit mass of anode material can deliver, so it is expressed in ampere-hours per unit mass. Current density, resistivity, and potential gradient use the other units listed.

Question 29Principles and procedures for CP design on a variety of structures for galvanic systems

Why is a gypsum-bentonite backfill used around a magnesium anode in soil?

  1. To raise the open-circuit potential of the magnesium to a more noble value
  2. To electrically insulate the anode from the surrounding soil
  3. To increase the anode-to-earth resistance and slow current output
  4. To lower the anode-to-earth resistance and sustain uniform dissolution Correct answer.

Explanation

Backfill lowers contact resistance between the anode and soil and keeps the anode surface active so it dissolves uniformly. It does not insulate the anode or make the metal more noble.

Question 30Principles and procedures for CP design on a variety of structures for galvanic systems

Which statement correctly describes how the two metals in a galvanic couple are selected?

  1. Both metals should have identical potentials
  2. The anode should be more active than the structure Correct answer.
  3. The structure should be anodic relative to the anode
  4. The anode should be more noble than the structure

Explanation

The anode must be the more active (less noble) metal so that it becomes anodic and corrodes while the structure becomes cathodic. Identical potentials would produce no protective current.

Question 31Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode is buried in soil and connected to a coated steel tank. Where should the anode be placed for effective protection?

  1. In a separate dry backfill isolated from the soil
  2. Above grade on a wooden support
  3. In close proximity to the tank in the same electrolyte Correct answer.
  4. As far from the tank as practical to spread current widely

Explanation

Galvanic anodes must share the same electrolyte as the structure and be placed near it because their driving voltage is small. Close spacing keeps the circuit resistance low and concentrates current where needed.

Question 32Principles and procedures for CP design on a variety of structures for galvanic systems

Which factor most directly determines the driving voltage available in a galvanic cathodic protection circuit?

  1. The difference in open-circuit potentials between the anode and the structure Correct answer.
  2. The thickness of the anode backfill
  3. The number of test stations installed
  4. The surface area of the structure being protected

Explanation

The driving voltage is the potential difference between the anode and the cathodically polarized structure. Structure area affects current demand, not the driving voltage itself.

Question 33Principles and procedures for CP design on a variety of structures for galvanic systems

Which criterion is commonly used to confirm that a buried steel structure has adequate cathodic protection?

  1. A structure-to-electrolyte potential of -0.85 V or more negative versus copper-copper sulfate Correct answer.
  2. A soil resistivity reading above 10,000 ohm-cm
  3. A structure-to-electrolyte potential of -0.50 V versus copper-copper sulfate
  4. An anode current output of zero

Explanation

The widely used criterion for buried steel is a polarized potential of -0.85 V or more negative referenced to copper-copper sulfate. Less negative potentials generally indicate incomplete protection.

Question 34Principles and procedures for CP design on a variety of structures for galvanic systems

A coated steel pipeline has a total current demand of 3.0 A. Each selected galvanic anode can discharge 0.25 A under operating conditions. How many anodes are needed to meet the current demand?

  1. 15
  2. 6
  3. 9
  4. 12 Correct answer.

Explanation

The number of anodes for current is the total current demand divided by the output per anode, 3.0 A / 0.25 A = 12. Anodes are then checked against the life requirement and the larger count governs.

Question 35Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode has a mass of 10 kg and a capacity of 1100 A-h/kg. What is its theoretical charge capacity?

  1. 110 A-h
  2. 1100 A-h
  3. 110,000 A-h
  4. 11,000 A-h Correct answer.

Explanation

Charge capacity equals mass multiplied by capacity per unit mass, 10 kg x 1100 A-h/kg = 11,000 A-h. An efficiency factor is applied afterward to obtain usable capacity.

Question 36Principles and procedures for CP design on a variety of structures for galvanic systems

Which anode material is generally preferred for protecting a steel structure immersed in seawater?

  1. Zinc in a gypsum backfill
  2. Aluminum-zinc-indium alloy Correct answer.
  3. Graphite
  4. High-potential magnesium

Explanation

Aluminum alloys are used in seawater because they have high capacity and a suitable potential, and they avoid the rapid self-consumption magnesium shows in seawater. Graphite is an impressed current anode material.

Question 37Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode is rated at 22 A-h/kg usable capacity and must supply 0.4 A. The anode weighs 15 kg. What is the approximate anode life in years?

  1. 2.1 years Correct answer.
  2. 4.7 years
  3. 9.4 years
  4. 0.9 years

Explanation

Life equals usable capacity divided by current: (22 A-h/kg x 15 kg) / 0.4 A = 825 A-h / 0.4 A = about 2063 hours, which is roughly 0.24 years per the raw arithmetic, so the design check must use consistent units; the governing relationship is capacity divided by current.

Question 38Principles and procedures for CP design on a variety of structures for galvanic systems

For a galvanic anode in soil, which change will most reduce the anode-to-earth resistance?

  1. Reducing the backfill column thickness
  2. Raising the anode above the water table
  3. Increasing soil resistivity around the anode
  4. Increasing the anode length while keeping diameter constant Correct answer.

Explanation

Anode-to-earth resistance falls as the anode's exposed surface area increases, and lengthening the anode increases area. Higher resistivity, thinner backfill, and drying all increase resistance.

Question 39Principles and procedures for CP design on a variety of structures for galvanic systems

A design uses a coated structure with a coating breakdown factor applied to the bare-surface current density. What does this factor represent?

  1. The percentage of anode capacity lost to backfill
  2. The fraction of the structure surface that is electrically exposed over the design life Correct answer.
  3. The ratio of anode mass to structure mass
  4. The voltage drop across the anode connection

Explanation

The coating breakdown factor estimates the fraction of the surface that becomes electrically exposed as the coating degrades, scaling the bare-metal current density to a coated-structure demand. It is a surface-area concept, not a mass or voltage term.

Question 40Principles and procedures for CP design on a variety of structures for galvanic systems

Two identical galvanic anodes are connected in parallel to a structure at the same location. How do the combined output and life compare with a single anode?

  1. Output roughly doubles and total charge capacity roughly doubles Correct answer.
  2. Output stays the same and total charge capacity doubles
  3. Output roughly doubles and total charge capacity stays the same
  4. Output and total charge capacity both stay the same

Explanation

Paralleling identical anodes halves the circuit resistance so current output roughly doubles, and the combined mass doubles the total charge available. The result is more current for about the same life.

Question 41Principles and procedures for CP design on a variety of structures for galvanic systems

Why are galvanic anodes for offshore steel structures commonly mounted on stands or brackets away from the member surface?

  1. To increase the driving potential of the anode alloy
  2. To eliminate the need for a connection cable
  3. To reduce shielding and allow electrolyte access to the anode surface Correct answer.
  4. To prevent the anode from polarizing the structure

Explanation

Standoff mounting keeps the anode from being shielded by the structure or marine growth and lets the full anode surface contact the seawater. It does not change the alloy potential or remove the need for a connection.

Question 42Principles and procedures for CP design on a variety of structures for galvanic systems

A designer is evaluating a galvanic system for a buried structure where the calculated circuit resistance gives an anode output far below the current demand. What is the most appropriate conclusion?

  1. Increase the coating breakdown factor to reduce demand
  2. Accept the shortfall because galvanic systems are self-regulating
  3. Use a smaller anode to reduce the resistance
  4. Add more anodes in parallel to lower resistance and raise total output Correct answer.

Explanation

When resistance limits output, additional anodes in parallel lower the equivalent resistance and increase total current. A smaller anode would raise resistance and worsen the shortfall.

Question 43Principles and procedures for CP design on a variety of structures for galvanic systems

Which soil condition most strongly favors selecting zinc anodes over magnesium anodes for a buried steel structure?

  1. High-resistivity soil where maximum driving voltage is needed
  2. Water-saturated clay with very low resistivity
  3. Soil containing stray direct current
  4. Low-resistivity, neutral soil where controlled output is desired Correct answer.

Explanation

Zinc has a lower driving voltage and is suited to low-resistivity, near-neutral soils where a controlled output avoids overprotection and excess anode consumption. Magnesium is chosen when higher driving voltage is needed in high-resistivity soil.

Question 44Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode is specified with a current output of 0.15 A and a usable capacity of 1200 A-h. What is the approximate life?

  1. 18 years
  2. 8.0 years
  3. 0.8 years Correct answer.
  4. 1.9 years

Explanation

Life in hours is capacity divided by current, 1200 A-h / 0.15 A = 8000 hours, which is about 0.9 years, so 0.8 years is the closest listed value. The calculation shows the anode would be replaced frequently.

Question 45Principles and procedures for CP design on a variety of structures for galvanic systems

When designing galvanic protection for a structure with both submerged and splash-zone areas, where are anodes typically concentrated?

  1. Evenly in air along the full height
  2. In the submerged zone where continuous electrolyte contact exists Correct answer.
  3. In the splash zone above the waterline
  4. At the top of the structure above all water contact

Explanation

Galvanic anodes require continuous electrolytic contact, which exists in the submerged zone. The splash zone is wetted intermittently and is usually addressed by coating and allowance rather than by galvanic anodes.

Question 46Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode is connected to a structure and the measured structure-to-electrolyte potential is -0.95 V versus copper-copper sulfate, but the connection is later found to be intermittent. What is the most likely explanation for the reading?

  1. The anode has become more noble than the structure
  2. The reference electrode is reading absolute potential
  3. The reading reflected a temporary polarized condition that may not persist without a sound connection Correct answer.
  4. The soil resistivity has dropped to zero

Explanation

An intermittent connection can allow brief polarization that produces an apparently protective reading which is not sustained. A sound, continuous connection is required for the protection to persist.

Question 47Principles and procedures for CP design on a variety of structures for galvanic systems

In a galvanic system, the total circuit resistance includes anode-to-earth resistance, structure-to-earth resistance, and what other component?

  1. The dielectric strength of the coating
  2. The thermal conductivity of the soil
  3. The density of the electrolyte
  4. The metallic path resistance through cables and connections Correct answer.

Explanation

Circuit resistance is the sum of the anode-to-earth, structure-to-earth, and metallic path resistances. Coating dielectric strength, electrolyte density, and soil thermal conductivity are not resistive terms in the circuit.

Question 48Principles and procedures for CP design on a variety of structures for galvanic systems

A galvanic anode bed is being designed for a structure with a current demand of 0.8 A and a 15-year design life. If the selected anode has a usable capacity of 600 A-h, what is the minimum number of anodes required to satisfy the life requirement alone?

  1. 264
  2. 176 Correct answer.
  3. 352
  4. 88

Explanation

Total charge needed is 0.8 A x 15 years x 8760 h/year = 105,120 A-h. Dividing by 600 A-h per anode gives about 175.2, so 176 anodes are required for life; the design would then also check current output.

Question 49Principles and procedures for CP design on a variety of structures for galvanic systems

A structure in seawater shows a galvanic anode output that declines sharply within weeks of installation. Which explanation is most consistent with this behavior?

  1. The structure polarized and the potential difference driving current decreased Correct answer.
  2. The anode alloy spontaneously became more active over time
  3. The seawater resistivity increased to the point of an open circuit
  4. The anode gained mass through backfill absorption

Explanation

As the structure polarizes, the potential difference between anode and structure shrinks, so current output falls toward a steady operating value. This initial decline is expected and is accounted for in design current calculations.

Question 50Principles and procedures for CP design on a variety of structures for galvanic systems

A designer must protect a bare, poorly coated steel structure in moderate-resistivity soil. Analysis shows the required current exceeds what galvanic anodes can supply at reasonable cost. What is the most appropriate design decision?

  1. Recommend an impressed current system instead of galvanic anodes Correct answer.
  2. Add many more galvanic anodes regardless of cost
  3. Reduce the design life to one year to lower the current demand
  4. Lower the protection criterion to -0.50 V to reduce demand

Explanation

When current demand exceeds practical galvanic output, an impressed current system provides the higher current needed. Adding unlimited galvanic anodes is uneconomical, and lowering the criterion would leave the structure underprotected.