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AMPP Corrosion Technologist practice questions

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Question 1Cathodic Protection

In a cathodic protection circuit, the structure being protected is electrically connected to which component?

  1. The electrolyte
  2. The anode Correct answer.
  3. The voltmeter
  4. The reference electrode

Explanation

A cathodic protection circuit is completed by connecting the structure to the anode through the electrolyte. The structure becomes the cathode where reduction reactions occur, while the anode corrodes. The reference electrode is only used for measurement, not to carry the protection current.

Question 2Cathodic Protection

Which criterion is commonly used as the minimum protective potential for steel in aerobic soil at a copper/copper sulfate reference?

  1. -1.20 V
  2. -0.50 V
  3. -2.00 V
  4. -0.85 V Correct answer.

Explanation

The widely accepted criterion for steel in aerated neutral soil is a potential of at least -0.85 V measured against a copper/copper sulfate reference electrode. More negative potentials may be required in anaerobic or high-resistivity environments. -2.00 V and -1.20 V are excessively negative for this standard criterion.

Question 3Cathodic Protection

A galvanic anode provides protection because of which fundamental property?

  1. It has a lower driving voltage than the structure
  2. It has a more negative electrochemical potential than the structure Correct answer.
  3. It has a more positive electrochemical potential than the structure
  4. It has a higher electrical resistance than the structure

Explanation

Galvanic anodes work because their open-circuit potential is more negative (more active) than the structure, creating a potential difference that drives protective current. This difference forces the structure to become cathodic. A more positive potential would make the anode cathodic instead.

Question 4Cathodic Protection

Which material is commonly used as an impressed current anode because of its low consumption rate in soil and water?

  1. Zinc
  2. High-silicon cast iron Correct answer.
  3. Aluminum
  4. Magnesium

Explanation

High-silicon cast iron is a durable impressed current anode material used in soils and aqueous environments because it resists consumption. Magnesium, zinc, and aluminum are typically galvanic anode materials, not impressed current anodes.

Question 5Cathodic Protection

What is the primary purpose of a reference electrode in cathodic protection testing?

  1. To supply protective current to the structure
  2. To act as a temporary anode during commissioning
  3. To provide a stable potential against which structure potential is measured Correct answer.
  4. To lower the soil resistivity around the structure

Explanation

A reference electrode provides a stable, known potential so that the structure's potential can be measured and compared to protection criteria. It does not carry protective current or alter soil resistivity. Reliable measurements depend on its stability and proper placement.

Question 6Cathodic Protection

A structure is protected by an impressed current system. If the rectifier output current is increased while soil conditions remain constant, what happens to the structure-to-electrolyte potential?

  1. It becomes more negative Correct answer.
  2. It remains unchanged
  3. It fluctuates randomly
  4. It becomes more positive

Explanation

Increasing impressed current increases cathodic polarization, driving the structure potential more negative. The protection criterion is met when potential reaches or exceeds the required negative value. Excessive current, however, can cause overprotection and coating disbondment.

Question 7Cathodic Protection

Which type of coating defect is most likely to concentrate cathodic protection current and cause a localized high-current demand?

  1. A coating applied at excessive thickness
  2. A coating with high dielectric strength
  3. A holiday in the coating Correct answer.
  4. A uniformly coated surface

Explanation

A holiday is a break or pinhole in the coating that exposes bare metal, concentrating protection current at that small area. This localized current demand can lead to inadequate protection elsewhere if the system is undersized. Intact coatings resist current flow.

Question 8Cathodic Protection

What does a close-interval potential survey primarily measure?

  1. Structure-to-electrolyte potential at closely spaced intervals Correct answer.
  2. Soil resistivity along a pipeline
  3. Anode consumption rate
  4. Coating thickness at welds

Explanation

A close-interval survey measures structure-to-electrolyte potentials at closely spaced intervals to identify areas of inadequate protection and potential gradients. It does not directly measure soil resistivity, coating thickness, or anode consumption. The data help locate coating defects and interference effects.

Question 9Cathodic Protection

A magnesium galvanic anode is installed to protect a buried steel structure. Which factor most directly limits the current output of the anode?

  1. The anode's open-circuit potential
  2. The structure's coating color
  3. The reference electrode type
  4. The total circuit resistance Correct answer.

Explanation

For galvanic systems, current output is governed by Ohm's law: the potential difference divided by total circuit resistance. High soil resistivity, backfill resistance, and anode-to-structure resistance all limit output. The open-circuit potential sets the driving voltage but resistance controls actual current.

Question 10Cathodic Protection

During a cathodic protection interference test, a foreign pipeline shows a potential shift toward more positive values near a protected structure. What does this most likely indicate?

  1. The foreign pipeline is experiencing stray current discharge Correct answer.
  2. The foreign pipeline is receiving cathodic protection benefit
  3. The foreign pipeline coating has improved
  4. The reference electrode is faulty

Explanation

A positive potential shift on a foreign structure near a protected one indicates stray current discharge, meaning current is leaving that structure and causing corrosion. This is cathodic interference and must be mitigated, often with bonds or drainage. A negative shift would indicate current pickup.

Question 11Cathodic Protection

An impressed current system uses a rectifier rated at 50 A and 50 V. If the circuit resistance is 1 ohm, what current flows?

  1. 5 A
  2. 0.5 A
  3. 50 A Correct answer.
  4. 500 A

Explanation

Using Ohm's law, current equals voltage divided by resistance: 50 V / 1 ohm = 50 A. This equals the rectifier's rated current, so the system operates at its limit. Actual field current depends on soil resistivity, anode resistance, and coating condition.

Question 12Cathodic Protection

Why is a backfill material such as coke breeze used around impressed current anodes in soil?

  1. To insulate the anode from the electrolyte
  2. To increase anode resistance and limit current
  3. To raise the soil pH to alkaline levels only
  4. To lower contact resistance and extend anode life Correct answer.

Explanation

Carbonaceous backfill lowers the anode-to-earth contact resistance and helps spread current, while also slowing anode consumption. Lower resistance improves current output and distribution. It does not insulate the anode or serve only to alter pH.

Question 13Cathodic Protection

A pipeline protected by cathodic protection shows a potential of -0.75 V versus copper/copper sulfate. Which action is most appropriate?

  1. Decrease the rectifier output to avoid overprotection
  2. Take no action because the criterion is met
  3. Replace the reference electrode immediately
  4. Increase the protection current or investigate the cause of low potential Correct answer.

Explanation

A potential of -0.75 V is less negative than the -0.85 V criterion, indicating inadequate protection. The appropriate response is to increase current or investigate causes such as coating damage, high resistivity, or interference. Simply decreasing current would worsen the situation.

Question 14Cathodic Protection

Which condition would most likely cause a galvanic anode system to fail to protect a structure despite adequate anode mass?

  1. High soil resistivity Correct answer.
  2. Low soil resistivity
  3. Adequate anode-to-structure potential difference
  4. Proper backfill installation

Explanation

High soil resistivity increases circuit resistance, reducing current output below what is needed for protection. Galvanic systems have limited driving voltage, so they are sensitive to resistance. Low resistivity and proper installation support adequate current flow.

Question 15Cathodic Protection

In a cathodic protection system, what is the purpose of a dielectric coating on the structure?

  1. To act as a conductor for protection current
  2. To increase the current required for protection
  3. To reduce the exposed bare area and lower current demand Correct answer.
  4. To replace the need for anodes entirely

Explanation

A dielectric coating reduces the exposed metal area, lowering the total current needed to polarize the structure. This improves current distribution and extends anode life. Coatings do not conduct protection current or eliminate the need for anodes.

Question 16Cathodic Protection

A structure is being protected with an impressed current system, and the potential is measured with the reference electrode placed far from the structure. What effect does this have on the reading?

  1. It includes IR drop from the soil and may overstate protection Correct answer.
  2. It measures only the anode potential
  3. It has no effect on the measured value
  4. It eliminates all IR drop and gives a true polarized potential

Explanation

Placing the reference electrode far from the structure includes the IR drop through the soil in the measured potential, which can make the reading appear more negative than the true polarized potential. This can overstate protection. Close placement or current interruption helps separate IR drop from polarization.

Question 17Cathodic Protection

Which practice helps ensure reliable structure-to-electrolyte potential measurements?

  1. Ensuring good electrical contact between the reference electrode and the electrolyte Correct answer.
  2. Measuring while the rectifier is at maximum output only
  3. Using a reference electrode with unknown calibration
  4. Placing the electrode in dry, non-conductive soil

Explanation

Reliable measurements require good contact between the reference electrode and the electrolyte so the circuit is completed properly. Dry or poorly contacted soil introduces error. Reference electrodes should be calibrated and measurements should follow established procedures, including current interruption where appropriate.

Question 18Cathodic Protection

A galvanic anode is being selected for a buried steel structure in soil with resistivity of 5000 ohm-cm. Which anode material is generally preferred for this application?

  1. Aluminum
  2. Magnesium Correct answer.
  3. Zinc
  4. Carbon

Explanation

Magnesium anodes have a higher driving voltage and are preferred in higher-resistivity soils where zinc and aluminum may not produce sufficient current. Zinc is typically used in lower-resistivity soils and waters, and aluminum is mainly for marine use. Carbon is not a galvanic anode material.

Question 19Cathodic Protection

What is the primary function of a test station on a cathodically protected pipeline?

  1. To inject protective current into the soil
  2. To store spare anodes
  3. To provide a location for measuring potentials and current Correct answer.
  4. To filter stray currents from the pipeline

Explanation

Test stations provide accessible points for measuring structure-to-electrolyte potentials and current, and for connecting test leads. They do not inject current or filter stray currents; those functions belong to other system components. Regular measurements at test stations support monitoring and compliance.

Question 20Cathodic Protection

A cathodic protection rectifier is installed, but the structure remains unprotected. Which troubleshooting step is most appropriate first?

  1. Replace all anodes immediately
  2. Reduce the coating thickness
  3. Verify the rectifier output and electrical connections Correct answer.
  4. Increase the reference electrode distance

Explanation

Before replacing components, verify that the rectifier is producing output and that connections, fuses, and wiring are intact. Many failures result from blown fuses, open connections, or incorrect polarity. Systematic troubleshooting avoids unnecessary replacement of anodes.

Question 21Cathodic Protection

Which statement best describes the difference between cathodic protection and anodic protection?

  1. Cathodic protection makes the structure cathodic, while anodic protection makes it anodic and relies on passivation Correct answer.
  2. Both methods make the structure cathodic
  3. Both methods rely on sacrificial anodes
  4. Cathodic protection makes the structure anodic, while anodic protection makes it cathodic

Explanation

Cathodic protection polarizes the structure to act as a cathode, suppressing metal dissolution. Anodic protection polarizes the structure anodically into a passive region, which works only for passivatable metals in specific environments. The two methods operate on opposite principles.

Question 22Cathodic Protection

A steel structure in anaerobic soil requires a more negative protection potential than the -0.85 V criterion. Which value is commonly cited for this condition?

  1. -0.95 V Correct answer.
  2. -0.65 V
  3. -0.85 V
  4. -0.75 V

Explanation

In anaerobic environments where sulfate-reducing bacteria are active, a potential of -0.95 V versus copper/copper sulfate is often cited as the criterion for steel. This more negative value accounts for the different corrosion conditions. The -0.85 V criterion applies to aerobic conditions.

Question 23Cathodic Protection

A pipeline has a coating with many defects, and the cathodic protection system cannot achieve adequate potentials. Which combination of actions is most technically sound?

  1. Reduce the reference electrode distance only
  2. Increase anode size only
  3. Decrease rectifier voltage to avoid overprotection
  4. Rehabilitate the coating and increase protection capacity Correct answer.

Explanation

A heavily defective coating creates high current demand that may exceed system capacity. Rehabilitating the coating reduces demand, and increasing protection capacity addresses remaining needs. Combining both actions is more effective than either alone. Decreasing voltage would reduce protection further.

Question 24Cathodic Protection

During a current interruption test, the potential of a protected structure shifts from -1.10 V to -0.80 V when the current is interrupted. What does the difference represent?

  1. The soil resistivity
  2. The open-circuit potential of the anode
  3. The IR drop in the circuit Correct answer.
  4. The polarized potential of the structure

Explanation

The immediate positive shift upon current interruption reflects the IR drop component, while the remaining potential reflects the polarized potential. The difference between the on and instant-off readings is the IR drop. This separation is important for accurate assessment of protection.

Question 25Cathodic Protection

Which factor most influences the choice between galvanic and impressed current cathodic protection for a large, poorly coated pipeline?

  1. The current demand and available driving voltage Correct answer.
  2. The number of test stations
  3. The type of reference electrode used
  4. The color of the coating

Explanation

Large, poorly coated structures require high current, which typically exceeds the capacity of galvanic anodes. Impressed current systems provide higher driving voltage and adjustable output. The choice depends on current demand, soil resistivity, and power availability, not on coating color or test station count.

Question 26Cathodic Protection

Which reference electrode is most commonly used for structure-to-electrolyte potential measurements on buried pipelines and tanks?

  1. Silver/silver chloride electrode
  2. Saturated calomel electrode
  3. Copper/copper sulfate electrode Correct answer.
  4. Zinc reference electrode

Explanation

The copper/copper sulfate electrode (CSE) is the standard field reference for buried steel structures because it is rugged, inexpensive, and stable in soil. Silver/silver chloride and calomel are used more often in seawater or laboratory settings, and zinc is used as a galvanic anode rather than a routine reference.

Question 27Cathodic Protection

The criterion of -0.85 V versus a copper/copper sulfate electrode is applied to steel in which condition?

  1. Steel in seawater at elevated temperature
  2. Steel in concrete exposed to chlorides
  3. Steel in aerated neutral soil Correct answer.
  4. Steel in anaerobic soil containing sulfate-reducing bacteria

Explanation

The -0.85 V CSE criterion is a general criterion for steel in aerated, neutral soils. Anaerobic soils with sulfate-reducing bacteria and elevated-temperature conditions call for more negative criteria, and steel in concrete has separate criteria.

Question 28Cathodic Protection

What is the principal electrochemical reaction that provides protection at the cathodic surface of a protected steel structure?

  1. Reduction of oxygen and generation of hydroxyl ions Correct answer.
  2. Evolution of chlorine gas
  3. Oxidation of iron to ferrous ions
  4. Dissolution of the anode backfill

Explanation

At the cathode, cathodic protection drives reduction reactions, primarily oxygen reduction in aerated environments, which produces hydroxyl ions and raises local pH. Iron oxidation is the anodic corrosion reaction that the system suppresses.

Question 29Cathodic Protection

Which property of a structure's coating has the greatest effect on the total current required from a cathodic protection system?

  1. Coating dielectric strength
  2. Coating color
  3. Coating application temperature
  4. Coating breakdown and defect area Correct answer.

Explanation

Total protective current scales with the exposed bare-metal area, so coating breakdown and defect area dominate current demand. A coating's color or dielectric strength does not determine how much bare steel is exposed to the electrolyte.

Question 30Cathodic Protection

A galvanic anode is connected to a structure, but the measured structure-to-electrolyte potential shows essentially no shift from the native potential. Which condition best explains this result?

  1. The anode-to-structure circuit has an open connection Correct answer.
  2. The structure coating is in good condition
  3. The reference electrode is too close to the structure
  4. The soil resistivity is unusually low

Explanation

If no potential shift occurs, current is not flowing, which points to an open circuit in the anode lead, bond, or connection. Low resistivity and good coating would improve performance rather than eliminate the shift.

Question 31Cathodic Protection

A structure is polarized to -1.05 V versus copper/copper sulfate, and current is interrupted. The potential immediately shifts to -0.78 V and then decays slowly. What does the immediate shift indicate?

  1. The immediate shift represents the IR drop that must be removed for accurate criteria evaluation Correct answer.
  2. The coating has disbonded over the entire structure
  3. The structure is fully protected by polarization
  4. The anode bed has failed completely

Explanation

The instantaneous potential change at current interruption is largely the IR drop in the soil and coating holidays. Removing it reveals the polarized potential used to judge compliance with protection criteria. The slow decay that follows reflects depolarization of the structure.

Question 32Cathodic Protection

When designing an impressed current anode bed, which arrangement places the anodes in a vertical column within a single deep borehole?

  1. Deep vertical anode bed Correct answer.
  2. Distributed shallow anode bed
  3. Remote surface anode bed
  4. Horizontal anode bed

Explanation

A deep vertical anode bed installs multiple anodes in one deep borehole, which is useful where land is limited or where deeper, lower-resistivity strata exist. Horizontal and shallow distributed beds spread anodes over a wide area near the surface.

Question 33Cathodic Protection

A pipeline crosses a region where a nearby impressed current system causes a potential shift in the positive direction on the pipeline. What is this condition called?

  1. Anodic polarization
  2. Stray current corrosion Correct answer.
  3. Galvanic coupling
  4. Cathodic protection interference

Explanation

When a foreign cathodic protection system discharges current from a pipeline into the electrolyte, the pipeline becomes anodic at that location, which is stray current corrosion. It is identified by a positive potential shift and is mitigated by drainage bonds or shielding.

Question 34Cathodic Protection

Why is a permanent reference electrode sometimes installed near a protected structure?

  1. To replace the need for a coating on the structure
  2. To act as a grounded connection for the rectifier
  3. To supply protective current to the structure
  4. To allow repeatable potential monitoring at a fixed location without excavation Correct answer.

Explanation

A permanent reference electrode provides a stable, fixed measurement point so that trends in potential can be tracked over time without repeated excavation. It does not supply current, provide grounding, or substitute for coating.

Question 35Cathodic Protection

A rectifier supplying an impressed current system shows normal DC voltage but zero DC current output. Which cause is most consistent with this reading?

  1. A short circuit between anode and structure
  2. Excessive soil resistivity at the anode bed
  3. An open circuit in the anode or structure circuit Correct answer.
  4. A failed structure coating

Explanation

Normal voltage with no current indicates an open circuit somewhere in the anode lead, header cable, bond, or structure connection. A short would drive current high, and high resistivity or coating failure would reduce but not eliminate current.

Question 36Cathodic Protection

Which statement correctly describes the relationship between current density and protection of a bare steel structure in soil?

  1. A minimum current density is needed to polarize the steel to the protection criterion Correct answer.
  2. Current density only affects the anode and not the structure
  3. Current density has no effect on the polarized potential
  4. Higher current density always produces a proportionally higher protection potential without limit

Explanation

A sufficient current density must reach the steel surface to polarize it to the applicable criterion. Beyond that point, additional current is largely wasted and can cause overprotection effects such as coating disbondment or hydrogen evolution.

Question 37Cathodic Protection

A structure protected by an impressed current system shows a potential of -0.95 V versus copper/copper sulfate measured with the reference electrode placed directly over a coating holiday. What does this reading most directly indicate?

  1. The anode bed is disconnected
  2. The structure is overprotected and the rectifier should be shut down
  3. The structure meets the -0.85 V criterion at that location Correct answer.
  4. The coating is fully intact at that location

Explanation

A potential of -0.95 V CSE is more negative than the -0.85 V criterion, so the criterion is satisfied at that measurement point. Overprotection is generally associated with substantially more negative potentials and specific adverse effects, not with -0.95 V alone.

Question 38Cathodic Protection

Two buried structures of the same material are bonded together and protected by a single impressed current system. One structure receives much less current than the other. Which factor most likely explains the imbalance?

  1. The rectifier voltage is too high
  2. The two structures have different coating quality and exposed areas Correct answer.
  3. Both structures use identical anode material
  4. The reference electrode is copper/copper sulfate

Explanation

When structures share a protection system, current distribution depends on the resistance paths and exposed bare area of each structure. A structure with poorer coating or a larger bare area draws more current, leaving less for the other.

Question 39Cathodic Protection

A cathodic protection system is designed for a structure in soil with resistivity of 10,000 ohm-cm. Which design consequence follows most directly from this high resistivity?

  1. Lower anode-to-electrolyte resistance allows smaller anodes
  2. Galvanic anodes become more effective than impressed current
  3. Higher anode-to-electrolyte resistance and therefore greater driving voltage or more anode surface area is needed Correct answer.
  4. The protection criterion becomes less negative

Explanation

Anode-to-electrolyte resistance rises with soil resistivity, so achieving a given current requires higher driving voltage or more anode surface area. High resistivity also tends to favor impressed current over galvanic anodes, and it does not change the protection criterion itself.

Question 40Cathodic Protection

During a close-interval survey, potentials along a pipeline vary from -1.20 V to -0.70 V versus copper/copper sulfate, with the least negative readings occurring between test stations. Which interpretation is most appropriate?

  1. The entire pipeline is uniformly protected
  2. Regions with potentials above the criterion indicate insufficient protection that may require additional anodes or coating repair Correct answer.
  3. The most negative readings indicate the pipeline is corroding
  4. The survey result is invalid because potentials vary

Explanation

Variation along the line shows that protection is not uniform. Locations where the potential is less negative than the applicable criterion are underprotected and need mitigation such as additional anodes, improved drainage, or coating repair.

Question 41Protective Coatings

Which surface preparation standard is most commonly specified for abrasive blast cleaning of steel to a near-white finish?

  1. SSPC-SP 2
  2. SSPC-SP 10 / NACE No. 2 Correct answer.
  3. SSPC-SP 7 / NACE No. 4
  4. SSPC-SP 3

Explanation

SSPC-SP 10 (NACE No. 2) defines near-white blast cleaning, leaving only very light staining. The other listed standards cover hand tool, power tool, and brush-off blast cleaning respectively.

Question 42Protective Coatings

A coating that cures by reacting with moisture in the air is best described as which type?

  1. Chlorinated rubber
  2. Moisture-cure urethane Correct answer.
  3. Epoxy polyamide
  4. Alkyd

Explanation

Moisture-cure urethanes crosslink by reaction with ambient moisture, allowing application in high humidity and at low temperatures. Epoxies and alkyds cure by other mechanisms and are not moisture-cured.

Question 43Protective Coatings

What is the primary function of a primer in a protective coating system?

  1. Provide slip resistance for walking surfaces
  2. Provide adhesion to the substrate and corrosion inhibition Correct answer.
  3. Provide ultraviolet resistance for the system
  4. Provide the decorative color and gloss

Explanation

The primer bonds to the prepared substrate and typically contains inhibitive pigments that suppress corrosion at the metal surface. Color, gloss, and UV resistance are usually functions of the topcoat.

Question 44Protective Coatings

Which unit is used to express dry film thickness of a coating in the SI/metric system?

  1. Micrometre (µm) Correct answer.
  2. Pound per square inch
  3. Ounce
  4. Mil

Explanation

Dry film thickness in metric practice is expressed in micrometres. A mil is the imperial unit equal to 25.4 µm, and the other options are unrelated units.

Question 45Protective Coatings

Why is a dehumidification system often used during coating application inside a tank?

  1. To remove abrasive dust from the steel surface
  2. To increase coating viscosity before application
  3. To accelerate solvent evaporation beyond the coating's design
  4. To control steel temperature and relative humidity within specification Correct answer.

Explanation

Dehumidification controls both the dew point and steel temperature so that the surface stays above dew point and within the coating's application window. It is not a viscosity-control or dust-removal method.

Question 46Protective Coatings

Which coating defect appears as small, pinhole-sized voids through the film that expose the substrate?

  1. Blister
  2. Holiday Correct answer.
  3. Orange peel
  4. Sag

Explanation

A holiday is a discontinuity such as a pinhole or void that leaves the substrate exposed and is detected by high-voltage or low-voltage holiday testing. Orange peel is surface texture, sag is downward flow, and blister is a raised pocket.

Question 47Protective Coatings

Which of the following best describes the term 'pot life' of a two-component coating?

  1. The time required for the coating to reach full cure
  2. The time the coating remains workable after application to the surface
  3. The usable time after mixing the components before the material must be discarded Correct answer.
  4. The shelf life of the unopened components

Explanation

Pot life is the working time of a mixed multi-component product before its viscosity rises beyond use. It begins at mixing and is distinct from shelf life, recoat time, and cure time.

Question 48Protective Coatings

What does the term 'wet film thickness' measure?

  1. The thickness after full cure
  2. The thickness of the coating immediately after application while still fluid Correct answer.
  3. The thickness of the primer only
  4. The thickness of the substrate

Explanation

Wet film thickness is measured while the coating is still wet and is used to estimate the resulting dry film thickness via the volume solids. It is not a cured-film or substrate measurement.

Question 49Protective Coatings

A coating is specified at 5 mils dry film thickness with a volume solids of 65%. What wet film thickness should be targeted?

  1. About 3.3 mils
  2. About 7.7 mils Correct answer.
  3. About 10.0 mils
  4. About 5.0 mils

Explanation

WFT = DFT ÷ volume solids fraction = 5 ÷ 0.65 ≈ 7.7 mils. The other values do not follow from the relationship between wet and dry film thickness.

Question 50Protective Coatings

Steel surface temperature is 40°F (4°C) and the dew point is 38°F (3°C). According to typical good practice, what should be done?

  1. Proceed if the relative humidity is below 50%
  2. Proceed because the steel is above the dew point
  3. Proceed if a fast-curing coating is used
  4. Postpone coating because the steel is not at least 5°F (3°C) above dew point Correct answer.

Explanation

Standard practice requires the surface to be at least about 5°F (3°C) above the dew point to avoid condensation. Here the margin is only 2°F, so coating should be postponed regardless of humidity or cure speed.