AMPP Senior Corrosion Technologist (NACE SCT) Practice Questions — 10 Free (2026)

An electrical resistance (ER) probe indicates corrosion because, as the sensing element corrodes:

• A. Its temperature rises, so its infrared emission increases
• B. Its cross-sectional area is reduced, so its electrical resistance increases ✓
• C. Its galvanic current output steadily decreases
• D. Its magnetic permeability rises with metal loss
• E. Its overall mass increases as corrosion product builds up on the sensing element

An ER probe's sensing element is made of the material of interest; as corrosion reduces its cross-sectional area, its electrical resistance increases, and the change is measured continuously or periodically. NACE Basic Corrosion Course, 8.3.3

An industrial atmosphere is harsher than a rural one mainly because of the sulfur released by burning fuel. What surface process makes that sulfur so damaging?

• A. Sulfur dioxide displaces oxygen from the air near the surface so that the metal can no longer form any protective oxide film in the first place
• B. Sulfur dioxide is selectively adsorbed and the metal oxide surface then catalyses its conversion to the trioxide, which forms sulfuric acid in humid conditions ✓
• C. Sulfur dioxide reacts with atmospheric nitrogen to give ammonium sulfate
• D. Sulfur dioxide dissolves the metal directly
• E. Sulfur dioxide combines with the dust in industrial air to form a hard abrasive deposit that continuously scours the corrosion product away from the metal surface as the wind moves it

The oxide covered metal surface acts as a catalyst, converting adsorbed sulfur dioxide to the trioxide, which with moisture forms sulfuric acid at the surface. That is why a small copper addition, or nickel and chromium additions, help by producing a tighter rust film, and why nickel and copper alloys with their insoluble sulfates are widely used in industrial air. It is also suggested that the survival of ancient iron owes more to a sulfur free atmosphere than to the metal itself. ASM Handbook Vol 13, Atmospheric Corrosion, contaminants

Two members are bolted up as a slip critical connection. Which coated condition of the faying surfaces gives an acceptable coefficient of friction?

• A. Solvent based inorganic zinc, which measures above the value obtained on a plain sandblasted surface ✓
• B. A conventional rust preventive oil based paint applied at the same film thickness as the primer used elsewhere on the structure
• C. Red lead paint
• D. Intact mill scale
• E. Hot dip galvanizing

Comparative testing places solvent based inorganic zinc at the top of the list, slightly above rusted and wire brushed steel and above plain blasted steel, while galvanizing, mill scale, rust preventive paint and red lead all fall lower. Any surface measuring under the blasted steel value should be rejected for bolted or riveted joints. Munger and Vincent, Corrosion Prevention by Protective Coatings, 2nd Ed 1999, Ch 3 (Friction Resistance)

What does increased agitation do to the diffusion layer at an electrode, and with what consequence?

• A. It thins the layer but leaves the limiting diffusion current unchanged
• B. It removes the layer completely, so concentration polarization is replaced by a resistance drop through the bulk electrolyte that grows with the square of the flow rate
• C. It thickens the layer
• D. It leaves the layer unchanged but raises the reversible potential
• E. Convection currents thin the layer ✓

The limiting current varies inversely with the thickness of the stagnant layer next to the metal, and stirring shortens the transport path. The layer is never abolished, and reversible potential is fixed by activities rather than by flow. Fontana Corrosion Engineering 3rd Ed, Sec 9-7

Under the polarized-potential criterion, the potential from structure to electrolyte must be at least:

• A. -500 mV CSE, IR-free
• B. -650 mV CSE, IR-free
• C. -1100 mV CSE, IR-free
• D. -850 mV CSE, IR-free ✓
• E. -1500 mV CSE, IR-free

A negative 850 mV IR-free (polarized/instant-off) potential relative to CSE is a recognized protection criterion. NACE SP0169 criteria (verify clause)

Coupons in a cooling water bypass loop are protected by the treatment while the plant exchanger tubes are not. What feature of the coupon arrangement explains that outcome?

• A. The coupon is smaller than the tube
• B. The coupon is made of a different heat of steel from the tube, and small differences in composition are known to change the response to inhibitor sharply
• C. The coupon has been cleaned before exposure whereas the tube carries its mill scale, and mill scale prevents inhibitor from adsorbing at all
• D. The coupon sits in the most turbulent part of the stream and adds turbulence itself, so inhibitor reaches its surface more readily than it reaches a tube wall ✓
• E. The coupon is at a lower temperature than the tube wall, and every inhibitor reaction that forms a protective film runs faster at the lower temperature because the film is thermodynamically less stable when hot

Transfer of inhibitor to a surface is controlled by the same mass transfer processes that control transfer of dissolved oxygen. A coupon mounted in the middle of the flow occupies the most turbulent region and disturbs the flow further, so it enjoys better inhibitor supply than a tube wall does. That is the recognised limitation of coupon testing in water systems, along with its failure to model the heat flux. Baboian, Corrosion Tests and Standards 2nd Ed, Ch 34 Industrial Waters

A pump impeller is damaged by vapour bubbles that form and then collapse against the metal in the presence of a corrodent. Under which heading is that damage placed?

• A. A subset of erosion corrosion known as cavitation ✓
• B. An example of filiform corrosion running under a coating
• C. A case of stress corrosion cracking, because collapsing bubbles supply the sustained tensile stress that cracking requires
• D. A form of intergranular corrosion
• E. A variant of selective leaching

Cavitation is treated as a subset of erosion corrosion because the high pressures generated by collapsing bubbles damage the protective film exactly as mechanical flow forces do. Fretting is the other named subset, arising from slight relative motion between contacting surfaces. Schweitzer, Fundamentals of Metallic Corrosion, Ch 1

A series of ionic liquids shares one cation and one alkyl chain but differs in the counter anion. How did the anion change the coverage obtained on the steel?

• A. Coverage improved as the anion radius increased, hexafluorophosphate ranking above tetrafluoroborate, bromide and chloride ✓
• B. Coverage fell steadily as the anion radius grew, so fluoride salts stood at the top of the ranking
• C. Only anions that carry a donor nitrogen atom gave any measurable coverage
• D. The anion made no measurable difference, because only the cation reaches the metal while the anion stays fully hydrated in the bulk acid at every concentration examined
• E. Chloride produced the widest coverage

The reported ranking of coverage follows the size of the anion, with the bulky fluorinated phosphate anion at the top and chloride at the bottom. A reversed ranking, or a claim that the anion is irrelevant, contradicts the comparison on which the ranking rests. Corrosion Inhibitors (Singh ed.), Ch 2 Structural Effect in Ionic Liquids, anion effect

Once the resistive component at a given test point has been assessed and judged acceptable, what shortcut does TM0497 allow later?

• A. Only close interval surveys may be used from then on
• B. The instant off value recorded at that time may be entered on every subsequent survey sheet without remeasurement, provided the rectifier output has not been adjusted since the evaluation was carried out
• C. No further readings are needed at that location
• D. The on potential value may be used for routine monitoring until a significant change occurs in the environment, the structure or the protection system ✓
• E. The location must be re-evaluated every thirty days

Once the resistive component at a site is understood, the simpler on reading can serve as the routine indicator, but that permission lapses when conditions change materially, such as piping changes, protection system changes, isolation failures, coating deterioration or foreign structure influence. NACE TM0497-2022, Paragraph 5.13

An inline isolator inadvertently left in a cathodic protection circuit would most likely cause what symptom?

• A. A drop in current output because the circuit resistance is increased or broken ✓
• B. A surge in current output
• C. No change at all given the site, service, and installation conditions described f
• D. A reversal of the reference electrode
• E. A decrease in soil resistivity

An unintended inline isolator interrupts or greatly increases the resistance of the current path, reducing or stopping current output; it is one of the causes to check when investigating low rectifier output. NACE CP 1 Course Manual, Ch. 9 (Low Output)