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AMPP Senior Corrosion Technologist study materials
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AMPP Senior Corrosion Technologist practice questions

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Question 1Metallurgy

Which crystal structure is characteristic of austenite (gamma iron)?

  1. Simple cubic
  2. Face-centered cubic Correct answer.
  3. Hexagonal close-packed
  4. Body-centered cubic

Explanation

Austenite, the high-temperature iron phase, has a face-centered cubic lattice with one atom at each corner and one at each face center. This structure provides more interstitial sites and greater solubility for carbon than ferrite.

Question 2Metallurgy

Ferrite (alpha iron) has which room-temperature crystal structure?

  1. Hexagonal close-packed
  2. Body-centered cubic Correct answer.
  3. Face-centered cubic
  4. Tetragonal

Explanation

Alpha iron is body-centered cubic at room temperature and remains so up to about 912 C. Its limited interstitial space gives ferrite low carbon solubility.

Question 3Metallurgy

In the iron-carbon system, what is the approximate maximum carbon solubility in austenite at 1147 C?

  1. 2.14 percent Correct answer.
  2. 0.022 percent
  3. 6.67 percent
  4. 0.77 percent

Explanation

Austenite can dissolve up to about 2.14 percent carbon at the eutectic temperature of 1147 C. This high solubility is why austenite forms readily during elevated-temperature processing.

Question 4Metallurgy

What is the eutectoid composition and temperature of the iron-carbon system?

  1. 2.14 percent C at 1147 C
  2. 4.3 percent C at 1147 C
  3. 0.022 percent C at 727 C
  4. 0.77 percent C at 727 C Correct answer.

Explanation

The eutectoid reaction transforms austenite of about 0.77 percent carbon into pearlite at roughly 727 C. This composition yields the finest lamellar mixture of ferrite and cementite.

Question 5Metallurgy

Pearlite is best described as which microstructure?

  1. A single-phase solid solution of carbon in ferrite
  2. Alternating lamellae of ferrite and cementite Correct answer.
  3. A dispersion of graphite nodules in ferrite
  4. A supersaturated tetragonal martensite

Explanation

Pearlite forms when austenite of eutectoid composition decomposes into alternating plates of ferrite and cementite. The lamellar spacing controls the strength of the constituent.

Question 6Metallurgy

Which phase is the hard, brittle compound of iron and carbon with the formula Fe3C?

  1. Martensite
  2. Ferrite
  3. Cementite Correct answer.
  4. Austenite

Explanation

Cementite is the intermetallic compound Fe3C containing about 6.67 percent carbon. It is hard and brittle and acts as a strengthening constituent in steels.

Question 7Metallurgy

Rapid quenching of austenite to form martensite primarily produces strengthening through which mechanism?

  1. Carbon supersaturation and lattice distortion Correct answer.
  2. Solid-solution softening of ferrite
  3. Coarsening of cementite lamellae
  4. Recrystallization into fine ferrite grains

Explanation

Martensite forms by a diffusionless shear transformation that traps carbon in a tetragonally distorted lattice. The trapped carbon and high dislocation density impede slip, raising hardness.

Question 8Metallurgy

Tempering of as-quenched martensite is performed primarily to accomplish which result?

  1. Reduce brittleness while retaining useful strength Correct answer.
  2. Increase hardness above the as-quenched value
  3. Restore the fully austenitic structure
  4. Eliminate all carbides from the matrix

Explanation

Tempering allows carbon to precipitate as fine carbides, relieving the internal stresses of martensite. This lowers hardness somewhat but improves toughness and ductility.

Question 9Metallurgy

Which quenching medium generally produces the slowest cooling rate for a given steel section?

  1. Still water
  2. Agitated oil
  3. Still air Correct answer.
  4. Brine

Explanation

Air provides a much lower heat-transfer coefficient than liquid quenchants, so cooling is slowest in still air. Slow cooling favors ferrite-pearlite formation over martensite.

Question 10Metallurgy

Which alloying element is added to stainless steel primarily to provide passivity?

  1. Molybdenum
  2. Carbon
  3. Chromium Correct answer.
  4. Nickel

Explanation

Chromium forms a thin, adherent chromium oxide film that passivates the steel surface. A minimum of roughly 10.5 to 12 percent chromium is needed for stainless behavior.

Question 11Metallurgy

In the 300-series stainless steels, what is the primary role of nickel?

  1. Promotes ferrite formation
  2. Stabilizes the austenitic structure Correct answer.
  3. Forms the passive oxide layer
  4. Increases carbon solubility in cementite

Explanation

Nickel is an austenite stabilizer that expands the austenite phase field to room temperature. This yields the austenitic microstructure typical of 304 and 316 alloys.

Question 12Metallurgy

Sensitization of austenitic stainless steel occurs by which mechanism?

  1. Precipitation of nickel-rich intermetallics
  2. Transformation of austenite to martensite
  3. Formation of chromium carbides at grain boundaries Correct answer.
  4. Dissolution of the passive film by chlorides

Explanation

Holding austenitic stainless steel in the 425 to 815 C range allows chromium carbides to precipitate at grain boundaries. The adjacent zones become chromium-depleted and lose corrosion resistance.

Question 13Metallurgy

Which stainless steel grade is most prone to sensitization because of its relatively high carbon content?

  1. Type 304 Correct answer.
  2. Type 316L
  3. Type 304L
  4. Type 321

Explanation

Standard Type 304 contains up to about 0.08 percent carbon, which can form chromium carbides during heating in the sensitizing range. Low-carbon L grades and stabilized grades reduce this risk.

Question 14Metallurgy

Grain boundaries are preferred sites for localized corrosion primarily because they do which of the following?

  1. Have a perfectly ordered lattice with no defects
  2. Exclude all impurity atoms
  3. Provide higher energy and possible composition differences Correct answer.
  4. Are enriched in chromium in all alloys

Explanation

Grain boundaries are regions of higher atomic disorder and energy and can differ in composition from the grain interior. These factors make them susceptible to preferential attack.

Question 15Metallurgy

Which microstructural feature most strongly increases the susceptibility of a steel to hydrogen-induced cracking?

  1. Hard martensitic regions and high hardness Correct answer.
  2. Fine equiaxed grain structure
  3. Low residual stress
  4. Coarse ferrite with low strength

Explanation

Hard martensitic microstructures are highly susceptible to hydrogen embrittlement and cracking. Limiting hardness and controlling microstructure reduce the risk.

Question 16Metallurgy

In a duplex stainless steel, the microstructure consists of which two phases?

  1. Austenite and graphite
  2. Ferrite and cementite
  3. Austenite and ferrite Correct answer.
  4. Martensite and bainite

Explanation

Duplex stainless steels contain a balanced mixture of austenite and ferrite, typically near 50/50. This combination provides high strength with good stress-corrosion resistance.

Question 17Metallurgy

Which of the following best describes a bainitic microstructure?

  1. A non-lamellar aggregate of ferrite and carbides formed at intermediate temperatures Correct answer.
  2. A single-phase austenitic solid solution
  3. A diffusionless tetragonal martensite
  4. A lamellar structure identical to pearlite

Explanation

Bainite forms at temperatures between those for pearlite and martensite and consists of ferrite with dispersed carbides rather than distinct lamellae. Its morphology differs from both pearlite and martensite.

Question 18Metallurgy

Increasing the carbon content of a plain carbon steel generally has which effect on hardness and weldability?

  1. Decreases hardness and increases weldability
  2. Increases hardness and increases weldability
  3. Increases hardness and decreases weldability Correct answer.
  4. Decreases hardness and decreases weldability

Explanation

Higher carbon raises hardenability and hardness but increases the risk of cracking and hydrogen problems during welding. This is why weldable structural steels are kept low in carbon.

Question 19Metallurgy

Which heat treatment is used to relieve internal stresses in a weldment without significantly altering the microstructure?

  1. Normalizing from the austenite range
  2. Stress-relief annealing at subcritical temperature Correct answer.
  3. Solution annealing above 1050 C
  4. Full austenitizing and rapid quench

Explanation

Stress-relief annealing is performed below the lower critical temperature so residual stresses relax without major phase changes. This preserves the existing microstructure while reducing cracking risk.

Question 20Metallurgy

Which cast iron type contains free graphite in the form of nodules and offers good ductility?

  1. Gray cast iron
  2. White cast iron
  3. Ductile (nodular) cast iron Correct answer.
  4. Malleable graphite flakes

Explanation

Ductile iron is treated with magnesium or cerium so graphite forms as nodules rather than flakes. The nodular shape reduces stress concentration and improves ductility.

Question 21Metallurgy

Which element is added to steel to improve resistance to pitting and crevice corrosion, particularly in chloride environments?

  1. Molybdenum Correct answer.
  2. Silicon
  3. Phosphorus
  4. Sulfur

Explanation

Molybdenum improves resistance to pitting and crevice corrosion, especially in chloride-containing environments. It is why 316 stainless outperforms 304 in marine and chemical service.

Question 22Metallurgy

The pitting resistance equivalent number (PREN) of a stainless steel is most strongly increased by which element?

  1. Molybdenum Correct answer.
  2. Manganese
  3. Carbon
  4. Copper

Explanation

PREN is calculated from chromium, molybdenum, and nitrogen contents, with molybdenum contributing a strong weighted term. Higher PREN indicates better resistance to pitting and crevice corrosion.

Question 23Metallurgy

Which mechanism explains why cold work can increase the susceptibility of austenitic stainless steel to stress-corrosion cracking?

  1. It increases the chromium content
  2. It introduces strain-induced martensite and dislocation structures Correct answer.
  3. It removes all residual stresses
  4. It forms a thicker passive film

Explanation

Cold work generates dislocations and may form strain-induced martensite, creating preferential paths for crack initiation and propagation. These features raise susceptibility to stress-corrosion cracking.

Question 24Metallurgy

Which of the following best describes the effect of grain size on the yield strength of a metal at room temperature?

  1. Strength decreases as grain size decreases
  2. Strength increases as grain size decreases Correct answer.
  3. Strength increases as grain size increases
  4. Strength is independent of grain size

Explanation

According to the Hall-Petch relationship, finer grains increase yield strength because more grain boundaries impede dislocation motion. Finer grains also generally improve toughness.

Question 25Metallurgy

A carbon steel weld shows a hard, untempered martensitic heat-affected zone after welding. Which change would most directly reduce the risk of hydrogen-assisted cracking in that zone?

  1. Increasing the carbon equivalent of the steel
  2. Increasing the cooling rate after welding
  3. Using a higher-strength filler metal
  4. Preheating and controlling heat input to soften the zone Correct answer.

Explanation

Preheating and controlled heat input slow cooling and temper the heat-affected zone, lowering hardness and reducing susceptibility to hydrogen cracking. Lower hardness and reduced residual stress are the key mitigation factors.

Question 26Metallurgy

In the iron-carbon equilibrium diagram, which phase has a face-centered cubic crystal structure and can dissolve up to about 2.1 wt% carbon at elevated temperature?

  1. Austenite Correct answer.
  2. Ferrite
  3. Cementite
  4. Delta ferrite

Explanation

Austenite is the face-centered cubic solid solution of carbon in iron and can hold substantially more carbon in solution than the body-centered cubic phases. Ferrite and delta ferrite are body-centered cubic and have very limited carbon solubility. Cementite is an orthorhombic compound rather than a solid solution phase.

Question 27Metallurgy

A plain carbon steel is slowly cooled from the austenite region through the eutectoid temperature. What microstructure forms?

  1. A mixture of austenite and cementite
  2. A single-phase martensitic structure
  3. Ferrite and pearlite in proportions set by the carbon content Correct answer.
  4. A fully bainitic structure

Explanation

Slow cooling allows the eutectoid reaction to proceed by diffusion, producing pearlite from the austenite and proeutectoid ferrite or cementite depending on carbon level. Martensite and bainite require faster cooling than equilibrium furnace cooling provides.

Question 28Metallurgy

Which of the following is the primary reason that a fine-grained microstructure generally improves the toughness of a structural steel relative to a coarse-grained one?

  1. It removes residual stresses from the part
  2. It eliminates all nonmetallic inclusions
  3. More grain boundary area arrests propagating cleavage cracks Correct answer.
  4. It converts pearlite into martensite

Explanation

A finer grain size provides a greater density of grain boundaries, which deflect or arrest brittle cleavage cracks and lower the ductile-to-brittle transition temperature. Grain refinement does not remove inclusions, relieve residual stress, or change the transformation products formed.

Question 29Metallurgy

A low-carbon steel component must be surface hardened while retaining a tough, ductile core. Which treatment is best suited to this requirement?

  1. Full through-hardening by austenitizing and quenching
  2. Annealing to produce coarse pearlite
  3. Stress relieving at 600 C after machining
  4. Carburizing followed by quenching and tempering Correct answer.

Explanation

Carburizing enriches the surface in carbon so that quenching hardens only the outer case, leaving a low-carbon tough core. Through-hardening would harden the entire section and reduce core toughness, while stress relieving and annealing do not produce a hard case.

Question 30Metallurgy

Which of the following best explains why an as-welded ferritic steel heat-affected zone can be more susceptible to sulfide stress cracking than the base metal?

  1. The HAZ is fully austenitic at ambient temperature
  2. The HAZ can contain hard untempered microstructures that raise local hardness and hydrogen sensitivity Correct answer.
  3. The HAZ carbon content is higher than that of the base metal
  4. The HAZ always has a coarser grain size than the base metal

Explanation

Fast weld cooling can produce hard martensitic or bainitic constituents in the HAZ, and high hardness increases susceptibility to hydrogen-assisted cracking under sour service. The carbon content of the HAZ is essentially that of the base metal, and the HAZ is not austenitic at ambient temperature.

Question 31Metallurgy

In a precipitation-hardenable alloy such as 17-4 PH stainless steel, what is the purpose of the aging treatment performed after solution annealing and quenching?

  1. To precipitate fine intermetallic particles that strengthen the matrix Correct answer.
  2. To relieve all residual stress without changing strength
  3. To dissolve coarse carbides into solid solution
  4. To convert retained austenite entirely into delta ferrite

Explanation

Solution annealing puts alloying elements into solid solution, and the subsequent aging treatment precipitates fine coherent intermetallic phases that impede dislocation motion and raise strength. Dissolution of carbides occurs during solution annealing, not aging.

Question 32Metallurgy

A steel is held at a temperature just below the eutectoid temperature for a long time after austenitizing. Which change in the cementite phase is expected?

  1. Lamellar cementite spheroidizes into rounded particles Correct answer.
  2. Cementite transforms into graphite
  3. Cementite becomes face-centered cubic
  4. Cementite dissolves completely into ferrite

Explanation

Prolonged holding at subcritical temperature reduces interfacial area by diffusion, causing lamellar cementite to break down into spheroids. This spheroidized structure is softer and more formable. Cementite does not dissolve completely, convert to graphite under normal conditions, or change crystal structure.

Question 33Metallurgy

Which feature of a cast microstructure most directly explains its typically lower ductility compared with a wrought product of the same composition?

  1. Coarse, segregated dendritic structure with porosity and large second-phase networks Correct answer.
  2. A uniformly fine equiaxed grain size
  3. An absence of grain boundaries
  4. A fully martensitic matrix throughout the casting

Explanation

Casting solidification produces coarse dendrites, segregation, shrinkage porosity, and continuous grain-boundary networks that act as crack initiation sites and reduce ductility. A uniformly fine equiaxed structure would be beneficial, and castings do contain grain boundaries.

Question 34Metallurgy

Which alloying element is added to steel primarily to increase hardenability by shifting the continuous-cooling transformation curve to longer times?

  1. Hydrogen
  2. Sulfur
  3. Phosphorus
  4. Manganese Correct answer.

Explanation

Manganese delays the diffusional transformation of austenite so that martensite can form at slower cooling rates, thereby increasing hardenability. Sulfur and phosphorus are generally residual or free-machining elements that do not serve this purpose, and hydrogen is detrimental rather than a hardenability addition.

Question 35Chemical Treatment

Which chemical is most commonly injected to scavenge dissolved oxygen in a closed cooling water system?

  1. Sodium sulfite Correct answer.
  2. Sodium hypochlorite
  3. Sodium chloride
  4. Sodium hydroxide

Explanation

Sodium sulfite reacts with dissolved oxygen to form sodium sulfate, removing oxygen that would otherwise drive corrosion. Hypochlorite is an oxidizer and would add oxygen demand, while hydroxide and chloride do not scavenge oxygen.

Question 36Chemical Treatment

A corrosion inhibitor that forms a thin adsorbed film on a metal surface by sharing electron pairs with the metal is best described as which type?

  1. Passivating inhibitor
  2. Precipitating inhibitor
  3. Adsorption (film-forming) inhibitor Correct answer.
  4. Vapor-phase inhibitor

Explanation

Adsorption inhibitors, typically organic amines or imidazolines, bond to the metal surface through polar groups and form a barrier film. Passivators instead build an oxide layer, and precipitating inhibitors form insoluble deposits at the surface.

Question 37Chemical Treatment

In a cooling water system, what is the primary purpose of adding a scale inhibitor such as a phosphonate or polymer?

  1. To kill bacteria in the bulk water
  2. To raise the pH of the water
  3. To scavenge dissolved oxygen
  4. To disperse and prevent deposition of mineral scale Correct answer.

Explanation

Scale inhibitors work by threshold inhibition, crystal distortion, and dispersion to keep sparingly soluble salts such as calcium carbonate from depositing on heat transfer surfaces. They do not primarily control pH, microbiological growth, or oxygen.

Question 38Chemical Treatment

Which parameter is most directly used to monitor the dosage and residual of a continuous biocide feed in an open recirculating cooling system?

  1. Biocide residual concentration Correct answer.
  2. Specific conductance
  3. Turbidity
  4. Silica concentration

Explanation

Biocide efficacy depends on maintaining a target residual concentration for a specified contact time, so residual measurement is the direct control parameter. Conductance tracks dissolved solids, turbidity tracks particulates, and silica is unrelated to biocide dosing.

Question 39Chemical Treatment

A corrosion inhibitor is described as anodic. What does this mean about its mechanism?

  1. It increases the conductivity of the water
  2. It slows the cathodic reduction reaction
  3. It buffers the solution pH
  4. It polarizes the anodic dissolution reaction Correct answer.

Explanation

Anodic inhibitors retard the metal dissolution half-reaction, typically by forming a protective film over anodic sites. Cathodic inhibitors instead suppress the reduction half-reaction, and conductivity or pH buffering are unrelated functions.

Question 40Chemical Treatment

Which chemical treatment program is typically used to protect wet, idle carbon steel equipment during a shutdown?

  1. A dry nitrogen blanket with no chemical
  2. A film-forming amine or oil-based preservative applied to wetted surfaces Correct answer.
  3. A scale inhibitor dosed at threshold levels
  4. A high-dosage oxidizing biocide

Explanation

Layup protection relies on excluding oxygen and applying a persistent film-forming or oil-based coating to wetted surfaces. Biocides do not prevent general corrosion, dry layup is not applicable to wet idle equipment, and threshold scale inhibitors do not protect against oxygen corrosion.

Question 41Chemical Treatment

What is the principal function of a chelating agent such as EDTA in an industrial water treatment program?

  1. To oxidize organic contaminants
  2. To increase the dissolved oxygen content
  3. To bind metal ions and prevent them from forming scale Correct answer.
  4. To neutralize acids in the system

Explanation

Chelating agents form stable soluble complexes with metal ions such as calcium and iron, keeping them from precipitating as scale. They are not oxidizers, acid neutralizers, or oxygen sources.

Question 42Chemical Treatment

Which water chemistry condition most strongly increases the risk of carbon dioxide corrosion in a condensate return line?

  1. High phosphate with low calcium
  2. High pH with low dissolved solids
  3. Low pH from dissolved carbon dioxide Correct answer.
  4. High silica with low hardness

Explanation

Carbon dioxide dissolves to form carbonic acid, lowering pH and driving general and pitting attack on carbon steel condensate lines. The other listed conditions do not describe the acid-forming mechanism responsible for condensate corrosion.

Question 43Chemical Treatment

A cooling water system has a calcium carbonate saturation index that indicates a strongly scaling tendency. Which corrective action is most appropriate?

  1. Add an oxygen scavenger at high dosage
  2. Increase the scale inhibitor dosage and lower the pH within the treatment envelope Correct answer.
  3. Reduce blowdown frequency
  4. Increase the cycles of concentration

Explanation

A scaling saturation index means the water is supersaturated with respect to calcium carbonate, so increasing inhibitor dosage and modestly lowering pH reduces the driving force for deposition. Raising cycles or reducing blowdown would concentrate the water further and worsen scaling.

Question 44Chemical Treatment

An anodic inhibitor such as nitrite is dosed at only half the recommended concentration in a closed loop. What is the primary risk?

  1. Localized pitting attack at unprotected anodic sites Correct answer.
  2. Complete loss of all corrosion protection with uniform attack
  3. Reduced heat transfer from scaling
  4. Increased microbiological growth

Explanation

Underdosing an anodic inhibitor can leave some anodic sites unprotected while cathodic areas remain active, concentrating corrosion current at the unprotected sites and causing pitting. Adequate dosage is required to fully cover the anodic area.

Question 45Chemical Treatment

A plant switches from a chromate-based to a phosphate-based cooling water program. Which change in operating practice is most important to maintain corrosion control?

  1. Maintain the pH and calcium within the range that allows protective phosphate film formation Correct answer.
  2. Lower the pH to 5.5 to activate the phosphate
  3. Discontinue all biocide addition
  4. Eliminate blowdown to conserve phosphate

Explanation

Phosphate programs require a specific pH and calcium window so that a protective calcium phosphate film can form on the metal surface without excessive deposition. Operating outside that window either fails to protect or causes fouling.

Question 46Chemical Treatment

A sulfite oxygen scavenger is being considered for a closed hot water loop operating at 180 C. What is the main limitation?

  1. Sulfite decomposes at high temperature and can form corrosive sulfide and sulfur species Correct answer.
  2. Sulfite cannot be measured analytically
  3. Sulfite raises the pH above 12
  4. Sulfite is ineffective below 100 C

Explanation

At elevated temperatures sulfite can break down into sulfate and sulfide species, and the sulfide can promote corrosion, so alternative scavengers such as hydrazine or carbohydrazide are used. Sulfite is effective at lower temperatures and is easily measured.

Question 47Chemical Treatment

Which combination of conditions most favors microbiologically influenced corrosion in a cooling water system?

  1. Low pH with high dissolved oxygen
  2. Warm temperature, low flow or stagnant zones, and adequate nutrients Correct answer.
  3. Low temperature, high biocide residual, low nutrient levels
  4. High flow velocity with continuous chlorination

Explanation

MIC thrives where warm temperatures, stagnation or low shear, and nutrients allow biofilms to establish and protect the organisms from biocide. High flow and maintained biocide residual suppress biofilm formation.

Question 48Chemical Treatment

A polymer dispersant is added to a cooling water program. What role does it play relative to scale control?

  1. It keeps fine suspended particles dispersed so they do not agglomerate and deposit Correct answer.
  2. It acts as a primary biocide
  3. It dissolves existing scale deposits chemically
  4. It raises the Langelier Saturation Index

Explanation

Dispersant polymers adsorb onto fine particles and prevent them from agglomerating and settling onto heat transfer surfaces. They do not dissolve existing deposits, alter saturation index, or function as biocides.

Question 49Chemical Treatment

A closed chilled water loop shows rising iron concentration and a falling nitrite residual. What is the most likely interpretation?

  1. The iron is coming from the makeup water only
  2. Corrosion is increasing and the inhibitor is being consumed, so dosage should be investigated Correct answer.
  3. The loop is overprotected and dosing should stop
  4. The nitrite is being converted to scale

Explanation

Rising dissolved iron indicates active corrosion, and a declining nitrite residual shows the inhibitor is being consumed faster than it is being replenished. The response is to find the cause, such as oxygen ingress, and restore proper dosage.

Question 50Chemical Treatment

What is the purpose of a tracer in a chemical treatment program?

  1. To neutralize chlorine residual
  2. To allow the actual product concentration in the system to be measured and controlled Correct answer.
  3. To reduce the scaling tendency of the water
  4. To increase the corrosion inhibitor's film strength

Explanation

A tracer is an easily measured marker incorporated into the treatment product so that product concentration in the system can be tracked accurately, even when the active ingredient is hard to analyze. It does not change the chemical performance of the product.