API-571

In API 571 language, what is a damage mechanism?

• AThe process that produces a specific type of metallurgical or corrosion deterioration
• BThe maximum corrosion allowance assigned during design
• CA code-required hydrotest performed after fabrication
• DAny inspection technique used to find wall loss

What does passivation mean for a corrosion-resistant alloy?

• AHydrogen is removed from the metal by heat treatment
• BThe alloy becomes immune to all chloride attack
• CA sacrificial anode is attached to the equipment
• DA thin protective surface film forms and slows further corrosion

In a galvanic couple, which side corrodes faster?

• ABoth metals corrode at exactly the same rate
• BOnly the metal with the thicker wall
• CThe more anodic or less noble metal
• DThe more noble cathodic metal

What is meant by dew-point corrosion in refinery service?

• ACracking caused by excessive residual welding stress
• BCorrosion caused when acidic or salt-forming species condense from the vapor phase onto a…
• CCorrosion that occurs only after a pump loses suction
• DAny corrosion found in a dry gas line above 800F

What does sensitization mean for austenitic stainless steel?

• AChromium carbides precipitate at grain boundaries, leaving adjacent metal chromium-deplet…
• BHydrogen blisters form in the steel mid-wall
• CGraphite nodules replace the ferrite matrix
• DA hard nitride case forms at the surface

What does HAZ stand for in welding and damage-mechanism discussions?

• AHydrogen-activated zone
• BHigh-alloy zeroing
• CHot acid zone
• DHeat-affected zone

What does HTHA stand for?

• AHydrogen thermal hardening assessment
• BHigh-toughness heat-affected area
• CHigh-temperature hydrogen attack
• DHeat-treated hydrogen alloying

What does HIC stand for in sour-service damage?

• AHydrochloric-induced corrosion
• BHydrogen-induced cracking
• CHigh-intensity corrosion
• DHeat-input cracking

What does SOHIC stand for?

• AStress-oriented hydrogen-induced cracking
• BSulfide-oriented high-intensity corrosion
• CStress-opened hot-intergranular cracking
• DScale-oxide hydrogen interaction control

What does SSC stand for in wet H2S damage terminology?

• ASurface sulfide corrosion
• BStress-sensitive carburization
• CScale-spallation cracking
• DSulfide stress cracking

What does MIC stand for?

• AMoisture-insulated cracking
• BMetallic intergranular corrosion
• CMicrobiologically influenced corrosion
• DMechanically induced cavitation

Why is PWHT often specified for sour-service weldments?

• ATo make ammonium chloride salts deposit at a higher temperature
• BTo help reduce hardness and residual stress that can contribute to cracking susceptibility
• CTo intentionally increase martensite hardness in the HAZ
• DTo guarantee immunity from all chloride attack

Why are dead legs important in damage-mechanism reviews?

• AThey often create low-flow or stagnant conditions that concentrate corrosion risk
• BThey always operate at the highest metal temperature in the unit
• CThey eliminate the need for thickness monitoring
• DThey prevent deposits and biofilms from forming

In high-temperature service, what is an oxide scale?

• AA hydrogen blister formed beneath the steel surface
• BA chloride deposit trapped under insulation
• CA graphite-rich zone left by graphitization
• DA surface oxide layer formed by reaction between the hot metal and an oxidizing environme…

What is 885F embrittlement?

• ACarbon pickup in hot carburizing gas
• BHydrogen blistering in wet H2S carbon steel
• CLoss of toughness in susceptible ferritic stainless alloys caused by long exposure near 8…
• DChloride cracking of austenitic stainless under insulation

What is spheroidization in steel?

• ARapid oxidation of sulfide scale during shutdown
• BA microstructural change in which carbides become more rounded, often reducing strength a…
• CFormation of hydrogen blisters beneath the surface
• DLocalized chloride attack inside a gasket crevice

What is a passive film?

• AA thin surface layer that greatly slows corrosion on a passive alloy
• BA grease coating applied after fabrication
• CA thick rust deposit left after shutdown
• DA hydrogen bubble trapped under scale

What does localized corrosion mean?

• ACorrosion that affects only nonmetallic components
• BAny wall loss measured with ultrasonic testing
• CA type of cracking caused only by thermal cycling
• DAttack concentrated at specific spots or small areas rather than spread evenly across the…

What does scale spallation mean in high-temperature damage?

• AA passive film becomes thicker and more protective
• BHydrogen blisters link through inclusions
• CA protective surface scale cracks or flakes off, exposing fresh metal to further attack
• DA weld HAZ is softened by PWHT

What is the key practical difference between HIC and SSC?

• AThere is no practical difference; the terms are interchangeable
• BHIC can occur in susceptible wet H2S steel without high applied stress, while SSC strongl…
• CHIC occurs only in stainless steel, while SSC occurs only in cast iron
• DHIC is a dry high-temperature mechanism, while SSC is a low-temperature oxidation mechani…

Which damage mechanism best matches this scenario: A 304 stainless exchanger handling chloride-bearing water shows deep isolated holes while most of the surface still appears bright and intact.

• APitting corrosion
• BGeneral corrosion
• CCaustic stress corrosion cracking
• DHigh-temperature sulfidation

Which material or service condition is most susceptible to Pitting corrosion?

• ANormalized carbon steel in dry hydrocarbon service
• B1.25Cr-0.5Mo steel in high-temperature hydrogen service
• CGraphitized cast iron at moderate steam temperature
• DPassive stainless steel in chloride-bearing aqueous service

Which field clue or location most strongly supports Pitting corrosion?

• AUniformly stressed hot shell courses far from deposits
• BRefractory hot faces with no electrolyte present
• CStagnant crevices or low-flow zones where chlorides concentrate
• DDry fired surfaces above the sulfur dew point

Which variable most strongly promotes Pitting corrosion?

• ALoss of creep strength after long-term overheating
• BLocal passive-film breakdown in the presence of chlorides
• CHydrogen diffusion into a hard weld HAZ under wet H2S
• DBulk sulfur diffusion at elevated temperature

Which action is most effective to reduce the risk of Pitting corrosion?

• AReduce chloride concentration and stagnancy, and upgrade to a more pitting-resistant allo…
• BRaise hardness above 22 HRC
• CAdd more neutralizing amine to the overhead system
• DIncrease metal temperature to keep the surface dry

Which damage mechanism best matches this scenario: A stainless flange face is badly attacked under a gasket while adjacent exposed metal remains largely unaffected.

• AGalvanic corrosion
• BMetal dusting
• CHydrogen-induced cracking
• DCrevice corrosion

Which material or service condition is most susceptible to Crevice corrosion?

• APWHT carbon steel in strong caustic service
• BFerritic stainless in the 885F embrittlement range
• CPassive alloys exposed to an aqueous environment with tight shielded gaps
• DDry carbon steel at elevated sulfidation temperatures

Which field clue or location most strongly supports Crevice corrosion?

• ARandomly through the entire wall with no shielding feature
• BUnder gaskets, lap joints, deposits, or threaded connections
• CWithin the hottest radiant tube span
• DAt polished coupon surfaces in high turbulence

Which variable most strongly promotes Crevice corrosion?

• ADifferential aeration and local chemistry changes inside the occluded gap
• BBulk hydrogen charging from wet H2S into hard steel
• CLong-term carbide spheroidization from high temperature
• DThermal cycling across a refractory anchor

Which action is most effective to reduce the risk of Crevice corrosion?

• AIncrease hardness to improve crack resistance
• BRaise sulfur activity to stabilize sulfide scale
• CUse more steam tracing to keep the crevice wet
• DEliminate or seal crevices, improve drainage, and use alloys resistant to crevice attack…

Which damage mechanism best matches this scenario: Tubing in aqueous service is most deeply attacked beneath adherent solids while nearby clean metal has much less damage.

• ATemper embrittlement
• BHigh-temperature hydrogen attack
• CUnderdeposit corrosion
• DUniform oxidation

Which material or service condition is most susceptible to Underdeposit corrosion?

• AAustenitic stainless in chloride-free demineralized water
• BEquipment where deposits, fouling, or solids can sit on wetted surfaces
• CDry clean gas service with no entrained solids
• DLow-alloy steel operating only in the creep range

Which field clue or location most strongly supports Underdeposit corrosion?

• ABeneath settled solids, tubercules, fouling layers, or process scale
• BOnly at hot shell-to-skirt welds
• COnly on polished high-velocity impingement zones
• DOnly at grain boundaries after sensitization

Which variable most strongly promotes Underdeposit corrosion?

• ASteady-state dry sulfidation at high temperature
• BResidual stress plus wet ammonia-rich amine
• CGraphitization after years of moderate-temperature exposure
• DLocalized concentration changes and differential aeration beneath deposits

Which action is most effective to reduce the risk of Underdeposit corrosion?

• ARaise sulfur content to maintain a sulfide film
• BIncrease hardness in the affected area
• CReduce fouling, improve cleaning and water chemistry control, and inspect after deposit r…
• DLower PWHT temperature below the temper embrittlement range

Which damage mechanism best matches this scenario: External wall loss is found on insulated carbon steel near supports and weather-barrier penetrations after years of intermittent wetting.

• ACarburization
• BCorrosion under insulation
• CAmmonium chloride corrosion
• DHydrogen blistering

Which material or service condition is most susceptible to Corrosion under insulation?

• AInsulated carbon steel or austenitic stainless steel that can trap water under damaged in…
• BBare carbon steel in dry nitrogen service
• CInternally clad stainless with no external insulation
• DHigh-silicon cast iron in concentrated sulfuric acid

Which field clue or location most strongly supports Corrosion under insulation?

• AOnly on clean uninsulated flat plate mid-span areas
• BOnly in dry radiant sections with no cladding
• COnly at the bottom of water-filled dead legs
• DSupports, insulation terminations, nozzles, clips, and jacket penetrations