API-571 Exam Questions Instant Access - No Installation Required

Question 1

For exchangers where the cooling water chemistry is poorly maintained, what can be done to improve corrosion resistance?

ALower the water velocity

BIncrease the tube diameter

CUpgrade the metallurgy of the exchanger

DIncrease the process side temperature above 212F (100C)

Answer : C

From API RP 571, under Cooling Water Corrosion:

''If proper water treatment is not feasible or consistently maintained, upgrading the metallurgy of exchanger tubes to more corrosion-resistant materials such as stainless steel or titanium may be necessary.''

''This is especially important in seawater or brackish water cooling applications or in once-through systems.''

(Reference: API RP 571, Section 4.3.1.1 -- Cooling Water Corrosion)

Thus, the most effective long-term solution in cases of uncontrolled water quality is to upgrade metallurgy, making option C correct.

Question 2

(Which damage mechanism occurs primarily as a result of exposure of interior vessel surfaces to air and moisture conditions during shutdown?)

APolythionic acid stress corrosion cracking

BWet hydrogen sulfide cracking

CCarbonate stress corrosion cracking

DSour water stress corrosion cracking

Answer : A

Comprehensive and Detailed Explanation From Exact Extract:

Polythionic acid stress corrosion cracking (PASCC) occurs when sulfide scales on stainless steel surfaces are exposed to oxygen and moisture, most commonly during shutdowns and outages.

Per API RP 571:

Polythionic acids form when iron sulfides react with air and water

Cracking occurs in austenitic stainless steels

Damage is most likely during shutdown, not normal operation

Therefore, PASCC is the damage mechanism directly associated with shutdown exposure conditions.

Referenced Documents (Study Basis):

API RP 571 -- Section on Polythionic Acid Stress Corrosion Cracking

Question 3

Short-term stress rupture is a/an:

Afailure caused by repeated cycling from elevated temperature, typically characterized by through-wall oxide filled ruptures with little bulging.

Belevated temperature failure caused by localized overheating, typically characterized by bulging and thinning.

Celevated temperature failure caused by diffusion of hydrogen into the material, typically characterized by blistering and cracking.

Dcracking failure caused by sulfides formed at elevated temperature that convert to acids on exposure to moisture and oxygen.

Answer : B

From API RP 571 Section 5.3.2.1 (Creep and Stress Rupture):

''Short-term creep rupture is often associated with localized overheating and results in bulging and thinning, often with a characteristic 'fish-mouth' rupture appearance. These failures occur under sustained load in a short time (hours or days), typically in high-temperature service due to a sudden increase in temperature or poor heat distribution.''

Thus, Option B accurately describes the mechanism and visual indications of short-term stress rupture.

Question 4

The remaining life of a component susceptible to creep damage can be cut in half by a/an:

Asudden change in temperature.

Bincrease in operating unit throughput.

Cincrease in temperature of 25F (15C).

Dincrease in stress of 10%.

Answer : C

According to API RP 571 Section 5.3.2.1 (Creep):

''Creep damage is exponentially dependent on temperature. A small increase in temperature (e.g., 25F or 15C) can reduce remaining life by more than half. This is because the creep rate increases rapidly with temperature, especially above design limits.''

Stress is a contributing factor, but the dominant and most sensitive variable is temperature.

Thus, Option C (increase in temperature of 25F/15C) is the correct answer.

Question 5

(Which of the following may be more susceptible to polythionic acid stress corrosion cracking?)

ASA-516 Grade 70 carbon steel

BType 304 stainless steel

CMonel 400

DType 321 stainless steel

Answer : B

Comprehensive and Detailed Explanation From Exact Extract:

Polythionic acid stress corrosion cracking (PASCC) occurs in austenitic stainless steels exposed to sulfur-containing environments during shutdowns, particularly when sulfide scales react with oxygen and moisture.

According to API RP 571:

Unstabilized stainless steels, such as Type 304, are most susceptible

Stabilized grades (e.g., Type 321, titanium-stabilized) are more resistant

Carbon steel and Monel are not susceptible to PASCC

Referenced Documents (Study Basis):

API RP 571 -- Section on Polythionic Acid SCC

Question 6

Which of the following damage mechanisms is related to steel hardness?

AStress-oriented hydrogen-induced cracking

BSulfide stress corrosion cracking

CHydrogen-induced cracking

DHydrogen blistering

Answer : B

API RP 571 details that:

''Sulfide Stress Cracking (SSC) susceptibility increases significantly with increased hardness of the steel.''

''NACE MR0175/ISO 15156 provides hardness limits for carbon and low-alloy steels to avoid SSC in sour environments. These are typically limited to 22 HRC or 248 Brinell.''

''High hardness promotes crack initiation under tensile stress in sour environments (i.e., containing HS).''

(Reference: API RP 571, Section 4.2.2.1 -- Sulfide Stress Corrosion Cracking)

While hydrogen-induced cracking (HIC) and blistering are related to hydrogen charging, SSC is the only mechanism directly and critically impacted by hardness, making option B correct.

Question 7

(Increased corrosion rates have been observed in equipment and piping in HF acid service at what minimum threshold temperature?)

A100 F (38 C)

B150 F (65 C)

C212 F (100 C)

D250 F (121 C)

Answer : B

Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, hydrofluoric (HF) acid corrosion rates increase significantly once operating temperatures exceed approximately 150 F (65 C).

Key points noted in API RP 571:

Below ~150 F, corrosion rates are relatively low due to formation of protective iron fluoride films.

Above 150 F, these films become unstable.

Corrosion rates increase rapidly with temperature, especially under high velocity and water contamination conditions.

Why the other options are incorrect:

Option A (100 F) is below the threshold for accelerated corrosion.

Option C and D are well above the onset temperature but are not the minimum threshold.

API RP 571 explicitly identifies 150 F (65 C) as the critical temperature where corrosion acceleration begins.

Referenced Documents (Study Basis):

API RP 571 -- Section on Hydrofluoric Acid Corrosion

API Alkylation Unit Corrosion Study Guide

API Corrosion and Materials API-571 Exam Questions