API API-571 Study Guide Archives Updated on Jul 19, 2025
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NEW QUESTION # 10
Which of the following is a contributing factor in caustic corrosion?
- A. Boiler feed water hardness
- B. Alkalinity of superheated steam
- C. Heat traced equipment
- D. Iron oxide concentration
Answer: C
Explanation:
API RP 571 describes under Caustic Corrosion:
"One of the significant contributing factors is caustic accumulation in low-flow or stagnant areas, especially in heat-traced lines or around steam injection points."
"Localized heating can concentrate caustic solutions, promoting corrosion even in carbon or stainless steels." Thus, option C (heat-traced equipment) is the correct and technically accurate choice.
NEW QUESTION # 11
Which of the following can increase the corrosion rate of carbon steel via hydrofluoric (HF) acid corrosion?
- A. HF acid concentration above 98%
- B. Oxygen contamination
- C. Weld hardness above 200 BHN
- D. High nitrogen content in process
Answer: C
Explanation:
According to API RP 571 and API RP 751:
"In HF alkylation units, carbon steel can be used if weld hardness is controlled to # 200 Brinell (BHN).
Exceeding this can significantly increase the corrosion rate and susceptibility to cracking."
"Hard welds act as preferential corrosion sites due to microstructural inhomogeneity and stress concentration." (Reference: API RP 571, Section 4.3.3.4 - Hydrofluoric Acid Corrosion; API RP 751, Section 5.3 - Materials of Construction) Thus, option D is correct.
NEW QUESTION # 12
Cracks associated with brittle fracture will typically be _________.
- A. Straight
- B. Branching
- C. Perpendicular
- D. Jagged
Answer: A
NEW QUESTION # 13
________ eliminates the susceptibility of most common steels to SCC.
- A. PWHT
- B. All of the above
- C. Preheat
- D. High temperature
Answer: A
NEW QUESTION # 14
Hydrogen stress cracking is normally found in:
- A. mild carbon steels at high temperatures and high hydrogen partial pressure.
- B. the presence of sulfuric acid.
- C. stainless steel internals such as trays.
- D. high strength low alloy steels and carbon steels.
Answer: D
Explanation:
Hydrogen Stress Cracking (HSC) is a subclass of environmental cracking that occurs in certain materials when hydrogen is present. According to API RP 571, HSC typically affects high-strength low alloy steels and carbon steels, particularly under tensile stress in a hydrogen-containing environment. This includes areas like weld-affected zones and hard spots in steels.
* From API RP 571 Section 5.1.2.1 (Hydrogen-Induced Cracking):
"Hydrogen stress cracking (HSC) can occur in carbon steel and low alloy steels in environments containing hydrogen at ambient to moderately elevated temperatures (up to 200°F or 93°C)... Hardness is a critical factor for HSC. High hardness in welds and heat affected zones (HAZ) are most susceptible."
* Additionally, API RP 939-C does not directly define HSC but reinforces the relationship between hydrogen exposure and metal integrity, particularly under conditions not exceeding 450 °F (230 °C) for hydrogen services.
Thus, option A is correct, as it directly reflects the metal types most susceptible to HSC in operational environments defined by API RP 571.
NEW QUESTION # 15
___________ cooling water outlet temperatures and/or process side outlet temperatures tend to __________ corrosion rates as well as fouling tendency.
- A. Decreasing, decrease
- B. Increasing, increase
- C. Increasing, decrease
- D. Decreasing, increase
Answer: B
NEW QUESTION # 16
Type 304L SS is satisfactory for phosphoric acid concentration of 100% up to about _________. Type 321 is required from there to 225º F.
- A. 140º F
- B. 150º F
- C. 100º F
- D. 120º F
Answer: D
NEW QUESTION # 17
With sour water corrosion, streams with a pH below ________ indicate the presence of a strong acid.
- A. 4.5
- B. 6.0
- C. 5.5
- D. 7.0
Answer: A
NEW QUESTION # 18
A loss in ductility of high strength steels due to the penetration of atomic hydrogen can lead to brittle cracking called hydrogen embrittlement. Which of the following materials is susceptible to HE.
- A. All of the above
- B. Low alloy steel
- C. Carbon steel
- D. 400 Series SS
Answer: A
Explanation:
Explanation
NEW QUESTION # 19
___________ is the result of cyclic stresses caused by variations in temperature.
- A. Thermal fatigue
- B. Stress fatigue
- C. Stress cracking
- D. Cyclic cracking
Answer: A
NEW QUESTION # 20
Amine cracking has been reported down to ambient temperatures with some amines. __________ temperatures and stress levels _______ the likelihood and severity of cracking.
- A. Increasing, reduces
- B. Decreasing increases
- C. Increasing, decreases
- D. Increasing increases
Answer: D
NEW QUESTION # 21
Thermal fatigue cracks propagate ________ to the stress and are usually dagger shaped, transgranular and oxide-filled.
- A. Transverse
- B. Diagonal
- C. Axial
- D. Angular
Answer: A
NEW QUESTION # 22
Stress relief and stabilization heat treatment of 300 Series SS for maximizing chloride SCC and PASCC resistance can cause ____________ problems, especially in thicker sections.
- A. HIC
- B. Thermal fatigue
- C. Reheat cracking
- D. Hydrogen
Answer: C
NEW QUESTION # 23
__________ is a form of damage found mostly in older vintage carbon steels and C-0.5 Mo low alloy steels under the combined effects of deformation and aging at an intermediate temperature.
- A. Thermal fatigue
- B. Strain aging
- C. None of the above
- D. Spheroidization
Answer: B
NEW QUESTION # 24
Which of the following are susceptible to thermal fatigue?
- A. All of the above
- B. SA-516-70
- C. SA-182 Gr B
- D. SA-53 Gr B
Answer: A
NEW QUESTION # 25
The presence of _________ can destabilize the scale and turn it into a nonprotective scale.
- A. H²O
- B. H²S
- C. O²
- D. H²
Answer: A
NEW QUESTION # 26
Regular and controlled carbon grades of stainless steels such as types 304/304H and 316/316H are particularly susceptible to sensitization in the weld HAZ. Low carbon "L" grades are less susceptible and usually can be welded without sensitizing. The "L" grades will not sensitize provided long term operating temperatures do not exceed about __________.
- A. 700(o) F
- B. 750(o) F
- C. 800(o) F
- D. 900(o) F
Answer: B
NEW QUESTION # 27
MIC is often found in _________, bottom water of storage tanks, piping with stagnant or low flow and piping in contact with some soils.
- A. Drums
- B. Heat exchangers
- C. All of the above
- D. Vessels
Answer: B
NEW QUESTION # 28
Hydrogen blisters may form at many different depths from the surface of the steel, in the middle of the plate or near a weld. In some cases, neighboring or adjacent blisters that are at slightly different depths (planes) may develop cracks that link them together. Interconnecting cracks between the blisters often have a __________ appearance.
- A. Step like
- B. Eyebrow
- C. Jagged
- D. Crescent
Answer: A
NEW QUESTION # 29
In most cases, brittle fracture occurs only at temperatures _________ the Charpy impact transition temperature.
- A. Around
- B. Below
- C. Inside
- D. Above
Answer: B
NEW QUESTION # 30
The most effective means of preventing caustic stress corrosion cracking is:
- A. Postweld heat treatment
- B. Controlling process temperature during steamouts
- C. Reducing caustic concentration
- D. Upgrading to 300 series stainless steel
Answer: A
Explanation:
According to API RP 571, under Caustic Stress Corrosion Cracking (Caustic Embrittlement):
"Cracking occurs in stressed components exposed to caustic (e.g., sodium hydroxide)."
"The most effective mitigation strategy is postweld heat treatment (PWHT), which relieves residual stress that promotes cracking."
"Upgrading materials or controlling concentration may help, but do not replace stress relief." (Reference: API RP 571, Section 4.2.2.3 - Caustic SCC) Thus, PWHT is the most effective prevention technique, making option A correct.
NEW QUESTION # 31
Hydrogen permeation or diffusion rates associated with wet H#S damage of carbon steel and low-alloy steels have been found to be minimal at a pH of:
- A. 0
- B. 1
- C. 2
- D. 3
Answer: D
Explanation:
API RP 571 discusses this under Wet H#S Damage - Hydrogen Blistering, HIC, SOHIC:
"Hydrogen generation is reduced as pH increases. At pH 9 and above, the corrosion potential is less favorable for hydrogen charging and thus permeation into the steel is minimal."
"Most wet H#S cracking damage mechanisms are accelerated under acidic conditions (pH < 7)." Hence, high pH (around 9) environments offer the most protection against hydrogen damage, making option D the correct choice.
NEW QUESTION # 32
Thermal fatigue cracks usually propagate _______ to the stress and they are usually dagger-shaped.
- A. Transverse
- B. Across
- C. Diagonal
- D. Parallel
Answer: A
NEW QUESTION # 33
The amplitude and frequency of vibration as well as the _________ of the components are critical factors in vibration-induced fatigue.
- A. Temperature
- B. Fatigue resistance
- C. Velocity
- D. Material properties
Answer: B
NEW QUESTION # 34
Temper embrittlement is defined as:
- A. A reduction in ductility and notch toughness caused by postweld heat treatment (PWHT) or low- temperature service below 120°F (49°C).
- B. A reduction in fracture toughness caused by long-term exposure in the temperature range of 650°F to
1070°F (345°C to 575°C). - C. An increase in ductility and notch toughness caused by postweld heat treatment (PWHT) or high- temperature service above 120°F (49°C).
- D. An increase in toughness caused by long-term exposure in the temperature range of 650°F to 1100°F (345°C to 595°C).
Answer: B
Explanation:
API RP 571 describes Temper Embrittlement as:
"A metallurgical degradation mechanism that leads to a reduction in fracture toughness due to long-term exposure in the temperature range of 650°F to 1070°F (345°C to 575°C)."
"It affects Cr-Mo steels and is not easily detected except by impact testing." Therefore, option C most accurately defines the condition based on the recognized API description.
NEW QUESTION # 35
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