Pass the API ICP Programs API-571 Questions and answers with ExamsMirror

API RP 571 on Chloride Stress Corrosion Cracking (Cl-SCC) clearly states:

“Austenitic stainless steels such as 304 and 316 are highly susceptible to Cl-SCC when subjected to tensile stress and exposed to chloride-bearing environments.”

“Susceptibility is greatest in non-stress-relieved weldments or cold-worked areas.”

Brass and carbon steels are not typical Cl-SCC candidates; low alloy steels such as 1.25Cr-0.5Mo are also not commonly affected.

Thus, option C is the correct answer.

API RP 571 defines Hydrogen Embrittlement as:

“Improper PWHT can trap hydrogen within the microstructure of carbon steel or fail to relieve residual stresses, both of which increase the risk of hydrogen embrittlement.”

“Moisture in electrodes contributes to hydrogen-induced cracking, but embrittlement from atomic hydrogen is more directly tied to heat treatment and microstructure.”

Thus, option D is the most accurate.

In API RP 571, Carbonate SCC and Alkaline SCC are both discussed under mechanisms that occur in basic (high pH) environments, often with similar contributing conditions and prevention methods. The document highlights:

“Carbonate SCC is considered a subcategory of alkaline stress corrosion cracking. It results from the concentration of alkaline carbonates under thermal insulation or deposits.”

“Both mechanisms involve the same key parameters: elevated temperatures, tensile stress, and high pH solutions.”

(Reference: API RP 571, 3rd Edition, Section 4.2.2.4 and 4.2.2.3)

Because these mechanisms share similar material susceptibility and operating conditions, they are indeed closely related—option B is therefore the accurate and supported answer.

According to API RP 571, under Naphthenic Acid Corrosion (NAC):

“The most severe corrosion is typically found in areas of high velocity and turbulence, such as at pump around nozzles, transfer lines, elbows, reducers, and orifices.”

“NAC is characterized by uniform thinning and can accelerate significantly where flow-induced erosion is present.”

(Reference: API RP 571, Section 4.3.4.1 – Naphthenic Acid Corrosion)

This clearly establishes that high velocity and turbulence increase NAC severity, making option D correct.

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.

From API RP 571 Section 5.1.2.1 and RP 941:

“High strength low alloy steels (HSLA) are more susceptible to hydrogen embrittlement, especially during cold work, forming, or welding. These materials, due to their higher tensile strengths, are more prone to cracking when exposed to hydrogen, particularly during fabrication or post-weld heat treatment operations.”

Therefore, Option A (High Strength Low Alloys) is the correct answer due to their known susceptibility during manufacturing and processing.

According to API RP 571 Section 5.3.2.3 (Spheroidization):

“Spheroidization is the transformation of the microstructure of carbon and low alloy steels when exposed to elevated temperatures for long durations. The rate of spheroidization depends on temperature, prior microstructure, and exposure time... The microstructure becomes less effective at carrying loads, and strength is reduced.”

Key influencing factors for the rate of spheroidization are:

Temperature (higher accelerates the process),

Microstructure (initial phase distribution and morphology).

Pressure and hydrogen partial pressure are not relevant for this transformation, nor is stress a primary driver.

Therefore, Option D (temperature and microstructure) is correct.

API RP 571 discusses this under Wet H₂S 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 H₂S 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.

API RP 751, which governs HF alkylation units, specifies:

“The total residuals of chromium, nickel, and copper in carbon steel used in HF service should be less than 0.15 wt.% to minimize corrosion risk.”

“Higher residuals increase the reactivity and corrosion rate of carbon steel in the presence of HF acid.”

(Reference: API RP 751, Section 5.3 – Materials Specification for HF Units)

Therefore, option A is the correct choice.

API RP 571 explains that both Sulfide Stress Cracking (SSC) and SOHIC are:

“Strongly influenced by material hardness. Carbon and low alloy steels with hardness exceeding 22 HRC (248 Brinell) are most susceptible.”

“They occur in hardened steels under tensile stress, in the presence of wet H₂S environments.”

(Reference: API RP 571, Sections 4.2.2.1 and 4.2.2.7 – SSC and SOHIC)

Therefore, hardened steels are the common factor for both mechanisms, making option C the correct choice.