API-571 Exam Dumps - API ICP Programs Questions and Answers

In API RP 571, under the section Polythionic Acid Stress Corrosion Cracking, it is stated:

“Sensitization of austenitic stainless steels occurs when the material is exposed to temperatures in the range of 800°F to 1500°F (427°C to 816°C), which causes chromium carbide precipitation at grain boundaries, depleting the adjacent areas of chromium.”

“Once sensitized, the steel becomes susceptible to attack in the presence of polythionic acids, particularly in environments containing sulfides and oxygen.”

(Reference: API RP 571, Section 4.2.2.5 – PTA SCC)

This makes option B (750°F to 1500°F / 400°C to 815°C) the most accurate and standard-aligned answer.

Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, chromium is the most effective alloying element for improving oxidation resistance in steels.

Chromium:

Forms a stable, adherent chromium oxide (Cr₂O₃) scale

Greatly reduces oxidation rates at elevated temperatures

Is the basis for oxidation-resistant alloys and stainless steels

Other alloying elements may provide secondary benefits, but chromium is the primary contributor to oxidation resistance.

Referenced Documents (Study Basis):

API RP 571 – Section on Oxidation and High-Temperature Corrosion

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

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API RP 571, under "Caustic Corrosion" (also referred to as Caustic Stress Corrosion Cracking or Caustic Cracking), notes that this form of damage is:

“Most commonly associated with the injection points of caustic (e.g., NaOH) in crude units, particularly upstream of desalter vessels and heat exchanger circuits.”

“This damage occurs due to the combination of caustic environment and tensile stress, especially in carbon steel and low alloy steels.”

“Stress relief heat treatment of welds can mitigate susceptibility.”

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

Thus, among the options, caustic injections in crude units are the most typical area of concern, making option C the correct answer.

Comprehensive and Detailed Explanation From Exact Extract:

High-Temperature Hydrogen Attack (HTHA) is described in API RP 571 and API RP 941 as a damage mechanism where hydrogen reacts with carbides at elevated temperature and pressure, forming methane and causing loss of strength and fissuring.

Prevention is primarily achieved by selecting materials with stable carbides that resist hydrogen attack. Chromium and molybdenum alloying elements:

Form more stable carbides

Reduce susceptibility to methane formation

Extend safe operating limits

Why the other options are incorrect:

Option B may be used in some services but is not the usual prevention method.

Option C is incorrect because RP 941 does not recommend high-nickel alloys as the primary solution.

Option D low-carbon steels are more susceptible, not resistant.

API RP 571 clearly identifies Cr-Mo alloy steels as the standard mitigation approach.

Referenced Documents (Study Basis):

API RP 571 – Section on High-Temperature Hydrogen Attack

API RP 941 – Nelson Curves and Material Selection

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Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, creep damage is a time-dependent, high-temperature damage mechanism that occurs when materials are exposed to stress at temperatures typically above about 700 °F (370 °C) for extended periods. Creep damage results in void formation, microcracking, grain boundary separation, and eventual rupture.

Once creep damage has occurred, it is considered irreversible metallurgical degradation. API RP 571 clearly states that heat treatments cannot restore creep life because the material’s microstructure has already been permanently damaged.

Option A (PWHT at 1150 °F) may relieve residual stresses but does not heal creep voids or microcracks.

Option B (Solution annealing) is applicable to certain stainless steels but is not effective for reversing creep damage, particularly in low-alloy and Cr-Mo steels.

Option D (Preheating during welding) helps prevent hydrogen-related cracking but has no effect on existing creep damage.

API RP 571 emphasizes that the only effective mitigation for creep damage is to remove the affected material and replace it with sound material, or to retire the component if damage is widespread. Fitness-for-service assessments (API 579-1/ASME FFS-1) may be used to evaluate remaining life, but mitigation requires material removal.

Referenced Documents (Study Basis):

API RP 571 – Section on Creep and Stress Rupture Damage

API Corrosion and Materials Study Guide

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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.

Comprehensive and Detailed Explanation From Exact Extract:

In HF Alkylation units, API RP 571 identifies certain residual alloying elements in carbon steel that can significantly increase corrosion rates in HF acid service.

The most detrimental residual elements are:

Chromium (Cr)

Copper (Cu)

Nickel (Ni)

These elements:

Disrupt formation of protective iron fluoride films

Increase general and localized corrosion rates

Are tightly controlled in carbon steel specifications for HF service

Referenced Documents (Study Basis):

API RP 571 – Section on Hydrofluoric Acid Corrosion

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From API RP 571 on Microbiologically Influenced Corrosion (MIC):

“MIC depends on the presence of water, nutrients, and specific microbial species such as SRB (sulfate-reducing bacteria).”

“While flow velocity may influence deposition and oxygen content, MIC can occur in both stagnant and flowing systems. Hence, it's not strongly dependent on velocity.”

Thus, option D is correct — MIC is largely independent of flow velocity.

Comprehensive and Detailed Explanation From Exact Extract:

Microbiologically Induced Corrosion (MIC) is one of the most universally applicable corrosion mechanisms, affecting:

Carbon steel

Low-alloy steel

Stainless steels

Copper alloys

Aluminum alloys

According to API RP 571, MIC can occur in any aqueous system where microorganisms are present, regardless of metallurgy.

By contrast:

Sour water corrosion and amine corrosion mainly affect carbon steel

Polythionic acid corrosion is limited to austenitic stainless steels

Referenced Documents (Study Basis):

API RP 571 – Section on Microbiologically Induced Corrosion