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

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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API RP 571 and RP 939-C define sulfidation conditions as:

“Sulfidation of iron-based alloys generally becomes significant at temperatures above 500°F (260°C) in hydrocarbon streams with sulfur but without hydrogen.”

“For hydrogen-containing environments, this threshold may be reduced to 450°F (230°C).”

(Reference: API RP 571, Section 4.2.1.1 – Sulfidation; API RP 939-C, Section 3.1)

Therefore, the correct answer is D.

API RP 571 – Sulfidation:

“Sulfidation generally results in uniform thinning of iron-based alloys at temperatures above 500°F (260°C).”

“It is classified as a form of general corrosion, although it can be accelerated in turbulent flow areas.”

So, option A is correct.

API RP 571 under Polythionic Acid Stress Corrosion Cracking (PTA SCC) specifies:

“Cracking is usually intergranular, and often localized, especially in sensitized austenitic stainless steels exposed to sulfur-containing environments during shutdown or cleaning.”

“It is not always visible on inspection and may only become evident when a leak occurs.”

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

Hence, option C is correct as it best describes the detection difficulty and behavior of PTA SCC.

According to API RP 571 Section 5.1.2.1 (Hydrogen-Induced Cracking) and Publ 939-A, blistering in carbon and low alloy steels exposed to wet H2S environments can be exacerbated by the presence of cyanides. These accelerate hydrogen entry into steel, increasing the chance of hydrogen blistering.

API RP 571 states:

“HIC and blistering are forms of hydrogen damage that occur in wet H2S environments. The presence of cyanides can significantly increase hydrogen entry and the risk of blistering.”

Publ 939-A (Research on Cracking in Wet H2S Service) also notes:

“Cyanides act as catalytic agents in hydrogen charging, which promotes internal pressure build-up and increases blistering.”

Thus, cyanides (Option B) are the most critical in enhancing blistering in H2S environments.

Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, corrosion fatigue results from the combined action of a cyclic stress and a corrosive environment. One of the most important distinguishing features between corrosion fatigue and SCC is crack morphology.

Corrosion fatigue cracks are typically transgranular and show little or no branching

Stress corrosion cracking is characterized by extensive crack branching

Therefore, the absence of significant branching is a key diagnostic feature of corrosion fatigue.

Referenced Documents (Study Basis):

API RP 571 – Section on Corrosion Fatigue

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Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, graphitization is a high-temperature degradation mechanism that occurs in carbon and carbon-molybdenum steels exposed for long periods at temperatures typically above 800 °F (425 °C).

In this process:

Iron carbides decompose into free graphite nodules

The steel loses strength, ductility, and pressure-retaining capability

Failures can occur without significant wall loss

Graphitization does not occur in aluminum, stainless steels, or nickel-copper alloys such as Monel.

Referenced Documents (Study Basis):

API RP 571 – Section on Graphitization

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API RP 571 explains under Condensate Corrosion (CO₂ Corrosion):

“In condensate systems, carbon dioxide dissolves in the water forming carbonic acid, which leads to localized corrosion, including grooving and under-deposit attack, especially at low points like the bottom of horizontal piping.”

“This is most commonly observed in steam condensate return lines, and the damage is localized due to stratification.”

This matches the scenario described, where internal grooving at the bottom of steam condensate piping is characteristic of CO₂-induced corrosion. Hence, option A is correct.

API RP 571 states in the section on Creep Damage:

“Creep damage in carbon steels generally becomes a concern above 700°F (371°C), especially for steels with higher tensile strength (greater than 60 ksi).”

“For prolonged exposure above this temperature, time-dependent deformation can lead to material degradation and cracking, especially at weldments and stress concentrations.”

Thus, the lowest threshold for creep in high-strength carbon steels is 700°F (371°C), making option B correct.

API RP 945, dedicated to environmental cracking in amine units, states:

“Carbon steel is widely used in amine systems but is particularly susceptible to localized corrosion, under-deposit corrosion, and stress corrosion cracking, especially in high-pressure or rich amine environments.”

“Proper control of amine quality, oxygen ingress, and temperature is critical to avoid accelerated corrosion in carbon steel equipment.”

Thus, carbon steels are the most commonly affected materials, making option C correct.