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

According to API RP 571, under the section on High Temperature Hydrogen Attack (HTHA) and Decarburization:

“Decarburization is typically confirmed by metallographic examination. This method reveals carbon loss and microstructural changes such as spheroidization or softening of pearlite.”

“Tensile or impact testing may not reveal early-stage decarburization, especially in partial layers.”

Therefore, metallographic testing is the standard and most direct method to confirm decarburization damage, making option D correct.

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.

Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571 and API RP 941 (Nelson Curves), 1 Cr–0.5 Mo steel is no longer recommended for services susceptible to High-Temperature Hydrogen Attack (HTHA).

API RP 941 documents industry experience showing that 1 Cr–0.5 Mo steels have suffered HTHA damage below previously assumed safe operating limits, due to insufficient carbide stability. As a result, this material has been removed from the Nelson Curves as an acceptable choice for new construction in hydrogen service.

By contrast:

Mn–0.5 Mo, C–0.5 Mo, and 1.25 Cr–0.5 Mo steels retain higher resistance due to more stable carbide structures.

Referenced Documents (Study Basis):

API RP 571 – Section on High-Temperature Hydrogen Attack

API RP 941 – Updated Nelson Curves and Material Recommendations

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Erosion and erosion-corrosion are mechanical degradation mechanisms enhanced by fluid motion, and typically result in directional or flow-oriented metal loss patterns.

According to API RP 571 Section 5.4.2 (Erosion and Erosion/Corrosion):

“Erosion typically results in localized thinning, often described as grooves, gullies, or horseshoe-shaped patterns... The metal loss is directional and may occur in elbows, tees, reducers, and pumps.”

Hence, Option C (grooves and gullies) most accurately describes erosion and erosion-corrosion characteristics.

According to API RP 571 Section 5.4.2 (Erosion and Erosion/Corrosion):

“Erosion can occur downstream of flow disturbances such as control valves, orifice plates, elbows... It is characterized by localized metal loss with a directional pattern such as grooves or sharp-edged pits in areas of high velocity or turbulence.”

Cavitation and flashing cause damage with different signatures like pitting and spongy surface texture, while sharp-edged pitting strongly indicates erosion, especially downstream of flow restriction devices.

Thus, the correct answer is Option C (Erosion).

Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, amine stress corrosion cracking (Amine SCC) is a form of environmentally assisted cracking that occurs in alkanolamine systems (e.g., MEA, DEA, DGA) used for acid gas treating. The cracking mechanism requires the simultaneous presence of tensile stress, susceptible microstructure, and an amine environment.

API RP 571 clearly states that Amine SCC occurs primarily in the weld heat affected zone (HAZ) of carbon and low-alloy steels. The reasons include:

The HAZ contains high residual stresses from welding.

The microstructure in the HAZ is metallurgically altered, making it more susceptible than base metal.

Cracks often initiate adjacent to welds, not in the weld metal itself.

Why the other options are incorrect:

Option A (Weld fusion line) is not the primary cracking location.

Option C (Weld metal) generally has different chemistry and lower susceptibility.

Option D (Base metal) typically has lower residual stress and is less prone.

API RP 571 specifically identifies the weld HAZ as the dominant cracking location for Amine SCC.

Referenced Documents (Study Basis):

API RP 571 – Section on Amine Stress Corrosion Cracking

API Corrosion and Materials Study Guide

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API RP 571 under Ammonium Chloride Corrosion details:

“The corrosion results from the deposition of ammonium chloride salts from high-temperature process streams as they cool.”

“This typically occurs in crude unit overheads or other systems where salts condense out as the stream temperature drops below their dew point.”

“Corrosion becomes especially aggressive when the salts are wetted by condensation.”

(Reference: API RP 571, Section 4.3.3.1 – Ammonium Chloride Corrosion)

Therefore, option A is technically accurate and supported.

API RP 571, under Chloride Stress Corrosion Cracking, notes:

“Cracking often appears as highly branched or ‘crazed’ networks on the surface, especially in austenitic stainless steels exposed to chlorides under tensile stress.”

“These cracks often initiate in the heat-affected zones or cold-worked areas and are intergranular in nature.”

This signature ‘crazed’ appearance with branching is diagnostic of Cl-SCC, making option C the correct and most descriptive 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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According to API RP 571, in the section on Boiler Water Condensate Corrosion:

“The major contributors to condensate corrosion are dissolved CO₂ and O₂. Carbon dioxide forms carbonic acid in the presence of water, lowering pH and causing generalized corrosion.”

“Oxygen causes pitting and localized corrosion unless chemically treated.”

Thus, option B (Carbon dioxide and oxygen) is the primary root cause and the correct answer.