API Updated API-571 Exam Questions and Answers by pola

Comprehensive and Detailed Explanation From Exact Extract:

Carbolic acid corrosion (phenol corrosion) is described in API RP 571 as a process-specific corrosion mechanism that may not produce distinct or easily detectable wall-loss patterns using conventional NDE methods.

API RP 571 emphasizes that confirmation of carbolic acid corrosion often requires:

Chemical identification of corrosion products

Metallurgical examination

Verification of acid presence and metal interaction

A boat sample (also known as a coupon or scoop sample) removed from the affected area and analyzed in a laboratory allows:

Identification of corrosion morphology

Chemical analysis of deposits

Confirmation of phenol-related attack

Why the other options are incorrect:

UT and RT detect wall loss but cannot identify the corrosion mechanism.

Acoustic emission detects active cracking, not specific corrosion chemistry.

Angle beam UT is for crack detection, not corrosion identification.

Therefore, laboratory analysis of a removed sample is the most useful method.

Referenced Documents (Study Basis):

API RP 571 – Section on Organic Acid Corrosion (Phenols)

API Corrosion Failure Analysis Study Guide

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Comprehensive and Detailed Explanation From Exact Extract:

Amine stress corrosion cracking is most frequently associated with rich amine services, where:

Acid gas loading (H₂S / CO₂) is high

Corrosive contaminants and degradation products are present

Higher operating temperatures and stresses exist

Per API RP 571, cracking is far more common in rich amine systems than in lean amine circuits.

Why the other options are incorrect:

Lean amine has lower acid gas content and reduced SCC risk

SCC is not limited to low temperatures

Concentration alone is not the dominant factor

Referenced Documents (Study Basis):

API RP 571 – Section on Amine Stress Corrosion Cracking

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 discusses Hydrogen-Induced Cracking (HIC) and Blistering:

“Postweld heat treatment (PWHT) does not significantly reduce susceptibility to HIC, as the mechanism is primarily driven by hydrogen charging in wet H₂S environments and steel cleanliness, not residual stresses.”

“PWHT is more effective for SSC, SOHIC, and other stress-driven mechanisms.”

Thus, HIC will not benefit much from PWHT, making option C correct.