API-571 Exam Dumps : Corrosion and Materials Professional

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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API RP 571, Naphthenic Acid Corrosion:

“Molybdenum significantly improves resistance to naphthenic acid attack. Alloys such as 317, 316Mo, and Alloy 20 are used in severe NAC environments due to higher Mo content.”

“Chromium and nickel play secondary roles; molybdenum is the key element.”

Answer is A – Molybdenum.

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).