API-571 Exam Dumps : Corrosion and Materials Professional

Comprehensive and Detailed Explanation From Exact Extract:

Grooving corrosion in cooling water systems is a well-documented damage mechanism in API RP 571, particularly associated with high-velocity flow conditions.

Flow-induced erosion (also referred to as erosion-corrosion or flow-assisted corrosion) occurs when:

High fluid velocity removes protective corrosion films

Local turbulence, elbows, or inlet zones focus mechanical wear

Soft metals or alloys are exposed to continuous impingement

This results in smooth, directional grooves or channels aligned with the flow direction, a classic signature described in API RP 571.

Why the other options are incorrect:

Option A: ERW defects affect weld seams, not general grooving patterns.

Option B: MIC typically causes localized pitting, not uniform grooving.

Option D: Underdeposit corrosion produces irregular pitting beneath deposits, not flow-aligned grooves.

API RP 571 specifically identifies flow-induced erosion as a primary cause of grooving in cooling water heat exchanger tubes.

Referenced Documents (Study Basis):

API RP 571 – Section on Erosion/Erosion-Corrosion

API Cooling Water System Corrosion Study Guide

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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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As defined in API RP 571, under Hydrogen Blistering and HIC/SOHIC:

“SOHIC typically manifests as subsurface stepwise cracking, generally oriented perpendicular to the direction of stress.”

“This mechanism initiates below the surface, typically in weld heat-affected zones, and requires metallographic or advanced ultrasonic methods to detect.”

By contrast, SSC, caustic cracking, and amine SCC are primarily surface-initiated, stress-related cracking mechanisms.

Thus, SOHIC is the subsurface mechanism in this list, making option D correct.