Discuss API API-571 Exam Topic 1 Question 131

(Grooving in cooling water tubes could be due to:)

AElectric resistance welds

BMicrobiologically induced corrosion

CFlow-induced erosion

DUnderdeposit corrosion

Suggested Answer: C

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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3 comments · newest first

Eden 2 days ago

I’m a bit confused about underdeposit corrosion. I think it has to do with deposits forming on surfaces, but I’m not clear if that leads to grooving specifically.

Tayna 7 days ago

I feel like flow-induced erosion could definitely cause grooving, especially in high-velocity systems. I saw a similar question in our practice tests.

Dana 12 days ago

I think I remember something about microbiologically induced corrosion being a common issue in cooling systems, but I'm not entirely sure if it applies to grooving.

API-571 Exam - Topic 1 Question 131 Discussion