API-571 Exam Dumps : Corrosion and Materials Professional

API RP 751 (referenced in RP 571) lists materials appropriate for HF acid alkylation service. It specifies:

“Chrome-moly steels such as ASTM A-193 B5 (5% Cr) bolts are preferred for their resistance to HF acid-induced cracking.”

“Standard low alloy steels (e.g., B7) are not considered adequately resistant.”

(Reference: API RP 571 summary & API RP 751, Section 5.6.3 – Bolting Materials)

Therefore, the correct and industry-approved answer is option A.

API RP 571 states under Chloride Stress Corrosion Cracking (Cl-SCC):

“Nickel contents above approximately 35% provide significant resistance to chloride stress corrosion cracking. Alloys such as Alloy 625 and Alloy 825 exhibit excellent resistance.”

“Austenitic stainless steels with lower nickel contents, such as 304 and 316, are more susceptible to Cl-SCC.”

Hence, option C (35%) is correct.

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

======================