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API-571 Exam Questions
- Topic 1: Terms, Definitions, and Acronyms: This domain covers the key terminology, standard definitions, and commonly used acronyms related to corrosion and materials. It ensures a clear understanding of technical language used throughout the API-571 body of knowledge.
- Topic 2: Damage Mechanisms: This domain explains various corrosion and damage mechanisms, including their characteristics, affected materials, causes, and visual appearance. It also covers where damage occurs, along with methods for prevention, mitigation, inspection, and monitoring.
Free API API-571 Exam Actual Questions
Note: Premium Questions for API-571 were last updated On Aug. 06, 2026 (see below)
Which type of corrosion is most likely to occur in hydroprocess reactor effluent streams in units producing alkaline sour water?
From API RP 571 and RP 932-B:
''In hydroprocessing reactor effluent systems, the most common corrosion mechanism is ammonium bisulfide (NHHS) corrosion, which forms in the presence of hydrogen sulfide and ammonia.''
''NHHS attacks carbon steel aggressively under turbulent flow and at low pH.''
Correct answer is B -- ammonium bisulfide corrosion.
Nitriding of steels becomes most severe at temperatures above:
API RP 571 under Nitriding (Section 4.2.16):
''Nitriding occurs at elevated temperatures and is most severe at temperatures above 900F (480C).''
''This mechanism is associated with the reaction of ammonia or other nitrogen-containing compounds with the steel surface, leading to brittle nitride formation.''
Therefore, the correct answer is D.
Which of the following weldments is most susceptible to dissimilar metal cracking when operating at high temperatures?
Dissimilar Metal Cracking (DMC) is a form of high-temperature cracking that frequently occurs in weld joints between carbon steel and austenitic stainless steel (such as Type 316 SS) due to differences in thermal expansion coefficients and mechanical properties.
From API RP 571 Section 5.2.3.1 (Dissimilar Metal Weld Cracking):
''Cracking frequently occurs in weld joints between ferritic and austenitic materials such as carbon steel to 300 series stainless steels due to thermal expansion mismatch during high temperature operation.''
Therefore, Option D (Carbon steel to 316 stainless steel) is the most susceptible combination and the correct answer.
(Cooling water corrosion usually increases with decreasing:)
Comprehensive and Detailed Explanation From Exact Extract:
According to API RP 571, corrosion in cooling water systems often increases at low flow velocities due to:
Stagnation
Deposit formation
Increased risk of underdeposit corrosion and MIC
Higher velocities tend to:
Sweep away deposits
Maintain protective films (within erosion limits)
Therefore, decreasing velocity is strongly associated with increased corrosion risk.
Referenced Documents (Study Basis):
API RP 571 -- Section on Cooling Water Corrosion
(Typically, surface decarburization will have what effect on steel components in high temperature service?)
Comprehensive and Detailed Explanation From Exact Extract:
According to API RP 571, surface decarburization is a metallurgical degradation mechanism that occurs when carbon is removed from the surface layers of steel due to exposure to oxidizing environments at elevated temperatures. This results in a carbon-depleted surface layer.
Carbon is a primary strengthening element in carbon and low-alloy steels. When carbon is lost from the surface:
Hardness and tensile strength are reduced
Creep resistance and load-carrying capability decrease
The component becomes more susceptible to plastic deformation and failure under stress
API RP 571 states that decarburization leads to loss of mechanical strength, especially critical in high-temperature service, where components already operate close to material limits.
Why the other options are incorrect:
Option A: Stress cracking is not the primary effect; loss of strength is.
Option C: Decarburization does not directly accelerate oxidation or sulfidation, although both may coexist.
Option D: This is incorrect; decarburization is considered detrimental in high-temperature applications.
Referenced Documents (Study Basis):
API RP 571 -- Section on Decarburization and Metal Dusting
API Corrosion and Materials Study Guide
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