API Corrosion and Materials API-571 Exam Questions

Answer : A

Chloride Stress Corrosion Cracking (Cl-SCC) is a serious form of corrosion primarily affecting austenitic stainless steels and some duplex stainless steels, particularly when exposed to chloride-containing environments at elevated temperatures.

According to API RP 571 Section 5.1.2.3 (Chloride Stress Corrosion Cracking -- Cl-SCC):

''Austenitic stainless steels (e.g., 300 series such as Types 304 and 316) are the most susceptible to Cl-SCC... Duplex stainless steels have greater resistance but are not immune, especially at temperatures >150F (65C)... Ferritic stainless steels (400 series) are generally not susceptible.''

Thus, Option A (400 Series Stainless Steel) is not susceptible to chloride SCC, making it the correct answer.

Answer : A

Comprehensive and Detailed Explanation From Exact Extract:

Per API RP 571, chloride stress corrosion cracking (Cl-SCC) of austenitic stainless steels is strongly influenced by low pH environments in the presence of chlorides, tensile stress, and elevated temperature.

API RP 571 identifies that:

Chloride SCC can initiate at very low pH levels

pH values near 2 represent a threshold where aggressive chloride attack and cracking become possible

Increasing acidity dramatically increases SCC susceptibility

Therefore, pH = 2 is the lowest and most critical value listed where chloride SCC can begin.

Referenced Documents (Study Basis):

API RP 571 -- Section on Chloride Stress Corrosion Cracking

Answer : D

Same as above. Sigma phase formation is a microstructural phenomenon and not typically detected by NDE methods like magnetic particle or surface hardness testing.

Therefore, metallographic testing remains the definitive detection method, confirming option D again as the correct answer.

Answer : D

As per API RP 571 and further clarified in API RP 939-C:

''An arbitrary threshold of 50 ppmw HS in the aqueous phase is often used to define when carbon and low alloy steels become susceptible to cracking damage in wet HS environments.''

''Below this level, the risk of SSC, HIC, and SOHIC is considered lower, although damage has still occurred at lower concentrations depending on stress and metallurgical conditions.''

Therefore, the correct answer is option D (50 ppmw).

Answer : A

API RP 571 explains the typical location of dissimilar metal weld (DMW) cracks as follows:

''DMW cracking usually occurs in the heat-affected zone (HAZ) on the ferritic side of the weld.''

''The difference in thermal expansion coefficients, grain structures, and creep rates between the ferritic and austenitic materials contributes to the development of high stress and strain concentrations in the HAZ of the ferritic material.''

(Reference: API RP 571, Section 4.2.1.6 -- Dissimilar Metal Weld Cracking)

Thus, these cracks do not occur in the center of the weld or on the austenitic side, but rather at the ferritic HAZ, making option A correct.

Answer : C

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

''Austenitic stainless steels such as 304 and 316 are highly susceptible to Cl-SCC when subjected to tensile stress and exposed to chloride-bearing environments.''

''Susceptibility is greatest in non-stress-relieved weldments or cold-worked areas.''

Brass and carbon steels are not typical Cl-SCC candidates; low alloy steels such as 1.25Cr-0.5Mo are also not commonly affected.

Thus, option C is the correct answer.

Answer : A

API RP 571 notes that for detecting existing cracks or flaws that may lead to brittle fracture, especially those that initiate at welds or surface stress points:

''Wet fluorescent magnetic-particle inspection is highly effective for detecting surface-breaking flaws in ferromagnetic materials that are susceptible to brittle fracture.''

''It is sensitive to tight cracks and surface discontinuities that may serve as initiation sites for brittle fracture.''

(Reference: API RP 571, Section 4.2.1.2 -- Brittle Fracture)

Therefore, option A is correct as it is the most effective NDE technique for detecting early signs of brittle cracking.