API-571 Online Practice Questions

Explanation:
API RP 751, which governs HF alkylation units, specifies:
“The total residuals of chromium, nickel, and copper in carbon steel used in HF service should be less than 0.15 wt.% to minimize corrosion risk.”
“Higher residuals increase the reactivity and corrosion rate of carbon steel in the presence of HF acid.”
(Reference: API RP 751, Section 5.3 C Materials Specification for HF Units)
Therefore, option A is the correct choice.

Explanation:
Comprehensive and Detailed Explanation From Exact Extract:
According to API RP 571, creep damage is a time-dependent, high-temperature damage mechanism that occurs when materials are exposed to stress at temperatures typically above about 700 °F (370 °C) for extended periods. Creep damage results in void formation, microcracking, grain boundary separation, and eventual rupture.
Once creep damage has occurred, it is considered irreversible metallurgical degradation. API RP 571 clearly states that heat treatments cannot restore creep life because the material’s microstructure has already been permanently damaged.
Option A (PWHT at 1150 °F) may relieve residual stresses but does not heal creep voids or microcracks.
Option B (Solution annealing) is applicable to certain stainless steels but is not effective for reversing creep damage, particularly in low-alloy and Cr-Mo steels.
Option D (Preheating during welding) helps prevent hydrogen-related cracking but has no effect on existing creep damage.
API RP 571 emphasizes that the only effective mitigation for creep damage is to remove the affected material and replace it with sound material, or to retire the component if damage is widespread. Fitness-for-service assessments (API 579-1/ASME FFS-1) may be used to evaluate remaining life, but mitigation requires material removal.
Referenced Documents (Study Basis):
API RP 571 C Section on Creep and Stress Rupture Damage API Corrosion and Materials Study Guide

Explanation:
As per API RP 571 on Sigma Phase Embrittlement:
“Sigma phase embrittlement occurs in stainless steels and nickel-based alloys due to the formation of a brittle intermetallic phase in the temperature range of 1050°F to 1650°F (565°C to 900°C).”
“This damage mechanism is not easily detected through surface or hardness testing and typically requires metallographic examination to confirm the presence of sigma phase in the microstructure.”
Metallographic testing allows clear identification of sigma phase particles and is thus the most reliable method, making option D correct.

Explanation:
According to API RP 571 Section 5.4.2 (Erosion and Erosion/Corrosion):
“Erosion can occur downstream of flow disturbances such as control valves, orifice plates, elbows... It is characterized by localized metal loss with a directional pattern such as grooves or sharp-edged pits in areas of high velocity or turbulence.”
Cavitation and flashing cause damage with different signatures like pitting and spongy surface texture, while sharp-edged pitting strongly indicates erosion, especially downstream of flow restriction devices.
Thus, the correct answer is Option C (Erosion).

Explanation:
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.