API API-571 Exam With Confidence Using Practice Dumps

According to API RP 571, Section 4.2.1.1 – Sulfidation, and also echoed in API RP 939-C, the presence of certain compounds significantly increases sulfidic corrosion:

“Chlorides are known to accelerate sulfidation and other high-temperature corrosion mechanisms by forming low-melting eutectics and breaking down protective scales on alloy surfaces.”

“Chlorine-containing species also interfere with the formation of stable sulfide or oxide scales, leading to more aggressive metal loss.”

Therefore, chlorides are the most critical accelerant among the listed substances in high-temperature sulfur compound environments, making option C correct.

According to API RP 571, under the section "4.2.1.2 Brittle Fracture", the following conditions are explicitly identified as most critical for brittle fracture risk:

"Most processes run at elevated temperature, so the main concern is for brittle fracture during startup, shutdown, hydrotest, or other situations where equipment may be exposed to low temperatures."

"Equipment fabricated from materials susceptible to brittle fracture (e.g., carbon steel) is most vulnerable when exposed to low temperatures combined with high stress or pressure."

"A brittle fracture is characterized by a sudden and rapid crack propagation with little or no plastic deformation."

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

Thus, while other options represent stress events, the main concern specifically noted by the standard is during start-up and shutdown—especially due to cooling and repressurization at low temperatures—making option A the most accurate choice.

From API RP 571 and RP 932-B:

“In hydroprocessing reactor effluent systems, the most common corrosion mechanism is ammonium bisulfide (NH₄HS) corrosion, which forms in the presence of hydrogen sulfide and ammonia.”

“NH₄HS attacks carbon steel aggressively under turbulent flow and at low pH.”

Correct answer is B – ammonium bisulfide corrosion.