API-571 Exam Dumps : Corrosion and Materials Professional

API RP 571 on HTHA states:

“Acoustic emission testing is not currently a proven or reliable method for identifying HTHA in refinery components.”

“HTHA typically occurs internally, not as surface blisters, and is not limited to welds. Austenitic (300 series) stainless steels are generally resistant at normal refinery conditions.”

(Reference: API RP 571, Section 4.2.1.3 – High Temperature Hydrogen Attack)

Thus, option A is the most accurate statement.

API RP 571 details that:

“Sulfide Stress Cracking (SSC) susceptibility increases significantly with increased hardness of the steel.”

“NACE MR0175/ISO 15156 provides hardness limits for carbon and low-alloy steels to avoid SSC in sour environments. These are typically limited to 22 HRC or 248 Brinell.”

“High hardness promotes crack initiation under tensile stress in sour environments (i.e., containing H₂S).”

(Reference: API RP 571, Section 4.2.2.1 – Sulfide Stress Corrosion Cracking)

While hydrogen-induced cracking (HIC) and blistering are related to hydrogen charging, SSC is the only mechanism directly and critically impacted by hardness, making option B correct.

API RP 571 on Thermal Fatigue:

“Mixing of hot and cold streams, particularly where hydrogen is present, can induce thermal cycling stresses, leading to thermal fatigue cracking, especially at fittings like tees.”

“Hydrogen embrittlement typically affects stressed zones, but this pattern strongly indicates thermal fatigue.”

So the correct answer is C – Thermal fatigue.