Comprehensive and Detailed Explanation From Exact Extract:
Wet H₂S damage mechanisms include hydrogen blistering, hydrogen-induced cracking (HIC), stepwise cracking (SWC), and stress-oriented hydrogen-induced cracking (SOHIC). These mechanisms are primarily internal and subsurface, as described in API RP 571.
Shear Wave Ultrasonic Testing (SWUT) is specifically highlighted in API RP 571 as a preferred screening and detection method for wet H₂S damage because it can detect subsurface planar defects with minimal surface preparation. Typically, only basic coupling and access are required.
Why the other options are incorrect:
Option A (ACFM) is a surface crack detection technique and requires relatively clean surfaces; it is not suitable for subsurface hydrogen damage.
Option C (WFMT – Wet Fluorescent Magnetic Particle Testing) requires extensive surface preparation, coating removal, and direct access to the surface, and only detects surface-breaking flaws.
Option D (LPT – Liquid Penetrant Testing) also requires clean, bare metal surfaces and cannot detect subsurface damage.
API RP 571 explicitly notes that ultrasonic techniques, particularly shear wave UT, are widely used for detecting internal hydrogen-related cracking with minimal disruption and surface preparation, making it the most effective choice for wet H₂S damage screening.
Referenced Documents (Study Basis):
API RP 571 – Section on Wet H₂S Damage (HIC, SOHIC, Blistering)
API Corrosion and Materials Inspection Study Guide
