Hydrogen-induced cracking (HIC) in sour service steel initiates internally — invisible on the surface — growing as planar hydrogen blisters, step cracks, and stress-oriented HIC (SOHIC) that progressively reduce the load-bearing cross-section of the steel without external indication. In pressure vessels, piping, and structural components in sour service, HIC is a primary integrity threat because it advances silently until the remaining wall is insufficient to sustain operational loads.
PAUT for In-Service HIC
Assessment
Full Volumetric Coverage at Defined Sensitivity
HIC can initiate at any through-wall position — at mid-wall, adjacent to
inclusions, or at the HAZ boundary in welded material. PAUT inspection
programmes for in-service HIC assessment provide 100% volumetric coverage of
the inspection zone at controlled sensitivity, ensuring that no laminar
cracking or blister formation above the detection threshold is missed in the
scanned area.
Through-Wall Sizing for CLR, CTR, and CSR
NACE TM0284 requires quantification of HIC
severity through Crack Length Ratio (CLR), Crack Thickness Ratio (CTR), and
Crack Sensitivity Ratio (CSR). PAUT provides the through-wall depth and lateral
extent sizing precision required for reliable CLR/CTR/CSR determination from
in-service assets — not just from laboratory test samples — enabling assessment
against specification limits for fitness-for-service decisions.
SOHIC Detection with Steep-Angle Focal Laws
Standard lamination scanning techniques — horizontal beam angle,
high-frequency UT — detect planar HIC blisters effectively but can miss the
vertically oriented connecting cracks that characterise SOHIC. Our HIC
inspection procedures include steep-angle PAUT focal laws and TOFD supplement
specifically configured for SOHIC connectivity detection — providing a complete
picture of the hydrogen damage morphology.
Immersion UT for HIC Test Sample
Evaluation
For HIC qualification testing of new
material procurement or test sample evaluation per NACE TM0284, Altair
Engineering Inspection provides immersion UT scanning in our ISO
17025-accredited laboratory — delivering 100% volumetric coverage at controlled
sensitivity, precise CLR/CTR/CSR quantification, and full calibration
traceability.
Reports include full scan imagery,
CLR/CTR/CSR calculations where applicable, individual crack dimension tables,
through-wall position data, damage mechanism classification, and pass/fail or
fitness-for-service disposition. For laboratory sample evaluation, reports
include calibration records, equipment traceability, and operator qualification
documentation as required by ISO 17025.