Hydrogen Induced Cracking Damage Estimation and Evaluation

New non-destructive testing (NDT) inspection technology, quantification of damage, and tensile testing, has enabled the assessment of conservatism associated with the hydrogen induced cracking (HIC) damage parameter (DH) currently used in API 579 – 1/ASME Fitness-For-Service (FFS) Part 7. To address HIC damage from an FFS perspective, the general requirements include addressing protection against plastic collapse and protection against cracking. The focus of this body of work is only to address conservatism regarding the protections against plastic collapse. The detrimental effects of HIC damage on plastic collapse is modeled through the DH parameter, currently set at 0.8 or an 80% strength loss in HIC damage material for the Level 2 HIC Assessment Procedure. Original development of the DH parameter was based on tensile testing of HIC damaged material performed in air, where the HIC damage was not sized or quantified, and a 30% margin was added to the maximum measured reduction in tensile strength to get to the 80% strength loss. Modification of the DH parameter is allowed in the Level 3 HIC Assessment Procedure, provided supporting testing data justifying a reduction is also provided with the assessment. For the tensile testing in air, the quantified HIC damage and tensile testing results are consistent with an 80% strength loss, without an added margin. A rigorous ultrasonic testing inspection using conventional phased array ultrasonic testing (PAUT) and PAUT with full matrix capture using the total focusing method (FMC/TFM) was performed on ex-service SA-212 Grade B material. Locations with service generated HIC damage were extracted and tensile tested in air and in gaseous hydrogen. Examination of the tensile specimen fracture surfaces allowed for quantification of HIC damage associated with final tensile failure. HIC damage measured with NDT was similar to the HIC damage on the fracture surface when characterized using the crack sensitivity ratio (CSR). The hydrogen tensile testing results suggested that for material still charged with hydrogen (not currently explicitly addressed in API 579 – 1/ASME FFS Part 7), the loss in strength may be larger than 80%.