Using ASME FFS-1 / API 579 to Assess HIC Damaged Equipment

By John Aumuller, P.Eng., Ph.D.

Hydrogen induced cracking (HIC) may occur in pressure equipment that contain wet H2S environments when hydrogen blisters form and are accompanied by cracks which link these blisters. Since the blisters can form at various depths, the cracking will appear as a stair step appearance. Hence, HIC may be referred to as “stepwise cracking.”

To assess HIC damage, the ASME FFS-1 / API 579 standard presents Part 7 methodologies which contain three levels of assessment sophistication. A recent project involved evaluation of HIC damage which failed to pass a Level 1 assessment. A Level 3 assessment was performed which encompassed other parts of ASME FFS-1 / API 579, notably general metal loss [GML], local metal loss [LML], and the assessment of crack-like flaws.

Several difficulties were revealed for practitioners in applying the various levels of analysis. These included, on the part of the practitioner:

Notwithstanding the meticulous step-by-step approach of the standard, these difficulties in implementing this methodology are due to document complexity, inconsistencies in formulations, and overlooking documentation required by regulators. Other industry practice documents for in-service inspection alert users to the difficulties of assessing vessels to HIC damage which may preclude extending continued operation of a vessel that experiences this degradation mechanism.

We have recently developed a program for a client to assess the current status of damage in a tower, monitor damage progression, identify mechanical integrity limits, and the safeguarding steps required to ensure that vessel integrity is maintained in order to operate to the planned turnaround date.

©2010 Carmagen Engineering, Inc.