Fitness-For-Service Assessments

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Fitness-For-Service assessments are quantitative engineering evaluations that are performed to demonstrate the structural integrity of in-service components that may contain a flaw or damage at specific operating conditions. The FFS approach provide technically sound, conservative and meticulous solutions to ensure the safety of plant personnel and the public in an environment where aging equipment continues to be operated. The additional benefits of FFS assessments are that they provide inputs for decisions to continue to run, alter, repair, monitor, retire or replace equipment. Often a rerating or reduction in operating temperature or pressure can allow components to be returned to service. It is customary to compliment FFS assessment with a Remaining Life Assessment (RLA).

Pipe elbow stress distribution following FEA analysis
Pipe elbow stress distribution following FEA analysis

Straight-forward and conservative calculations are occasionally found in design or construction codes for certain deviations or manufacturing flaws. However, API 579-1/ASME FFS-1 allows for a more sophisticated assessment of metallurgical conditions and analyses of local stresses to conclude if equipment is fit for its intended service or whether particular fabrication defects or in-service degradation threatens its integrity.  Accordingly, the active degradation mechanisms are identified as a first step. Theoretical and practical knowledge of the degradation process are then combined with knowledge of materials and structural behaviour to establish if continued operation is feasible and safe.

SecMet is well positioned and experienced with regard to Fitness-For-Service and Remaining Life assessments. We make use of leading standards and documents such as BS 7910, API  579-1 / ASME FFS-1, 2016 and specialist software in this regard. Our strong metallurgical and materials engineering background, combined with state-of-the-art structural modelling and testing capabilities, results in word-class Fitness-For-Service assessments.

State of the art modelling
State of the art modelling

The assessment techniques we employ would allow us to evaluate flaws or equipment in terms of:

  • General and localized corrosion
  • Widespread and localized pitting
  • Blisters and hydrogen damage
  • Weld misalignment and shell distortions
  • Crack-like flaws including environmental cracking
  • Laminations
  • Dents and gouges
  • Remaining life for components operating in the creep range
  • Resistance to brittle fracture
  • Long-term creep damage
  • Fire damage
Example of a level one, finite surface crack assessment
Example of a level one, finite surface crack assessment

Possible in-service equipment that may warrant a fitness-for-service assessment pertain to equipment that are or were subject to:

  • Time-dependent (long-term) degradation
  • Upset operating conditions (pressure or temperature)
  • Intense fluid-material interactions (e.g. corrosion)
Schematic indicating the FFS assessment of a crack-like flaws using the Failure Assessment Diagram (FAD) and the attributes that influence the abscissa.
Schematic indicating the FFS assessment of a crack-like flaws using the Failure Assessment Diagram (FAD) and the attributes that influence the abscissa.