Fitness-For-Service: API 579/ASME FFS-1-2016


API 579-1/ASME FFS-1-2016 Fitness-For-Service


Standards for pressurized equipment, such as those developed and published by the American Petroleum Institute (API) and the American Society of Mechanical Engineers (ASME), detail guidelines for the fabrication, design, inspection, and testing of new pressure vessels, piping systems, and storage tanks used in the oil and gas chemical process. However, while these codes and recommendations do prepare the equipment for use after manufacturing, they generally do not address deficiencies and acceptable flaws that arise after its long-term service use.

Despite this, standards for the inspection, repair, alteration, and rerating of in-service pressure vessels, piping systems, and storage tanks do allude to the fact that equipment degrades in-service, even if all guidelines and requirements have been fulfilled. Specific standards addressing this are API 510, API 570, API 653, and NB-23. Necessary to supplement these standards is the process of fitness-for-service (FFS), which is defined in API 579-1/ASME FFS-1-2016 - Fitness-For-Service as:

“Quantitative engineering evaluations that are performed to demonstrate the structural integrity of an in-service component that may contain a flaw or damage, or that may be operating under a specific condition that might cause a failure.”

The API 579-1/ASME FFS-1-2016 standard  provides the means to carry out fitness-for-service by covering a broad list of assessment methods based on the condition of the equipment  tested. In addition, it compiles the responsibilities of every individual involved, including the Owner-User (who has complete responsibility over the FFS), Inspector (who works in conjunction with the Nondestructive Examination (NDE) engineer to assure that requirements for testing and inspection have been met), and Engineer (who may need to provide input from the following disciplines: Materials or Metallurgical Engineering, Mechanical or Structural Engineering, Inspection Engineering, Fracture Mechanics Engineering, Nondestructive Examination (NDE) Engineering, and Process Engineering).


API 579-1/ASME FFS-1-2016 Fitness-For-Service


Ultimately, the FFS assessment procedures in API 579-1/ASME FFS-1-2016 include a comprehensive approach to thoroughly assessing the state of the damage to the equipment and its projected remaining life. This sophisticated assessment of metallurgical conditions and analyses of local stresses and strains gives a precise indication of the equipment’s fitness-for-service.

Please note that this standard, which first appeared as an API publication, is the second edition of the jointly-published document, and different updates have been made to this latest revision to keep it current. Changes to the 2016 publication of API 579-1/ASME FFS-1 include the following modifications and technical improvements:


  • Reorganized the standard to facilitate use and updates.
  • Expanded equipment design code coverage.
  • Added Annex for establishing an allowable Remaining Strength Factor (RSF).
  • Simplified Level 1 criterion for the circumferential extent of a Local Thin Area (LTA) through the modification of the Type A Component definition and subdivision of Type B Components into Class 1 or Class 2.
  • Updated crack-like flaw interaction rules.
  • Re-wrote weld residual stress solution Annex for use in the assessment of crack-like flaws. 
  • Updated guidance on material toughness predictions for use in the assessment of crack-like flaws.
  • Updated evaluation procedures for the assessment of creep damage.
  • Added Annex covering metallurgical investigation and evaluation of mechanical properties in a fire damage assessment.
  • Developed new Part 14 covering the assessment of fatigue damage.


API 579-1/ASME FFS-1-2016 - Fitness-For-Service is now available on the ANSI Webstore.
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