Fitness-For-Service API 579-1/ASME FFS-1: Substantive Changes to the 2016 Edition

Fitness-For-Service API 579-1/ASME FFS-1: Substantive Changes to the 2016 Edition


Contributing Authors: Eileen Chant, Greg Epremian, Ranjan Nadarajah, Mark Stonehouse 

Summarized herein are the substantial changes to API 579-1/ASME FFS-1, Fitness for Service, that were incorporated in the 2016 edition, as reviewed by Becht Fitness for Service experts.

API 579-1/ASME FFS-1 is a Standard jointly published by API and ASME.  The purpose of the document is to provide a consensus of methods to quantitatively evaluate commonly observed damage to in-service pressure equipment.  Since it was first issued by API in 2000, this Fitness-For-Service standard has been used worldwide as a means of evaluating whether pressure equipment was fit for continued service, and in many cases, for how long.  This standard has been used to avoid costly and unnecessary unplanned outages, while maintaining safe and reliable equipment.

 The Second Edition was released in 2007, followed by the most current release of the document in June of 2016.  In addition to the many clarifications, updated references to codes and standards, several changes and additions have been made to improve the standard in its most recent update.  A change log has not been provided by the Joint API/ASME FFS Committee and this blog post aims to highlight the substantial changes.

Organization of the Standard

In the 2007 edition, material properties needed for FFS assessments were provided in Annex F. In the 2016 edition, the material properties are no longer in a separate annex, but are instead moved to the assessment part where they are mostly referenced. For example, material data needed for creep assessments – Part 10 – are now found in Annex 10B. Another example is the previous Annex B1, which contained the procedures for demonstrating protection against various failure modes using stress analysis, which is now under Part 2 in Annex 2D.

Several of the assessment methodologies are no longer shown in full, e.g. plastic collapse analysis. Instead, the user is pointed to the corresponding Design-By-Analysis paragraphs of ASME BPVC Section VIII Division 2. Only differences between these two standards are explicitly addressed in API 579-1/ASME FFS-1, e.g. use of Remaining Strength Factor (RSF), β-factor in elastic-plastic analyses, etc.

Introduction – Part 1

  • Scope of the standard has been expanded to include additional Construction Codes.

FFS Procedures – Part 2

  • New Annex 2F with guidance for selecting RSF.

Brittle Fracture – Part 3

  • MAT calculations now always required in Level 1 assessments (exemptions removed).
  • Clarifies applicability of Div 1, Div 2 and B31.3 toughness rules in Level 1 assessments.
  • Clarifies stress determination in assessment of piping systems – Method A.

General Metal Loss – Part 4

  • Revised definitions of corrosion losses.
  • The Standard now has a lower minimum thickness limit for piping than for vessels.
  • Revised definition of average thickness, which now includes FCA. Since the FCA is included in the acceptance criteria, this appears to be a double counting error and we expect future errata documents will remedy this.
  • Revised procedure for Critical Thickness Plane (CTP) assessments.

Local Metal Loss – Part 5

  • Revised definitions of corrosion losses.
  • The Standard now has a lower minimum thickness limit for piping than for vessels.
  • Revised procedure for assessing groove-like flaws.
  • New Level 1 and Level 2 criteria for circumferential extent of flaw.
  • Change in Level 2 procedure for combining closely spaced flaws.

Pitting – Part 6

  • Includes criteria for minimum acceptable thickness.
  • New criteria for evaluating pitting damage as LTA.

Crack-like Flaws – Part 9

  • Revised method for calculating plasticity interaction factor.
  • Partial Safety Factors (PSF) have been removed from the Level 2 procedure.
  • Clarification of weld joint efficiency in stress computations for Crack-like flaw evaluations.
  • Completely rewrite of old Annex E for residual stresses in what is now Annex 9D.
  • Updated flaw interaction rules.
  • Updated guidance on material toughness in crack-like flaw evaluations.
  • Influence coefficient tables expanded to allow for assessment of ID surface cracks in thick walled cylindrical components (for t/Ri up to 3.0).

Creep – Part 10

  • The standard now advises a higher allowable creep damage.
  • Suggested creep strain acceptance criteria are now offered.
  • Guidance is given for how to implement the MPC Omega method in numeric analysis, i.e. FEA.
  • The Creep Crack-growth, Creep Buckling and Dissimilar Weld Joint Creep procedures have been revised.
  • The MPC Omega creep data have been expanded with additional materials.
  • The Larson-Miller parameters have been updated with WRC 541 data.

Laminations – Part 13

  • Re-arranging of the assessment procedures with unfortunate modifications that results in Level 1 and Level 2 assessment to yield identical results.

Fatigue – Part 14 

  • The new Part 14 includes the procedures for demonstrating protection against cyclic failure previously found in Annex B1. These procedures have been divided into assessment levels with the screening methods as Level 1 and the stress analyses methods (S-N curve and Structural Stress) as Level 2.
  • A Level 3 assessment is introduced in the form of a new strain-life assessment procedure with mean stress correction using the critical plane approach. This method is complex and will for all but the simplest cases require dedicated post-processing software.

BechtFFS tanks piping

Becht Engineering has extensive experience and expertise in the conduct of Fitness-For-Service. We have performed evaluations for all damage mechanisms covered in API 579-1/ASME FFS-1 for clients around the world. Our wealth of knowledge and experience enables us to provide authoritative, practical, knowledge based answers, and to solve your problems.

Additionally, our FFS experts developed and optimized our proprietary BechtFFS software. BechtFFS software is an API 579-1/ASME FFS-1 (2016 edition compliant) web-based software designed to assist operators/owners in evaluating equipment items which have developed defects in service. Read more about the software HERE.


If you are interested in trying out BechtFFS Software, please contact Eileen Chant (CLICK) to receive a free, 30-day trial.


About The Author

Magnus Gustafsson has over 10 years experience in the design and analysis of mechanical components and systems in the Petrochemical and Railway industries. His experience includes Fitness-for-service assessments and design support of pressurized equipment including elastic-plastic Finite Element Analysis, transient heat transfer analysis, creep, high-and low cycle fatigue, fracture mechanics, fluid surge and piping flexibility analysis.

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