Fitness-For-Service API 579-1/ASME FFS-1 – Substantive Changes in the 2016 Edition

Fitness-For-Service API 579-1/ASME FFS-1 – Substantive Changes in the 2016 Edition

Authors: Eileen Chant, Greg Epremian, Magnus Gustafsson, Ranjan Nadarajah, Mark Stonehouse

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

  • 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.

Hydrogen Blisters and Hydrogen Damage Associated with HIC and SOHIC – Part 7

  • Increased definition of when Part 7 should be used instead of Part 13 (Laminations)
  • Level 1 Assessments are limited to Type A components only (as defined in Part 4).
  • Level 2 Assessments are limited to Type A and Type B Class 1 components.

Weld Misalignment – Part 8

  • The equations for calculating the bending stress multiplier for flat plates, cylinders (longitudinal and circumferential joints) and spheres have been revised. In particular, the methodology for the longitudinal cylinder joint bending stress multiplier is completely different from before.
  • Limitations on centerline offset for have been added for flat plates and revised for cylinders.

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.

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.

Fire Damage – Part 11

  • A major Annex 11B has been added to provide guidelines for performing metallurgical investigations and mechanical testing after a fire event.
  • Added Table 11.12 to describe typical material degradation and damage that may occur in various steels due to heat exposure during fire.
  • Added color photos to Table 11.18 to show tempering colors of steel due to different temperature exposures.

Dents, Gouges, and Dent Gouge Combinations – Part 12

  • Modification of the calculation to determine the wall thickness to be used in the assessments.
  • Minor reference and typographical changes.

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.
  • The fatigue curve fit equations and coefficients have been changed and the applicable stress amplitudes for the various equations are now temperature dependent.
  • 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.

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About The Author

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Dr. Eileen Chant has 25 years of experience in the areas of engineering project management, modeling and performance evaluation of mechanical and energy systems. She has managed a number of projects developing and applying risk-based inspection methodologies and software tools for use by the process and power industry in developing cost-effective inspection and maintenance programs in accordance with API RP-580 and the ASME Inspection Planning Document, PCC-3. She has also managed projects developing andapplying fitness-for service software tools in accordance with API 579/FFS-1 and new methodologies for collection, management and statistical analysis of NDE data.

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