API 579-1/ASME FFS-1
Fitness-For-Service Fitness-For-Service (FFS) assessments are 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. This standard provides guidance for conducting FFS assessments using methodologies specifically prepared for pressurized equipment. The guidelines provided in this standard can be used to make run-repairreplace decisions to help determine if components in pressurized equipment containing flaws that have been identified by inspection can continue to operate safely for some period of time. These FFS assessments are currently recognized and referenced by the API Codes and Standards (510, 570, and 653), and by NB-23 as suitable means for evaluating the structural integrity of pressure vessels, piping systems, and storage tanks where inspection has revealed degradation and flaws in the equipment. The methods and procedures in this standard are intended to supplement and augment the requirements in API 510, API 570, Std 653, and other post-construction codes that reference FFS evaluations such as NB-23. The assessment procedures in this standard can be used for FFS assessments and/or rerating of equipment designed and constructed to the following codes: (a) ASME B&PV Code, Section VIII, Division 1; (b) ASME B&PV Code, Section VIII, Division 2; (c) ASME B&PV Code, Section I; (d) ASME B31.1 Piping Code; (e) ASME B31.3 Piping Code; (f) ASME B31.4 Piping Code; (g) ASME B31.8 Piping Code; (h) ASME B31.12 Piping Code; (i) Std 650; (j) Std 620; and (k) Std 530. The assessment procedures in this standard may also be applied to pressure-containing equipment constructed to other recognized codes and standards, including international and internal corporate standards. This standard has broad applications since the assessment procedures are based on allowable stress methods and plastic collapse loads for non-cracklike flaws, and the Failure Assessment Diagram Approach for crack-like flaws. The FFS assessment procedures in this standard can be used to evaluate flaws commonly encountered in pressure vessels, piping, and tankage. The procedures are not intended to provide a definitive guideline for every possible situation that may be encountered. However, flexibility is provided to the user in the form of an advanced assessment level to handle uncommon situations that may require a more detailed analysis.
BS 7910, the UK procedure for the assessment of flaws in metallic structures, was first published almost 30 years ago in the form of a fracture/fatigue assessment procedure, PD6493. It provided the basis for analysing fabrication flaws and the need for repair in a rational fashion, rather than relying on long-established (and essentially arbitrary) workmanship rules. The UK offshore industry in particular embraced this new approach to flaw assessment, which is now widely recognised by safety authorities and specifically referred to in certain design codes, including codes for pressure equipment. Since its first publication in 1980, PD6493/BS 7910 has been regularly maintained and expanded, taking in elements of other publications such as the UK power industry's fracture assessment procedure R6 (in particular the Failure Assessment Diagram approach), the creep assessment procedure PD6539 and the gas transmission industry's approach to assessment of locally thinned areas in pipelines. The FITNET European thematic network, run between 2002 and 2006, has further advanced the state of the art, bringing in assessment methods from SINTAP (an earlier European research project), R6, R5 and elsewhere. In particular, the FITNET fracture assessment methods represent considerable advances over the current BS 7910 methods; for example, weld strength mismatch can be explicitly analysed by using FITNET Option 2, and crack tip constraint through Option 5. Corrosion assessment methods in FITNET are also more versatile than those of BS 7910, and now include methods for vessels and elbows as well as for pipelines. In view of these recent advances, the BS 7910 committee has decided to incorporate many elements of the FITNET procedure into the next edition of BS 7910, to be published c2012. This paper summarises the history of the development of BS 7910, its relationship with other flaw assessment procedures (in particular FITNET and R6) and its future.