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-repair-replace 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, API 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) API Std 650
j) API Std 620
k) API 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-crack-like 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.