The urgent and growing need by the petroleum industry for peer-reviewed, industry-wide accepted fitness-for-service (FFS) procedures for pressure vessels, piping and storage tanks led to the formation of a Materials Properties Council (MPC) Joint Industry Project (JIP) focused on sponsoring work toward meeting that objective. The MPC FFS JIP immediately attracted participation from U.S. and overseas refiners, and others involved in petroleum and chemical operations that were willing to share their best practices and pool their technical and financial resources to get the job done quickly.A team of engineers with practical knowledge regarding corrosion, hydrogen embrittlement and attack, fabrication, stress analysis, and fracture mechanics was organized and charged with developing a draft document for the JIP sponsors to review and begin to implement. That team prepared MPC document FFS-26, which captured the proven FFS technology of the petroleum industry.FFS-26 served as a road map of applicable fitness-for service technology that refiners and their contractors needed to identify, understand, and perform FFS assessments. It provided an introduction to modern fracture mechanics procedures including calculating limiting flaw sizes. It included a compendium of inspection methods useful to refiners and summarized the applicability, advantages, and limitations of proposed NDT techniques. It provided an introduction into the important aspects of and reasons for the details of flaw characterization, including depth and orientation, and outlined how to implement such information in modern FFS methods including flaw assessment diagrams. Radiographic, ultrasonic, magnetic particle, and other inspection methods were summarized in terms of relevance in FFS evaluations. The topics of flaw sizing, safety margins, leak-before-break, and local thin areas (LTA’s) were introduced. Procedures for estimation of residual stresses and toughness were among the many essential topics introduced to industry engineers.The treatment of cracks was comprehensive. Stress intensity solutions, not just for semielliptical and through-wall cracks in plates, but also for edge cracks, cracks in spheres, cracks at fillet welds, etc., were provided. Environments of concern in regard to acceleration of crack propagation were addressed. These ranged from caustic to ammonia and polythionic acid. Of course, the subjects of hydrogen embrittlement and hydrogen attack were covered in depth.Other practical matters addressed were concepts for sizing for multiple and non-planar flaws and issues associated with the use of NDE techniques. Included was estimating the probability of detection and other uncertainties. Application examples and guidance concerning mixed mode damage assessment and discussions of the performance of stress relieved as compared to as-welded components were included.In time the FFS assessment procedures in FFS-26 were updated and expanded to produce the first edition of API 579 Fitness-For-Service in 2000. Important updating of procedures, local thin areas, and pitting were included. Also, sections were added to cover evaluation of misalignment and out-of-roundness and fire damage. The procedures in API 579 should be used today in preference to the earlier ones included in FFS-26. However, publication of the FFS-26 at this time was deemed necessary by the Welding Research Council, (WRC), the successor organization to the MPC, in order to record the roadmap used to create the first edition of API 579, and the valuable background information contained therein.The wide implementation and international acceptance of the first edition of API 579 prompted adoption by ASME and in 2007, the second edition was produced and co-branded as API 579-1/ASME FFS-1 Fitness-For-Service. In 2009, an example problem manual illustrating the use of the FFS assessment procedures was produced as API 579-2/ASME FFS-2 Fitness-For-Service Example Problem Manual.