This bulletin is part of a series of WRC Bulletins that contain the technical background and other information to evaluate damage mechanisms in various industries to facilitate the use of API 579. These bulletins@ shown below@ will be updated based on the latest knowledge and technology developed for identification of damage mechanisms. ? WRC 488 - Damage Mechanisms Affecting Fixed Equipment In The Pulp And Paper Industry ? WRC 489 - Damage Mechanisms Affecting Fixed Equipment In The Refining Industry ? WRC 490 - Damage Mechanisms Affecting Fixed Equipment In Fossil Electric Power Industry The series of WRC Bulletins shown above is a valuable tool to assist plant personnel in Risk-Based Inspection studies performed in accordance with ANSI/API RP 580 Risk-Based Inspection because identification of damage mechanism is central to a successful implementation of this technology. In addition@ in order to create and maintain an effective equipment reliability or integrity program it is essential that active and potential damage mechanisms are identified. There are significant economic benefits in continuing the operation of aging pressure vessels@ piping@ and tankage. API 579 Recommended Practice for Fitness-For-Service was developed to provide a central reference for flaw evaluation and damage assessment of this aging equipment. The fitness-for-service assessment procedures in API 579 are intended to supplement the requirements in the current in-service inspection codes API 510@ API 570@ API 653@ and NBIC: (i) to ensure safety of plant personnel and the public while older equipment continues to operate; (ii) to provide technically sound fitness-for-service assessment procedures to ensure that different service providers furnish consistent life predictions; and (iii) to help optimize maintenance and operation of existing facilities@ maintain availability of older plants@ and enhance long-term economic viability. API 579 is organized by damage type (localized metal loss@ crack like flaws@ fire damage@ etc.). The first step in a Fitness-For-Service (FFS) assessment is to identify the source of the damage or deterioration in order to select the correct assessment methodology. Several resources are available to help identify the damage mechanisms. However@ most of these guidelines are incomplete in regards to the satisfying the requirements for damage mechanism identification contained in API 579. Appendix G in API 579 was specifically developed to provide guidelines for damage mechanism identification to the FFS practitioner. However@ it became apparent that more comprehensive guidelines were required to assist plant personnel in the identification of damage mechanisms. In addition@ guidelines for identification of damage mechanisms were required to be industry specific in order to properly address the diversity and complexity of equipment and operating environments found in today's industries