API RP 581 Risk-Based Inspection Methodology Revisions

The American Petroleum Institute (API) Risk-Based Inspection Methodology Third Edition has been released after a thorough review and revision starting in 2012.  The initial Base Resource Document was the prepared as a result of an API lead Sponsor Group project originally released in 1994 and revised and updated by the group to 2000.  The Base Resource Document was published by API in 2000 as a detailed semi-quantitative risk-based inspection technology and was further developed as a recommended practice when the Second Edition was published in 2008. Since 2008 significant changes had been made in the risk-based methods. As part of the regular API document review process, API RP 581 was reviewed and revised. This article highlights the major changes made and reflected in the Third Edition.

The first change is the document name was changed from “Risk-Based Inspection Technology” to “Risk-Based Inspection Methodology” to reflect that the document is a systematic set of methods to be used to develop equipment inspection plans based on risk and not only a technical way to calculate risk.

The document is still comprised of three Parts:

  • Part 1 Inspection Planning Methodology
  • Part 2 Probability of Failure (POF) Methodology
  • Part 3 Consequence of Failure (COF) Methodology

Structural changes include the consolidation of all the definitions and acronyms into Part 1.  Significant revisions and additions were made to the list of definitions and acronyms. Definitions and acronyms are used consistently in all of the document Parts.  Another structural change involves handling of Inspection Effectiveness guidance.  All relevant information and the example related to Inspection Effectiveness were combined from Part 1 Section 4.4.5 and other areas in the document to a new Annex 2C.

Overall changes were made through out the document to clarify concepts, move sections and information around for better readability, revise calculation procedures to correct errors or omissions found. Overall the task group intended the changes to help users follow the calculation steps. The following will summarize changes that either add or change technical content and not highlight the numerous editorial changes.