Inspectioneering Journal

Tank RBI: Not Just an Inspection Deferral Tool

By Joel Andreani, P.E., Senior Vice President, Knowledge Management; Principal Engineer II at The Equity Engineering Group, Inc. This article appears in the July/August 2021 issue of Inspectioneering Journal.


In recent editions of API STD 653, Tank Inspection, Repair, Alteration and Reconstruction, the use of risk-based inspection (RBI) has been permitted as a means of determining the next inspection date for initial and subsequent internal inspection of storage tanks. In accordance with API 653, the RBI assessment must consist of a systematic evaluation of risk, which is the product of the likelihood or probability of failure (POF), and the associated consequence of failure (COF) in accordance with API RP 580, Risk-Based Inspection. To evaluate a tank’s risk of failing, tank RBI methodologies range from highly qualitative (various tank experts subjectively ranking POF and COF) to quantitative (POF and COF calculated based on various design, inspection, operations, and maintenance factors). One highly quantitative method of performing the systematic risk evaluation required by API 653 is the tank RBI technology detailed in API RP 581, Risk-Based Inspection Methodology.  

This article is accompanied by a Jurisdictional Regulations for Tank Risk-Based Inspection Guide PDF that readers can download and refer to alongside this article. Click the button below to learn more and download the guide.

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Tank RBI has often been used by owner-users as a means of evaluating a deferral of an internal inspection that was scheduled based on a prescriptive (or time-based) interval when RBI was permitted to be used in this manner by the jurisdiction. However, tank RBI has other uses, such as determining and optimizing inspection activities for all tanks in a terminal or facility’s tank farm. This article will examine the quantitative tank RBI method found in API 581 (Part 5), discuss how tank RBI is another integral part of the facility’s overall tank integrity management program (IMP), and examine uses for tank RBI other than deferral of scheduled internal inspections.

API 581 Tank RBI Overview

In API 581 tank RBI, the risk of each shell course and the bottom is calculated from the POF and COF. The POF is defined as... 

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