Inspectioneering
Inspectioneering Journal

Aboveground Storage Tanks and the Responsible Use and Application of RBI

By Mark Geisenhoff at Flint Hills Resources. This article appears in the July/August 2002 issue of Inspectioneering Journal

Background

Risk Based Inspection (RBI) analysis is a powerful tool that all of us can use to help with the complex issues of risk. The opportunities for application are exciting and open the door for new ways of conducting business and focusing resources. Along with these new and exciting opportunities comes the responsibility for all of us to apply RBI in a responsible manner.

The approach has evolved as a viable tool for risk analysis and inspection planning of Atmospheric Storage Tanks (AST’s). The API 580 standard is the governing document with which all approaches should comply. The standard defines the principles and sets the minimum standards required for a Risk Based Inspection approach.

The API 581 guideline is one tool that is designed in compliance with the API 580 principles. The API 581 standard is a product of a joint industry project with more than 20 actively involved sponsors. The API 581 approach is widely acknowledged in the petrochemical industry today.

Pine Bend recently initiated a project to evaluate the potential of using RBI as an inspection planning tool for atmospheric storage tanks. We determined that before we could launch into the implementation of the tool, we needed to validate the technology and methodology with actual case histories.

Requirements

Any company has the option to define and design their own RBI tool, but it must comply with the principles of API 580 for quantitative Risk Based Inspection. The tool can be paper-based or electronic.

For this particular site, in order to consider RBI as a tool for inspection planning, without infringing with the operating permit, the RBI approach that is applied must be acceptable to the state of Minnesota.

Tables 1 and 2 shown below were drafted to help evaluate if a RBI approach is “acceptable”. The State of Minnesota is currently reviewing the document. The objective is that any relevant person within the company shall be able to do, or at least fully understand, the basis for and steps through a RBI analysis. Working with the same set of data and information, two individuals must be able to arrive at very similar analysis results, just by following the procedural document.

Table 1 continuedTable 1 continued

Table 2: List of Required Items for both API 581 and other API 580 Approaches - DraftTable 2: List of Required Items for both API 581 and other API 580 Approaches - Draft

Pilot Study

The pilot study was started with twenty tanks, all of which had unique histories that could be used for validation. The selection of tanks included tanks with past corrosion and floor replacements, tanks with minimal corrosion and no past floor replacements and floors with past failures. Each tank was evaluated as though we did not know the outcome over its entire history. Risk plots were developed showing calculated risk over time versus actual history. This data was used to calibrate the model and to identify the critical parameters and sensitivity of their changes.

We discovered during this process that objectivity and consistency were critical to the outcome for success. Standards were set for handling corrosion rates, soil conditions, inspection effectiveness, and other key parameters where consistency is essential to accurate results.

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