Inspectioneering Journal

Risk Based Inspection - Understandings and Expectations

By Greg Alvarado, Chief Editor at Inspectioneering. This article appears in the January/February 1998 issue of Inspectioneering Journal.

There is a potential for misconceptions about terms regarding risk by non-risk management professionals. Understand that some risk is unavoidable. We can attempt to minimize risk to any extent desired, but without an effective process that addresses all the parameters we consider important, it is more likely our level of effectiveness will suffer. There is more to these considerations than likelihood of failure, which most inspection, materials, and corrosion specialists understand.

The other side of the equation, consequence, is just as important and needs serious consideration when deciding what RBI technology you will use. In addition to probably leak/failure scenarios, a manager should consider including certain specific consequence parameters (e.g. business interruption, equipment replacement, environmental costs, injury costs, etc.) too. These parameters can be expressed in terms of toxic exposure, effected area, and financial terms too.

Be cautious! Here it is easy for inspection corrosion and materials specialists to buy into technology of insufficient depth and/or validity, if they don’t understand it. After all, consequence modeling is not our area of expertise. Make sure your risk and reliability professionals thoroughly examine the logic of software, technology, and methodology and buy into it, in order to increase overall acceptance of the results.

When it comes to software, verify that the parameters you and your risk specialists feel are important are actually linked to the working algorithms. Output consequence or likelihood values should change to an appropriate extent, depending on “weight” when input values change. Otherwise these are just informational “place holders.” Make sure the weighing is reasonable, these factors are multiplied or added to others.

While it is important to understand all of the figures are not exact, including “absolute” and relative risk numbers, a good RBI technology should at least get you in the “ballpark” consequence-wise. Our object is to risk rank equipment, hence our activities and resource allocation. It does not mean practitioners won’t address lower risk items. It does mean RBI must provide a consistent, reproducible, and as accurate a technological approach for risk ranking as current knowledge will give us. Read the definition of relative risk near the end of this article for further clarification.

Industry consensus may be important to you for many reasons (e.g. synergy, global information resources, and professionals from both sides of the risk equation building the technology, regulatory, etc.). The American Petroleum Institute’s RBI technology is a good example of this, with 21 member sponsor companies. For your information, OSHA’s Process Safety Management (PSM) Rule states as an objective to reduce the risk of catastrophic events.

For many years, process industry specialists in the pressure vessel and piping engineering areas considered discussions about actually taking risks taboo. That includes inspections specialists too. Some of this was driven by the fact that the public attached a stigma to the consideration of risk by inspection specialists in refineries and chemical plants; i.e. “If we don’t say it, than it doesn’t exist.” Not very realistic, is it?

In actuality, when we begin to analyze the risks associated with, say, the likelihood and consequences associated with loss of containment (leaks, which incidentally can be a functional failure not considered by most Reliability Centered Maintenance) we become more empowered to manage and mitigate risks. Why? Because it should require us to more thoroughly consider the parameters affecting the likelihood of the event and the consequences should the event occur. The basis for RBI is to rank equipment based on risk, the combined consideration of likelihood and consequence.

Naturally, some equipment will be ranked higher than others. So there are opportunities to mitigate high risk and to identify relatively low risk items. Identify where resources are disproportionately allocated to low risk items. Perform “what if” analyses to see what happens to risk with reallocation of resources to the higher risk equipment from the lower risk equipment. The analyses shows the effects of the proposed risk mitigation on the high risk equipment and any risk increase in the low risk equipment items, which must be kept within acceptable risk limits.

Risk is not static. Therefore:

  • Rerun your RBI calculations to show the equipment in the future with the same conditions to see how risk changes with time.
  • Rerun with changing conditions such as new pH, moisture content, etc.
  • Run calculations at appropriate intervals to track changing risk.

Helpful hint for management of change: Test key variable ranges to see where significant changes in risk occur. Define these for operations. Ask them to let you know when they get outside of these risk-affecting ranges such as pH, temperature, hydrogen content, moisture content, pressure, etc.

When one begins to consider risk limits, either imposed by regulatory agencies or company policy, then risk targets are set. This is what’s thought of as absolute risk.1 An industrial risk analyst’s definition of absolute risk is “the application of chemical process quantitative risk analysis in which the results of the analysis are compared against the predetermined risk targets.”1

Definitions to put things in context1:

Risk: A measure of economic loss or human injury in terms of both the incident likelihood and the magnitude of loss or injury.

Relative Application of Chemical Process Quantitative Risk Analysis: A comparison and ranking of various risk estimates to prioritize the risk reduction strategies based on their competitive effectiveness.

Risk Analysis: The development of a quantitative estimate of risk based on engineering evaluation and mathematical techniques for combining estimates of incident consequences and frequencies.

It is important for management, regulators, and the public to realize that the knowledgeable and responsible use of solid RBI methodologies will help us operate our plants more effectively. There is a world of power in the “what if” scenario modelling you should be able to do with the technology you choose.

I have not covered the working process yet. Perhaps in the next IJ. This process is critical to assure you do not expand either too much or too little effort in implementing and maintaining your RBI program. Inordinate amounts of implementation effort have “soured” attitudes toward RBI and RCM (risk centered maintenance) in the past. Balance and ROI (return on investment) are key.

Please drop me an email with questions, comments, or ideas for follow up articles at

References and Acknowledgements

  1. “Guidelines for Chemical Process Quantitative Risk Analysis,” copyright 1989, American Institute of Chemical Engineers, Center for Process Safety
  2. American Petroleum Institute Base Resource Document, API 581
  3. “Update on API Risk Based Inspection Project – Parts I & II.” By Editor Josh Reynolds, Shell Oil Co. Inspectioneering Journal Issues 5 and 6, 1996.

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