Short answer
Risk-based inspection (RBI) is a method to plan inspections by risk. Risk is the product of the probability of failure (PoF) and the consequence of failure (CoF). RBI puts the inspection effort on the assets with the highest risk, and less effort on assets with low risk. API 580 gives the principles. API 581 gives the calculation methods.
How an RBI assessment works
An RBI assessment looks at each asset in turn. It identifies the active damage mechanisms, such as thinning, cracking or pitting. API 571 describes these damage mechanisms for fixed equipment in refineries.
For each damage mechanism, the assessment estimates the probability of failure. The estimate depends on the damage rate, the age of the asset and the quality of past inspections. API 581 calls this quality the inspection effectiveness, on a scale from A to E.
The assessment also estimates the consequence of failure. The consequence depends on the fluid, the pressure, the inventory and the people and equipment near the asset. API 581 expresses it as an affected area or as a financial cost.
Risk is the product of the two values. Each asset gets a place on a risk matrix. The inspection plan then gives the most attention to the assets at the top of the matrix.
What an RBI plan decides
An RBI plan answers four questions for each asset:
- Which assets to inspect first.
- Which inspection method can find the active damage mechanism.
- How much of the asset to inspect. This is the coverage.
- When to inspect next, within the limits of the inspection code.
RBI and the inspection codes
RBI does not replace the inspection codes. API 510 covers pressure vessels, API 570 covers piping and API 653 covers storage tanks. Each code sets a maximum interval between inspections. Each code also lets an RBI assessment set the interval, under conditions that the code states.
For thickness data, Reliatic sets the next inspection of each CML to the lesser of half the remaining life and the code maximum. The guide to remaining life shows a worked example.
How Reliatic supports RBI
Reliatic records each RBI assessment with its probability and consequence scores, on a scale from 1 to 5. It shows the assets in a ranked queue and on a risk matrix.
We designed Reliatic to support API 580 and API 581 workflows. Reliatic is not certified to either standard. It does not replace a qualified RBI analyst or a certified RBI study.
Questions and answers
What is the difference between RBI and time-based inspection?
Time-based inspection uses one fixed interval for every asset of a type. RBI sets the interval and the method from the risk of each asset. An asset with low risk can wait longer, within the code limits. An asset with high risk gets an earlier and more thorough inspection.
Which standards describe RBI?
API 580 gives the principles of an RBI program. API 581 gives the quantitative methods for the probability and the consequence of failure. ASME PCC-3 also describes inspection planning with risk-based methods.
Does RBI reduce the cost of inspection?
It can, but no fixed percentage applies to every plant. RBI moves effort from assets with low risk to assets with high risk. The result depends on the plant, its data and its damage mechanisms.
Is Reliatic certified to API 580 or API 581?
No. We designed Reliatic to support API 580 and API 581 workflows. It does not replace a qualified RBI analyst or a certified RBI study.