In depth · Risk-Based Inspection

RBI: risk-based inspection for petrochemical and power plants

I consult on and implement RBI, from the methodology to getting it into software and into daily use. The tool I currently work with is TWI's RiskWISE.

Talk about RBITry the risk matrix

PoF × CoF

probability times consequence

API 580 / 581

methodology framework

Petrochemical · Power

focus sectors

Consulting + Implementation

scope of work

Fixed-interval inspection treats every item alike. RBI ranks equipment by risk, then puts inspection effort where risk is high and relaxes it where risk is low, with reasons that are written down and can be checked.

1. What can fail?

   Which equipment, where, and by which damage mechanism.

2. How large is the risk?

   Risk = probability of failure (PoF) × consequence of failure (CoF).

3. How to inspect?

   What to inspect, where, with which method and when.

1. Scope and data

   Equipment in scope, design data, materials, operating conditions, inspection and repair history. The quality of this step sets the quality of every step after it.

2. Corrosion loops

   Groups of equipment and piping with the same material, fluid and operating conditions, and therefore the same damage mechanisms.

3. Damage mechanisms

   Identify the credible mechanisms for each loop: thinning, stress corrosion cracking, corrosion under insulation, high-temperature damage and so on (see API RP 571).

4. Probability of failure

   From corrosion rate, remaining life, susceptibility to cracking mechanisms and the effectiveness of past inspections.

5. Consequence of failure

   Safety of people, the environment, and the cost of lost production and repair.

6. Ranking and inspection plan

   Place each item on the risk matrix, then decide the method, location, extent and timing of inspection that keeps risk below the acceptance level.

7. Keep it current

   After every inspection, process change (MOC) or integrity operating window (IOW) exceedance, risk is recalculated. RBI is a living programme, not a one-off report.

Click a cell to see the risk rank and the usual direction of response.

An illustrative matrix. Each company defines its own matrix, rating scales and risk acceptance levels.

For uniform thinning, remaining life is the spare wall thickness divided by the corrosion rate.

Measured thickness (mm)Minimum required thickness (mm)Corrosion rate (mm/year)

Remaining life

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Half remaining life

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Half the remaining life is a familiar reference point for setting the next inspection. The actual limits come from the inspection code and the regulations that apply to the equipment. This calculation does not replace the judgement of a competent engineer.

• Design data and inspection history are missing or unreliable, so the result only looks good on paper.
• Corrosion loops are drawn too coarsely and hide spots with a different damage mechanism.
• The effectiveness of past inspections is rated too high.
• It is done once and shelved: no update after inspection, after an MOC or when an IOW is exceeded.
• The inspection plan never reaches the CMMS/EAM, so it never becomes work orders.

Work for companies is delivered together with Avenue JSC, where I am Senior Presales Consultant.

Each task has 20 bilingual prompt styles: draft, review, checklist, risk register, executive brief and more.

Talk about RBI for your plant

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