API 580 and API 581
RBI risk rank calculator
Enter the remaining life, governing corrosion rate, the fitness-for-service status and the consequence inputs. The calculator scores probability and consequence on 1 to 5 scales, multiplies them, and returns the risk rank the platform uses to set a base inspection interval.
Probability score
3 · medium
Consequence score
3 · medium
Risk score (P x C)
9
Risk rank
3
Base interval for rank
24months
Interval after half-life cap
24months
Advisory result. Provisional until a qualified inspector or engineer verifies it against the governing code edition.
How it works
- 01Probability 5: remaining life at or under two years, or a failed FFS screen with a rate above 0.25 mm per year.
- 02Probability 4: remaining life at or under five years, or a rate above 0.25 mm per year.
- 03Probability 3: remaining life at or under ten years, or a rate above 0.15 mm per year. Probability 2: at or under twenty years, or a rate above 0.05. Otherwise 1.
- 04Consequence: lethal fluid 5; critical system 5 (4 when the fluid is flammable); flammable fluid or important system 3; non-flammable in a normal system 2; otherwise 1.
- 05Risk = probability times consequence. Rank 1 at 20 or more, rank 2 at 12, rank 3 at 6, rank 4 at 3, rank 5 below.
Formulas
Risk = P (1 to 5) x C (1 to 5)1: 20+, 2: 12+, 3: 6+, 4: 3+, 5: below 3Read before you rely on it
- This is a semi-quantitative screen in the spirit of API 580 and 581, not the full API 581 damage factor and consequence area model.
- An unsigned provisional FFS result never lowers probability; the platform treats it as not acceptable until an engineer signs off.
- Consequence inputs are simplified categories. A real program calibrates them against inventory, toxicity and business impact.
Answers
Questions about this calculator
Is this the API 581 quantitative method?
No. It is a semi-quantitative screen: probability banded from remaining life and corrosion rate, consequence banded from fluid category and system criticality. API 581's damage factors and consequence areas are a separate, fuller calculation.
How does the risk rank set the inspection interval?
The platform maps rank 1 to a 6-month base interval, rank 2 to 12, rank 3 to 24, rank 4 to 48 and rank 5 to 120 months, then caps the result at half the remaining life. The interval calculator on this site shows that step.
Why does a failed FFS screen raise probability?
A component that does not pass a Level 1 screen while corroding faster than 0.25 mm per year is closer to its limit than the remaining life alone suggests, so the score moves to the highest band.
Does intelliSPEC use this scoring?
Yes. The platform's RBI function scores probability and consequence exactly this way and ranks 1 to 5, feeding the interval and disposition functions in intelliINTEGRITY.