Contents
About this tool
The Tank RBI tool records a qualitative risk-based inspection assessment of one storage tank. It takes a probability and consequence of failure for each component and damage mechanism, places them on a risk matrix, ranks them, and checks the API 653 rules for setting the internal inspection interval by RBI.
Built on API RP 580, 3rd edition (February 2016), the text on file, with API 653 (5th edition, Addendum 4) 6.4.2.1.2 and 6.4.2.2.2. The 4th edition of RP 580 (2023) is current and has not been compared; the tool will be upgraded when that text is available. The page, the report and this manual say so.
RP 580 sets out the elements of an RBI programme; it does not give formulas. The category scales and the risk matrix here are its examples (Tables 2, 3 and 5, Figure 7), which an owner should set to its own criteria (11.7). For a quantitative assessment, API RP 581 (4th edition, 2025) has tank-specific methods.
Quick start
- 1Enter the tank, or load a sample. Section 1: product, capacity, release prevention barrier, service, whether you are setting the initial or a subsequent interval, the proposed interval, the dates and the team.
- 2Section 2: consequence categories for safety and health and for the environment, and an economic estimate. The tank takes the highest.
- 3Section 3: one row per component and damage mechanism. Enter the susceptibility, the rate and its source, the remaining life and the inspection effectiveness. Read the suggested probability category; set your team’s in the last column.
- 4Tick the API 653 likelihood and consequence factors as the team evaluates them.
- 5Read the matrix and register (Section 4) and the interval and review dates (Section 5); save and print.
Categories
| Probability | Annual frequency (RP 580 Table 2) |
|---|---|
| 1 | below 0.0001 (remote to very low) |
| 2 | 0.0001 to 0.001 (low) |
| 3 | 0.001 to 0.01 (moderate) |
| 4 | 0.01 to 0.1 (high) |
| 5 | above 0.1 (very high) |
| Consequence | Safety, health, environment (Table 5) | Economic (Table 3, adjustable) |
|---|---|---|
| A | no significant consequence | below 10 k |
| B | first-aid injuries, minimal environmental impact | 10 k – 100 k |
| C | minor injuries, short-term impact | 100 k – 1 M |
| D | serious injuries, significant impact | 1 M – 10 M |
| E | fatalities, major long-term impact | above 10 M |
- RP 580’s six-level tables are condensed to five to fit the 5 × 5 matrix: Remote and Very low form probability 1; Major and Catastrophic form consequence E.
- The economic bands are in the currency you choose; RP 580 notes that a severe loss differs with the size of the company, so set them to yours.
- A row can take its own consequence where its failure mode differs from the tank’s worst case: a pinhole in the bottom of a tank on a release prevention barrier is not a shell rupture.
The suggested probability
RP 580 leaves the probability category to the team’s judgement (9.3.2), based on the damage mechanisms and rates and on how effective inspection has been (9.4). To make that consistent, the tool suggests a category. This screening aid is Tank Protocol’s, not an RP 580 method; hover over the suggestion to see its basis.
| Basis | Category |
|---|---|
| Remaining life ÷ proposed interval: 4 or more | 1 |
| 2 to 4 | 2 |
| 1 to 2 | 3 |
| 0.5 to 1 | 4 |
| below 0.5 | 5 |
| No remaining life: susceptibility low / medium / high / not known | 2 / 3 / 4 / 4 |
| Inspection effectiveness: high / medium / low or none | −1 / 0 / +1 |
- The team’s category in the last column overrides the suggestion. Where it is lower, the tool asks you to record why (16.5, 16.6).
- API 653 6.4.2.2.2: corrosion rates used in RBI must come from high or medium effectiveness inspections. A rate from a low-effectiveness inspection such as spot UT fails the check.
Risk matrix and register
Risk is placed on RP 580’s Figure 7 example matrix:
| Risk | Cells |
|---|---|
| Lower | A1, A2, A3, B1, B2, C1 |
| Higher | C5, D4, D5, E3, E4, E5 |
| Medium | the other 13 cells |
- The register ranks the items, highest risk first, and says what drives each: probability (inspection and monitoring can reduce it, 12.2) or consequence (inspection will not reduce it much; consider mitigation such as a release prevention barrier, leak detection, inventory or containment, Section 13).
- Choose the owner’s acceptable risk: lower and medium, or lower only. Items above it need mitigation, and API 653 says a tank is removed from service when its risk exceeds the acceptance criteria.
Interval and review (API 653 6.4.2)
| Rule | Clause |
|---|---|
| Initial internal interval set by RBI: at most 20 years without a release prevention barrier, 30 years with one | 6.4.2.1.2 |
| The limit does not apply after an RBI assessment for viscous products that solidify below 43 °C, or for non-hazardous products with no impact beyond the facility | 6.4.2.1.2 |
| Subsequent interval set by RBI: no fixed cap (the 20 / 30 year cap is for the corrosion-rate method of 6.4.2.2.1) | 6.4.2.2.2 |
| The assessment reviewed and approved at intervals not exceeding 10 years, or sooner after changes | 6.4.2.2.2 |
| Methodology validated, preferably by an entity outside the team | 6.4.2.2.2 |
| Interval within the shortest remaining life | tool check |
The tool gives the next internal inspection date from the last one and the proposed interval, and the RBI review date. It flags reassessment after significant change, after mitigation and around turnarounds (RP 580 14.3). External inspections still follow API 653 6.3.
API 653 factors
- Likelihood (6.4.2.2.2.1, a – r): bottom thickness, weld type and age; how corrosion rates were found; inspection history; soil resistivity; pad quality; berm drainage; cathodic protection; temperature; product effects; lining; steam coils and water draws; maintenance quality; design codes; materials; inspection effectiveness; functional failures; settlement; construction QA.
- Consequence (6.4.2.2.2.2, a – m): release prevention barrier; product and volume; failure mode; environmental receptors and distance; leak detection; product mobility; receptor sensitivity; remediation, cleaning and loss-of-use costs; public safety; dike containment.
- Each list must be fully evaluated; the summary shows how many are ticked.
Saving and the report
- Fill in Identification (company, tank or item ID, location) and the record type: Just for research stays private to you; Official is visible to your company.
- Calculate & Save stores the inputs and results in the
rbiTankCalcscollection. - Print / PDF report opens a printable page of everything on screen: identification, the standard and edition, each section’s inputs and results, and any notes. Use Save as PDF in the print dialog. The report includes the matrix, the register with each category’s basis, both API 653 factor lists and the RP 580 Section 16 documentation checklist.
Limits
- RP 580 3rd edition (2016) basis; the 4th edition (2023) has not been compared.
- Qualitative. It does not compute probabilities or consequences from first principles (API RP 581 does).
- The suggested probability is a screening aid; the team’s judgement and the owner’s validated procedure govern.
- Use the Shell Evaluation, Inspection Interval, Tank Shell FFS and API 571 tools for the remaining lives and mechanisms you enter here.