API 510 and API 570
Corrosion rate and remaining life calculator
Enter three thickness readings and the minimum required thickness. The calculator returns both corrosion rates the standards define, picks the governing rate the way the platform does, and shows the remaining life and the half-life cap on the next interval.
Long-term rate
0.137mm/yr
Short-term rate
0.150mm/yr
Governing rate
0.150mm/yr
Remaining life
14.0years
Half-life interval cap
7.0years
Advisory result. Provisional until a qualified inspector or engineer verifies it against the governing code edition.
How it works
- 01Long-term rate: initial thickness minus latest thickness, divided by the years between them.
- 02Short-term rate: previous thickness minus latest thickness, divided by the years between them.
- 03Governing rate: the higher of the two (a negative rate is treated as zero and flagged).
- 04Remaining life: latest thickness minus tMin, divided by the governing rate.
- 05Interval cap: half the remaining life, which API 510 and API 570 apply alongside the code maximum.
Formulas
LT = (t initial - t latest) / years since initialST = (t previous - t latest) / years since previousRL = (t latest - tMin) / max(LT, ST)Read before you rely on it
- A short interval with a small thickness change is mostly gauge noise; the standards let a corrosion specialist select the rate that reflects current conditions.
- The governing rate here is the maximum, the conservative default. A documented override belongs on the CML record, not in a spreadsheet.
- Results are advisory and must be verified by a qualified inspector or engineer before they set an inspection date.
Answers
Questions about this calculator
Which corrosion rate governs, short term or long term?
The conservative default is the higher rate, which gives the shorter remaining life. API 510 and API 570 allow the inspector, with a corrosion specialist where needed, to choose the rate that best reflects current conditions, and the reason should be recorded.
What if the short-term rate is negative?
A negative rate means the wall appeared to grow, which it did not. Treat it as zero for the calculation and look for a measurement, location or unit error in the readings.
How is remaining life used to set the interval?
API 510 and API 570 cap the inspection interval at half the remaining life, subject to the maximum the code sets for the equipment class. The calculator shows that half-life figure.
Does intelliSPEC compute this the same way?
Yes. The platform stores short-term, long-term and maximum rates on each CML, takes the maximum as governing, and computes remaining life as latest thickness minus tMin over the governing rate. Results stay provisional until an engineer verifies them.