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Remaining life calculator for pressure vessels and piping

Estimate years to an entered required thickness using a selected corrosion rate. Explore a proposed next inspection date with an editable interval rule for API 510 and API 570 study. The required thickness is your input; this tool does not calculate ASME minimum thickness.

Method checked against NASA, Reliability-Centered Maintenance Guide for Facilities and Collateral Equipment, p. 6-37 on 17 Oct 2026. A calculation aid for study and estimating, not a substitute for the listed equipment's documentation or the AHJ.

Download your inputs, results, interval assumptions, warnings and references as a free CSV for Excel, Google Sheets or Numbers. No account needed.

Estimate remaining life and an inspection date

Fictional example loaded. Replace the inputs, including the example interval cap. Results update as you type and stay on your device.

Unit changes convert the values. Required thickness must come from a verified design or engineering evaluation. This tool does not compute ASME minimum thickness. Use the responsible inspector's selected corrosion rate.

Editable interval rule: min(fraction × remaining life, maximum)

The example uses half the remaining life (0.5), capped at an example 5 years. This is a general planning approach. Confirm the rule, maximum and inspection type against your code edition and jurisdiction; these settings do not establish code compliance.

Calculation results

Thickness above required
0.15 in
Remaining life
30 years
Proposed inspection interval
5 years
Proposed next inspection date
2031-01-01

RL = (0.4 − 0.25) in / 0.005 in/yr. Interval = min(0.5 × 30 years, 5 years). Dates use 365.25 days/year, rounded down to whole days from the actual reading date.

Remaining life calculation formula

Remaining life (years) = (t_actual − t_required) / corrosion rate.

Use actual and required thickness in the same units, and corrosion rate in those thickness units per year. For a rate in mils/yr and thickness in inches, divide the rate by 1,000 first. With millimeters, use mm/yr. One mil is 0.001 in = 0.0254 mm.

Source: NASA, Reliability-Centered Maintenance Guide for Facilities and Collateral Equipment, p. 6-37. This linear model divides the thickness margin by an assumed future rate. It estimates time to the entered required thickness, not time to rupture and not a guarantee of safe service.

Worked example

For fictional readings of t_actual = 0.400 in, an independently established t_required = 0.250 in, and a selected rate of 5 mils/yr = 0.005 in/yr, the thickness margin is 0.150 in. Remaining life = 0.150 / 0.005 = 30 years.

Using an example rule of half the remaining life and an example maximum of 5 years, the proposed interval is min(0.5 × 30, 5) = 5 years. Starting on 1 January 2026, the calculator adds floor(5 × 365.25) = 1,826 calendar days, giving 1 January 2031. This example cap is not a prescribed code maximum.

Inspection interval: an editable rule, not a code determination

The common general planning approach is interval = min(fraction × remaining life, user-entered maximum), often starting with fraction = 0.5. You must confirm the fraction, cap, inspection type, exceptions and jurisdictional rules against your applicable code edition, approved procedure and responsible inspector/engineer. RBI, service changes and other damage mechanisms can change the appropriate interval.

The interval equation above simply implements your chosen rule. Dates use UTC calendar days and 365.25 days/year, rounded down to avoid extending the numeric interval. Confirm how your inspection program schedules calendar years and due dates.

API's public Body of Knowledge section pointers are API 510 §7.1, §7.2 and §6, and API 570 §7.1.2, §7.2 and §6.3.3. See API 510 and API 570. Section numbering can vary by edition. No code text, inspection-interval tables or ASME design equations are reproduced here.

Zero rate and thickness at or below the required value

At zero rate with a positive thickness margin, division gives no finite life estimate. The tool withholds a proposed interval and date: zero observed loss does not justify unlimited service life or removal of inspections.

At t_actual ≤ t_required, the tool flags at or below required thickness: engineering evaluation needed, displays zero calculated remaining life and calculates no future inspection date. A positive corrosion rate cannot restore a consumed thickness margin.

Negative rates are invalid for this projection. Apparent metal growth should be investigated as measurement error or a change in conditions before selecting a representative rate. The AMPP monitoring study below discusses how temperature and repeatability affect thickness comparisons.

Using the result in Excel

The CSV is a snapshot of the current inputs and computed values, with units, references and calculation-aid notices. It contains no executable spreadsheet formulas. To check the worked example in your own worksheet, convert 5 mils/yr to 0.005 in/yr, then divide (0.400 − 0.250) by 0.005.

Calculate short-term and long-term corrosion rates → Use comparable readings from one CML and confirm the selected rate with the inspector. This tool does not evaluate localized damage, cracks, creep or interacting thickness effects.