Roof evaluation of an existing tank to API 653 4.2: the roof plate thickness rule of 4.2.1.2 (average over any 250 mm × 250 mm area, holes), cracks, punctures and through-pitting of floating roofs before the next internal inspection (4.2.3.1, 4.2.3.2), the roof supports, frangible joint and appurtenances (4.2.2, 4.2.3.3, 4.2.3.4), and what a change of service brings in (4.2.4)
New here? Read the User Manual — the roof areas, the pitting projection, supports and change of service, with a worked example.
◉ API 653 5TH ED. (2014) ADDENDUM 4 (JULY 2025) 4.2 · API 650 14TH ED. ANNEXES C, H, F, M, V, 5.10.2.6 · NOT A REGULATORY SUBMISSION TOOL
⚠ Indicative tool only. Follows API 653, 5th edition (2014) with Addendum 4 (July 2025), 4.2, checked against that text. The units also choose the printed limit (1.1.3): 2.2 mm over 250 mm × 250 mm in SI, 0.09 in. over 100 in.² in US customary. Corrosion rates are linear. The structural adequacy of the roof and its supports (4.2.1.1), floating roof buoyancy and the frangible joint are judged by the inspector and the storage tank engineer, with the Roof Design, Floating Roof and Frangible tools where they apply.
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Identification
API 653 prints the limit in both systems (1.1.3): the tool checks against the set you choose. Records are kept in SI.
Summary of checks
Choose the roof type and enter the roof areas.
1. Roof and Inspection Plan
2. Roof Plates and Pontoons (4.2.1.2, 4.2.3.1, 4.2.3.2)
One row per area examined: the thinnest areas found, each over 250 mm × 250 mm. Give the average for the area, or type the readings over it (comma separated) to have them averaged. Enter the least thickness at pits to check through-pitting before the next internal inspection; a blank rate is estimated from the nominal thickness and the years in service. Tick the box for any hole, crack or puncture.
Area
Location
Average mm
Readings mm
Least at pits mm
Rate mm/yr
Hole / crack
Result
3. Supports, Joints and Appurtenances (4.2.1.1, 4.2.2, 4.2.3.3, 4.2.3.4)
The condition found for each item: acceptable, repair or replace, or not inspected / not applicable. Distorted (for example out-of-plumb columns), corroded and damaged members are evaluated and repaired or replaced if necessary (4.2.2.1).
4. Change of Service (4.2.4)
Tick what changes with the new service. Each brings in the requirement of 4.2.4 and the tool that covers it.
5. Evaluation Record (4.2)
Tick each item once it is confirmed. Items that don’t apply are hidden.
Save & Report
Inputs are kept on this device as you type and offered back if the page is closed before saving. Roof repairs follow API 653 9.12 (fixed roofs), 9.13 (floating roofs) and 9.14 (floating roof seals).