Maximum capacity, net working capacity, and the resulting fill levels (API 650 §5.2.6, Figure 5-4, and §H.5.3 for internal floating roof tanks)
◉ API 650 §5.2.6 / §H.5.3 STYLE CHECK · NOT A REGULATORY SUBMISSION TOOL
Where this comes from: §H.5.3 (the section this was originally scoped from) turns out to have no formula of its own — it's a procedural clause: the Purchaser sets the actual levels per NFPA 30 and API RP 2350, and for internal floating roof tanks the Manufacturer separately supplies the floating roof/seal geometry needed to check clearances. The genuine computable relationship lives in §5.2.6 and Figure 5-4 in the main body, which applies to any tank, not just floating-roof ones — that's what this tool implements. The overfill protection and minimum operating requirements themselves are Purchaser-specified per API RP 2350, not computed here; enter them as given.
Identification
Research entries stay private to you for practice/testing. Switch to Official once this is a real design your company should see.
Tank Geometry & Maximum Capacity (§5.2.6.2)
Result
Cross-sectional area—
Maximum capacity (§5.2.6.2)—
Overfill Protection & Minimum Operating Requirements (Purchaser-specified per API RP 2350)
Enter height only, or both height and volume to cross-check them against each other using the tank's cross-sectional area.
Consistency Check
Overfill protection: entered volume vs height-derived—
Minimum operating: entered volume vs height-derived—
Resulting Levels & Net Working Capacity (§5.2.6.3, Figure 5-4)
Top of shell / Design liquid level—
↓ Overfill protection requirement—
Normal fill level—
⋮ Net working capacity zone
Minimum fill level—
↓ Minimum operating volume remaining—
Top of bottom plate at shell0
Result
Net working capacity (volume-based, §5.2.6.3)—
Net working capacity (height-based cross-check)—
Internal Floating Roof Considerations (§H.5.3)
For tanks with an internal floating roof, the Normal Fill Level and Overfill Protection Level above must also clear the floating roof's own geometry: shell obstructions (nozzles, stairway, overflow slots), the roof's design flotation level, and the level at which its pressure/vacuum relief vents begin to open. The floating roof Manufacturer provides this dimensional profile (§H.5.3.2) — check the computed Normal Fill Level above against it manually; this tool doesn't have that geometry to check automatically.
Per §H.5.3.3: overflow slots shall be sized to discharge at the tank's pump-in rate (using the greater of product specific gravity or 1.0 to set slot position), covered with 13 mm (½ in.) corrosion-resistant coarse-mesh screen, and shall not be the primary means of detecting an overfill. Their open area may count toward the §H.5.2.2.1 circulation-vent requirement only if at least 50% of that circulation-vent area stays unobstructed during an emergency overflow. The standard doesn't give a discharge-rate formula (it references net open area and head pressure, not exceeding the top of the opening, without a stated equation) — this tool doesn't compute a slot size.