Top and intermediate wind girder section modulus, and unstiffened shell height (API 650 §5.9)
◉ API 650 §5.9 STYLE CHECK · NOT A REGULATORY SUBMISSION TOOL
⚠ Indicative tool only. Formulas are sourced directly from API 650 §5.9 (Top and Intermediate Stiffening Rings) as provided, and were checked against the actual page images, not just extracted text, since this document was a scanned/OCR'd PDF. Covers open-top tanks requiring wind girders per §5.9.1. For tank diameters over 60 m (200 ft), the required section modulus may be reduced by agreement between Purchaser and Manufacturer, but not below what's required for a 61 m (200 ft) tank — this tool computes the raw formula value and doesn't apply that negotiated reduction. Confirm this is your current edition of API 650 before relying on this for a real design.
Identification
Research entries stay private to you for practice/testing. Switch to Official once this is a real design your company should see.
Design Basis
Default 190 km/h (120 mph) matches the standard's own reference basis (§5.9.7.1 Note 2) — replace with your actual site/Purchaser-specified design wind speed per the Data Sheet.
Top Wind Girder (§5.9.6.1)
Include any freeboard provided above the maximum filling height as a guide for a floating roof.
Result
Required minimum section modulus Z—
Maximum Height of Unstiffened Shell (§5.9.7.1)
Per Note 1: this check uses nominal dimensions unless "Check Buckling in Corroded Cond." = Yes on the tank's Data Sheet, in which case use nominal minus the specified corrosion allowance.
Enter each shell course's actual width (height) and nominal thickness. The tool transposes each course to an equivalent width at the thinnest course's thickness, sums them for the transformed shell height, and compares against H1 above.
If the intermediate girder's section modulus includes a portion of the tank shell as part of the composite section, this is the total effective width (as-built thickness at the attachment).