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API 650 Tank Wind Girder & Stiffening Ring Calculator engineering
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API 650 Tank Wind Girder & Stiffening Ring Calculator

Determine required section modulus (Z) for top and intermediate wind girders and calculate maximum allowable unstiffened shell height (H1) per API 650 Section 5.9.

Tank Geometry & Wind Load

API 650 standard base: 190 km/h (120 mph)

Stiffener Section Modulus & Spacing

Top Girder Modulus (Z_top):
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Max Unstiffened Height H_1:
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Intermediate Girders Needed:
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Intermediate Modulus (Z_int):
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Wind Buckling Stability Verdict:
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Frequently Asked Questions

What is a wind girder on an API 650 storage tank?

A wind girder is a structural horizontal ring (formed by structural angles, channels, or fabricated flanges) welded circumferentially around the tank shell to maintain roundness and prevent inward elastic buckling under external wind pressures.

Why do open-top floating roof tanks need a mandatory top wind girder?

Unlike fixed cone-roof tanks where the top angle is rigidly stabilized by radial roof rafters, open-top tanks have an open rim vulnerable to wind distortion and ovaling, which would jam the floating roof seal.

How does high design wind speed affect intermediate girder spacing?

Allowable unstiffened shell height H1 scales inversely with design wind speed (H1 ∝ 1/V). Increasing wind speed from 190 km/h to 240 km/h cuts allowable unstiffened height by over 20%, necessitating additional intermediate stiffening rings.