API 650 Storage Tank Seismic Overturning Moment Calculator

Determine impulsive (Mi) and convective sloshing (Mc) overturning moments and verify self-anchorage stability per API Standard 650 Appendix E.

Tank Dimensions & Seismic Site Hazard

Tank Diameter D (m):

Liquid Height H (m):

Seismic Impulsive Acceleration A_i (g):

Convective Sloshing Coeff A_c (g):

Stored Product Specific Gravity G:

Importance Factor I:

Overturning Moment & Anchorage

Design Ring Moment (M_rw):

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Anchorage Ratio J:

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Impulsive Moment (M_i):

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Sloshing Wave Moment (M_c):

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Anchorage Requirement:

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Frequently Asked Questions

What is the physical difference between impulsive and convective seismic mass in a storage tank?

Under earthquake ground shaking, the lower portion of the liquid moves rigidly in unison with the vibrating tank shell (impulsive mass Wi). The upper liquid surface sloshes back and forth in a slow, long-period gravitational wave (convective mass Wc).

What is the API 650 seismic anchorage ratio J?

The anchorage ratio J compares the overturning seismic moment against the restoring moment provided by shell deadweight and the liquid weight resting on the uplifted bottom annular plate. If J ≤ 0.785, the tank is fully self-anchoring.

Why is seismic anchorage required if J > 0.785?

When J exceeds 0.785, severe base uplift tears the bottom-to-shell fillet weld ("elephant foot buckling"), allowing contents to spill and sparking tank farm fires.