Tank - Wind

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API 2006 Storage Tank ConferenceTulsa, Oklahoma

Preparing Tanks for Hurricanes

Presented By:Ray Penny

Prepared By:Steven L. Braune, PE

Tank Industry Consultants, Inc.

Katrina at Landfall August 29, 2005

You own a bunch of tanksand there is a big storm coming……

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Now what?

API Standard 650 has provisionsfor addressing some of the stormrelated issues that affect storage

tanks.

Storage Tanks Vulnerabilities

• Wind Issues…– Shell Buckling– Tank Overturning– Roof Damage

• Flooding Issues…– Floating Off of Foundation– Shell Buckling

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Wind Loads on Tanks

• API Standard 650 has specificrequirements for shell bucklingand tank overturning

• There are no requirements in thecurrent Standard that address roofdamage

Shell Buckling

• In general, new tanks are designed toresist wind speeds of 100 mph

• In the absence of an owner-specifiedwind speed, manufacturer may selectshell thicknesses only for liquid loads…and then report the permissible windspeed to the purchaser

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API-650 Shell Stability

• Tank is most vulnerable when empty

• API procedures originated in early 1960s

• Methods based on uniform vacuumanalogy using the maximum windpressures on shell

Shell Buckling DuringConstruction

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Shell Buckling When Empty

Shell Buckling After Loss ofRoof

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No shell Buckling after loss of roof

Tornado Damage

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Buckling on Windward Side

StorageTank

Wind

Empty Tank Shell Stability

Diameter, D

Check permissibleunstiffened shell height,

H1

HH1

3

1 )(000,600 !"

#$%

&=DttH

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My Tank Engineer says…• Tanks constructed to API-12C are

generally resistant to wind buckling forwind speeds in the range of 95 to 120 mph

• Resistance to wind buckling varies fortanks constructed to API-650. The typicalwind speeds are in the range of 80 to 105mph

• Tank diameters up to 260’ and shellheights to 48’

What if shell is not stable for theexpected wind speed?

• Hope for the best (we can do better than that)

• Fill tank with product, if possible

• Partially fill tank

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Add Product to Tank to ReduceRisk of Shell Buckling

H1

Your Tank Engineer candetermine a recommended

product depth using API-650principles

Wind Overturning

• Primarily a problem for small diametertanks that are empty

• Doesn’t happen often, but should beconsidered

• API-650 has simplified procedures toverify

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Wind Overturning Loads

W

D

OverturningMoment, M

Per API-650

M max = WD/2

(Tank Empty)

Tank Industry Consultants

Knocked Over Tanks

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Tank Industry Consultants

Toppling of Small Diameter Tanks

Tank Toppling Speed(40 ft High Tank)

0

50

100

150

200

0 10 20 30 40 50

Tank Diameter (ft)

Win

d Ve

loci

ty(m

ph)

Add Product to Tank toPrevent Overturning of

Unanchored Tanks

Your Tank Engineer candetermine a recommended

product depth

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Fixed Roof Damage• Roof uplift pressure

will occasionallydamage tanks

• Roof -to-shell jointmay tear and “peel”away roof plate

• Roof structure may bedislodged bydistortion of shell

Wind

Peeling Off of Roof Plate

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Plate Pulled Off Tank Roof

Floating Roof Damage• Roof uplift pressure and

wind forces may causeponded water to “shift” ona floating roof.

• Unsymmetrical load maylead to roof structuralfailure

• Water may shift awayfrom location of roofdrains… overloads withwater may result

Wind

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Floating Roof Damage

Rolling Ladder Damage

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Tank Flotation

• Tanks are most vulnerable to floatationwhen empty

• Minimal flood depth required to float atank off of its foundation

• Wind may displace a floating tanklaterally

Dike FloodingFlood depths of less than

two feet will float most largediameter storage tanks when

they are empty

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AST Displaced by Flooding

ASTs Displaced by Flooding

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ASTs Displaced by Flooding

Avoid Tank Flotation

Your Tank Engineer candetermine a recommended

product depth

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Avoid Tank Flotation

If tank is empty and clean,leave the shell manholes open

Shell Buckling Due to DikeFlooding

Water pressure may causecollapse of the shell, if it isempty and anchored

Your Tank Engineer candetermine a recommended

product depth

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Summary• Design for the expected conditions (primarily

wind)• Maintain your tanks• A well maintained tank will fair better than a

ragged tank.• Add liquid to prevent flotation, overturning,

wind buckling, & shell buckling from externalpressure (rising water)

• A full tank will fair better than an empty tank.

QUESTIONS?Steven L. Braune, P.E.

804-897-7176 office

804-897-7178 fax

804-307-5609 mobile

[email protected]