api 650 appendix e

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Seismic Designof Liquid Storage Tanks

UpdateAPI 650 Appendix E

September 2006Presented by:

John M. Lieb PETank Industry Consultants

[email protected]

Why has Appendix E changed?

•Update API 650 to State of the Art Practice•Make API 650 More Consistent with Building

Codes and Standards•ASCE 7•International Building Code (IBC)•National Earthquake Hazard Reductions Program

(NEHRP)•Replace “Seismic Zone”Concept with More

Accurate Approach

Tank Industry Consultants

mailto:[email protected]

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How has Appendix E changed?•Incorporated newer definitions of ground motion in the

US,•Added a procedure to address regions outside the US,•Expanded and generalized the equations to improve

programming applications and reduce reliance on plots,•Added hydrodynamic hoop stresses and vertical

earthquake,• Included information and equations previously found

only in outside reference materials,•Revised the combination of impulsive and convective

forces to use the SRSS method instead of direct summethod.


How has Appendix E changed?•Introduced concept of an “anchorage ratio”, J, for

clarity,

•Permit the use of soil structure interaction formechanicallyanchored tanks,

•Added detailing requirements for freeboard, pipeflexibility, and other components,

• Improved maintainability,•Added Commentary with example problems.


?54.1)4.01((2 ≤

+−=

avt

rw

wAwDMJ

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How Will New Appendix E AffectTank Design?

•Parametric study concluded:•For overall tank population –not much difference from

previous appendix.•For some areas, e.g., Houston, TX, new rules are

“more stringent”•For other areas, e.g. Some parts of California, new

rules are “less stringent”.


When was Appendix E Published?

API 650 included the revised Appendix in the10th Edition, Addendum 4.

The Commentary to Appendix E will beincorporated in the 11th Edition.


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Appendix E Outline

• Design Spectral Accelerations (defining therequired ground motions)

• Seismic Design Factors (I and Rw to define thedesign level forces)

• Design (base shear, impulsive and convectiveloads, vertical effects, overturning moment, SSI,allowable stresses)

• Detailing Requirements (piping, anchorage,freeboard, connections, sliding)


Ground Motion ASCE 7 Method

• Response spectra, mapped or defined by regulations

1.0 4.00

1

0 1 2 3 4 5Period, T (sec)

Spec

tral R

espo

nse

Acc

eler

atio

n,Sa

(g)

DSS

D1S

0T ST

D1ai

SS

T=

1.5 D1ac

SST

=

26 D1

acSST

=

Recurrenceinterval

Soil Effects


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Ground Motion for Regions OutsideUSA

• Peak Ground Acceleration, Sp

Ss = 2.5 Sp

S1=1.25 Sp


Ground Motion Site Specific

• Sitespecific ResponseSpectra

Probabilistic, Deterministic

5%, 0.5%

Includes Soil Effects

Recurrence Interval


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Generalized Equations

•Examples,impulsive coefficient

ringwall moment

=

=

wa

wDSi R

ISQFRISA 05.2

[ ] [ ]22 )()( cccrrssiiirw XWAXWXWXWAM +++=


What’s Next?

•API 650–Publish Commentary to Appendix E in 11th

Edition•API 620

–Rewrite Appendix L, Address:–Operating Basis Earthquake (OBE)–Safe Shutdown Earthquake (SSE)


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Joint API/PAJ* Research Project

UpdateFloating Roof Stability

*Petroleum Association of Japan

Information in this portion of the presentation wasprovided by Takayasu Tahara, Dr. Eng. Of PAJ andPhil Myers, P.E., of Chevron.

Floating Roof StabilityThis portion of the presentation addresses the joint API/PAJ researchproject to develop seismic design provisions for floating roofs. Theproject is intended to do the technical work needed to understand thebehavior of floating roofs under loading conditions including sloshingwaves. Why?

•Many floating roofs exist which do not meet the broad API 650strength requirements outlined in API 650 Appendices C and H.

•Currently the purchaser relies on the manufacturer to provide a floatingroof that has sufficient strength to meet the standards. Many examplesand case histories show that this is not the case.

•By performing this work not only will the provisions of API 650provide the industry with a tool to easily assess the strength of floatingroofs to perform as intended but the work will also provide the basis fordesigns needed in regions and areas subject to seismic activity.

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Is Your Facility Vulnerable?

REGIONS WHERE RESEARCH WORK WILL HAVE HIGHEST IMPACT

Floating Roof Critical to Tank Safety•Controls Product Vaporization•Limits Fire Risk to Rim Fires•Reduces Fire Protection Needs (Foam, etc)

to Rim Area (not Tank Area)•Prevents Escalation to Fully Involved Tank

and Terminal Fires•Single Most Important Fire and Safety

Defense of All Tank Components

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Floating Roof Vulnerabilities

•Floating Roofs Are Vulnerable to:–Sinking–Rain (In Houston, Hurricane Allison Caused

Over 100 Floating Roofs to Sink)–Gas (as From Producing or Pipeline Operations)–Corrosion–API 650 has Performance Based Rules Which

Have Proven to be Inadequate

Is API 650 Adequate?• Rules Require 2 Flooded Compartments Plus Center Deck and,• 10 Inches of Rainfall in 24 Hour Period• Very Few Know How to Design to Meet the Structural

Requirements• Industry Depends on Tank and Roof Manufacturers for Safe

Designs• Many Lawsuits Have Resulted From Floating Roofs Sinking• Industry Needs to Have Simple Rules, Tables and Formulas that

Ensure the Floating Roof is Strong Enough for LoadingConditions

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Seismic Background

• Seismic Technology Changed –So Codes Changed• API 650 Appendix E Revised Accordingly• But Job is Not Complete• Seismic Committee Intended to Address

–Tank Shell and Bottom First (Appendix E DoesThis)

–Then Floating Roof Stability (This is CurrentProposal)

Common Seismic Failure Modes• Tearing Piping

• Shell Elephant’s Foot

• Bottom Separates From Shell

• Floating Roof Collapse/Sinking

• First 3 covered by new Appendix E• Floating Roof (Yet to Complete)

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Seismic waves cause floatingroof to lose buoyancy

Seismic waves cause failure deck andfloating roof sinking

This can result in full surface fire andtank burndown

Damage Observed in a Recent Major Refinery Earthquake Dueto Tank Sloshing Waves

Ismit, Turkey 1998

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Ismit, Turkey 1998

Is Floating Roof Damage From a SloshingWave a Real Risk?

• Hokkaido, Japan– 4 Fully Involved Tank Fires– 2 Fully Involved Due to Floating Roof Collapse from Sloshing Waves– 50% Due to Sloshing Wave

• Ismit, Turkey– 23 Major Tank Fires– 17 Due to Sloshing Waves– >50% Due to Sloshing Wave

• Anchorage, Alaska– Commingled Data But Many Floating Roofs Collapsed

• API AST Leadership Committee Thinks Seismic Work Not Complete• Seismic Sloshing is Important and Should be Completed

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Business Case• At Least 25 Floating Roofs per Year Sinking in US Alone• About ½ are Due to Corrosion; Other Half Due to Water or Gas• Of the Half, About 1/3 are Due to Inadequate Design• This is About 4 per Year Sinking Due to Inadequate Structural

Stability• Floating Roof Sinkings Can be Reduced or Prevented if API

Companies Have Simple Means to Evaluate Floating Roof Stability• Proposed Work Will Result in This Deliverable• The Lower Bound Estimate for the Ismit and Hokkaido Incidents are

$100 million• At least ½ of the Floating Roofs Causing Fires Would Not Have

Occurred• Cost Savings From These Standards Would be Roughly $30 million

Final Statement of Benefit To Cost

• Benefits– Project Has High Value in Seismically Active Areas– Major Oil Companies Support this Activity– Work Will Result in Adequate Floating Roofs for

Seismic Areas– Will Result in General Understanding of Floating Roofs

for Other Load Conditions (Gas, Rainwater, etc)– Project is Leveraged

• Costs– $25,000 in 2007

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Thank You !

Questions ?

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