View
182
Download
3
Category
Preview:
DESCRIPTION
API Standard 653Appendix BPresented by:Steven L. Braune, PETank Industry Consultants
Citation preview
Edge Settlementof
Storage Tank Bottoms
API Standard 653
Appendix B
Presented by:
Steven L. Braune, PETank Industry Consultants
API-653, First Edition
� The allowable edge settlement limit
� Very conservative
� Based on several published articles
� A recommendation only
R37.0B ====
Early Experience
� Observed edge settlement typically exceeded API recommendations
� API-653 permitted a more detailed evaluation
� Many oil companies developed methods
Tank Settlement Revision Task Group… mid-1990s
� Initial recommendations revised
� Several API-member companies shared in-house practices
� Current recommendations are about 2 to 4 times greater than original limit
Finite Element Models
� Two oil companies had extensive experience using FEA for edge settlement evaluations
� Analysis procedures and evaluation criteria differed… similar in principle
� Formed basis for API Task Group work
Appendix B RevisionsSettlement Curves
� Settlement curves varied by diameter
� Accepts two inches of settlement
� Additional NDE required for edge settlements > 75% of allowable
� Limits based on fillet weld strength
Bew–Maxim
um Allowable
Settlement (inches)
Figure B-10 for Bew
R – Radius of Settled Area (feet)
Figure B-10… Lap Welds Approximately Parallel to Shell
R – Radius of Settled Area (feet)
Figure B-11… Lap Welds Approx. Perpendicular to Shell
Be–Maxim
um Allowable
Settlement (inches)
Figure B-11 for Be
Bottom Weld Orientation
� Edge settlement, B limited to…
� Bew= Allowable for weld parallel to shell
� Be= Allowable for weld perpendicularto shell
� Weld angle relative to radial line
αααα−−−−−−−−==== sin)BB(BB ewee
A Rigorous Stress Analysis
� If actual settlements exceed recommended limits…
� Repair the tank
� Perform a rigorous stress analysis
A Recent Result…
� A rigorous stress analysis was performed on a tank with edge settlements of near 90% of limit
� Client wanted to know if tank should be repaired now or could they monitor settlement for a few more years
Finite Element Analysis Results
90% of API limit
150% of API limit
Tank Shell
Current Settlement
Profile
Projected Settlement Profiles
Recommended