An Overview of Seismic Design of Field Erected Aboveground Storage Tanks in Accordance with API Standard 650, Appendix E

Abstract

The American Petroleum Institute (API) Standard 650 Welded Steel Tanks for Oil Storage has become a leading specification for the design of field erected aboveground storage tanks (AST) worldwide. Tanks designed and erected under this standard store a wide variety of products. These include crude and refined petroleum products (gasoline, fuel oils, and asphalt), chemicals (fertilizers, pesticides, solvents and sulfuric acid), animal fats and oils (used in cosmetics and soaps), vegetable oils (used in food products), molasses and alcohols. The proper design and detailing of large field erected AST's is not only important from the potential environmental and safety impact in the event of a failure, but becomes a serious issue for our public security as many of these tanks constitute a vital link in our critical infrastructure. Appendix E of API Standard 650 deals with the seismic design of storage tanks. The latest revision to the standard, released in early 2006, is Addendum 4 of the 10th Edition. This was an extensive revision of Appendix E which incorporated new definitions, more open and expanded equations, as well as analytical methodologies and ground motion requirements that are consistent with ASCE 7-02 Minimum Design Loads for Buildings and Other Structures. The revision also provides new detailing recommendations for serviceability limits for items such as pipe flexibility and freeboard. This paper will briefly review the applicability of the API 650 Standard, summarize the specific Addendum 4 changes to Appendix E, and provide a complete seismic design example based on the new provisions.