Session: DA-08-03 Developments in FFS Assessment

Paper Number: 122263

122263 - Evaluation of Storage Tank Bottom Settlement 

Localized bottom settlement is a form of settlement on storage tank bottom. The tank bottom is made out of  lap welded plates. Generally, localized bulges, ridges or depression can result in lap weld failure which could lead to a leak. Some of the early work on localized bottom settlement was done by Hayashi and Guber based on large deflection theory for circular plate based on Timoshenko.  This work was eventually used as the basis for the allowable settlement in API-653 for bottom settlement remote from tank shell. Currently there are numerous tank in the industry where the bottom settlement has exceeded the API 653 criterion and they have to be evaluated on a case by case basis using a combination of inspection and numerical analysis to determine whether they are fit for service.

In this paper two different approaches are proposed to evaluate the bottom settlement. The first method is using the current approach in API 653 with a higher allowable failure stress obtained from available experimental published data. The second method is based on a parametric study using non-linear elastic plastic finite element analysis. The results from both study could be used to determine whether a tank with bottom settlement which exceeds API 653 limits is still fit for service.

Presenting Author: Chithranjan Nadarajah Becht

Presenting Author Biography: Dr. Nadarajah’s career has spanned over 30 years of worldwide involvement in petrochemical industries for Becht and ExxonMobil Research and Engineering. He has worked in more than a dozen countries worldwide to solve complex mechanical plant problems as well as mechanical support for large scale projects. He has extensive knowledge in pressure vessels, piping, and storage tanks design and maintenance code. Beside plant support he also has extensive knowledge in fitness for service and design by analysis. He is a currently member of the ASME Working Group on Section VIII, Division II, Design by Analysis and the Chairman of Working Group on Elevated Temperature design. He has more than thirty publications in leading journals and conferences, and one patent.

Authors:

Chithranjan Nadarajah Becht