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The American Petroleum Institute (API) provides a series of standards and specifications on storage tanks, in which API 12F specification provides twelve tank designs that can be fabricated in shop and transported to field. The nominal capacity of the twelve API 12F tank designs ranges from 90 bbl. (14.3 m3) to 1000 bbl. (158.99 m3). The minimum required thickness and operational pressure levels that each tank case can sustain is given in Table 1 of current 13th edition of API 12F [1]. The objective of this study is to estimate the fatigue life of API 12F tanks under normal operation pressure cycles following procedure presented in ASME VIII-2. The stored liquid product specific gravity is assumed to be 1.2 when the liquid height is half of tank height, while the specific gravity is assumed to be 0.7 when the stored liquid height is 18 in. (460 mm). Meanwhile, a new roof-shell attachment detail is proposed in this study, the new rectangular cleanout junction detail presented in the 13th edition of API 12F is modeled, and various component thickness combinations are considered to investigate the effect of component thickness on fatigue life. Stress classification is performed at each location of interest to obtain the stress components to calculate stress range within each loading cycle that is needed to perform fatigue evaluation. The results and discussion about fatigue evaluation of API 12F tanks are presented in this report.

The API 12F is the specification for vertical, aboveground shop-welded storage tanks published by the American Petroleum Institute (API). The nominal capacity for the twelve tank designs given in the current 13th edition of API 12F ranges from 90 bbl. (14.3 m3) to 1000 bbl. (159 m3). The minimum required component thickness and design pressure levels are also provided in the latest edition. This study is a part of a series research project sponsored by API that dedicates to ensure the safe operation of API 12 series storage tanks. In this study, the twelve API 12F tank designs presented in the latest edition are studied. The elastic stress analysis was conducted following the procedures presented in the ASME Boiler and Pressure Vessel Code 2019, Section VIII, Division 2 (ASME VIII-2). The stress levels at the top, bottom, and cleanout junctions subject to the design pressures are determined through finite element analysis (FEA). The bottom uplift subjected to design pressures are obtained, and the yielding pressure at the roof-shell and shell-bottom junctions are also determined. The specific gravity of the stored liquid is raised from 1.0 to 1.2 in this study. A new roof-shell attachment detail is proposed, and a 0.01 in. (0.254 mm) gap between the bottom shell course and the bottom plate is modeled to simulate the actual construction details. In addition, the flat-top rectangular cleanout presented in the current edition of API 12F is modeled.