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CONCLUSIONS An out-of-service inspection in accordance with API 653 was performed on this tank by PRI on February 20 to 22, 2007 — see PRI Report No. 102695 1/4. I reviewed that report and agree with the recommendations provided therein and found no procedural omissions that need to be addressed. The design of a coned tank bottom supported above the grade by legs is not addressed by API 653, for that specific case I used as a guide API Standard 620 Design and Construction of Large, Welded, Low Pressure Storage Tanks. API 620 covers that particular design configuration. Calculations (see Appendix A for details) indicate that the shell, the cone bottom, and the as built construction of the shell-to-bottom joint are fit for service. The evaluation was done with an assumed specific gravity of 1.0 and atmospheric pressure inside the vessel. DISCUSSION AND ANALYSIS The reinforcement at the shell-to-bottom junction was evaluated in accordance with API 620 to determine if enough cross sectional reinforcement area exist using the actual measured thicknesses. Calculations indicate that the as-built junction meets API 620 criteria and therefore is acceptable. It should be noted that an elevated cone bottom tank of this configuration with liquid in it tends to induce compressive stress at the bottom of the shell, therefore this region must be reinforced either by the inherent thickness of the shell and tank bottom or by additional structural steel members if needed. The tank did not have any structural members that could be given credit for reinforcing this region. Since this tank did not have a nameplate indicating that it was designed and built to account for this concern, for a proper tank evaluation, it was necessary to verify the existing design. Cone bottom tanks of this type are subject to biaxial stress in the cone region and should be checked for suitability when any thinning has occurred or when no name plate or design information is available to the inspector. API Recommended Practice 579, Fitness For Service mentions that an allowable stress design analysis be performed for this type of tank, which is what was done in the attached calculations. A conservative assumption of an allowable stress of 15,200 psi was used and the thickness of the cone was checked due to circumferential stress and due to meridonal stress. In both cases the actual cone thickness was greater than required by a comfortable margin. The thickness of the shell was checked as well and found to be well within the range of acceptability. Evaluated by: George Roni, P.E. API 653 Cert. No. 2042, Exp. 4/30/08