Analysis of Loads for Nozzles in API 650 Tanks

Abstract

The analysis of tank nozzles for API 650, (American Petroleum Institute, 1998, API Standard 650, 10th ed.) tanks is a complex problem. Appendix P of API 650 provides a method for determining the allowable external loads on tank shell openings. The method in Appendix P is based on two papers, one by Billimoria and Hagstrom, 1997, ASME Paper No. 77-PVP-19 and the other by Billimoria and Tam 1980, ASME Paper No. 80-C2/PVP-5. Although Appendix P is optional, the industry has used it for a number of years for large diameter tanks. For tanks less than 120feet(33.6m) in diameter this Appendix is not applicable. In previously published papers, the authors used finite element analysis (FEA) to verify the experimental results reported by Billimoria and Tam for low-type nozzles. The analysis showed the variance between stiffness coefficients and stresses obtained by FEA and API 650 methods for tanks. In this paper, the authors have expanded the scope to include almost any size of nozzle as well as tank size. Stress factors for nozzles at different elevations on the shell are provided. Nozzles located away from a discontinuity are analyzed based on the method provided by the Welding Research Council (WRC), New York, Bulletin No. 297, 1987. Stress reduction factors have been developed using FEA for nozzles located closer to a discontinuity. Mathematical equations are provided together with the curves for the stress factors. The results of this paper have been incorporated into Appendix P of API 650 with the Addendum 3 of the 10th edition which was issued in 2003.