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.

The analysis of tank nozzles for API Standard 650 [1] 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 [2] and the other by Billimoria and Tam [3]. Although Appendix P is optional, industry has used it for a number of years for large diameter tanks. For tanks less than 120 feet (33.6 m) in diameter, Appendix P is not applicable. In previously published papers [4–10], the authors used finite element analysis (FEA) to verify the experimental results reported by Billimoria and Tam for shell nozzles. The analysis showed the variance between stiffness coefficients and stresses obtained by FEA and API 650 methods for tanks. In this follow-up paper, the authors present stiffness coefficients for tank nozzles located away from a structural discontinuity. Factors to establish spring rates for nozzles varying from 6 to 48 inches and tank diameters from 30 feet to 300 feet and for nozzles at different elevations on the shell are provided. Mathematical equations are provided together with graphs for the stiffness coefficient factors.

Code Case 2286-1 [1] of the ASME Boiler and Pressure Vessel Code [2][3] provides alternate rules for determining the allowable external pressure and compressive stresses for cylinders, cones, spheres, and formed heads in lieu of the rules of Section VIII, Divisions 1 and 2. The authors in this paper present a comparison of the longitudinal and circumferential compressive stresses in pressure vessels based on the methods outlined in Paragraph UG-28 of Division 1, Section VIII of the ASME Code and Code Case 2286-1. The Do/t ratio in this paper is limited to 600 which covers the majority of pressure vessel designs found in the petrochemical industry. A sample vessel shell design is presented applying both the ASME Code, Section VIII, Div. 1 method and that of Code Case 2286-1.