ASME Boiler and Pressure Vessel Code, Section III, Mandatory Appendix XXVI provides rules for buried High Density Polyethylene (HDPE) Pipe for service water or cooling water piping systems. Section III has recently developed rules for above ground High Density Polyethylene (HDPE) piping systems in a Code Case (Code Case N886) that was published with the 2019 edition of the ASME Boiler and Pressure Vessel Code. This paper presents the technical basis of this above ground High Density Polyethylene (HDPE) piping Code Case. It provides the background on the development of the rules for above ground High Density Polyethylene (HDPE) piping systems. The authors completed extensive material testing over last 10 years to build the foundation of the Code Case rules. In addition, the historical background of the testing is given to provide the basis for the stress limits in the above ground case and the stress intensification factors. This paper will also explain the considerations for the selection of a dynamic load factor, the capacity of bolted flanged connections, and the considerations of buckling, which unlike buried pipe apply to above ground piping systems. A complete history and technical background for the basis of the above ground High Density Polyethylene (HDPE) code case rules will be presented in this paper.