Design and Analysis of Buried Liquid Petroleum Gas Storage Bullets Supported on Multiple Saddles (PVP2010-25052)

The use of large, high pressure liquid petroleum gas (LPG) storage bullets has become a common, and often assumed safe, practice in the petrochemical industry. The Engineering Equipment and Materials Users Association (EEMUA) is an organization that has attempted to address design aspects related to mounded or buried bullets; Publication No. 190 published by the EEMUA (2000, Guide for the Design, Construction and Use of Mounded Horizontal Cylindrical Vessels for Pressurized Storage of LPG at Ambient Temperatures, EEMUA, London, England.) became a standard practice in the industry. However, the design recommended, and therefore addressed, by Publication 190 is for bullets directly supported by soil (i.e., without saddle supports). However, it has been noticed by the authors that many users are requesting these storage bullets be supported by saddles resting on foundations in order to minimize the chance of unexpected settling and any motion of the bullets underground. The large span of these bullets requires more than two saddles adding to the complexity of the design due to statically indeterminate construction, differential settlement, and uneven supports. This paper focuses on major issues related to the design of such bullets. First, the loads induced by mound weight, pressure due to mound, and the loads due to longitudinal thermal expansion and soil resistance to this expansion is analyzed. Next, a method for calculating the multiple saddle reactions and bending moments at spans and supports is provided. A simplified method for assessing the effect of differential settlement between saddles is proposed.