The differences in the weight and pricing between the Phase I preliminary design estimates and the more detailed Phase II design estimates are a result of detailed production consideration, specifically that of the domes. Phase I estimates were calculated primarily based upon cylinder sections only. Considerable cost and weight are added in order to adequately close the cylinder section by utilizing the domes.
Alternative Underground Propane Tank Materials, Phase II—Final Report
September 2009 Battelle and Lincoln Composites