The tank design was to conform to ASME Boiler and Pressure Vessel Code, Section X: Fiber- Reinforced Plastic Pressure Vessels for the primary design and AWWA Fiberglass Pipe Design Manual M45 to account for the buried installation. This was consistent with the recommendations of the Phase I PERC study, Study of Alternative Tank Materials, Docket 11728. As previously mentioned, NFPA 58 requires tanks to be designed in accordance with metallic tank guidelines. Regulatory authorities accept ASME in general, which permits the use of Section X for building codes, and NFPA 58 could be revised to change regulatory view of the loading stresses on a freshly buried and unfilled tank.
LPG Tank Design Development and Selection
The product designed is a 500-gallon composite propane tank for underground use. Physical dimensions for the tank are specified in Table 2. A survey of product literature for similarly sized steel tanks suggests a 3-foot diameter x 10-foot length to be typical. LPG storage tanks are often installed underground; the tank is designed to be compatible with this type of environment. The proposed design consists of an FRP (fiber reinforced plastic) structural shell with an internal HDPE copolymer liner. The FRP shell is a multi-layered angle-plied filament wound composite structure consisting of continuous glass fiber in an epoxy resin. The liner is constructed of a high-density polyethylene (HDPE) copolymer, which provides a gas containment barrier. Steel tanks typically have a side port for appurtenance hardware. As a consequence of the nature of laminated composites and the filament winding process, a side port presents a significant challenge which can lead to reduced safety margins in the wall and higher manufacturing costs. Thus, the baseline configuration utilizes a port in one head. A hardware configuration has been proposed for accommodating this setup.
Other shapes were not considered for this prototypical design. Other shapes could be envisioned that would still use Lincoln Composites’ 41-inch winder limitation, such as cylindrical. However, a 41-inch diameter sphere would yield a tank with only approximately 170 gallons.
Lincoln Composites’ polymer-lined composite propane tank consists of a high-density polyethylene liner fully wrapped with a glass fiber-reinforced epoxy. A section view illustrating the tank construction is provided in Figure 1.
Alternative Underground Propane Tank Materials, Phase II—Final Report
September 2009 Battelle and Lincoln Composites