COMPOSITE MATERIALS COMPATIBILITY
In order to lend further credence to the choice of composite materials for the underground propane tank application described in the Detailed Design section, material components were assessed with regard to chemical compatibility with components found in commercial propane. As no data were available in the open literature for the chemical compatibility of the composite system as a whole, individual composite components were considered separately in terms of their propane compatibility.
The original materials system selected for the underground propane tank preliminary composite design at the end of Phase I of this program was fiberglass- (E-glass or E-CR glass) reinforced isophthalic polyester. These materials were chosen primarily by considering performance and cost. The detailed design of the current Phase II effort has included emphasis on manufacturing, in addition to the previous two considerations of cost and performance. Our manufacturing partner, Lincoln Composites, recommends a different composite system at this stage of development: fiberglass- (E-CR glass) reinforced epoxy with a high-density polyethylene (HDPE) copolymer liner. Although this composite system is more expensive than that recommended for the preliminary design, there are several reasons for this recommendation. Lincoln Composites has several decades of experience using a hybrid- (carbon and E-CR glass fibers) reinforced epoxy system with an HDPE liner for pressure vessels in the petrochemical, transportation, and aerospace industries. This composite system has been used by Lincoln to manufacture CNG cylinders for decades. As the operating pressure requirements for propane tanks is approximately an order of magnitude less than those for CNG cylinders, the E-CR glass is recommended as a more cost-effective alternative than the combination of carbon and E-CR glass fibers, while also providing the necessary performance. Additionally, there are health and environmental hazard concerns when handling the isophthalic polyester in a manufacturing facility. Isophthalic polyester is used by Lincoln’s sister company, Ragasco*, in its Norway composite cylinder production plant. Additional personnel and environmental protective equipment is required when handling this resin, thus increasing the manufacturing costs. Furthermore, Lincoln Composites already has an ongoing production process in place using the current composite system, so changing the production process to accommodate the resin change would result in significant additional production costs. Lincoln Composites has stated that if production volume of the composite underground propane tanks were to become sufficiently high in the future as to offset the production costs to change resins, then reconsideration of changing the resin to isophthalic polyester would be merited at that time.
A literature review was conducted to assess the compatibility based upon published information of the selected tank materials with the compounds in commercial propane. Compositional requirements of commercial propane are referenced in recognized standards (ASTM D1835-05 and GPA 2140-97) and a commercial supplier’s MSDS (AmeriGas, 2009). A previous PERC project that addressed field samples (PERC Docket # 11354, Osborne 2006) was also considered for expected propane compositions. This information is outlined in Table 10.
Lincoln Composites Inc. and Ragasco AS are subsidiaries of Hexagon Composites ASA of Norway
Alternative Underground Propane Tank Materials, Phase II—Final Report
September 2009 Battelle and Lincoln Composites