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Opportunities for Price Reduction

The current design leverages heavily from Lincoln Composite’s current 41-inch diameter tank design. The Lincoln Composite product using the 41-inch design is for containment of much higher pressure. The liner comprises a considerable portion of the tank cost, and is a prime candidate for price reduction. Efforts have been made for this design to scale down the bosses and thus reduce cost; however, it is believed that there are still more opportunities in this area. For the proposed design, the liner is essential a heavy-walled (nearly one inch thick) polyethylene pipe. The wall thickness must be heavy to prevent the large diameter from sagging or flexing during the winding process. The pipe/liner is used as the winding mandrel, upon which the fibers are wound. Other possible designs for supporting the liner, rather than shear bulk, could consider either an internal mechanical "spider" or internal pressurization that would keep a thinner liner in shape during the winding. A one-piece molding of the entire self- supporting liner (with the heads integrally molded with the cylindrical section) would be difficult and much more costly that the extruded pieces of the proposed design. Currently on the market are composite cylinders (10-lb, 20-lb, and 33-lb lift truck) with no liners (http://www.litecylinder.com). This cylinder is made in halves without any end penetrations. The end connections – one in the standard cylinder and multiples for the forklift cylinder – are drilled after the cylinder is wound, epoxy-impregnated, and cured. Thus the winding is not affected by the presence of the end connections. The two-piece cylinder requires precision- ground ends where the two halves are joined. Variations of more than a few 1/1000ths of an inch can substantially reduce the joint strength. Making these ground joints on a diameter of over 40 inches would be very difficult and quite expensive. However for this study, only techniques and materials that were familiar to Lincoln Composites were considered, as the project scope did not include testing of new approaches.

For this Phase II report, a relatively low production rate was assumed. An increase in the production rate would reduce the unit cost for the tanks. The pricing for this tank was based on the current winder capacity for 41-inch diameter tanks. This limits production to winding one tank at a time. Investment in additional winders would allow multiple units to be produced simultaneously and to thus reduce the tank price. As a result of the large quantities of materials used to produce tanks of this size, it may be possible to negotiate a reduction of raw material pricing.

Table 9 shows the estimated composite tank costs from Figure 5, compared with steel tank costs. Using engineering judgment and experience, Lincoln Composites and the Battelle team have estimated that if efforts addressed in the previous paragraph are successful in reducing the manufacturing costs, costs shown in the column labeled Potential in Table 9 can be achieved. Current (December 2008) steel tank prices are shown for comparison. All prices are FOB factory and include riser, combination valve, and anodes (for steel tank). As shown, there will likely be a premium for a composite tank ($470 for a 250-gallon, $680 for a 500-gallon, and $790 for a 1000-gallon tank) even after significant cost reductions.

Alternative Underground Propane Tank Materials, Phase II—Final Report


September 2009 Battelle and Lincoln Composites

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