Glass Fiber Reinforced Polymer Water Storage Tank

Fiberglass Reinforced Polymer (FRP) storage tanks are used to store a variety of liquids and come in many different shapes and sizes depending upon the application. Additionally, FRP fittings such as pipe connections and manways may also be necessary. For this CP, the scope was limited to single-walled, underground storage tanks. Fittings were not included since they are highly customizable and to simplify the geometry for calculations. Applications for FRP water tanks include the storage of potable water, storm water runoff, greywater, rain water, and water for back-up fire supression systems. FRP tanks are constructed of multiple layers of fiberglass and binder, which may be a vinyl ester polyester, as modeled in this CP, or unsaturated polyester resins; see CP 172 for information on unsaturated polyester resins. Fiberglass reinforcements included in this CP are surfacing veils, chopped strand mat, woven roving, and continuous strand roving. FRP tanks are constructed as a multi-layered laminate, made in three main pieces: the cylindrical tank form, commonly made using the filament winding process and two head pieces, constructed via contact molding or hand lay-up process. Both processes start by applying a surfacing veil, the most common being one made of woven c-glass, and saturating it with resin. This layer is typically resin rich in order to create a corrosion resistant layer. For additional corrosion resistance, a layer, commonly referred to as the corrosion layer, is added on top of the surface layer. The corrosion layer is composed of at least two layers of chopped strand mat saturated with resin. The structural layer is applied next. Structural layers vary by thickness depending upon the desired stregth of the FRP composite. In the filament winding process, which is done mechanically, the structural layer is made using continuous strand roving which is saturated just prior to application. Contact molded laminates have a structural layer made of alternating layers of resin saturated chopped strand mat and woven roving. The last 2-3 mils of the structural layer include a small amount of paraffin wax to create a top coat that helps surfaces exposed to the air cure properly. Once the laminate pieces have hardened, the heads are joined to the tank form with additional laminate overlay at the joint. The overlay includes a surfacing layer, corrosion layer, and paraffin top coat. The constructed tank undergoes additional curing and may undergo more stringent curing processes to remove more styrene residual from the tank interior surface.