FRP Tank Cover and Roof Design

Open liquid storage tanks release vapors, allow dust and rain to enter, and create odor problems. A fitted FRP (glassfiber reinforced plastic) cover controls emissions, reduces evaporation, and protects stored product from contamination. This guide describes the cover types, loads, and details to consider.

Cover Types

• Flat cover: simple and economical for small tanks; suitable for atmospheric tanks with no internal pressure.

• Conical (frustum) cover: provides self-supporting slope; common on tanks up to about 6 m diameter.

• Dome cover: preferred for large tanks and where live snow or wind load is high; fabricated from FRP segments.

• Floating cover: used on large atmospheric tanks to reduce vapor space; the deck floats on the liquid surface.

Loads and Design

Design the cover for the weight of the FRP itself, rainwater ponding, snow load, occasional maintenance live load (1.5 kN per person), and wind uplift. For tanks storing warm or odorous liquids, include a pressure-vacuum relief vent to avoid over-pressurization or vacuum collapse during filling and emptying.

Appurtenances

Access to the tank interior is through a manway with hinged cover and a quick-release latch. Sample ports, thermowells, and level gauge nozzles are installed through the cover. For odor control, connect a vent line to a scrubber or activated carbon unit.

Installation

Cover segments are trial-fitted on the ground before lifting. Seal joints with a compatible mastic and strap-bolt around the perimeter. After installation, check that the cover sits evenly and that all gaskets are compressed.

Conclusion

An FRP cover protects product, reduces emissions, and lowers odor complaints. Select the cover type based on tank diameter, vapor control requirements, and local weather loads.

References

• API 650 — Welded Steel Tanks for Oil Storage (Annex on Roof Design)

• AWWA D100 — Welded Steel Tanks for Water Storage