Oil/water separator covers are typically made of lightweight and easy-to-maintain materials like aluminum or fiberglass reinforced plastic (FRP) instead of steel and concrete.  An arched or sloped roof design discourages liquid ponding and snow accumulation, and helps direct corrosive condensate that forms on the underside of the cover toward the tank walls.  A drip lip attached to the cover conveys the condensate into the tank to prevent it from concentrating and, in turn, deteriorating the separator tank.

Low profile aluminum, used to make oil/water separator covers, expands and contracts with temperature fluctuations.  Variations between ambient and wastewater temperatures of 10°C to 50°C (50°F to 120°F) are common and, as a result, a vapor-tight seal may be difficult to achieve and maintain under normal operating conditions.  Additional caulking may help ensure a vapor-tight enclosure.  A corrosion-resistant coating should be used to reduce the potential for chemical ignition from aluminum alkyls.  The structure should also be grounded to reduce the potential for mechanical ignition. 

FRP covers are not as susceptible to thermal expansion as aluminum.  They are typically custom-molded and usually contain resin additives that resist fire and other environmental elements, improve structural integrity and dissipate static charges.  In addition, the covers’ molded construction also accommodates variations in the design of external separator tank drive arrangements yet still maintains a positive seal at the cover penetration.  The high humidity within the enclosure makes ignition from static charges unlikely.   

Gasketing and caulking material used with oil/water separator covers must withstand the aggressive atmosphere within the enclosure.  For example, closed cell nitrile foam type SBE42 per ASTM D1-56-67 provides a chemically resistant, durable and vapor-tight seal for oil/water separators used in treating refinery petroleum wastewater.

A safety-relief device protects the separator cover from internal pressure and vacuum conditions that may compromise the enclosure’s structural design.  Pressure-vacuum relief valves allow air and/or vapors to escape and not damage the enclosure.  A flame arrester and additional emergency venting capacity further relieve pressure in the oil/water separator tank that may result from fire outside of the enclosure.

Vent Devices
Vapor Control Device
Enclosed Combustion Devices
Vapor Recovery Devices
Flare Devices
Ignition Sources