Cone-roof tank

Storage of Flammable Materials. The preferred storage for flammable Hquids or gases is in properly designed tanks. Floating roof tanks frequently are used in the petroleum industry for flammable cmdes and products (see Tanks and pressure vessels). The vents on cone roof tanks should either be equipped with flame arrestors or the vapor space above the contents should be inerted with a nonflammable gas or vapor, unless the flash point is weU above the maximum ambient temperature, the contents are not heated above the flash point, and the tank is not exposed to other tanks containing flammable Hquids. 

Cone-Roof Tanks. Cone-roof tanks are cylindrical shells having a vertical axis of symmetry. The bottom is usually flat and the top made ia the form of a shallow cone. These are the most widely used tanks for storage of relatively large quantities of fluid because they are economic to build and the market supports a number of contractors capable of building them. They can be shop-fabricated ia small sizes but are most often field-erected. Cone-roof tanks typically have roof rafters and support columns except ia very small-diameter tanks when they are self-supporting (see Fig. 4b and c Table 3). 

Umbrella- and Dome-Roof Tanks. UmbreHa-roof tanks are similar to cone-roof tanks, but have roofs that look like umbreHas. They are usuaHy constmcted to diameters not much larger than 60 ft (18 m). These tank roofs can be self-supporting, ie, having no column supports that must be mn to the bottom of the tank (see Fig. 4d). 

Example 7-11 Storing Benzene in Cone Roof Tank... 

Figure 7-31. Foam Chambers in a Cone Roof Tank Application...

The number of foam chambers required is determined by the tank diameter. Where two or more chambers are required, they should be designed to deliver foam at approximately the same rate. Table 7-12 (Modified from NFPA 11) indicates the number of chambers required for various diameter cone-roof tanks. 

The foam concentrate used with subsurface systems should be a fluoroprotein type for best results, although some AFFF foams are listed for substitutable application (because of their "fuel shedding" properties). The minimum foam solution rate should be 0.3 gpm/ft (12 Ipm/m ). The supply of foam liquid should be adequate to operate the system for 20 minutes. The foam injection point must be above the level of any residual water in the bottom of the tank. Subsurface foam application is not recommended for open or covered floating roof tanks or cone roof tanks with internal floating covers. 

The base quantity of foam liquid concentrate that should be stocked is the greatest amount calculated to be needed for any fire in a fire risk area. Normally, this involves either the largest cone roof tank or the seal of the largest floating roof tank and includes hose streams for ground fires around the tank. In addition, a supplementary supply of foam concentrate equal to 100% of the base supply should be readily available within 24 hours. 

Fixed (cone) roof tanks Vent fire Overfill ground fire Unobstructed full liquid surface area Obstructed full liquid surface fire if frangible roof remains partially in tank For volatile liquids, the rich vapor space typically prevents ignition within the tank. Environmental regulations typically prevent storage of Class 1 flammable liquids in larger fixed roof tanks. 

Cone Roof Tanks with Internal Floating Roofs... 

Table 8-12 summarizes the protection measures that should be provided for vertical atmospheric storage tanks to protect them against fire risks. Fixed or semi-fixed fire protection for cone-roof tanks should be provided as follows ... 

A cone roof tank with an internal floating roof that does not meet these criteria or uses plastic foam for flotation, even if encapsulated in metal or fiberglass, should be fire protected by side wall foam chambers suitable for the full (surface) area of the tank. This type of internal floating-roof installation is not recommended, particularly for flammable liquids. 

Portable hose lines forseaE fire protection. Yes Bond and ground aN metal tank parts. Provide shunts where required. Yes Same requirement as for cone roof tanks. None requited... 

C37) 4 No foam system recomrrrended, Fexed foam system for seal fire may be provided if desired. Yes Tank desi provides lightning p(ttectk>n Yes Same requirement as fix cone roof tanks. Vere according to API sdbsa... 

Cone roof tank—an atmospheric storage tank with a fixed cone-shaped roof. 

Cone roof tank with internal floatingcover—an atmospheric storage tank with a fixed cone-shaped roof and an internal floating cover of one of the following designs ... 

Table 2. Atmospheric cone-roof tanks selected for the case-study.

Cone Roof Tank External Floating Bin Tank Roof... 

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