Fixed roof tank

Fig. 4. Fixed-roof tanks (a) self-supported cone roof (b) center-supported cone roof (c) column-supported cone roof and (d) dome or umbrella roof...

EFR tanks have no vapor space pressure associated with them and operate strictly at atmospheric pressure. IFR tanks, like fixed-roof tanks, can operate at or above atmospheric pressure in the space between the floating roof and the fixed roof. 

Specifications. Eor fuel-grade MTBE, the typical specification of merchant product is 95 wt % minimum purity ia the United States and 98% minimum ia Europe. The maximums for impurities are usually 0.5 wt % for methanol, and 0.15 wt % for water. To maintain quaUty, fuel-grade MTBE is normally stored ia fixed-roof tanks, to keep rain water out, with internal floaters, to minimise vapor losses. 

Fixed-roof atmospheric tanks require vents to prevent pressure changes which would othei wise result from temperature changes and withdrawal or addition of liquid. API Standard 2000, Venting Atmospheric and Low Pressure Storage Tanks, gives practical rules for vent design. The principles of this standard can be applied to fluids other than petroleum products. Excessive losses of volatile liquids, particularly those with flash points below 38°C (100°F), may result from the use of open vents on fixed-roof tanks. Sometimes vents are manifolded and led to a vent tank, or the vapor may be extracted by a recov-eiy system. 

Inert gas is used to blanket certain fixed-roof tanks for safet. Here is how to determine the inert gas requirements. Inert gas is lost in two ways breathing losses from day/night temperature differential, and working losses to displaee changes in active level. 

Example A fixed-roof tank D = 128 ft Height = 36 ft Avg. outage = 12 ft Annual throughput = 300,000 bbl Location = New Orleans Detennine monthly inert gas usage Solution ... 

When the tank was refilled with warm crude oil at 37°C. vapor was pushed out into the space above the floating roof and then out into the atmosphere through vents on the fixed-roof tank (Figure 5-16). This vapor was ignited at a boiler house some distance away. 

An explosion and fire occurred on a fixed-roof tank that was supposed to be blanketed with nitrogen. After the explosion, it was found that the nitrogen supply had been isolated. Six months before the explosion the manager had personally checked that the nitrogen blanketing was in operation. But no later check had been carried out [8]. 

Evaporadon Loss from Fixed-Roof Tanks... 

Weak roof-to-shell attachment for fixed roof tanks, as per API-Std-650 for Welded Steel Tanks for Oil Storage. The joint fails and excess pressure can be relieved (above the normal design provided). Such tanks do not require additional emergency vent equipment however, it can be provided in order to prevent the roof seam failure with its attendant replacement/ maintenance requirements. This type can only be used outside of a building, not confined. 

Liquids are usually stored in bulk in vertical cylindrical steel tanks. Fixed and floating-roof tanks are used. In a floating-roof tank a movable piston floats on the surface of the liquid and is sealed to the tank walls. Floating-roof tanks are used to eliminate evaporation losses and, for flammable liquids, to obviate the need for inert gas blanketing to prevent an explosive mixture forming above the liquid, as would be the situation with a fixed-roof tank. 

Atmospheric fixed roof tanks built according to API requirements will have a weak seam at the junction of the roof with tank side. If there is internal overpressure, such as an explosion, the seam will part or the roof blows off, leaving the shell in place to retain its contents. The resulting fire will therefore only initially involve the exposure surface of the liquids still in the tank. 

Fixed-roof tanks, 24 288-289 Fixed surface aerators, 26 159, 160 Fixed valve plates, 3 763-764 Fixing agents color film, 19 261 photographic, 19 213 Fixolide, 24 494 Flake... 

Petrolenm Liqnid Storage in External Floating Roof Tanks Petrolenm Liqnid Storage in Fixed Roof Tanks Petrolenm Refinery Eqnipment Leaks... 

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. 

Becoming jammed in one position during filling or empting of the tank (open or fixed roof tanks). 

A fixed roof tank with an internal floating roof should have fixed fire protection only for the floating roof seal area when the tank design satisfies the following criteria ... 

Fixed monitor nozzles can be considered as the primary means of protection for fixed-roof tanks up to 60 ft (18 m) in diameter. Foam hand lines should not be considered as the primary means of protection for fixed-roof tanks over 30 ft (9 m) in diameter or those over 20 ft (6 m) in height. 

Fixed-Roof Tanks. The effect of internal pressure on plate structures, including tanks and pressure vessels, is important to tank design. If a flat plate is subjected to pressure on one side, it must be made quite thick to resist bending or deformation. A shallow cone-roof deck on a tank approximates a flat surface and is typically built of 3/ 16-in. (4.76-mm) thick steel (Fig. 4a). This is unable to withstand more than a few inches of water column pressure. The larger the tank, the more severe the effect of pressure on the structure. As pressure increases, the practicality of fabrication practice and costs force the tank builder to use shapes more suitable for internal pressure. The cylinder is an economic and easily fabricated shape for pressure containment. Indeed, almost all large tanks are cylindrical. The problem, however, is that the ends must be closed. The relatively flat roofs and bottoms or closures of tanks do not lend themselves to much internal pressure. As internal pressure increases, tank builders use roof domes or spheres. The spherical tank is the most economic shape for internal pressure storage in terms of required thickness, but it is generally more difficult to fabricate than a dome- or umbrella-roof tank because of its compound curvature. 

Se. Option 5d + Secondary Seals on Fixed Roof Tanks Install secondary rim mounted seals on all floating roof tanks and then install a floating roof with a primary and secondary seal on all fixed roof tanks. 

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