Vapor Losses

Vapors emitted from the vents and/or relief valves of a storage tank are generated in two ways:  they are forced out of the tank during filling operations and  they are generated by vaporization of the liquid stored in the tank. Technical Data used in the field explained in petroleum courses in Rawalpindi. The total vapor produced in these two instances is the volume that would be available for recovery.

Filling Losses

Vapors that are forced out of the tank are generally called “filling losses.” A storage tank generally is not pumped completely dry when emptied. The vapor above the remaining liquid in the tank will expand to fill the void space at the vapor pressure of the liquid stored in the tank at storage temperature. As the tank is filled, the vapors are compressed into a smaller void space until the set pressure on the vent/relief system is reached. There are also some filling losses that are associated with the expansion of the liquid entering the tank. provides a graphical approach to estimating the filling losses as a percentage of the liquid being pumped into the tank. Some more details of petroleum courses in rawalpindi are as under.

Vaporization Losses

This type of loss is characterized as the vapors generated by heat gain through the shell, bottom. and roof. The total heat input is the sum of the radiant, conductive, and convective energy forces. This type of loss is especially prevalent where light hydrocarbon liquids arc stored in full-pressure or refrigerated storage. This is less prevalent but still quite common in crude oil and finished product storage tanks. These vapors may be recovered by the use of a vapor-recovery system.

Crude oils and condensates are composed of many different paraffin hydrocarbons. Propane is the lightest hydrocarbon found in any measureable amount and the hydrocarbon with the greatest tendency to evaporate or vaporize from the liquid stored. When propane and other hydrocarbons pass into the vapor phase by vaporization, the volume of the liquid stored is decreased. and because these lighter hydrocarbons arc not now present in their initial amounts, the API gravity of the crude is decreased. There is a definite relationship between API gravity lost and volume lost. depending on the character of the crude. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Islamabad.

Tank Grades

Selection of the proper location on the lease for storage tanks is of prime importance. Technical Data used in the field explained in  petroleum courses in Rawalpindi. The location should provide good drainage and be on well-packed soil-not a fill-if possible. The tank foundation or grade should be slightly elevated, level, and somewhat larger in diameter than the tank itself. 

For steel tanks, either bolted or welded, the best grade is one made of small gravel. crushed rock, etc., held in place by steel bands. This type of grade allows no water to stand underneath the tank and provides air circulation. If the tank is to be set directly on the ground, felt tar paper should be applied to the grade first and the tank set on this. If concrete is used for the grade, it should be slightly larger in diameter than the tank and have shallow grooves on the surface to provide air circulation. Many codes. standards, and specifications regulate the location, design, and installation of storage tanks dependent on their end use. Selecting the proper specification and  providing adequate fire protection for  the installation may lower insurance rates over the life of the installation. Some more details of petroleum courses in rawalpindi are as under.

Firewalls or Dikes. Dikes are provided to contain the volume of a certain portion of the tanks enclosed depending on the tank contents. They are used to protect surrounding property from tank spills or fires. In general, the net volume of the enclosed diked area should be the volume of the largest tank enclosed (single-failure concept). The dike walls may be earth, steel, concrete, or solid masonry designed to be watertight with a full hydrostatic head behind them. Local codes and specifications may govern construction. If more than one tank is within the diked area, curbs or preferably drainage channels should be provided to subdivide the area to protect the adjacent tanks from possible spills. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in Islamabad.

Tank-Battery Installation and Hookup

A tank battery should contain at least two tanks and usually have a capacity equal to 4 days’ production. Technical Data used in the field explained in petroleum courses in Rawalpindi. All tanks should be level with each other and have a minimum spacing of 3 ft between tanks. Local codes or specifications may require a firewall and different spacing.

Constant attention should be given to the hazardous condition created by iron sulfide deposits. These occur most frequently within the vapor space and particularly on the underneath exposed side of the deck. These iron sulfide deposits generate severe corrosion that can go unnoticed when deck conditions are observed from the topside only.

When sour crude is stored, all openings on the tanks should be kept closed since hydrogen sulfide is poisonous. This can be accomplished by equipping the tanks with some type of ground-level gauging and thermometers located in the tank shell. Gauges and temperatures then can  be read from the ground without the tank being opened. These gauging devices usually require approval by the crude purchaser. Ground-level sampling also can be accomplished by installing pipes that extend into the tank at any desired level and to any desired distance. Valves are located at a convenient level to permit sampling on the ground without the tanks being opened. If available. a small amount of sweet gas should be fed into the top of the tank continuously to establish a “gas sweep.” This will ensure positive pressure within the tank at all times and will prohibit air from entering the tank, thereby greatly reducing corrosion. It is advisable to extend the tank vent line well beyond the tank battery and to use a backpressure valve and flash arrester in the vent line to burn the vapors. Some more details of petroleum courses in rawalpindi are as under. Steel tanks should be kept clean and free from spilled oil or other material. They should be kept painted and all water or accumulated dirt should be removed from around  the bottom edge of the tanks. Thief hatches and vent-line valves should be kept closed and inspected periodically for proper operation and gasket condition. Should any leaks occur, they may be repaired temporarily with lead sealing plugs or toggle bolts. These leaks should be repaired permanently as soon as possible.

When a closing gauge is taken, and before the tank is filled again, the pipeline valve should be sealed closed, the drain valve checked to ensure that it is closed and the seal removed, and then the seal from the equalizer-line valve removed. Before the tank is accepted by the crude purchaser, the water should be drained from the tank if necessary and the valve sealed closed. All other valves should be sealed closed except the vapor-recovery-line valve if such a system is in use. The pipeline valve is then unsealed and opened for delivery to the purchaser. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in Islamabad.

Production Equipment

The suggested setting and connection plan for a typical tank battery is shown in Figs. 1 I .5 and I I .6. The pipeline connection in the tank should be located directly below the thief hatch and a minimum of 12 in. above the tank bottom. Technical Data used in the field explained in petroleum courses in Rawalpindi. It should be equipped with a valve and sealing device immediately adjacent to the tank. Pipeline valves should be checked frequently for leaks.Inlet connections preferably should be located in the deck of the tank and should have a valve located near the inlet capable of closing off against pressure.

Drain connections should be located immediately above the tank bottom in the side of the tank or in the tank bottom  immediately adjacent to the side. They should be equipped with a valve and sealing device located next to the tank. Drains from all tanks in a battery should be connected together and piped well away from the tanks. Equalizer or overflow connections should be installed below the deck in the tank shell. A valve and sealing device should be installed immediately ad,jacent to the tank if more than two tanks are in the battery and should be connected in such a manner that any two tanks can be equalized together. Some more details of petroleum courses in rawalpindi are as under.

Vent connections should be installed in the center of the tank deck and all tanks connected to a common line. This line should have a pressure-vacuum valve installed in the line or on the end of it. The line should be sloped to prevent accumulation of liquids in it or in the valve. The use of gas to roll stored products is usually considered poor practice, and should be restricted to temporary or emergency use. If a roller line is used, it should enter the tank through the deck and be equipped with a valve next to the tank. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in Islamabad.

Materials of Construction

Shop- and field-welded, and bolted storage tanks are customarily fabricated from mild-quality carbon steel. Most common for welded tanks are A-36 structural steel and A-283 Grade C structural-quality carbon steel. Technical Data used in the field explained in petroleum courses in Rawalpindi. Sheet gauge steel for bolted tanks is of commercial quality having a minimum tensile strength of 52,000 psi. For hydrogen sulfide crude storage, aluminum bolted tanks or aluminum decks only are often used. Various API codes (listed in General References) to which the storage tank is fabricated set forth the welding procedures. Inspection procedures. and testing requirements.

Nonmetallic tanks customarily are constructed from plastic materials. These have the advantage of being no corroding. durable, low-cost, and lightweight. Plastic materials used in the construction are polyvinyl chloride, polyethylene, polypropylene, and Fiberglas +reinforced polyesters (FRP’s). The FRP tanks are available in the larger sizes and are the most common.* FRP tanks are suitable for outdoor as well as indoor applications. Some more details of petroleum courses in Rawalpindi are as under.

Aboveground vertical FRP tanks can store 24.000 gal and more, depending on the shell construction. The temperature limits of plastic tanks are approximately 40 to 150°F. Color must be added to the outer  liner for protection against ultraviolet radiation. The inner liner must be selected for compatibility with the product stored. Protection from mechanical abuse such as impact loads is necessary. Good planning dictates that plastic storage should not be located next to flammable storage tanks.

Special attention should be given to local codes, ordinances, and provisions for insurance relative to storing a flammable product in a flammable container. All plastic tanks used for storage service should be equipped with pressure-relief devices if designed for relatively low-pressure storage. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Islamabad.

Requirements for Normal Venting Capacity.

The normal venting capacity shall be obtained without exceeding the pressure or vacuum that may be applied intermittently to a tank without causing physical damage or permanent deformation to the tank. Technical Data used in the field explained in petroleum courses in Rawalpindi.

The total normal venting capacity shall be at least the sum of the venting requirements for oil movement and thermal effect. * Inbreathing (Vacuum Relief). The requirement for venting capacity for maximum oil movement out of a tank should be equivalent to 560 cu ft/hr of free air for each 100 bbl (4.200 gal)/hr of maximum emptying rate, including the gravity flow rate to other tanks, for oils of any flash point. Some more details of petroleum courses in Rawalpindi are as under.

The requirement for venting capacity for thermal inbreathing for a given tank capacity for oils of any flash point should be at least that shown in Col. 2 of Table I I .3. Out breathing (Pressure Reliefi. The requirement for venting capacity for maximum oil movement into a tank and the resulting evaporation for oil with a flash point of 100°F or above should be equivalent to 600 cu ftihr of free air for each 100 bbl (4,200 gal)/hr of maximum filling rate.**

The requirement for venting capacity for maximum oil movement into a tank and the resulting evaporation for oil with a flash point below 100°F should be equivalent to 1,200 cu ftihr of free air for each 100 bbl (4,200 gal)ihr of maximum filling rate. ’ The requirement for venting capacity for thermal out breathing, including thermal evaporation, for a given tank capacity for oil with a flash point of 100°F or above should be at least that shown in Col. 3 of Table 11.3. The requirement for venting capacity for thermal out breathing, including thermal evaporation, for a given tank capacity for oil with a flash point below 100°F. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in Rawalpindi.