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More than two dozen storage tanks holding crude oil, gasoline, and other contaminants ruptured or otherwise failed when Harvey slammed into the Texas coast, spilling at least 145,000 gal of fuel and spewing toxic pollutants into the air, according to an AP analysis of pollution reports. Measuring product in oilfield storage tanks can pose significant risks to workers if proper precautions are not taken. This video discusses the risks and ways they can be reduced to protect workers. Italian oil major Eni said on 18 April it had decided to temporarily shut down a treatment plant serving its biggest domestic oil field in southern Italy to meet a local order.
Production, refining, and distribution of petroleum products require many different types and sizes of storage tanks. Small bolted or welded tanks might be ideal for production fields while larger, welded storage tanks are used in distribution terminals and refineries throughout the world. Product operating conditions, storage capacities, and specific design issues can affect the tank selection process. This chapter discusses the types of storage tanks most commonly used with emphasis on welded construction. General guidelines are provided that aid in the selection of the correct tank.
Production, refining, and distribution of petroleum products require many different types and sizes of storage tanks. Small bolted or welded tanks might be ideal for production fields while larger, welded storage tanks are used in distribution terminals and refineries throughout the world. Product operating conditions, storage capacities, and specific design issues can affect the tank selection process. Storage tanks come in all sizes and shapes. Special applications might require tanks to be rectangular, in the form of horizontal cylinders, or even spherical in shape.
Specially designed pressure/vacuum vent valves should be provided to protect the tank against overpressure or vacuum conditions. Safety should be a primary concern when selecting a storage tank vent system for a specific application. In production operations, this normally means that a safe way of handling vapors that evolve from the liquid must be designed into the system, and air must be excluded from entering the tank and mixing with hydrocarbon in the vapor space. Fixed-roof tanks should be configured to operate with a suitable gas blanketing system that maintains the tank at positive pressures under all operating conditions. Tank vent piping should include flame arrestors such as that shown in Figure 1, which protect the tank against ignition of the vent gases owing to lightning strike or a discharge of static electricity at the vent location.
A typical tank battery contains two or more tanks and usually has a capacity equal to four days production. The suggested setting and connection plan for a typical tank battery is shown in Figs. 1 and 2. The pipeline connection in the tank should be located directly below the thief hatch and a minimum of 12 in. 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 and capable of closing off against pressure.
Floating roof tanks are a type of atmospheric storage tank. When product vapor pressure is greater than 0.5 psia (more in some states) but less than 11.1 psia, the U.S. Environmental Protection Agency permits the use of a floating-roof as the primary means of vapor control from the storage tank. Floating-roof tanks are not intended for all products. In general, they are not suitable for applications in which the products have not been stabilized (vapors removed). The goal with all floating-roof tanks is to provide safe, efficient storage of volatile products with minimum vapor loss to the environment.
Fixed roof tanks are common in production facilities to store hydrocarbons with vapor pressures close to atmospheric pressure. In this use, they should be equipped with pressure-vacuum valves and purged with natural gas to eliminate air intake into the vapor space. Product evaporative losses can be high especially when crude is added to the tank and vapors are expelled through the pressure vent valve. In crude oil terminals and pumping stations, internal floating roofs may be added to the fixed-roof tank to reduce product vapor losses if the crude oil has been stabilized to vapor pressures less than 11 psia. Examples of fixed-roof tanks are shown in Figure 1.