Storage Tank

storage tank banner 1Storage tanks, abbreviated as TK, are containers used to store liquids, gases, or solids for various purposes, such as in industrial processes, commercial or residential use, or for transportation.  They come in a variety of shapes, sizes, and materials depending on the specific requirements of the application.  Storage tanks can be made from a wide range of materials, including steel, aluminum, fiberglass, and plastic.  They can be designed to hold various types of liquids, such as water, oil, chemicals, and fuels, and can be equipped with a variety of features, such as vents, pumps, and level gauges, depending on the intended use.

Storage Tank Index

Some common types of storage tanks

  • Above-ground storage tanks (AST)  -  These are tanks that are located on the ground, typically in a vertical or horizontal configuration.
  • Underground storage tanks (UST)  -  These are tanks that are buried underground, often used for storing petroleum products or hazardous chemicals.
  • Portable storage tanks (PST)  -  These are tanks that can be moved from one location to another, often used for transportation of liquids or gases.

Storage tanks play a critical role in many industries and applications, such as in the energy, chemical, and food processing industries.  They must be designed, installed, and maintained properly to ensure safety and environmental protection.


Science Branches

Applied Science
Mechanical Engineering

 Storage Tank Design Classification

  • horizontal tank 1Horizontal Tank (double wall and single wall)  -  A cylindrical steel tank with flat or dished end operating at atmospheric conditions or at pressure and provided with suitable support saddles intended for aboveground storage of non-corrosive, stable, flammable and combustible liquids.
    • Single Skin Oil Tank  -  The body of the horizontal tank consists of cylindrical and end wall parts.  The cylindrical part is called a wall and the ends called  bottoms.  These tanks are used to store non-aggressive and environmentally frendly liquids.
    • Double Skin Oil Tank  -  A special vessel with two shells and a free space between them.  The interspace, the area between two shells, is filled with antifreeze or gaseous nitrogen.  The thickness of this tank ensures oil, oil products, and hazardoud chemical products will not leak into the environment.
    • LPG Storage Tank (Bullet Tank)  -  A specialized type of storage tank used for the storage of Liquefied Natural Gas.  LNG Storage tanks have the ability to store LNG at the very low temperature of -162°C.  LNG storage tanks have double containers, where the inner contains LNG and the outer container contains insulation materials.
  • Rectangular Tank  -  This tank can be used to store dry or liquid materials. The main advantage of rectangular tanks is that they can be stacked on top of each other to save space.
  • spherical tank 1Spherical Tank  -  These tanks are a closed container designed to hold gas or liquid at a significantly different pressure with the external environment.




  • vertical tank 1Vertical Tank (bolted and welded) (double wall and single wall)  -  Vertical storage tanks are most frequently used for bulk storage of water, fertilizer, agricultural and industrial chemicals.
    • Open Top Tank (atmospheric)  -  Normally for petroleum products but can contain cooling water and fire water.
    • Fixed Roof Tank (atmospheric, low pressure, high pressure)  -  Can either be self supported or rafter/trusses supported depending on the size of this non moving roof.  They have a solid top that is attached directly to the shell. Depending on age and design, these tanks may or may not be vapor and liquid tight.  These tanks meet the minimum requirements for storing most liquids and are the cheapest to construct.
      • Cone Roof Tank (supported and self supported)
      • Dome Roof Tank (supported and self supported)
      • Internal Floating Roof Tank (supported and self supported)
    • Floating Roof Tank  -  Roof sits directly on top of product.  These tanks are designed to reduce vapor emissions and volume inside of the tank. This is achieved with the roof floating on the surface of the liquid inside the vessel.  The roof raises and lowers with the liquid level, preventing a buildup of vapor inside.
      • External Floating Roof Tank  -  The roof floats directly on top of the product or on pontoons at the liquid level.  The tank is open to the atmosphere.
        • Double-type Floating Roof Tank
        • Pan-type Floating Roof Tank
        • Pontoon-type Floating Roof Tank
      • Internal Floating Roof Tank  -  This tank has two roofs.  The floating roof is the internal component, floating on the liquid.  Above it, there is a fixed roof at the top of the storage vessel.


Storage Tank Corrosion

Corrosion in metals is a natural phenomenon.  Unless protective measures are taken, above and below metal tanks, piping, and other metal components of the storage systems corrode and eventually leak product into the environment.  All corrosion protection systems must be operated and maintained to continuously provide corrosion protection to the metal components of the tank and piping that come in contact with the ground.


Storage Tank Standards

API Standards

  • API Std 620 - Standard for Design and Construction of Large, welded, Low-pressure Storage Tanks
  • API Std 650 - Standard for Welded Steel Tanks for Oil Storage
  • API RP 651 - Recommended Practice for Cathodic Protection of Aboveground Storage Tanks
  • API RP 652 - Recommended Practice for Cathodic Protection of Aboveground Storage Tanks
  • API Std 653 - Standard for Tank Inspection, Repair, Alteration, and Reconstruction
  • API Std 2000 - Standard for Venting Atmospheric and Low-pressure Storage Tanks: Nonrefrigerated and Refrigerated
  • API Std 2015 - Standard for Requirements for Safe Entry and Cleaning of Petroleum Storage Tanks

NACE Standards

  • NACE RP0193 - External Cathodic Protection of On-grade Metallic Storage Tank Bottoms
  • NACE SP0102 - In-Line Inspection of Pipelines
  • NACE SP0106 - Control of Internal Corrosion in Steel Pipelines and Piping Systems
  • NACE SP0169 - Control of External Corrosion on Underground or Submerged Metallic Piping Systems
  • NACE SP0188 - Discontinuity (Holiday) Testing of Protective Coating
  • NACE SP0193 - External Cathodic Protection of On-Grade Carbon Steel Storage Tank Bottoms
  • NACE SP0216 - Steel-Cased Pipeline Practices
  • NACE SP0205 - External Corrosion Control of Underground Storage Tank Systems by Cathodic Protection
  • NACE SP0285 - Corrosion Control of Underground Storage Tank Systems by Cathodic Protection
  • NACE SP0502 - Pipeline External Corrosion Direct Assessment Methodology
  • NACE SP0607 - Petroleum and Natural Gas Industries Cathodic Protection of Pipeline
  • NACE Publication 51317 - Performance Failure of API 650 Oil Storage Tank Bottom Plates Due to Soil Side Corrosion
  • NACE Publication 51318-11258 - Robotic Online Storage Tank Floor Inspection Case Study
  • NACE Publication 51318 - Linings of Aboveground Storage Tanks
  • NACE Publication 1E100 - Engineering Symbols Related to Cathodic Protection
  • NACE TR21447 - Consequences of Coating Failures as Related to Interaction with Cathodic Protection


 Storage Tank Abbreviations

  • Above Ground Storage Tank (AST)
  • Cathodic Protection (CP)
  • Corrective Action Plan (CAP)
  • Hazardous Material (HAZMAT)
  • Leaking Underground Storage Tank (LUST)
  • Liquid Storage Tank (LST)
  • Line Leak Detector (LLD)
  • Manual Tank Gauge (MTG)
  • Maximum Containment Level (MCL)
  • Oil Water Separator (OWS)
  • Petroleum Storage Tank (PST)
  • Standard Operating Procedures (SOP)
  • Underground Storage Tank (UST)


Storage Tank Glossry


  • Absolute Pressure  -  A pressure at absolute zero can only exist in a total vacuum and any pressure above this is called absolute pressure.
  • Acid Gas (Sour Gas)  -  Any significant amount of hydrogen sulfide (H2S) and carbon dioxide (CO2) contains a natural gas that can cause corrosion.
  • Anchor Bolt  -
  • Anode  -
  • API Std 650 Tank Calculator  -  The API Std 650 standard published by the American Petroleum Institute (API) is designed to provide the petroleum industry with welded steel tanks for use in the storage of petroleum products and other liquid products commonly handled and stored by the various branches of the petroleum industry.
  • API Tank Size  - Based on 8.337 lbs/gallon and is based on stated capacity, not total volume.
  • Atmospheric Pressure  -  The pressure exerted upon the earth's surface by the air because of the gravitational attraction of the earth.
  • Atmospheric Storage Tank  -  A storage tank which has been designed to operate at pressures from atmospheric through 0.5 psig.
  • Autoignition Temperature  -  The temperature to which a flammable mixture of vapor and air in the explosive range must be heated for ignition to occur spontaneously without external source of ignition.
  • Automatic Sample  -  A sample taken by automatic means.


  • Baffle  -  Reduces disturbance and surges from the inlet fluids in horizontal or vertical.  The most used type is a perforated plate in the shape of a segmented circle.
  • Base Plate  -  A plate attached to the bottom of the support that sits on the foundation.
  • Barlow's Formula  -  The point just before or at when a pipe or tubing fails under pressure.
  • Blind Flange  -  A piping component for covering or closing the end of a pipe, valve, vessel or tank.
  • Bottom Sample  -  A spot sample taken from the material at the bottom of the tank.
  • Breathing Loss  -  Loss associated with thermal expansion and contraction of the vapor space, resulting from the daily temperature cycle or any such temperature cycle that can be induced by weather conditions such as rainstorms.


  • Catalyst  -  A material that aids or promotes a chemical reaction between other substances but does not react itself.
  • Cavitation  -  The creation and collapse of bubbles in a liquid.
  • Closed Gauging System  -  A method of obtaining measurements of the tank contents without opening the tank.  This may be accomplished by using automatic tank gauges or by taking measurements through a pressure/vapor lock standpipe.  This type of gauging is done extensively on vessels with inert gas systems.
  • Closed System Gauging Unit  -  Closed gauging system measurement equipment specially designed to be used with a specific type of standpipe/vapor lock.  The unit may have a single purpose such as taking temperature, ullages, watercuts or samples, or may be a combined unit capable of performing all necessary measurement functions.
  • Coalescer  -  A device used to cause the separation and removal of one liquid from another such as water from a petroleum liquid.
  • Corrosion  -  The thinning of a pipe wall that is typically caused by a chemical reaction from a corroding fluid or agent and is limited almost exclusively to metal products.
  • Corrosion Allowance  -  The amount of material in a pipe or vessel that is available for corrosion without affecting the pressure containing integrity.
  • Corrosion Inhibitor  -  A substance that slows down the chemical reaction rate of corrosion on metal that is exposed to the environment.
  • Critical Zone  -  A term used to define the liquid level in a floating roof type storage tank from the point where floating of the roof begins to the point where the roof is fully floating.  Sometimes known as the “inaccurate zone” or “partially floating region.”
  • Crude  -  A mixture of naturally occuring liquid hydrocarbons before refining.
  • Crude Oil  -  See crude


  • Data Plate  -  On all vessels. Gives the manufacturer, year manufactured, pressure, temperature, and any other indormation needed about the vessel.
  • Davit Arm  -
  • Design Pressure  -  The pressure the vessel is designed for.
  • Design Temperature  -  The temperature the vessel is designed for.
  • Distillate  -  Products of distillation formed by condensing vapors.


  • Enthalpy  -  Measures the sum of internal energy changes in heat under constant pressure of the system.
  • Explosive Limits  -  These are the limits of the explosive (flammable) range, the range between the minimum and maximum concentrations of a flammable vapor in air, which form explosive mixtures.  These conditions may exist in the vapor space of ordinary fixed roof tanks.


  • Flange  -  A bolted connection where two pieces of pipe, equipment, fittings or valves are connected together to form a piping system.
  • Flocculation  -  The process in which small pieces in a solution form clumps of fine particles which can rise or fall to the bottom of the tank.
  • Flow-proportional Sample  -  A sample taken by an automatic sampler from a pipeline at a rate that is proportional to the liquid flow rate.
  • Flush Nozzle  -  A rectangular tank nozzle which enters the side of the tank and has the underside flush with the tank bottom.
  • Flush-type Cleanout  -


  • Gate Valve  -  One of the most frequently used valve in piping systems and is classified as either "rising-stem" or "nonrising-stem" valves.
  • Gas Boot Vapor  -
  • Gauge Hatch  -
  • Globe Valve  -  A type of valve used for regulating fluid flow, both on/off and throttling, it is a control valve.
  • Gross Tankage Volume  -  The total geometric tank volume below the shell height.
  • Grounding Lug  -
  • Gusset Plate  -  A thick steel plate used to strengthen joints on new and retrofitted structures.


  • Head  -  The end closure of the vessel.
  • Heat  -  A form of energy that causes physical change in what is being heated.
  • Heat Transfer  -  The exertion of power that is created by heat, or the increase in temperature.
  • Heating Coils  -  See Tank Coils
  • Heavy Crude  -  Crude oil with a high proportion of heavy hydrocarbons and metallic content.
  • Holiday  -  A discontinuity in painted or coated surfaces.



  • Jacket Vessel  -  An external cavity around the vessel, controlling the temperature of the contents of the vessel through a cooling or heating fluid.



  • Latent Heat  -  The energy absorbed or released by a substance during a constant temperature or phase change from a solid to liquid, liquid to gas or vise versa.
  • Level Interface  -
  • Level Switch  - Provides a discrete input to the PLC.  The level switch is typically used as a method of control in tanks and vessels.
  • Light Crude  -  Crude oil with a light proportion of light hydrocarbons fractions and low metallic compounds.
  • Liquid  -  A specific volume and can hold any shape it is contained within.
  • Liquefied Natural Gas  -  Natural gas cooled to a liquid state.
  • Lower Sample  -  A spot sample obtained at the midpoint of the lower third of the tank contents.


  • Manway  -  An opening on a tank or vessel designed as an entryway for personal access and equipment.
  • Mass Flow Rate  -  The average velocity of a mass that passes by a point.
  • Maximum Operating Pressure  -  The maximum pressure permissible at the top of the vessel during normal operation.
  • Maximum Operating Pressure  -  The maximum temperature permissible that provides sufficient flexability during normal operation.
  • Middle Sample  -  A spot sample obtained at the midpoint of the middle of the tank contents.


  • Nameplate  -  On all vessels. Gives the manufacturer, year manufactured, pressure, temperature, and any other indormation needed about the vessel.
  • Net Tank Volume  -  The total usable volume inside a tank. Net volume equals gross volume less the volume equivalent attributable to tank heel.
  • Pour Point  -  The lowest temperature at which oil will pour or flow when it is chilled under prescribed ASTM test condition.
  • Nozzle  -  An opening in a tank or vessel for a flanged connection.



  • Petroleum  -  See crude
  • PH  -  How acidic or alkakine water is.
  • Pour Point  -  The lowest temperature at which oil will pour or flow when it is chilled under prescribed ASTM test conditions.
  • Pressure  -  It is the force exerted perpendicular to the surface of an object and is expressed as force per unit area.
  • Pressure Differential  -  The pressure difference between two points of a system.
  • Pressure Loss  -  The difference in upstream and downstream pressure.
  • Pressure Safety Valve  -  Used to protect vessels and tanks from overpressure. It is designed to protect critical system components such as pressure vessels, tanks and flange ratings.
  • Programmable Logic Controller  -  The types of signals are analog output (AO), analog input (AI), discrete output (DO), and discrete Input (DI).



A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

  • Raw Water  -  Untreated water.
  • Reinforcing Pad  -  A plate formed to the shape of the tank or vessel around a nozzle for extra strength. Also known as repad or weld pad.
  • Rundown Line  -  The pipeline from a process unit to a tank, through which the unit's production flows.
  • Running Sample  -  A sample obtained by submerging an unstoppered beaker or bottle from the surface of the liquid to a point as near as possible to the shore tank draw off point or about one foot above the level of the free water in a ship tank, and then raising it without letting it rest, at a rate so that it will be about 75% full as it emerges from the liquid.


  • Saddle  -  Used to support horizontal and vertical designs in locations to support the concentrated loads at on each end of the vessel.
  • Sampling  -  The process of obtaining a sample of the material in the tank, container or pipeline to use for testing or other purposes. This can be achieved by automatic or manual means.
  • Sample Box  -  A sample box is a series of pipe, valves and fittings located on a pressure vessel or tank that is used to manually determine the height of the liquid or where the interface between oil and water resides.
  • Sand Pan  -
  • Saturated Steam  -  The point (temperature and pressure) when steam is in contact with the liquid water (boiling) it came from.
  • Sensible Heat  -  The heat added to a substance which increases its temperature but not the phase is called sensible heat.
  • Shell  -  The cylinder portion of the vessel.
  • Shell Nozzle  -
  • Shell Platform  -
  • Slip-on Flange  -  Designed to slip over the outside of pipe, long-tangent elbows, reducers, and swages.
  • Sour Gas  -  See acid gas
  • Specific Gravity  -  The density or ratio of any substance to another substance.
  • Spot Sample  -  A sample taken at a specific “spot” within a tank using a stoppered bottle or beaker and lowering it to the level of desired sample then opening it and allowing it to remain at that level until full. A thief or a zone sampler may also be used to obtain spot samples.
  • Stack Gas  -  Anything that comes out of a burner stack in gaseous form.
  • Storage Tank Capacity Calculator  -  This calculates the working volume of a tank.  The working volume is the maximum usable capacity of a storage tank.
  • Stress  -  The force per unit area of cross-section.
  • Stub End  -  Allows a flange to swivel in order to mate with another flanges bolt holes that may not align perfectly.
  • Sweet Crude  -  Crude oil with a sulfur content less than 0.5% by weight, no sulfur smell.


  • Tail Gas  -  The lightest hydrocarbon gas released from a refining process.
  • Tank Blanketing  -  The injection of gas into a storage tanks vapor space.  The purpose of the blanket is to maintain a layer of gas above the liquid to prevent the entrance of air into the tank.
  • Tank Blanketing (Tank Padding)  -  , also known as tank padding, is the injection of a gas into the open space of a liquid storage tank.
  • Tank Coils  -  Placed in tanks and are designed to transfer heat from steam vapor or condensate to the tank.
  • Tank Foundation  -  The purpose of a tank foundation is to provide a level surface for the tank and to equally transmit the load of the tank and its contents to the soil.
  • Tank Padding  -  See Tank Blanketing (Tank Padding)
  • Tank Vent  -  It relieves over pressure and under pressure scenarios caused by the process.
  • Tap Sample  -  A sample taken from a valve or connection on a tank or pipeline.
  • Temperature  -  The amount of heat or cold, but it is neither heat or cold.
  • Tension Strength  -  The capacity of a material to resist a force tending to stretch it.
  • Thermal Expansion  -  The increase in length, area or volume due to the increase (in some cased decrease) in temperature.
  • Thermowell  -  Used in temperature measurement and provide isolation from the temperature sensor and the process fluid.
  • Time-proportional Sample  -  A sample taken from a pipeline at regular intervals during a batch transfer period.
  • Truck Connection  -


  • Upper Sample  -  A spot sample obtained at the midpoint of the upper of the tank contents.


  • Vacuum Breaker  -  A vent on top of the vessel that allows air to be pulled into the tank.
  • Vacuum Tank  -  Uses high-pressure hoses to clean out liquids and sludges without any damage to the object being cleaned.
  • Vapor Recovery  -  A vapor recovery system is a series of components that work together to keep fugitive emissions from escaping into the surrounding environment.
  • Venting Roof Nozzle  -
  • Vessel Internals  -  Vessels have internals to help them effectively process the fluids go through it.
  • Viscosity  -  The measure of the internal friction/resistance to the flow of a liquid.
  • Vortex Breaker  -  When the flow exits a nozzle it will create a vortex.  A cross of plates on the discharge nozzle will prevent the discharge from swirling.


  • Water  -  Can exist in three of the four phases of matter: gas, liquid, or solid.
  • Water Hammer  -  A valve is suddenly opened or closed.
  • Water Outlet  -
  • Weep  -  A term applied to a minute leak.
  • Welding  -  The fabrication process that fuses like materials togeather by heating them to a suitable temperatures, this can be acomplished by brazing, soldering or welding.
  • Wet Gas  -  A gas containing a relatively high portion of hydrocarbons that are recoverable as liquids.
  • Wier Box  -
  • Working Pressure  -  The normal pressure that a system operates at.



  • Yield Strength  -  The minimum stress that leads to permanent deformation of the material.


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