Pressure vessels, abbreviated as PV, are designed to hold or contain process fluids, liquids or gas, at a pressure significantly higher or lower than the ambient pressure, either internally or externially. Each pressure vessel must be operated within it's design temperature and pressure, which is the vessel's safety limits. These vessels serve many functions. They can used for storage of high pressure gas, gas scrubbers, two and three phase separators and other functions. They can have various internals depending on the process. Two phase separators may have a wave breaker, vortex breaker, mist eliminator and splash plate. Three phase separators will typically contain a the same components with the addition of a weir to help ensure separation.
Nomenclature & Symbols
Pressure Vessel Index
- Pressure Vessel Purpose
- Pressure Vessel Use
- Pressure Vessel Geometry
- Pressure Vessel Orientation
- Pressure Vessel Material Selection
- Pressure Vessel Materials
- Pressure Vessel Walls
- Pressure Vessel Pressure
- Pressure Vessel Temperature
- Pressure Vessel Stress
- Pressure Vessel Components
- Pressure Vessel Heat Transfer Surfaces
- Pressure Vessels in the Oil & Gas Industry
- Pressure Vessel Codes
- Pressure Vessel Standards
- Pressure Vessel Abbreviations
- Pressure Vessel Glossary
- Boiler - A closed vessel in which water or other fluid is heated under pressure for generating steam or other hot fluids. When sizing a boiler you must have enough capacity to handle the maximum hourly load of the system.
- Heat Exchanger - Heat exchanger is a device used to transer heat from one medium to another at different temperatures. The heat transfer can be air or a liquid such as water or oil. A heat exchanger has many functions. They are critical to the process industries as they used to condense, heat, cool, or chill a fluid. It also can be used to change the phase of a fluid (liquid to vapor or vapor to liquid) like a boiler.
- Storage Pressure Vessel - Storage vessels temporarily hold liquids, vapors, and gases. The vessel may be used to contain fluids in a later process, or for storing finished products such as compressed natural gas and liquid nitrogen. Examples are storage tanks.
- Process Presser Vessel - This vessel in which various processes are performed, such as breaking down a process, combining products, removing various elements or aspects of a product and more. Some examples are separators, drums, reactores, distillation tower fractioning tower, heat exchangers, etc.
Pressure vesses are used are used in a variety of applications in both industry and private sector. They appear in these sectors as industrial compressed air receivers and domestic hot water storage tanks in the pharmacutical, food, and petroleum industry, etc.
- Cylindrical Pressure Vessel - These vessels have a cylindrical shell and one or more heads. The cylindrical shell is the main body of the pressure vessel. The heads are like end caps that cover the contents of the vessel and may have a flatter or more rounded profile. They are less expensive to produce than spherical vessels but not as durable. It then requires cylindrical pressure vessels to have thicker walls to withstand equal amounts of pressure than a spherical vessel.
- Spherical Pressure Vessel - These vessels are suitable for holding liquids under a lot of pressure. Spherical vessels will use less material than cylindrical vessels if they are the same size. Spheres also don’t take up as much space as other shapes. The pressure is spread out evenly on the sphere, so there are no weak points. Spherical vessels are also less likely to transfer heat than other shapes due to their smaller surface area.
- Horizontal Pressure Vessel - These vessels are used if your well stream has a large liquid to gas ratio and maintains a constant flow. If your well stream experiences foamy productions where the large liquid surface are available will allow greater gas break out and foam breakdown. If your production facility has vertical height limitations. If your well stream requires three-phase liquid separation with difficult to separate liquids, such as a free water knockout.
- Vertical Pressure Vessel - These vessels are used if your well stream has a large gas to liquid ratio. If you need a sand scrubber or a separator that can tolerate sand and mud. If your well stream has slugs or large instantaneous volumes of liquid. If the area has horizontal space limitations such as off-shore platforms. If the vessel is being placed downstream of equipment that causes liquid condensation such as coolers.
- Strength Requirement - Can the material meet the strength requirement of a particular application. Materials must withstand specific internal and external pressures, and structural stresses during the pressure vessel's service life.
- Corrosion Resistant - This is one of the most important properties of the vessel since it is expected to be reliable in harsh environments.
- Ease of Fabrication and Maintenance - The sheet metal is formed into a shape, it must have good machinability and weldability. Vessel internals must be easily installed.
- Availability - Standard sizes for vessel materials must be readily available.
- Return on Investment - Cost of materials, fabrication, and maintenance must be considered during the lifecycle of the vessel.
- Alluminum - Aluminum has a high strength-to density ratio, means it has high strengty and lightweight at the same time. Also having a good corrosion resistance. However, it is not suitable for high pressure applications since it has less density.
- Carbon Steel - Carbon steel vessels have a high tensial strength for a minimal wall thickness. But it can be difficult to bend due to its high strength.
- Hastelloy - It has excellent corrosion resistance, cracking, and oxidation reducing properties. It maintains its strength at high temperatures. It is easily welded, formed, and shaped due to its ductability.
- Nickel Alloys - These alloys offer a good corrosion and weathering resistance, and protection against thermal expansion. It is more difficult to work with.
- Stainless Steel - This material is known for its chemical, corrosion, and weather resisytance. It has high strength for a lower wall thickness. It is easier to form than carbon steel due to its increased ductility and elasticity.
- Titanium - Titanium has a high strength-to-density ratio, which means it has high strength and lightweight at the same time, and also has a good corrosion resistance.
- Thin Vessel - The value of the ratio of wall thickness and internal diameter of a pressure vessel is less than or equal to 1/20, the pressure vessel is considered a thin pressure vessel. Thin pressure vessels are generally employed where the holding pressure of gas or liquid is not very high.
- Thick Vessel - The value of the ratio of wall thickness and internal diameter of a pressure vessel is greater than 1/20, the pressure vessel consider as a thick pressure vessel. Thin pressure vessels are generally employed where the holding pressure of gas or liquid is very high.
The design pressure is derived from the maximum operating pressure, which is the anticipated surges in pressure during upset conditions such as start-ups, emergency shutdowns, and process changes. The maximum allowable working pressure is the highest permissible preasure measured at the top of the equipment at which the vessel must operate based on it's design temperature. The design pressure of the pressure vessel is divided into four pressure levels.
- Low Pressure Vessel (code L) - 0.1 MPa ≤ p < 1.6 MPa
- Medium Pressure Vessel (code M) - 1.6 MPa ≤ p < 10.0 MPa
- High Pressure Vessel (code H) - 10.0 MPa ≤ p < 100.0 MPa
- Ultra High Pressure Vessel (code U) - p ≥ 100.0 MPa
The maximum allowable stress is highly dependent on the temperature, as strength decreases with increased temperature and becomes brittle at very low temperatures. The vessel should not operate at a higher temperature where the maximum allowable pressure is elevated.
The maximum allowable stress is obtained by multiplying a safety factor to the value of maximumstress of the material can withstand.
- Shell - The shell in most vessels is what provides the longitudinal length of the vessel. Or all vessels, the thickness of the shell is based on the pressure the shell will see (both internal and external), plus any additional loads created by the supports, nozzles or other attachments. Most shells are circular in shape. This is based partially on economics of forming the shell but mostly is due to the equal distribution of forces on the circular shape.
- Head - A head is one of the end caps on a cylindrically shaped pressure vessel. The inward pressure of each type of head determines the range of its use.
- Dish Radius - Also know as crown radius. It is the major radius of the formed head, usually measured from the inside.
- Inside Depth of Dish - Measurement from the inside center of the head to the tangent line.
- Knuckle Radius - Also known as corner radius. It is the formed radius of the head which transitions the dish portion to the straight flange. This process is done on a flanging machine.
- Straight Flange - Is the straight portion of the head measured from the tangent line to the edge of the head. The industry standard is 1 1/2".
- Tangent Line - The point on the head where the knuckle radius meets the straight flange. Refers to the point of contact, tangency, between the cylinder and the knuckle portion of the vessel head. The distance from the tangent line on one head to the tangent line on the opposite head is known as the straight side or tangent-to-tangent.
- Nozzle - Nozzles are inserted into the shell or head and are the first step of what connects to the process piping. Nozzles can connect to flanges or threaded fittings depending on the design. Nozzles must be designed depending on the metallurgy of the shell & nozzle, internal and external projections of the nozzle, orientation of the nozzle and internal and external forces on the nozzle, such as pressure and piping forces.
- Slirt and Legs - The saddle is another designed component which carries the weight of the vessel. A saddle is a plate that supports a pressure vessel and connects to the foundation. The design of this component takes the physical dimensions of the vessel (weight, length and design) and external forces (Seismic Zones and Wind Forces, for example).
- Internals - Pressure vessels usually have internals that are specific to the process. Click on for more reading on Vessel Internals.
When selecting a pressure vessel, it is important to understand the amount of potential heat transfer between the exterior environment and the contents of the vessel. This entails in-depth knowledge of the vessel’s contents, the expected temperature at the beginning and end of the process, insulation quantity and the projected length of time for the process.
- Conventional Jacket - A cover over all or part of the vessel, with an annular space between the outer vessel wall and the inner jacket wall. This space is generally concentric and is the most popular jacket.
- Dimpled Jacket - Surface consists of a sheet of metal uniformly embedded with divots, or dimples, equally spaced across its surface. The jacket is typically attached to the surface by welds at the bottom of each depression.
- Half Pipe Coil Jacket - Consist of metal shaped into concentric circles or coils and welded to the exterior of the container. They are useful for rapid heating or cooling of the contents of the container and are stronger than mechanical dimpled jackets.
- Insulation and Sheathing - If pressure vessels are equipped with heat transfer jackets, they should be insulated and sheathed or covered in cladding to minimize external environmental influences on the vessel.
- Internal Coil - Internal coils are utilized inside vessels for transient heating or cooling of the liquid contained in the tank typically on a batch basis.
In the upstream oil and gas industry, pressure vessels are used from air accumulators (to help control the frequency an air compressor turns on and off while the system is under heavy load) to three phase separators (which separate oil, water and gas from the production stream). Some examples of pressure vessels and their usage are shown below. Each is linked to a page with more information about the individual piece of equipment:
- Free Water Knockout
- Gas Liquid Cylindrical Cyclone Separator
- Heater Treater
- Three Phase Separator
- Two Phase Separator
Pressure vessels are designed to operate safely at a specific pressure and temperature. A vessel that is inadequately designed to handle pressures beyond its maximum allowable working pressure (MAWP) is a very significant safety and environmental hazard.
- API 510 - Pressure Vessel Inspection Code: In-service Inspection, Rating, Repair, and Alteration
- ASME B1.1 - Unified Inch Screw Threads (UN and URN Thread Forms)
- ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard
- ASNE B18.2.2 - Nuts for General Applications: Machine Screw Nuts, Hex, Hex Flange, and Coupling Nuts (Inch Series)
- ASME B1.20.1 - Pipe Threads, General Purpose, Inch
- ASME B31.1 - Power Piping
- ASME B31.2 - Fuel Gas Piping
- ASME B31.3 - Process Piping
- ASTM B36.10M - Welded and Seamless Wrought Steel Pipe
- ASTM B36.19M - Stainless Steel Pipe
- ASME PCC-1 - Guidelines for Pressure Boundary Bolting Flange Joint Assembly
- ASME PCC-2 - Repair of Pressure Equipment and Piping
- ASME PTC-25 - Pressure Relief Devices
- ASME QAI -1 - Qualifications for Authorized Inspection
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- 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.
- Agitation - Can be used in jacketed vessels and with internal coils to improve the homogeneity of the fluid properties. Agitation is commonly used in batch applications.
- Atmospheric Pressure - The pressure exerted upon the earth's surface by the air because of the gravitational attraction of the earth.
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- 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.
- Bladder Tank - A steel tank that has a liquid tight rubber bladder inside that contains pressurized air and water separated by a flexible membrane. As water pressure changes, the volume of air in a bladder tank contracts and expands. Periodically, the amount of air in the tank should be measured and the tank recharged if the air is too low.
- Blanket Gas - A gas phase in a vessel above a liquid phase. The purpose may be for protecting the liquid from contamination, for reducing the hazard of detonation, or for pressuring the liquid. The source of the gas is external to the vessel.
- Blind Flange - A piping component for covering or closing the end of a pipe, valve, vessel or tank.
- Blowdown - The act of emptying or decompressing a vessel. This may also refer to the discarded material such as blowdown water from a boileror cooler tower.
- Boiler - A closed vessel in which water or other fluid is heated under pressure for generating steam or other hot fluids.
- Bottoms - The liquid or residual matter which is withdrawn from the bottom of a fractionator or other vessel during processing or while in storage, also, the heaviest product remaining in the liquid phase after distillation.
- Breathing - The moment of vapor in or out of a storage tank because of the change of level of the storage liquid, a change in the temperature of the vapor space above the liquid, or of atmospheric pressure.
- Bubble Point - The temperature at a given pressure at the instant the liquid is in equilibrium with the vapor phase in the containing vessel.
- Buffer Tank - It provides additional water storage in the heating system.
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- Carbon Dioxide - CO2
- Carbon Monoxide - CO
- 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.
- Clean in Place - This system sanitize the interior surfaces of pressure vessels used in the production of food and beverages, medical devices, and pharmaceutical products, among others. CIP systems do eliminate the need to completely disassemble the equipment in order to clean in between uses.
- Conical Head - Posses more inherent strength than flat heads.
- Conventional Jacket Vessel - Used for small volume applications less than 300 gallons.
- 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.
- Crude - A mixture of naturally occuring liquid hydrocarbons before refining.
- Crude Oil - See crude
- Design Pressure - The pressure the vessel is designed for.
- Design Temperature - The temperature the vessel is designed for.
- Dimple Jacket Vessel - Normally deals with internal vessel pressure around 300 PSI.
- Dished Head of End - The end of a cylindrically shaped vessel.
- Dish Radius - Also known as crown radius. It is the major radius of the formed head, usually measured from the inside of the head.
- Distillate - Products of distillation formed by condensing vapors.
- Dry Gas - A natural gas with with very little liquid hydrocarbons or water vapor.
- Elastic Modulus - The ratio of the stress applied to a body or substance to the resulting strain within the elastic limits.
- Eliptical Head - The most common type of head.
- Enthalpy - Measures the sum of internal energy changes in heat under constant pressure of the system.
- Expansion Joint - Heat and cold causes piping systems to expand and contract.
- Expansion Tank - Ensures that constant pressure is maintained within the pipes so there is no damage to the pipes.
- Field Separator - A vessel in the oil or gas field for separating the gas, hydrocarbon, liquid, and water from each other.
- Flange - A bolted connection where two pieces of pipe, equipment, fittings or valves are connected together to form a piping system.
- Flash Point - The temperature at which combustion is initiated.
- Flat Head - Consisting of a toroidal knuckle connecting to a flat plate.
- Flue - A passage for combustable products.
- Flue Gas - A combustable product that flows through a flue.
- Free Water Knockout - A pressure vessel that uses residence time to separate water from the production process.
- Gas Liquid Cylindrical Cyclone Separator - The design is a very simple two phase metering unit designed to measure two phase flow. It consists of a vertical cylinder with an inclined, tangential inlet.
- Gate Valve - One of the most frequently used valve in piping systems and is classified as either "rising-stem" or "nonrising-stem" valves.
- Globe Valve - A type of valve used for regulating fluid flow, both on/off and throttling, it is a control valve.
- Gusset Plate - A thick steel plate used to strengthen joints on new and retrofitted structures.
- Half Pipe Jacket Vessel - Normally deals with internal vessel pressure up to 750 PSI.
- Head - The end closure of the vessel.
- Heat - A form of energy that causes physical change in what is being heated.
- Heat Exchanger - A device used to transer heat from one medium to another at different temperatures.
- Head Terminology - Head Terminology refers to the terms used by the Industry to describe the different attributes that make up the heads of the tank. The tank heads are also sometimes called domed or dished ends.
- Heat Transfer - The exertion of power that is created by heat, or the increase in temperature.
- Heavy Crude - Crude oil with a high proportion of heavy hydrocarbons and metallic content.
- Hemispherical Head - Half-sphere is the ideal shape for a vessel head.
- Holiday - A discontinuity in painted or coated surfaces.
- Hoop Stress - The circumferential and perpendicular stress to the axis imposed on a cylinder wall when exposed to an internal pressure load.
- Hot Water Tank - Stores the heated water from gas or oil firing for comercial or residential use.
- Insulation - A material with low thremal conductivity used to reduce heat loss.
- Jacket Vessel - An external cavity around the vessel, controlling the temperature of the contents of the vessel through a cooling or heating fluid.
- Knuckle Radius - Also known as inside corner radius. It is the formed radius of the head which transitions the dish portion of the head to the straight flange.
- 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.
Leg - The most common support used for pressure vessels and are typically mounted at equal distances underneath the container. They are usually composed of I or L channel and are simple and inexpensive to install. Legs also have the added benefit of providing access to the underside of the vessel.
- 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.
Load Cell - Vessel supports that contain sensors for gauging the weight of the tank. They allow operators to better weigh and measure the contents of a container.
- Lug - A projection used for grasping or lifting.
- 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 temperature permissible that provides sufficient flexability during normal operation.
- Modulus of Elasticity - See Elastic Modulus
- Nameplate - On all vessels. Gives the manufacturer, year manufactured, pressure, temperature, and any other indormation needed about the vessel.
- Natural Gas - A naturally occuring hydrocarbon gas consisting primarly of methane.
- Nozzle - A nozzle, abbreviated as NOZ, is a An opening in a tank or vessel for a flanged connection.
- Oil Burner - A burner for firing oil.
- Operating Pressure - The operating pressure of equipment occurs when the plant or process is operating at steady state conditions.
Outlets and Drains - Pressure vessels typically contain a drain or outlet at or near the lowest point of the tank. The outlet and joint must be able to withstand the pressure held in the tank to avoid leaks or blowouts. Drains for containers in sanitary services must be placed carefully and at minimal lengths to ensure that the vessel will drain completely.
- Over-all Height - This is the total height of the head and is measured by adding inside depth of dish, straight flange height, and the thickness together.
- Oxidation - The loss of electrons in a chemical reaction in which an element combines with oxygen. Oxidation and reduction always occur at the same time in equal amounts.
- Oxidation Atmosphere - An atmosphere which tends to promote the oxidation of immersed materials.
Pad Mounted Vessel - A pressure vessel will sometimes be mounted on a dedicated pad of poured concrete. This pad may be sloped or leveled as needed for drainage. But on its own, a pad-mounted vessel does not allow access to the underside of the container.
- Petroleum - See crude
- PH - A scale that indicates the degree of acidity or alkalinity of a solution.
- Pitting - A non-uniform corrosion of a metal, not in the form of cracks, whereby a number of cavities, are formed in the surface.
- Portible Vessel - Pressure vessels may be constructed with supports that provide easier portability, including legs and casters. They may also be built onto carts and trolleys with axles and wheels to facilitate easy transport.
- 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).
- Pulsation - Rapid changs in pressure.
- Raw Water - Untreated water.
- Relative Humidity - A measure of the amount of moisture in the air with respect to the temperature.
- Saddle - Used to support horizontal and vertical designs in locations to support the concentrated loads at on each end of the vessel.
- 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.
- 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 Coupling - A threaded coupling for connecting gauges, instrumentation, or even sample box valving.
Sidewall Support - In the event that the vessel cannot be supported from the bottom on a flat surface, it can be bolted to an external frame attached to the sidewall.
- Sight Glass - Can be a liquid level gauge, sight flow indicator, circular sight window, or fuse sight glass.
Skid Supported Vessel - Similar to the sidewall support, a pressure vessel can be supported by the installation of a cylindrical or conical steel skirt attached to the sidewall and mounted on a concrete pad. This can both support the container and protect the underside of the vessel. In addition, it can be used to protect any attachments that exist on the bottom of the container.
- Slip-on Flange - Designed to slip over the outside of pipe, long-tangent elbows, reducers, and swages.
- Solar Tank - Stores the heated water from the sun or comercial or residential use.
- Sour Gas - See acid gas
- Specific Gravity - The density or ratio of any substance to another substance.
- Stack - A vertical conduit.
- Stack Gas - Anything that comes out of a burner stack in gaseous form.
- Steam - The invisible vapor (gas) when water is heated to its boiling point and passes from a liquid to a gaseous state.
- Stean in Place - This system rellies on steam to sterilize equipment.
- Straight Flange - The straight flange refers to the straight potion of the head measured from the tangent line to the edge of the head. The industry standard is 1 1/2” for ASME F&D’s and 2.0” for ellipticals, but most head manufactures can change this to suit your needs.
- 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.
- Surge - The sudden displacement or movement of liquid in a closed vessel or drum.
- Surge Tank - These tanks are installed on large pipelines to relieve excess pressure caused by water hammer and to provide a supply of water to reduce negative pressure if a valve is suddenly opened.
- 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.
- Tangent Line - The tangent line describes the point on the head where the knuckle radius meets the straight flange.
- 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.
- Three-phase Separator - Most, if not all, production meters require conditioning of the process stream prior to measurement. The conditioning process allows for solids to drop out of the stream, entrained gas to break out of the stream or oil/water/gas separation.
- Torque - A rotational moment.
- Two-phase Separator - A two phase separator is used to separate fluid into gas and liquid.
- Thermal Efficiency - The fraction of heat that is converted to work or desired output divided by required input.
- Thermal Expansion - The increase in length, area or volume due to the increase (in some cased decrease) in temperature.
Thermal Shocking - Introduces alternating low and high temperatures for rapid cooling and / or heating applications.
- Thermowell - Used in temperature measurement and provide isolation from the temperature sensor and the process fluid.
- Torispherical Head - Sometimes referred to as flanged and dished heads after the manufacturing process.
- Vacuum Breaker - A vent on top of the vessel that allows air to be pulled into the tank.
- Vacuum Tank - A system that filters air or fluids through suction or other techniques. Not all vessels are able to withstand the difference in internal and external pressure that results from a vacuum. For this reason, when designing a system that will utilize variations in internal and external pressure, it is critical to consider if a vacuum tank will be necessary to ensure the system’s success as well the safety of the operator.
- Vapor - The gas state of a liquid or solid. Both vapor and gas are basically the same thing.
- Vaporization - A physical change of a substance from a liquid phase to a gas phase.
- 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 Pressure Tank - This tank works by keeping the water store in a constant state of pressure. When water leaves the tank, the pressure level drops. When the pressure reaches a pre-set threshold, the well pump activates and replaces the water in the tank. As the water replenishes, the pressure then rises.
- 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.
- Wetted Surface - The area of contact between the liquid and the wall of the tank often used to determine the emergency venting capacity required for the tank.
- Working Pressure - The normal pressure that a system operates at.
- Yield Strength - The minimum stress that leads to permanent deformation of the material.