Leak
Encyclopedia
A leak is a hole or other opening, usually unintended and therefore undesired, in a container or fluid
-containing system, such as a tank or a ship's hull
, through which the contents of the container can escape or outside matter can enter the container. Another use for the word "leak" can be found on the urban dictionary. The word "leak" is also used as a verb; matter going through the opening is said to leak. The entry, exit, or exchange of matter through the leak is called leakage
, the subject of another disambiguation article. The matter leaking in or out can be gas
, liquid
, a highly viscous
paste, or even a solid
such as a powdered
or granular solid or other solid particles. A leak can be between two (or more) fluid-containing systems, allowing transfer of matter from either system to the other, or even an exchange of matter between them. Leakage of matter into a container or other system could be called inleakage. Leakage of matter out of a container or other system could be called outleakage. The presence of a leak does not necessarily mean there is always leakage of matter; it just implies there could be leakage through the opening. If the container or system is empty in an empty environment, there is no leakage at that time. Sometimes the word "leak" is used to refer to leakage in a certain situation, for example the passing or making public of secret information.
or other corrosion
hole, very tiny pinhole leak (possibly in imperfect welds
), crack or microcrack, or inadequate sealing between components or parts joined together. When there is a puncture, the size and shape of the leak can often be seen, but in many other cases, the size and shape of the leak opening may not be so obvious. In many cases, the location of a leak can be determined by seeing material drip out at a certain place, although the leak opening itself is not obvious. In some cases, it may known or suspected there is a leak, but even the location of the leak is not known. Since leak openings are often so irregular, leaks are sometimes sized by the leakage rate, as in volume of fluid leaked per time, rather than the size of the opening.
Common types of leaks for many people include leaks in vehicle
tire
s, causing air to leak out resulting in flat tires, and leaks in containers, spilling the contents. Leaks can occur or develop in many different kinds of household, building, vehicle, marine, aircraft, or industrial fluid systems, whether the fluid is a gas or liquid. Leaks in vehicle hydraulic systems such as brake
or power steering
lines could cause outleakage of brake or power steering fluid resulting in failure of the brakes, power steering, or other hydraulic system. Also possible are leaks of engine coolant - particularly in the radiator
and at the water pump
seal, transmission fluid, motor oil
, and refrigerant
in the air conditioning
system. Some of these vehicle fluids have different colors to help identify the type of leaking fluid.
The water
supply system or a wastewater
system in a house or other building may have a leak in any of numerous locations, causing dripping out or spillage of the water. Gas leak
s, e.g. in natural gas
lines allow flammable and potentially explosive gas to leak out, resulting in a hazardous situation. Leaks of refrigerant may occur in refrigerator
s or air conditioning systems, large and small. Some industrial plants, especially chemical
and power plants, have numerous fluid systems containing many types of liquid or gas chemicals, sometimes at high temperature
and/or pressure
. An example of a possible industrial location of a leak between two fluid systems includes a leak between the shell and tube sides in a heat exchanger
, potentially contaminating either or both fluid systems with the other fluid. A system holding a full or partial vacuum
may have a leak causing inleakage of air from the outside. Hazmat procedures and/or teams may become involved when leakage or spillage of hazardous materials occurs. Leaks while transporting hazardous materials could result in danger; for example, when accidents occur. However, even leakage of steam
can be dangerous because of the high temperature and energy of the steam.
Leakage of air or other gas out of hot air balloon
s, dirigibles, or cabins of airplane
s could present dangerous situations. A leak could even be inside a body, such as a hole in the septum
between heart
ventricles causing an exchange of oxygenated and deoxygenated blood, or a fistula
between bodily cavities such as between vagina
and rectum
.
There can be numerous causes of leaks. Leaks can occur from the outset even during construction
or initial manufacture/assembly of fluid systems. Pipe
s, tubing
, valve
s, fitting
s, or other components may be improperly joined or welded together. Components with threads may be improperly screwed together. Leaks can be caused by damage; for example, punctures or fracture. Often leaks are the result of deterioration of materials from wear or aging, such as rusting or other corrosion or decomposition of elastomer
s or similar polymer
materials used as gasket
s or other seals
. For example, wearing out of faucet washer
s causes water to leak at the faucets. Cracks may result from either outright damage, or wearing out by stress such as fatigue failure
or corrosion such as stress corrosion cracking
. Wearing out of a surface between a disk and its seat in a valve could cause a leak between ports (valve inlets or outlets). Wearing out of packing around a turning valve stem or rotating centrifugal pump
shaft could develop into fluid outleakage into the environment. For some frequently operating centrifugal pumps, such leakage is so expected that provisions are made for carrying away the leakage. Similarly, wearing out of seals or packing around piston-driven pumps could also develop into outleakage to the environment.
The pressure difference between both sides of the leak can affect the movement of material through the leak. Fluids will commonly move from the higher pressure side to the lower pressure side. The larger the pressure difference, the more leakage there will typically be. The fluid pressures on both sides include the hydrostatic pressure, which is pressure due to the weight
from the height of fluid level above the leak. When the pressures are about equal, there can be an exchange of fluids between both sides, or little to no net movement of fluid across the leak.
which can be detected. Tires, engine radiators, and maybe some other smaller vessels may be tested by pressurizing them with air and submerging them in water to see where air bubble
s come out to indicate a leak. If submerging in water is not possible, then pressurization with air followed by covering the area to be tested with a soap
solution is done to see if soap bubbles form, which indicate a leak. Other types of testing for gas leaks may involve testing for the outleaking gases with sensors which can detect that gas, for example - special sensing instruments for detecting natural gas. U.S. federal safety law now requires natural gas companies to conduct testing for gas leaks upstream of their customer's gas meters. Where liquids are used, special color dyes may be added to help see the leakage. Other detectable substances in one of the liquids may be tested, such as saline to find a leak in a sea water system, or detectable substances may even be deliberately added to test for leakage.
Newly constructed, fabricated, or repaired systems or other vessels are sometimes tested to verify satisfactory production or repair. Plumber
s often test for leaks after working on a water or other fluid system. A vessel or system is sometimes pressure tested by filling with air and the pressure monitored to see if it drops, indicating a leak.
A very commonly used test after new construction or repair is a hydrostatic test
, sometimes called a pressure test. In a hydrostatic test, a system is pressurized with water to look for a drop in pressure or to see where it leaks out. Helium
testing may be done to detect for any very small leakage such as when testing certain diaphragm or bellows valves, which are made to be practically leak-proof. Helium
and Hydrogen
have very small molecule
s which can go through very small leaks.
Leak testing is part of the non-destructive test NDT
portfolio that can be applied to an art to verify its conformity; depending on material, pressure, leak tightness specifications, different methods can be applied. International standards has been defined to assist in these choices. For example BS EN 1779:1999; it applies to assessment of leak tightness by indication or measurement of gas leakage, but excludes hydrostatic, ultrasonic or electromagnetic methods.
Other standards also apply:
In shell and tube heat exchanger
s, Eddy current
testing is sometimes done in the tubes to find locations on tubes where there may be leaks or damage which may eventually develop into a leak.
Leaks are often repaired by plugging the leaking holes or using a patch to cover them. Leaking tires are often fixed this way. Leaking gaskets, seals, washers, or packing can be replaced. Use of welding, soldering, sealing, or gluing may be other ways to fix leaks. Sometimes, the most practical solution is to replace the leaking unit. Leaking water heaters are often replaced by home or building owners.
If there is a leak in one of the tubes of a shell and tube heat exchanger
, that tube can be plugged at both ends with specially sized plugs to isolate the leak. This is done in the plenum(s) at the points where the tube ends connect to the tubesheet(s). Sometimes a damaged but not yet leaking tube is pre-emptively plugged to prevent future leakage. The heat transfer
capacity of that tube is lost, but there are usually plenty of other tubes to pick up the heat transfer load.
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
-containing system, such as a tank or a ship's hull
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
, through which the contents of the container can escape or outside matter can enter the container. Another use for the word "leak" can be found on the urban dictionary. The word "leak" is also used as a verb; matter going through the opening is said to leak. The entry, exit, or exchange of matter through the leak is called leakage
Leakage
Leakage may refer to:*Leakage *Memory leak, in computer science*Leakage *Leakage *Leakage *Leakage...
, the subject of another disambiguation article. The matter leaking in or out can be gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
, liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
, a highly viscous
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
paste, or even a solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
such as a powdered
Powder (substance)
A powder is a dry,thick bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material...
or granular solid or other solid particles. A leak can be between two (or more) fluid-containing systems, allowing transfer of matter from either system to the other, or even an exchange of matter between them. Leakage of matter into a container or other system could be called inleakage. Leakage of matter out of a container or other system could be called outleakage. The presence of a leak does not necessarily mean there is always leakage of matter; it just implies there could be leakage through the opening. If the container or system is empty in an empty environment, there is no leakage at that time. Sometimes the word "leak" is used to refer to leakage in a certain situation, for example the passing or making public of secret information.
Leak types and possible causes
Types of leak openings include a puncture, gash, rustRust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...
or other corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
hole, very tiny pinhole leak (possibly in imperfect welds
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
), crack or microcrack, or inadequate sealing between components or parts joined together. When there is a puncture, the size and shape of the leak can often be seen, but in many other cases, the size and shape of the leak opening may not be so obvious. In many cases, the location of a leak can be determined by seeing material drip out at a certain place, although the leak opening itself is not obvious. In some cases, it may known or suspected there is a leak, but even the location of the leak is not known. Since leak openings are often so irregular, leaks are sometimes sized by the leakage rate, as in volume of fluid leaked per time, rather than the size of the opening.
Common types of leaks for many people include leaks in vehicle
Vehicle
A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....
tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
s, causing air to leak out resulting in flat tires, and leaks in containers, spilling the contents. Leaks can occur or develop in many different kinds of household, building, vehicle, marine, aircraft, or industrial fluid systems, whether the fluid is a gas or liquid. Leaks in vehicle hydraulic systems such as brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
or power steering
Power steering
Power steering helps drivers steer vehicles by augmenting steering effort of the steering wheel.Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver needs to provide only modest effort regardless of conditions. Power steering helps considerably when a...
lines could cause outleakage of brake or power steering fluid resulting in failure of the brakes, power steering, or other hydraulic system. Also possible are leaks of engine coolant - particularly in the radiator
Radiator
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...
and at the water pump
Water Pump
Water Pump is one of the neighbourhoods of Gulberg Town in Karachi, Sindh, Pakistan. It is near main Water Pump that supplies fresh water to the city of Karachi....
seal, transmission fluid, motor oil
Motor oil
Motor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...
, and refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...
in the air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
system. Some of these vehicle fluids have different colors to help identify the type of leaking fluid.
The water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
supply system or a wastewater
Wastewater
Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...
system in a house or other building may have a leak in any of numerous locations, causing dripping out or spillage of the water. Gas leak
Gas leak
In common usage, a gas leak refers to a leak of natural gas, from a pipe or other containment, into a living area or any other area where the gas should not be...
s, e.g. in natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
lines allow flammable and potentially explosive gas to leak out, resulting in a hazardous situation. Leaks of refrigerant may occur in refrigerator
Refrigerator
A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...
s or air conditioning systems, large and small. Some industrial plants, especially chemical
Chemical plant
A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use special equipment,...
and power plants, have numerous fluid systems containing many types of liquid or gas chemicals, sometimes at high temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
and/or pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
. An example of a possible industrial location of a leak between two fluid systems includes a leak between the shell and tube sides in a heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
, potentially contaminating either or both fluid systems with the other fluid. A system holding a full or partial vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
may have a leak causing inleakage of air from the outside. Hazmat procedures and/or teams may become involved when leakage or spillage of hazardous materials occurs. Leaks while transporting hazardous materials could result in danger; for example, when accidents occur. However, even leakage of steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
can be dangerous because of the high temperature and energy of the steam.
Leakage of air or other gas out of hot air balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology. It is in a class of aircraft known as balloon aircraft. On November 21, 1783, in Paris, France, the first untethered manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air...
s, dirigibles, or cabins of airplane
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
s could present dangerous situations. A leak could even be inside a body, such as a hole in the septum
Septum
In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
between heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
ventricles causing an exchange of oxygenated and deoxygenated blood, or a fistula
Fistula
In medicine, a fistula is an abnormal connection or passageway between two epithelium-lined organs or vessels that normally do not connect. It is generally a disease condition, but a fistula may be surgically created for therapeutic reasons.-Locations:Fistulas can develop in various parts of the...
between bodily cavities such as between vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
and rectum
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
.
There can be numerous causes of leaks. Leaks can occur from the outset even during construction
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...
or initial manufacture/assembly of fluid systems. Pipe
Pipe (material)
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...
s, tubing
Tube (fluid conveyance)
A tube, or tubing, is a long hollow cylinder used to convey fluids .The terms "pipe" and "tube" are almost interchangeable, although minor distinctions exist — generally, a tube has tighter engineering requirements than a pipe. Both pipe and tube imply a level of rigidity and permanence,...
, valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
s, fitting
Fitting
Fitting can refer to:* A dress fitting.* Any machine, component, piping or tubing part that can attach or connect two or more larger parts. For examples, see coupling, compression fitting or piping and plumbing fittings....
s, or other components may be improperly joined or welded together. Components with threads may be improperly screwed together. Leaks can be caused by damage; for example, punctures or fracture. Often leaks are the result of deterioration of materials from wear or aging, such as rusting or other corrosion or decomposition of elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
s or similar polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
materials used as gasket
Gasket
thumb|sright|250px|Some seals and gaskets1. [[o-ring]]2. fiber [[Washer |washer]]3. paper gaskets4. [[cylinder head]] [[head gasket|gasket]]...
s or other seals
Seal (mechanical)
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage , containing pressure, or excluding contamination...
. For example, wearing out of faucet washer
Washer (hardware)
A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring , wear pad, preload indicating device, locking device, and to reduce vibration...
s causes water to leak at the faucets. Cracks may result from either outright damage, or wearing out by stress such as fatigue failure
Fatigue (material)
'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...
or corrosion such as stress corrosion cracking
Stress corrosion cracking
Stress corrosion cracking is the unexpected sudden failure of normally ductile metals subjected to a tensile stress in a corrosive environment, especially at elevated temperature in the case of metals. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when...
. Wearing out of a surface between a disk and its seat in a valve could cause a leak between ports (valve inlets or outlets). Wearing out of packing around a turning valve stem or rotating centrifugal pump
Centrifugal pump
A centrifugal pump is a rotodynamic pump that uses a rotating impeller to create flow by the addition of energy to a fluid. Centrifugal pumps are commonly used to move liquids through piping...
shaft could develop into fluid outleakage into the environment. For some frequently operating centrifugal pumps, such leakage is so expected that provisions are made for carrying away the leakage. Similarly, wearing out of seals or packing around piston-driven pumps could also develop into outleakage to the environment.
The pressure difference between both sides of the leak can affect the movement of material through the leak. Fluids will commonly move from the higher pressure side to the lower pressure side. The larger the pressure difference, the more leakage there will typically be. The fluid pressures on both sides include the hydrostatic pressure, which is pressure due to the weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...
from the height of fluid level above the leak. When the pressures are about equal, there can be an exchange of fluids between both sides, or little to no net movement of fluid across the leak.
Leak testing
Containers, vessels, enclosures, or other fluid system are sometimes tested for leaks - to see if there is any leakage and to find where the leaks are so corrective action can be taken. There are several methods for leak testing, depending on the situation. Sometimes leakage of fluid may make a soundSound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
which can be detected. Tires, engine radiators, and maybe some other smaller vessels may be tested by pressurizing them with air and submerging them in water to see where air bubble
Liquid bubble
A bubble is a globule of one substance in another, usually gas in a liquid.Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.-Common examples:...
s come out to indicate a leak. If submerging in water is not possible, then pressurization with air followed by covering the area to be tested with a soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
solution is done to see if soap bubbles form, which indicate a leak. Other types of testing for gas leaks may involve testing for the outleaking gases with sensors which can detect that gas, for example - special sensing instruments for detecting natural gas. U.S. federal safety law now requires natural gas companies to conduct testing for gas leaks upstream of their customer's gas meters. Where liquids are used, special color dyes may be added to help see the leakage. Other detectable substances in one of the liquids may be tested, such as saline to find a leak in a sea water system, or detectable substances may even be deliberately added to test for leakage.
Newly constructed, fabricated, or repaired systems or other vessels are sometimes tested to verify satisfactory production or repair. Plumber
Plumber
A plumber is a tradesperson who specializes in installing and maintaining systems used for potable water, sewage, and drainage in plumbing systems. The term dates from ancient times, and is related to the Latin word for lead, "plumbum." A person engaged in fixing metaphorical "leaks" may also be...
s often test for leaks after working on a water or other fluid system. A vessel or system is sometimes pressure tested by filling with air and the pressure monitored to see if it drops, indicating a leak.
A very commonly used test after new construction or repair is a hydrostatic test
Hydrostatic test
A hydrostatic test is a way in which leaks can be found in pressure vessels such as pipelines and plumbing. The test involves placing water, which is often dyed for visibility, in the pipe or vessel at the required pressure to ensure that it will not leak or be damaged. It is the most common method...
, sometimes called a pressure test. In a hydrostatic test, a system is pressurized with water to look for a drop in pressure or to see where it leaks out. Helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
testing may be done to detect for any very small leakage such as when testing certain diaphragm or bellows valves, which are made to be practically leak-proof. Helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
and Hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
have very small molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s which can go through very small leaks.
Leak testing is part of the non-destructive test NDT
Nondestructive testing
Nondestructive testing or Non-destructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage....
portfolio that can be applied to an art to verify its conformity; depending on material, pressure, leak tightness specifications, different methods can be applied. International standards has been defined to assist in these choices. For example BS EN 1779:1999; it applies to assessment of leak tightness by indication or measurement of gas leakage, but excludes hydrostatic, ultrasonic or electromagnetic methods.
Other standards also apply:
- BS EN 13184:2001 Non-destructive testing. Leak testing. Pressure change method
- BS EN 13185:2001 Non-destructive testing. Leak testing. Tracer gas method
- BS EN 13192:2002 Non-destructive testing. Leak testing. Calibration of reference leaks for gases
In shell and tube heat exchanger
Shell and tube heat exchanger
A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell with a...
s, Eddy current
Eddy current
Eddy currents are electric currents induced in conductors when a conductor is exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of...
testing is sometimes done in the tubes to find locations on tubes where there may be leaks or damage which may eventually develop into a leak.
Corrective action for leaks
In complex plants with multiple fluid systems, many interconnecting units holding fluids have isolation valves between them. If there is a leak in a unit, its isolation valves can be shut to "isolate" the unit from the rest of the plant.Leaks are often repaired by plugging the leaking holes or using a patch to cover them. Leaking tires are often fixed this way. Leaking gaskets, seals, washers, or packing can be replaced. Use of welding, soldering, sealing, or gluing may be other ways to fix leaks. Sometimes, the most practical solution is to replace the leaking unit. Leaking water heaters are often replaced by home or building owners.
If there is a leak in one of the tubes of a shell and tube heat exchanger
Shell and tube heat exchanger
A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell with a...
, that tube can be plugged at both ends with specially sized plugs to isolate the leak. This is done in the plenum(s) at the points where the tube ends connect to the tubesheet(s). Sometimes a damaged but not yet leaking tube is pre-emptively plugged to prevent future leakage. The heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
capacity of that tube is lost, but there are usually plenty of other tubes to pick up the heat transfer load.