Leak
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A leak is a hole or other opening, unintended and undesired, in containers or fluid-reservoirs such as a tank or ship's hull through which contents within can escape or outside matter can enter the container. The matter leaking in or out may be gas, liquid, highly viscous liquids, or even solids such as powders or colloidal solids. By analogy, the term "leak" can refer to the unintended release of private or secret information by an organization (see disambiguation page).
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[edit] Leak types and possible causes
Types of leak acts or leakages includes puncture, gash, corrosion hole, pincusion and porosity leakages (possible in imperfect weldings), cracks or microcrackings, or inadequate sealing between joints. When there is a puncture, the size and shape of the leak often are seen, by its size, shape, geometry and depth of the "leakage opening that" may become. In many cases, the location of a 'leak' is determined by visual inspection of material or "drip" at high probability place. In some cases, one may known or suspect there is a leak, but even so the location of the leak is not revealed. Since leak openings may be irregular-round-shaped1 or long irregular shaped, leaks are sometimes sized by flow rate as volume of fluid passing per unit time. Intensity of flow depends of the pressure and size of the opening.
Commonly encountered leaks include:
- Leaks in vehicle tires, causes air to leak out resulting in flat tires.
- Leaks in containers with pressurized contents inside resulting in spillage of the contents.
- Leaks in household, building, vehicle, marine, aircraft, or industrial fluid systems.
- Leaks in hydraulic systems such as vehicle brake, or power steering lines causing loss of function of these systems. Other hydraulic pressurized systems include engine cool systems (radiator, water pump seal, transmission fluid, motor oil, cooling systems such as air conditioning units).
In some systems a colored dye (often blue)is added to a fluid to help identify type of leaking fluid as toxic or to assist in identifying a leak site. In other systems the additive is odorous (typically gas systems) and serves as an early warning of leak.
[edit] Physics
Physics systems generating full or partial vacuum space obtain void by leaking out air from the active reciepent, and its principle is used by the volume compressor with multiple stages. """Chazmat procedures""" and/or teams become involved when leakage or spillage of hazardous materials occurs. Leaks while transporting hazardous materials could result in danger thus requireng ADRS-certification.
Leakage of air or other gas out of hot air balloons, dirigibles, or cabins of airplanes 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.
[edit] Rhyobology
Leaks can be caused by damage; punctures or fracture. Often leaks are the result of deterioration in material fabric from wear or aging, such as rust or other corrosion catalysts. for decompose low quality elastomer, polymer fabric seals. For instance wearing out of faucet washer causes sink to leak around 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.
[edit] 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 sound 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 bubbles 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. Plumbers 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 molecules 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:
- 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 exchangers, 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.
[edit] 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, 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.
