Pigging
Encyclopedia
Pigging in the context of pipelines
refers to the practice of using pipeline inspection gauges or 'pigs' to perform various maintenance operations on a pipeline. This is done without stopping the flow of the product in the pipeline.
These operations include but are not limited to cleaning and inspecting of the pipeline. This is accomplished by inserting the pig into a 'pig launcher' (or 'launching station') - a funnel
shaped Y section in the pipeline. The launcher / launching station is then closed and the pressure
driven flow of the product in the pipeline is used to push it along down the pipe until it reaches the receiving trap - the 'pig catcher' (or receiving station).
If the pipeline contains butterfly valve
s, the pipeline cannot be pigged. Ball valve
s cause no problems because the inside diameter of the ball can be specified to be the same as that of the pipe (assuming they are full bore valves).
Pigging has been used for many years to clean larger diameter pipelines in the oil industry. Today, however, the use of smaller diameter pigging systems is now increasing in many continuous and batch process plants as plant operators search for increased efficiencies and reduced costs.
Pigging can be used for almost any section of the transfer process between, for example, blending, storage or filling systems. Pigging systems are already installed in industries handling products as diverse as lubricating oils, paints, chemicals, toiletries, cosmetics and foodstuffs.
Pigs are used in lube oil or painting blending: they are used to clean the pipes to avoid cross-contamination, and to empty the pipes into the product tanks (or sometimes to send a component back to its tank). Usually pigging is done at the beginning and at the end of each batch, but sometimes it is done in the midst of a batch, e.g. when producing a premix that will be used as an intermediate component.
Pigs are also used in oil and gas pipelines: they are used to clean the pipes but also there are "smart pigs" used to measure things like pipe thickness and corrosion along the pipeline. They usually do not interrupt production, though some product can be lost when the pig is extracted. They can also be used to separate different products in a multiproduct pipeline.
derived from the initial letters of the term 'Pipeline Inspection Gauge' or possibly 'Pipeline Inspection Gizmo' or 'Pipeline Internal Geometry' or 'Pipeline Inspection Gadget').
Without the need for line flushing, pigging offers the additional advantage of a much more rapid and reliable product changeover. Product sampling at the receipt point becomes faster because the interface between products is very clear, and the old method of checking at intervals, until the product is on-specification, is considerably shortened.
Pigging can also be operated totally by a programmable logic controller
(PLC).
(PCB), which has been found to be carcinogenic. All of these problems can now be eliminated due to the very precise interface produced by modern pigging systems.
The pig is pushed either with an inert gas or a liquid; if pushed by gas, some systems can be adapted in the gas inlet in order to ensure pig's constant speed, whatever the pressure drop is. The pigs must be removed, as many pigs are rented, pigs wear and must be replaced, and cleaning pigs push contaminants from the pipeline such as wax, foreign objects, hydrates, etc., which must be removed from the pipeline. There are inherent risks in opening the barrel to atmosphere and care must be taken to ensure that the barrel is depressured prior to opening. If the barrel is not completely depressured, the pig can be ejected from the barrel and operators have been severely injured when standing in front of an open pig door. When the product is sour, the barrel should be evacuated to a flare system where the sour gas
is burnt. Operators should be wearing a self-contained breathing apparatus when working on sour systems.
A few pigging systems utilize a "captive pig", and the pipeline is only opened up very occasionally to check the condition of the pig. At all other times, the pig is shuttled up and down the pipeline at the end of each transfer, and the pipeline itself is never opened up during process operation. These systems are not common.
Modern intelligent pigs are highly sophisticated instruments that vary in technology and complexity by the intended use and by manufacturer. An intelligent pig, or smart pig, includes electronics and sensors that collects various forms of data during the trip through the pipeline.
The electronics are sealed to prevent leakage of the pipeline product into the electronics since products can range from highly basic to highly acidic and can be of extremely high temperature. Many pigs use specific materials according to the product in the pipeline. Power for the electronics is provided by onboard batteries which are also sealed. Data recording may be by various means ranging from analog tape, digital tape, or solid state memory in more modern digital units.
The technology used to accomplish the service varies by the service required and the design of the pig, each pigging service provider may have unique and proprietary technologies to accomplish the service. Surface pitting and corrosion, as well as cracks and weld defects in steel/ferrous pipelines are often detected using magnetic flux leakage
(MFL) pigs. Other "smart" pigs use electromagnetic acoustic transducers to detect pipe defects. Caliper pigs can measure the "roundness" of the pipeline to determine areas of crushing or other deformations. Some smart pigs can combine technologies such as MFL and Caliper into a single tool. Recent trials of pigs using acoustic resonance technology
have been reported.
During the pigging run the pig is unable to directly communicate with the outside world due to the distance underground or underwater and/or materials that the pipe is made of. For example, steel pipelines effectively prevent any reliable radio communications outside the pipe. It is therefore necessary that the pig use internal means to record its own movement during the trip. This may be done by gyroscope-assisted tilt sensors, odometer
s and other technologies. The pig will record this positional data so that the distance it moves along with any bends can be interpreted later to determine the exact path taken.
Location verification is often accomplished by surface instruments that record the pig’s passage by either audible or gravinometric (or other) means. The sensors will record when they detect passage of the pig; this is then compared to the internal record for verification or adjustment. The external sensors may have GPS
capability to assist in their location or even to transmit the pig’s passage, but the pig itself usually cannot use GPS as it requires being able to receive the satellite signals.
After the pigging run has been completed, the positional data is combined with the pipeline evaluation data (corrosion, cracks, etc.) to provide a location-specific defect map and characterization. In other words, the combined data will tell the operator the location and type and size of each pipe defect. This is used to judge the severity of the defect and help repair crews locate and repair the defect quickly without having to dig up excessive amounts of pipeline. By evaluating the rate of change of a particular defect over several years, proactive plans can be made to repair the pipeline before any leakage or environmental damage occurs.
A pipeline inspection gauge or "PIG" in the pipeline
industry is a tool that is sent down a pipeline and propelled by the pressure
of the product in the pipeline itself. There are four main uses for pigs:
The original pigs were made from straw wrapped in wire used for cleaning. They made a squealing noise while traveling through the pipe, sounding to some like a pig
squealing. The term "pipeline inspection gauge" was later created as a backronym
.
One kind of pig is a soft, bullet
shaped polyurethane
foam
plug that is forced through pipeline
s to separate products to reduce mixing. There are several types of pigs for cleaning. Some have tungsten
studs or abrasive wire mesh on the outside to cut rust
, scale
, or paraffin
deposits off the inside of the pipe. Others are plain plastic covered polyurethane.
Inline inspection pigs use various methods for inspecting a pipeline. A sizing pig uses one (or more) notched round metal plates that are used as gauges. The notches allow different parts of the plate to bend when a bore restriction is encountered. More complex systems exist for inspecting various aspects of the pipeline. Intelligent pigs, also called smart pigs, are used to inspect the pipeline with sensors and record the data for later analysis. These pigs use technologies such as MFL and ultrasonics
to inspect the pipeline. Intelligent pigs may also use caliper
s to measure the inside geometry of the pipeline.
In 1961, the first intelligent pig was run by Shell Development. It demonstrated that a self-contained electronic instrument could traverse a pipe line while measuring and recording wall thickness. The instrument used electromagnetic fields to sense wall integrity. In 1964 Tuboscope ran the first commercial instrument. It used MFL technology to inspect the bottom portion of the pipeline. The system used a black box similar to those used on aircraft to record the information.
A pig has been used as a plot device in three James Bond
films: Diamonds Are Forever
, where Bond disabled a pig to escape from a pipeline, The Living Daylights
, where a pig was modified to secretly transport a person through the Iron Curtain
, and The World Is Not Enough
, where a pig was used to move a nuclear weapon through a pipeline.
A pig was also used as a plot device in the Tony Hillerman
book The Sinister Pig
where an abandoned pipeline from Mexico to the United States was used with a pig to transport illegal drugs.
Capacitive sensor probes are used in the process of detecting defects in polyethylene pipe gas pipeline. These probes are attached to the pig in which the pig is sent through the polyethylene pipe that will detect any defects in the outside of the pipe wall. This is done by using a triple plate capacitive sensor in which the electrostatic waves are propagated outware through the pipe's wall. Any change in dielectric material will result in a change in capacitance. Testing was conducted by NETL DOE research lab at the Battelle West Jefferson’s Pipeline Simulation Facility
(PSF) near Columbus, Ohio.
Pipeline transport
Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....
refers to the practice of using pipeline inspection gauges or 'pigs' to perform various maintenance operations on a pipeline. This is done without stopping the flow of the product in the pipeline.
These operations include but are not limited to cleaning and inspecting of the pipeline. This is accomplished by inserting the pig into a 'pig launcher' (or 'launching station') - a funnel
Funnel
A funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, spillage would occur....
shaped Y section in the pipeline. The launcher / launching station is then closed and the 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 :...
driven flow of the product in the pipeline is used to push it along down the pipe until it reaches the receiving trap - the 'pig catcher' (or receiving station).
If the pipeline contains butterfly valve
Butterfly valve
A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve...
s, the pipeline cannot be pigged. Ball valve
Ball valve
A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends...
s cause no problems because the inside diameter of the ball can be specified to be the same as that of the pipe (assuming they are full bore valves).
Pigging has been used for many years to clean larger diameter pipelines in the oil industry. Today, however, the use of smaller diameter pigging systems is now increasing in many continuous and batch process plants as plant operators search for increased efficiencies and reduced costs.
Pigging can be used for almost any section of the transfer process between, for example, blending, storage or filling systems. Pigging systems are already installed in industries handling products as diverse as lubricating oils, paints, chemicals, toiletries, cosmetics and foodstuffs.
Pigs are used in lube oil or painting blending: they are used to clean the pipes to avoid cross-contamination, and to empty the pipes into the product tanks (or sometimes to send a component back to its tank). Usually pigging is done at the beginning and at the end of each batch, but sometimes it is done in the midst of a batch, e.g. when producing a premix that will be used as an intermediate component.
Pigs are also used in oil and gas pipelines: they are used to clean the pipes but also there are "smart pigs" used to measure things like pipe thickness and corrosion along the pipeline. They usually do not interrupt production, though some product can be lost when the pig is extracted. They can also be used to separate different products in a multiproduct pipeline.
Etymology
Pigs get their name from the squealing sound they make while travelling through a pipeline. (Disputed: 'PIG' is an acronym or backronymBackronym
A backronym or bacronym is a phrase constructed purposely, such that an acronym can be formed to a specific desired word. Backronyms may be invented with serious or humorous intent, or may be a type of false or folk etymology....
derived from the initial letters of the term 'Pipeline Inspection Gauge' or possibly 'Pipeline Inspection Gizmo' or 'Pipeline Internal Geometry' or 'Pipeline Inspection Gadget').
Product and time saving
A major advantage of piggable systems is the potential resulting product savings. At the end of each product transfer, it is possible to clear out the entire line contents with the pig, either forwards towards the receipt point, or backwards to the source tank. There is no requirement for extensive line flushing.Without the need for line flushing, pigging offers the additional advantage of a much more rapid and reliable product changeover. Product sampling at the receipt point becomes faster because the interface between products is very clear, and the old method of checking at intervals, until the product is on-specification, is considerably shortened.
Pigging can also be operated totally by a programmable logic controller
Programmable logic controller
A programmable logic controller or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines...
(PLC).
Environmental issues
Pigging has a significant role to play in reducing the environmental impact of batch operations. Traditionally, the only way that an operator of a batch process could ensure a product was completely cleared from a line was to flush the line with a cleaning agent such as water or a solvent or even the next product. This cleaning agent then had to be subjected to effluent treatment or solvent recovery. If product was used to clear the line, the contaminated finished product was downgraded or dumped. In some cases, the finished product could contain polychlorinated biphenylPolychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...
(PCB), which has been found to be carcinogenic. All of these problems can now be eliminated due to the very precise interface produced by modern pigging systems.
Safety considerations
Pigging systems are designed so that the pig is loaded into the launcher, which is pressured up to launch the pig into the pipeline through a kicker line. In some cases, the pig is removed from the pipeline via the receiver at the end of each run. All systems must allow for the receipt of pigs at the launcher, as blockages in the pipeline may require the pigs to be pushed back to the launcher. Most of the time, systems are designed to pig the pipeline in either direction.The pig is pushed either with an inert gas or a liquid; if pushed by gas, some systems can be adapted in the gas inlet in order to ensure pig's constant speed, whatever the pressure drop is. The pigs must be removed, as many pigs are rented, pigs wear and must be replaced, and cleaning pigs push contaminants from the pipeline such as wax, foreign objects, hydrates, etc., which must be removed from the pipeline. There are inherent risks in opening the barrel to atmosphere and care must be taken to ensure that the barrel is depressured prior to opening. If the barrel is not completely depressured, the pig can be ejected from the barrel and operators have been severely injured when standing in front of an open pig door. When the product is sour, the barrel should be evacuated to a flare system where the sour gas
Sour gas
Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide . Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume...
is burnt. Operators should be wearing a self-contained breathing apparatus when working on sour systems.
A few pigging systems utilize a "captive pig", and the pipeline is only opened up very occasionally to check the condition of the pig. At all other times, the pig is shuttled up and down the pipeline at the end of each transfer, and the pipeline itself is never opened up during process operation. These systems are not common.
Intelligent pigging
The electronics are sealed to prevent leakage of the pipeline product into the electronics since products can range from highly basic to highly acidic and can be of extremely high temperature. Many pigs use specific materials according to the product in the pipeline. Power for the electronics is provided by onboard batteries which are also sealed. Data recording may be by various means ranging from analog tape, digital tape, or solid state memory in more modern digital units.
The technology used to accomplish the service varies by the service required and the design of the pig, each pigging service provider may have unique and proprietary technologies to accomplish the service. Surface pitting and corrosion, as well as cracks and weld defects in steel/ferrous pipelines are often detected using magnetic flux leakage
Magnetic flux leakage
Magnetic flux leakage is a magnetic method of nondestructive testing that is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. The basic principle is that a powerful magnet is used to magnetize the steel. At areas where there is corrosion or...
(MFL) pigs. Other "smart" pigs use electromagnetic acoustic transducers to detect pipe defects. Caliper pigs can measure the "roundness" of the pipeline to determine areas of crushing or other deformations. Some smart pigs can combine technologies such as MFL and Caliper into a single tool. Recent trials of pigs using acoustic resonance technology
ART (Acoustic Resonance Technology)
Acoustic Resonance Technology is an acoustic inspection technology developed by Det Norske Veritas over the past 20 years. ART exploits the phenomenon of half-wave resonance, whereby a suitably excited resonant target exhibits longitudinal resonances at certain frequencies characteristic of the...
have been reported.
During the pigging run the pig is unable to directly communicate with the outside world due to the distance underground or underwater and/or materials that the pipe is made of. For example, steel pipelines effectively prevent any reliable radio communications outside the pipe. It is therefore necessary that the pig use internal means to record its own movement during the trip. This may be done by gyroscope-assisted tilt sensors, odometer
Odometer
An odometer or odograph is an instrument that indicates distance traveled by a vehicle, such as a bicycle or automobile. The device may be electronic, mechanical, or a combination of the two. The word derives from the Greek words hodós and métron...
s and other technologies. The pig will record this positional data so that the distance it moves along with any bends can be interpreted later to determine the exact path taken.
Location verification is often accomplished by surface instruments that record the pig’s passage by either audible or gravinometric (or other) means. The sensors will record when they detect passage of the pig; this is then compared to the internal record for verification or adjustment. The external sensors may have GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
capability to assist in their location or even to transmit the pig’s passage, but the pig itself usually cannot use GPS as it requires being able to receive the satellite signals.
After the pigging run has been completed, the positional data is combined with the pipeline evaluation data (corrosion, cracks, etc.) to provide a location-specific defect map and characterization. In other words, the combined data will tell the operator the location and type and size of each pipe defect. This is used to judge the severity of the defect and help repair crews locate and repair the defect quickly without having to dig up excessive amounts of pipeline. By evaluating the rate of change of a particular defect over several years, proactive plans can be made to repair the pipeline before any leakage or environmental damage occurs.
Pipeline Inspection Gauge
Pipeline transport
Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....
industry is a tool that is sent down a pipeline and propelled by the 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 :...
of the product in the pipeline itself. There are four main uses for pigs:
- physical separation between different liquids being transported in pipelines;
- internal cleaning of pipelines;
- inspection of the condition of pipeline walls (also known as an Inline Inspection (ILI) tool);
- capturing and recording geometric information relating to pipelines (e.g. size, position).
The original pigs were made from straw wrapped in wire used for cleaning. They made a squealing noise while traveling through the pipe, sounding to some like a pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
squealing. The term "pipeline inspection gauge" was later created as a backronym
Backronym
A backronym or bacronym is a phrase constructed purposely, such that an acronym can be formed to a specific desired word. Backronyms may be invented with serious or humorous intent, or may be a type of false or folk etymology....
.
One kind of pig is a soft, bullet
Bullet
A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...
shaped polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
foam
Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...
plug that is forced through pipeline
Pipeline transport
Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....
s to separate products to reduce mixing. There are several types of pigs for cleaning. Some have tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
studs or abrasive wire mesh on the outside to cut rust
Rust
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...
, scale
Fouling
Fouling refers to the accumulation of unwanted material on solid surfaces, most often in an aquatic environment. The fouling material can consist of either living organisms or a non-living substance...
, or paraffin
Paraffin
In chemistry, paraffin is a term that can be used synonymously with "alkane", indicating hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to a mixture of alkanes that falls within the 20 ≤ n ≤ 40 range; they are found in the solid state at room temperature and begin to enter the...
deposits off the inside of the pipe. Others are plain plastic covered polyurethane.
Inline inspection pigs use various methods for inspecting a pipeline. A sizing pig uses one (or more) notched round metal plates that are used as gauges. The notches allow different parts of the plate to bend when a bore restriction is encountered. More complex systems exist for inspecting various aspects of the pipeline. Intelligent pigs, also called smart pigs, are used to inspect the pipeline with sensors and record the data for later analysis. These pigs use technologies such as MFL and ultrasonics
Ultrasonics
Ultrasonics is a term meaning the application of ultrasound. It is often used in industry as a shorthand term for any equipment employing ultrasonic principles....
to inspect the pipeline. Intelligent pigs may also use caliper
Caliper
A caliper is a device used to measure the distance between two opposing sides of an object. A caliper can be as simple as a compass with inward or outward-facing points...
s to measure the inside geometry of the pipeline.
In 1961, the first intelligent pig was run by Shell Development. It demonstrated that a self-contained electronic instrument could traverse a pipe line while measuring and recording wall thickness. The instrument used electromagnetic fields to sense wall integrity. In 1964 Tuboscope ran the first commercial instrument. It used MFL technology to inspect the bottom portion of the pipeline. The system used a black box similar to those used on aircraft to record the information.
A pig has been used as a plot device in three James Bond
James Bond
James Bond, code name 007, is a fictional character created in 1953 by writer Ian Fleming, who featured him in twelve novels and two short story collections. There have been a six other authors who wrote authorised Bond novels or novelizations after Fleming's death in 1964: Kingsley Amis,...
films: Diamonds Are Forever
Diamonds Are Forever (film)
Diamonds Are Forever is the seventh spy film in the Eon Productions James Bond series, and the sixth and final Eon Productions film to star Sean Connery as the fictional MI6 agent James Bond. The film is based on Ian Fleming's 1956 novel of the same name, and is the second of four James Bond films...
, where Bond disabled a pig to escape from a pipeline, The Living Daylights
The Living Daylights
The Living Daylights is the fifteenth entry in the James Bond series and the first to star Timothy Dalton as the fictional MI6 agent 007. The film's title is taken from Ian Fleming's short story, "The Living Daylights"...
, where a pig was modified to secretly transport a person through the Iron Curtain
Iron Curtain
The concept of the Iron Curtain symbolized the ideological fighting and physical boundary dividing Europe into two separate areas from the end of World War II in 1945 until the end of the Cold War in 1989...
, and The World Is Not Enough
The World Is Not Enough
The World Is Not Enough is the nineteenth spy film in the James Bond film series, and the third to star Pierce Brosnan as the fictional MI6 agent James Bond. The film was directed by Michael Apted, with the original story and screenplay written by Neal Purvis, Robert Wade and Bruce Feirstein. It...
, where a pig was used to move a nuclear weapon through a pipeline.
A pig was also used as a plot device in the Tony Hillerman
Tony Hillerman
Tony Hillerman was an award-winning American author of detective novels and non-fiction works best known for his Navajo Tribal Police mystery novels...
book The Sinister Pig
The Sinister Pig
The Sinister Pig is the sixteenth in the Chee/Leaphorn Navajo Tribal Police series of crime fiction novels by Tony Hillerman and a New York Times best-seller.-Plot summary:...
where an abandoned pipeline from Mexico to the United States was used with a pig to transport illegal drugs.
Capacitive sensor probes are used in the process of detecting defects in polyethylene pipe gas pipeline. These probes are attached to the pig in which the pig is sent through the polyethylene pipe that will detect any defects in the outside of the pipe wall. This is done by using a triple plate capacitive sensor in which the electrostatic waves are propagated outware through the pipe's wall. Any change in dielectric material will result in a change in capacitance. Testing was conducted by NETL DOE research lab at the Battelle West Jefferson’s Pipeline Simulation Facility
(PSF) near Columbus, Ohio.