about pipeline pigs

5/28/12 About Pipeline Pigs

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About Pigs

Pipeline pigs are devices that are inserted into andtravel throughout the length of a pipeline driven by aproduct flow. They were originally developed toremove deposits which could obstruct or retard flowthrough a pipeline. Today pigs are used during allphases in the life of a pipeline for many differentreasons.

Although each pipeline has its own set ofcharacteristics which affect how and why pigging isused, there are basically three reasons to pig apipeline:

To batch or separate dissimilar products;

For displacement purposes;

For internal inspection.

The pigs which are used to accomplish these tasks can be divided into three categories:

Utility Pigs, which are used to perform functions such as cleaning, separating, or dewatering.

In Line Inspection Tools, which provide information on the condition of the line, as well as theextent and location of any problems.

Gel Pigs, which are used in conjunction with conventional pigs to optimize pipelinedewatering, cleaning, and drying tasks.

The type of pig to be used and its optimum configuration for a particular task in a particular pipelineshould be determined based upon several criteria, which include:

The purposeType,

location, and volume of the substance to be removed or displaced in conventionalpigging applications,

Type of information to be gathered from an intelligent pig run,

Objectives and goals for the pig run.

The line contentsThe contents of the line while pigging,

Available vs. required driving pressure,

Velocity of the pig.

Characteristics of the pipelineThe minimum and maximuminternal line sizes,



internal line sizes,

Maximum distance pig musttravel,

Minimum bend radius, andbend angles,

Additional features such as valve types, branch connections, and the elevation profile.

UTILITY PIGS

Utility pipeline pigs can be divided into two groups based upontheir fundamental purpose:

Cleaning Pigs, which are used to remove solid orsemi-solid deposits or debris from the pipeline.

Sealing Pigs, which are used to provide a good seal inorder to either sweep liquids from the line, or provide aninterface between two dissimilar products within thepipeline.

Within these two groups, a further subdivision can be made to differentiate among the various typesor forms of pigs:

• Mandrel pigs, which have a central body tube, or mandrel, andvarious components which can be assembled onto the mandrel toconfigure a pig for a specific duty;

• Foam pigs, which are molded frompolyurethane foam with variousconfigurations of solid polyurethane stripsand/or abrasive materials permanently

bonded to them;

• Solid cast pigs, which are moulded in onepiece, usually from polyurethane, and;

• Spherical pigs or spheres, which are of either a solid composition or inflated to their optimum

diameter with glycol and/or water.

GEOMETRY PIGS

A geometry / caliperpig is a configurationpig designed torecord conditions,such as dents,

wrinkles, ovality, bend radius and angle, and occasionallyindications of significant internal corrosion by makingmeasurements of the inside surface of the pipe.



IN LINE INSPECTION TOOLS (ILI) / SMART PIGS

In Line Inspection provides information on the conditionof the pipe and/or its contents. With few exceptions, theIn Line Inspection Tool itself is simply the tool whichgathers the data, which is then analysed by theengineers and technicians to determine and report onthe condition of the line.

Although the two most common requirements are for geometry/diameter measurement and for metal-loss/corrosion devices, the information which can be provided by these intelligent pigs covers a muchwider range of inspection and troubleshooting needs which include:

Diameter /geometrymeasurements;

Curvaturemonitoring;

Pipeline profile;

Temperature /pressurerecording;

Bendmeasurement;

Metal-loss /corrosiondetection;

Photographicinspection;

Crack detection;

Wax depositionmeasurement;

Leak detection;

Productsampling, and;

Mapping.



PLUGS

A plug is a specialist pig that can be used to isolate a section of pipeline at pressure while someremedial work is undertaken. The plugs can withstand pressures up to 200 bars typically. The plugworks by gripping into the line pipe and then having a separate sealing system. Lower pressuretechniques include High Friction pigs, which provide a barrier for depressurised systems.

GEL PIGS

Gel pigs are a series of gelled liquid systems which have been developed for use inpipeline operations, either during initial commissioning, or as a part of a continuingmaintenance program. Most pipeline gels are water-based, but a range ofchemicals, solvents, and even acids can be gelled. Some chemicals can be gelledas the bulk liquid and others only diluted in a carrier. Gelled diesel is commonlyused as a carrier of corrosion inhibitor in gas lines. There are four main types of gel



used as a carrier of corrosion inhibitor in gas lines. There are four main types of gelthat are used in pipeline applications:

Batching, or separator gel

Debris pickup gel

Hydrocarbon gel

Dehydrating gel

As a liquid, although highly viscous, the gel can be pumped through any line which will acceptliquids. Gel pigs can be used alone (in liquid lines), in place of batching pigs, or in conjunction withvarious types of conventional pigs. When used with conventional pigs, gelled pigs can improve overallperformance while almost eliminating the risk of sticking a pig.

Gel pigs do not wear out in service like conventional pigs. They can, however, be susceptible todilution and gas cutting. Care must be taken, therefore, when designing a pig train that incorporatesgel pigs to minimize fluid bypass of the pigs, and to place a conventional pig at the back of the trainwhen displacing with gas.

The principle pipeline applications for gel pigs are as follows:

Product separation

Debris removal

Line filling/hydrotesting

Dewatering and drying

Condensate removal from gaslines

Inhibitor and biocide laydown

Special chemical treatment

Removal of stuck pigs

Specially formulated gels have also been used to seal valves during hydrostatic testing. Gels havebeen developed with a controlled gellation time and a controlled viscosity for temporary pipelineisolation purposes.

PIG TRAPS/LAUNCHERS/RECEIVERS

Pig traps are used forinserting pigs into apipeline thenlaunching, receiving,and finally removingthem without flowinterruption. Pig trapsare not generallyproprietary productsand are usually madeto a specification

drawn up by the user. However, pig trap closures are proprietary products and form a criticallyimportant part of a pigging system. Safety is a major consideration in the selection of a closure. Allclosures must have a built-in safety lock which prevents them being opened while the trap ispressurised.



To learn more about pipeline pigging see PPSA Publication, "An Introduction to Pipeline Pigging."

about pipeline pigs

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