If you are a pigging industry veteran, you already know that pipeline pigging is more of an art, than a science.  You also know that like any other industry, it has its own language. Learning to speak “Pigging” isn’t easy, but if you decide you want to make this industry your home, or just want to “dip your toe” to see if it’s a good fit, learning some basic terms will make exploring the world of pipeline pigging much easier.  Happy Learning!

Batching Pigs: A utility pig that forms a moving seal in a pipeline to separate liquid from gas media, or to separate two different products being transported in the pipeline.  The most-common configuration of batching pigs are cup pigs and sphere pigs.

Bellhole: An excavation in a local area to permit a survey, inspection, maintenance, repair, or replacement of pipe section.

Buckle: A partial collapse of the pipe due to excessive banding associated with soil instability, landslides, washouts, frost heaves, earthquakes, etc.

Calibration Digs: Exploratory excavations, or bellholes, of portions of the pipeline in which an in-line inspection tool has recorded an indication.

Camera Pig: A configuration pig that carries a video of film camera and light sources for photographing the inside surface of a pipe on an intermittent or continuous basis.

Cleaning Pig: A utility pig that uses cups, scrapers, or brushes, to remove dirt, rust, mill scale, or other foreign matter from the pipeline.  Cleaning pigs are run to increase the operating efficiency of a pipeline or to facilitate inspection of the pipeline.

Configuration Pig: An instrumented pig that collects data relating to the inner contour of a pipe wall or of the pipeline.  Geometry pigs, camera pigs, and mapping pigs are types of configuration pigs.

Corrosion: The various types of corrosion are defined below:

  • General External – Metal loss due to electrochemical, galvanic, microbiological, or other attach on the pipe due to environmental conditions surrounding the pipe.
  • General Internal – Metal loss due to chemical or other attack on the steel from liquids on the inside of the pipe. Electrochemical attack can also occur on the local cells, but this condition is less frequent.
  • Pit – Local concentrated cell corrosion on the external or internal surfaces that results from the generation of the potential (voltage) difference setup be variations in oxygen concentrations within and outside the pit.  The oxygen-starved pit acts as the anode, and the pipe surface acts as the cathode.
  • Selective Corrosion –  A localized corrosion attack along the bond line of electric-resistance welds (ERW) and flash welds (FW), that leads to the development of a wedge-shaped groove that is often filled with corrosion products.
  • Stress -Corrosion Cracking – a progressive intergranular and/or transgranular cracking that results from a combination of applied tensile stress, cathodic protection currents, and a suitable corrosive environment.

Cracks: The three types of cracks are defined below:

  • Fatigue – Progressive cracking in the base material, weld, or weld zone, that is caused by pressure cycling or oscillatory stresses associated with the operation of the system.
  • Girth Weld – Cracks in the weld or weld zone of the longitudinal seam weld of the pipe.
  • Seam weld – cracks in the weld or weld zone of the longitudinal seam weld

Cup Pig: A utility pig that is supported and driven by cups made of a resilient material such as neoprene or polyurethane.  At least one of the cups forms a piston-like seal inside the pipe. Click here to learn more about our Uni-Cup® pig.

Dent: A local depression in the pipe surface caused by mechanical damage that produces a gross disturbance in the curvature of the pipe without reducing the pipe wall thickness.  The depth of a dent is measured as a gap between the lowest pint of the dent and a prolongation of the original contour of the pipe.

Disbonded: Any loss of bond between the protective coating and steel pipe as a result of coating adhesion failure, chemical attack, mechanical damage, hydrogen concentrations, etc.

Erosion: Destruction or removal of material by abrasive action of moving fluids (or gases), usually accelerated by the presence of solid particles or matter in suspension.

Gauging Pig:  A utility pig that is permanently deformable by obstructions in the pipeline and thus, upon retrieval from the line, provides evidence of the worst-case obstruction in a given pipeline segment. Click here to read an article on our blog about Gauging Pigs.

Gel Pig:  A utility pig that is composed o f a highly-viscous gelled liquid.  These pigs are often used for pipeline cleaning and are sometimes called gelly pigs.

Geometry Pig:  A configuration pig designed to record conditions, such as dents, wrinkles, ovality, bend radius and angel, and occasionally indication of a significant internal corrosion, by making measurements of the inside surface of the pipe.

Gouges: Mechanical or forceful removal of metal from a local area of the surface on the pipe that may work to harden the pipe and make it more susceptible to cracking.

Hard Spots: Local changes in hardness of the steel in the pipe resulting from non-uniform quenching procedures during manufacture, or change in chemistry of the steel. Hard spots, when stressed, are subject to failure from mechanisms such as hydrogen-stress cracking.

Holidays: Discontinuities in a coating, such as pinholes cracks, gaps or other flaws, that allow areas of the base metal to be exposed to any corrosive environment tat contacts the coating surface.

Inclusions: Foreign material or particles in a metal matrix.  These are usually compounds, such as oxides, sulfides, or silicates , but may be any substance that is foreign to the matrix, whether it is soluble or insoluble

In-Line Inspection (ILI): The inspection of a pipeline from the interior of the pipe using an in-line inspection tool.

In-Line Inspection Tool: The device of vehicle, also known as an “intelligent”or “smart” ILI Tool pig, that uses a non-destructive testing technique to inspect the wall of a pipe.  An in-line inspection tool is one type of instrumented tool.

Intelligent Pig or Tool:  See In-Line Inspection Tool.

Instrumented Pig:  A vehicle or device used for internal inspection of a pipe. which contains sensors, electronics, and recording or output functions integral to the system.  Instrumented pigs are divided into two types:

  • Configuration Pigs – which measure the pipeline geometry or the conditions of the inside surface of the pipe; and
  • In-Line Inspection Tools – that use non-destructive testing techniques to inspect the wall of the pipe for corrosion, cracks, or other types of anomalies.

Lack of Fusion (LOF): In a weld, any area or zone that lacks complete melting and coalescence (fusion) of a portion of the weld.  This may occur between weld passes or between weld and base materials.

Lamination: A type of imperfection or discontinuity with separation or weakness, usually aligned parallel to the worked surface of metal.

Launcher: A pipeline facility used for inserting a pig into a pressurized pipeline.

Mapping Pig: A configuration pig that uses inertia sensing or some other technology to collect the data that can be analysed to produce an elevation and plan view of the pipeline route.

Mechanical Damage: Damage from outside forces that modifies the dimensions or profile of the pipe (dents, gouges).

Metal Loss:  Any number of types of anomalies in a pope in which metal has been removed from the pipe surface, usually due to corrosion or gouging.

Obstructions: Any restriction or foreign object that reduces or modifies the cross-section of the pope to the extent that flow is affected or in-line inspection pigs can become stuck (ovality, collapse, dents, undersized valves, wrinkles, bends, weld drop-through). Also, any foreign object in the pipeline.

On-Line Inspection: See In-Line Inspection.

Ovality: A condition in which a circular pipe forms into an ellipse, usually as the result of external forces.

Pig: A generic term signifying any independent, self-contained device, tool, or vehicle, that moves through the interior of a pipeline for purposes of inspecting, dimensioning, or cleaning. Click here to learn more about our selection of pipeline cleaning pigs.

Porosity: Small voids or pores, usually gas filled, in the weld metal.

Radius Bends: The radius bend in the pipe as related to the pipe diameter (D). Example: a 3D bend would have a radius of three times the diameter of the pipe measured to the centreline of the pipe.

Receiver: A pipeline facility used for removing a pig from a pressurized pipeline.

Smart Pig: See In-Line Inspection Tool.

Slivers: A thin elongated anomaly caused when a piece of metal is rolled into the surface of the pipe.  a sliver is usually metallurgically attached at only one end.  In MFL inspections, a sliver is sometimes called a lamination.

Sphere Pig: Spherical utility pig made of rubber or urethane .  The sphere may be solid, or hollow, filled with air or liquid. The most common use of sphere pigs is an a batching pig.  Click here to learn more about our Sphere pigs.

Trap: Pipeline facility for launching and receiving tools and pigs.

Utility Pig: Pig that performs relatively-simple mechanical functions, such as cleaning the pipeline.

Wrinkles:  Ripples that occur on the inner radius of a pipe when the pipe is cold bent.


A special thanks to PPSA (Pigging Products & Services Association) for providing the above terms and definitions.  For more information about PPSA visit www.ppsa-online.com.