Pigging Terminology, Abbreviations and Formulae
The following material is reproduced from the PPSA publication
"An Introduction to Pipeline Pigging"
contains the following sections:
Definitions and Terminology
- Batching pig
- 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 configurations of batching pigs
are cup pigs and sphere pigs.
- An excavation in a local area to permit a survey, inspection,
maintenance, repair, or replacement of pipe section.
- 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 or 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.
- 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.
- 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.
- Gel pig
- A utility pig that is composed of 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 angle, and occasionally indications
of significant internal corrosion, by making measurements of the inside surface
of the pipe.
- 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 or 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
- 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:
(1) configuration pigs, which measure the pipeline geometry
or the conditions of the inside surface of the pipe; and
(2) 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.
- A pipeline facility used for inserting a pig into a
- Mapping pig
- A configuration pig that uses inertial sensing or some other
technology to collect the data that can be analysed to produce an elevation and
plan view of the pipeline route.
- Metal loss
- Any of a number of types of anomalies in pipe in which metal
has been removed from the pipe surface, usually due to corrosion or gouging.
- On-line inspection
- see In-line inspection.
- A generic term signifying any independent, self-contained
device, tool, or vehicle, that moves through the interior of the pipeline for
purposes of inspecting, dimensioning, or cleaning.
- A pipeline facility used for removing a pig from a pressurized
- Smart pig
- see In-line inspection tool.
- 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 as a batching pig.
- Pipeline facility for launching and receiving tools and pigs.
- Utility pig
- Pig that performs relatively-simple mechanical functions,
such as cleaning the pipeline.
Abbreviations and acronyms
|AGA ||American Gas Association|
|API ||American Petroleum Institute|
|ASME ||American Society of Mechanical Engineers|
|BS ||British Standard|
|DICA ||Direction Des Carburants (France)|
|DIN ||German Standards|
|DNV ||Det Norske Veritas (Norway)|
|GRI ||Gas Research Institute (US)|
|ILI ||In-line inspection|
|ISO ||International Standards Organization|
|IP ||Institute of Petroleum (UK)|
|MAOP ||Maximum allowable operating pressure|
|MFL ||Magnetic-flux leakage|
|NACE ||National Association of Corrosion Engineers (US)|
|NDE ||Non-destructive evaluation|
|NDT ||Non-destructive testing|
|NPD ||Norwegian Petroleum Directorate|
|OPS ||Office of Pipeline Safety, a division
of the US Department of Transportation (DOT)|
|SMYS ||Specified minimum yield stress|
|TUV ||Technischer Uberwachungs Verein (Germany)|
|UT ||Ultrasonic testing|
Descriptions of pipeline imperfections and conditions
The following are descriptions
of imperfections anomalies, defects, and conditions that are found in natural
gas transmission pipelines. The definitions have been obtained from different
technical references and dictionaries, but have been selected as relating to
pipelines. The descriptions are intended to be generic, but may apply to other
structures and materials. The ultimate goal is to provide a common language
within the pipeline-pigging industry, world-wide.
- A partial collapse of the pipe due to excessive bending
associated with soil instability, landslides, washouts, frost heaves,
- (a) general external: metal loss due to electrochemical,
galvanic, microbiological, or other attack on the pipe due to environmental
conditions surrounding the pipe.
(b) 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 local cells, but this condition is less frequent.
(c) pit: local concentrated cell corrosion on the external or
internal surfaces that results from the generation of a potential (voltage)
difference set up 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
(d) 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
(e) 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
- (a) 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.
(b) girth weld: cracks in the weld or weld zone of the butt
weld that connect sections of pipe.
(c) seam weld: cracks in the weld or weld zone of the
longitudinal seam weld of the pipe.
- 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 point of the dent and a prolongation of the original contour
of the pipe.
- 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.
- 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.
- 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 changes in
chemistry of the steel. Hard spots, when stressed, are subject to failure from
mechanisms such as hydrogen-stress cracking.
- Discontinuities in a coating, such a pinholes cracks, gaps,
or other flaws, that allow areas of the base metal to be exposed to any
corrosive environment that contacts the coating surface.
- Foreign material or particles in a metal matrix. These are
usually compounds, such as oxides, sulphides, or silicates, but may be any
substance that is foreign to the matrix, whether it is soluble or insoluble.
- 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.
- Lack of penetration
- In the welding process, failure to achieve fusion of the base
metal to the desired or planned depth.
- A type of imperfection or discontinuity with separation or
weakness, usually aligned parallel to the worked surface of a metal.
- Mechanical damage
- Damage from outside forces that modifies the dimensions or
profile of the pipe (dents, gouges).
- Any restriction or foreign object that reduces or modifies
the cross section of the pipe 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.
- A condition in which a circular pipe forms into an ellipse,
usually as the result of external forces.
- Small voids or pores, usually gas filled, in the weld metal.
- Radius bends
- The radius of the 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.
- 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
- Ripples that occur on the inner radius of a pipe when the
pipe is cold bent.
Some useful conversion factors
|1in ||= 25.40 mm|
| ||= 2.540 cm|
| ||= 0.0254 m|
|1ft ||= 304.80 mm|
| ||= 30.480 cm|
| ||= 0.3048 m|
|1 mile ||= 1.6094 km|
|1mm ||= 0.0394 in|
|1cm ||= 0.3937 in|
|1m ||= 39.370 in|
| ||= 3.2808 ft|
| ||= 0.6214 miles|
|1 barrel ||= 42 US gallons (liquid)|
| ||= 34.9909 Imperial gallons|
| ||= 5.6146 cu ft|
| ||= 158.9871 li|
| ||= 0.1590 cu m|
|1 US gallon (liquid) ||= 0.0238 barrel|
| ||= 0.1337 cu ft|
| ||= 0.00379 cu m|
| ||= 3.7854 li|
|1 US gallon (liquid) ||= 0.0038 cu m|
| ||= 0.8327 Imperial gallons|
|1 Imperial gallon ||= 0.0286 barrel|
| ||= 0.1605 cu ft|
| ||= 277.4171 cu in|
| ||= 4.5460 li|
| ||= 0.0045 cu m|
| ||= 1.2009 US gallons (liquid)|
|1 li ||= 0.001 cu m|
| ||= 1000.0000 cu cm|
| ||= 0.2200 Imperial gallons|
| ||= 0.2642 US gallons (liquid)|
|1 mile/hour (mph) ||= 0.0167 miles/min|
| ||= 0.0003 miles/sec|
| ||= 88.000 ft/min|
| ||= 1.4667 ft/sec (fps)|
| ||= 1.6094 kilometres/hour (kph)|
| ||= 26.8225 m/min|
| ||= 0.4470 m/sec|
|1 kilometre/hour (kph) ||= 0.01667 kilometres/minute|
| ||= 0.0003 kilometres/sec|
| ||= 16.6667 m/min|
| ||= 0.2778 m/sec|
| ||= 0.6214 mph|
| ||= 54.6800 ft/min|
| ||= 0.9113 ft/sec|
|1 ft/sec ||= 0.6818 mph|
| ||= 1.0973 kph|
| ||= 0.3048 m/sec|
|1 m/sec ||= 3.6000 kph|
| ||= 2.2369 mph|
| ||= 3.2808 ft/sec|
|1 pound (lb) ||= 0.4536 kg|
|1 kg ||= 2.2046 lb|
Weight of water @ 62°F/16.67°C
|1 barrel ||= 349.9860 lbs|
| ||= 158.7512 kg|
|1 US gallon ||= 8.337 lbs|
| ||= 3.7820 kg|
|1 Imperial gallon ||= 10.0122 lbs|
| ||= 4.5420 kg|
Approx weight of carbon steel
|1 cu in ||= 0.283 lbs|
| ||= 0.128 kg|
|1 cu ft ||= 489.0 lbs|
| ||= 221.8 kg|
|1 cu cm ||= 0.008 kg|
| ||= 0.017 lbs|
|1 cu m ||= 7810 kg|
| ||= 17300 lbs|
|1 ft head water @ 60°F ||= 0.4335 pounds/square inch (psi)|
| ||=0.0305 kilogrammes/square centimetre|
| ||= 0.0299 bars|
| ||= 0.3048 m of water|
|1 m of water ||= 0.1000 kg/sq cm|
| ||= 0.0967 bars|
| ||= 3.2808 ft of water|
|1 psi ||= 0.0689 bars|
|1 bar ||= 14.5039 psi|
|1 Newton ||= 0.225 lbs|
|1 lb ||= 4.448 Newtons|
|Flow in a pipeline: ||m/sec = (brl/day) / 275d2|
| ||ft/sec = (brl/d) / 83.82d2|
| ||where d = inside diameter of pipe in