Pigging Terminology, Abbreviations and Formulae

The following material is reproduced from the PPSA publication "An Introduction to Pipeline Pigging", and contains the following sections:

Definitions and Terminology
Abbreviations and acronyms
Descriptions of pipeline imperfections and conditions
Some useful conversion factors

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.

Bellhole

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 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:

(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.

Launcher

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

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.

Pig

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. 

Receiver

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

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.

Trap

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.

Buckle

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

Corrosion

(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 cathode.

(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 corrosion products.

(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 environment.

Cracks

(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.

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 point 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.

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 changes 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 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. 

Inclusions

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.

Lamination

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).

Obstructions

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.

Ovality

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

Porosity

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.

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.

Wrinkles

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

Some useful conversion factors

Length

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

Volume

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)

Velocity

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

Mass

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

Pressure

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

Miscellaneous conversions

1 Newton	= 0.225 lbs
1 lb	= 4.448 Newtons

Useful formulae

Flow in a pipeline:	m/sec = (brl/day) / 275d2
	ft/sec = (brl/d) / 83.82d2
	where d = inside diameter of pipe in inches