Applied Magnetic Field. The strength of the magnetization field that is produced in a pipe wall by a magnetizing system in an in-line inspection tool.
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.
Camera Pig. A configuration pig that carries a video or film camera and light sources for photographing the inside surface of a pipeline on an intermittent or continuous basis.
Cathodic Protection. A technique to protect steel pipelines against the various forms of corrosion to which they are susceptible. Most pipelines are coated externally to offer protection against the natural corrosive qualities of the soil in which they are buried. Most also have some sort of cathodic protection to prevent corrosion – using either sacrificial anodes or impressed current anodes. Regulations regarding cathodic protection are found for Gas pipelines in 49 CFR 192.463, and for Hazardous Liquid pipelines in 49 CFR 195.563.
Characterization. The process of quantifying the size, shape, orientation, and location of an anomaly, defect, or critical defect after it has been detected. There are many degrees to which characterization can be successful. For example, one type of characterization of a mechanical-damage defect may be to determine whether the defect contains a cold worked region (severe) or not (less severe).
Class Location. A criterion for pipeline design set by the Code of Federal Regulations. Class 1 is rural and Class 4 is heavily populated. A class location is based on the number and type of buildings situated in an area that extends 220 yards on either side of the centerline of any continuous 1-mile length of a pipeline.
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.
CLs. Community Liaisons – see PHMSA Community Liaison Services website for more details.
Cold working. Distortion of the grains in the vicinity of a gouge. Cold working often occurs immediately under the visible gouge and can significantly reduce the mechanical properties of a pipe steel.
Compression. (1) The process of increasing the pressure of gas to maintain its flow in a pipeline system. Compressing gas is analogous to pumping liquids, such as water or oil. (2) The process of reducing the amount of data to be stored in an in-line inspection tool.
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.
- General External – Metal loss due to electrochemical, galvanic, microbiological, or other attack 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 in 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 a potential (voltage) difference set up by 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.
- 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.
- 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.
- 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.
Critical Defect. As used in this text, a subset of defect, for which an analysis, such as ASME B31G, would indicate that the pipe is approaching failure at pressures equal to maximum operating pressure or the maximum allowable operating pressure for the pipe.
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 pipeline.
Defect. As used in this text, an anomaly for which an analysis, such as ASME B31G, would indicate that the pipe is approaching failure as the nominal hoop stress approaches the specified minimum yield stress of the pipe material.
Detection. The process of obtaining an inspection signal that is recognized as coming from a defect or anomaly. An in-line inspection tool can detect only those defects that produce signals that are both measurable and recognizable. Not all defects are detectable with all inspection systems.
Excess Flow Valves (EFVs). Devices designed to be installed in natural gas service lines, that automatically shut off the flow of natural gas in a service line when the line is ruptured. See more about EFVs here.
Flux. The (scalar) number of flux lines crossing a unit area at right angles to the unit area. See magnetic flux.
Fusion Bonded Epoxy (FBE). A type of pipeline coating widely used to protect steel pipelines from corrosion. Pipeline coating is used together with cathodic protection to prevent corrosion on most steel pipelines. Regulations regarding pipeline coatings are found for Gas pipelines in 49 CFR 192.461, and for Hazardous Liquid pipelines in 49 CFR 195.557.
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 pipeline.
Hard Spots. Local changes in hardness of the steel in the pipe resulting from nonuniform quenching procedures during the 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 as 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.
Identification. The process of differentiating a signal caused by one type of defect from signals caused by other types of defects or pipeline features. Identification is particularly important for mechanical damage defects because their signals are so small that they can be mistaken as due to benign conditions. Mechanical-damage signals are also small compared to signals from metal loss and features such as valves.
Incident. An event that is reported to U.S. Department of Transportation Office of Pipeline Safety that involves fatalities, injuries, property damage in excess of $50,000, unintentional release of natural gas, customer outages, or other conditions that, in the opinion of the pipeline operator, are significant enough that they should be reported.
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.
Indication. (1) Any measured signal or response from an inspection of a pipe above the normal baseline signal. (2) Measurements made during monitoring of cathodic protection systems.
Inspection. (1) The process of examining a pipe using a destructive or nondestructive testing technique to look for anomalies or to evaluate the nature or severity of an indication. (2) The process of running a configuration tool or an in-line inspection tool through a pipe to detect anomalies.
In-Line Inspection Tool (ILI Tool). The device or vehicle, also known as an intelligent or smart pig, that uses a nondestructive testing technique to inspect the wall of a pipe. An in-line inspection tool is one type of instrumented tool.
Intelligent Tool. See in-line inspection tool.
Instrumented Tool or Pig. A vehicle or device used for internal inspections of a pipe, which contains sensors, electronics, and recording or output functions integral to the system. Instrumented tools are divided into two types: (a) configuration pigs, which measure the pipeline geometry or the conditions of the inside surface of the pipe, and (b) in-line inspection tools that use nondestructive testing techniques to inspect the wall of the pipe for corrosion, cracks, or other types of anomalies.
Karst. Landscapes in which surface and groundwater flow occurs over and through soluble rocks with minimal filtration, such as limestone, resulting in changes over time that alter the bedrock and aquifer characteristics, and which can result in caves, caverns, sinkholes, and other irregular formations. The Virginia Cave Board has put together a useful FAQ on karst which can be downloaded here.
Launcher. A pipeline facility used for inserting a pig into a pressurized pipeline.
Magnetic Flux Leakage. An inspection technique in which a magnetic field is applied to a pipe section and measurements are taken of the magnetic flux density at the pipe surface. Changes in measured flux density indicate the presence of a possible defect. Also called MFL.
Mapping Pig. A configuration pig that uses inertial sensing or some other technology to collect data that can be analyzed to produce an elevation and plan view of the pipeline route.
Maximum Operating Pressure (MOP). The maximum internal pressure expected during the operation of a pipeline, which cannot normally exceed the maximum allowable operating pressure.
Measurable. Producing an inspection signal that is above the noise level inherently present in the pipe.
Mechanical Distortion. Changes in wall thickness or changes in the cylindrical shape of a pipe. A gouge, because it includes cold working, residual stresses, plastic strains, and moved or removed metal, contains both mechanical and magnetic distortion.
MFL. An inspection technique in which a magnetic field is applied to a pipe section and measurements are taken of the magnetic flux density at the pipe surface. Changes in measured flux density indicate the presence of a possible defect. Also called magnetic flux leakage.
Monitoring. Measurements or periodic inspections made at selected locations along the pipeline.
Nondestructive Testing Method (NDT Method). A particular method of nondestructive testing, such as radiography, ultrasonics, magnetic testing, liquid penetrants, visual, leak testing, eddy current, and acoustic emission.
Nondestructive Testing Technique (NDT Technique). A specific way of utilizing a particular nondestructive testing method that distinguishes it from other ways of applying the same nondestructive testing method. For example, magnetic testing is a nondestructive testing method while magnetic flux leakage and magnetic particle inspection are nondestructive testing techniques. Similarly ultrasonics is a nondestructive testing method, while contact shear-wave ultrasonics and contact compression-wave ultrasonics are nondestructive testing techniques.
Obstructions. Any restriction or foreign object that reduces or modifies the cross section of the pipe to the extent that gas 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. (See
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. All pigs in this report are either utility pigs or instrumented tools.
Pipeline. That portion of the pipeline system between the compressor stations including the pipe, protective coatings, cathodic protection system, field connections, valves and other appurtenances attached or connected to the pipe.
Pipeline Component. A feature, such as a valve, cathodic protection connection or tee that is a normal part of the pipeline. The component may produce an indication that is recorded as part of an inspection by an in-line inspection tool or configuration pig.
Pipeline System. All portions of the physical facilities through which gas moves during transportation including pipe, valves, and other appurtenances attached to the pipe, such as compressor units, metering stations, regulator stations, delivery stations, holders and other fabricated assemblies. (See 49 Code of Federal Regulations 192)
Pole Spacing. The distance between pole pieces of a magnetizing assembly.
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 centerline of the pipe.
Receiver. A pipeline facility used for removing a pig from a pressurized pipeline.
Remanent Magnetization. The magnetization level left in a steel pipe after the passage of a magnetic in-line inspection tool.
Rerounding. The process of changing the dent depth and shape by internal pressure in the pipe. Generally, dents due to third-party contact will reround, while dents due to rocks will not unless the rock causing the dent is removed.
Residual Stresses. Elastic stresses that were not present within the pipe wall before mechanical damage but that are present after the damage has occurred.
Scabs. See slivers .
SCC. Stress-corrosion cracking. Environmentally assisted cracking that can result when the combined action of stress, an electrochemical cracking environment, and temperature causes cracks to initiate and grow in a susceptible line-pipe steel.
Shielded Corrosion. corrosion between the pipe and the protective coating, which is not controlled by cathodic protection currents.
Sizing. See characterization.
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.
Smart Pig. See in-line inspection tool.
Specified Minimum Yield Strength or Stress (SMYS). A required strength level that the measured yield stress of a pipe material must exceed, which is a function of pipe grade. The measured yield stress is the tensile stress required to produce a total elongation of 0.5 percent of a gage length as determine by an extensometer during a tensile test.
Stress-Corrosion Cracking. Environmentally assisted cracking that can result when the combined action of stress, an electrochemical cracking environment, and temperature causes cracks to initiate and grow in a susceptible line-pipe steel. Also called SCC.
Survey. Measurements, inspections, or observations intended to discover and identify events or conditions that indicate a departure from normal operation of the pipeline.
Testing. See hydrostatic retesting.
Transmission Line. A pipeline, other than a gathering or distribution line, that transports gas from a gathering or storage facility to a distribution center or storage operates at a hoop stress of 20 percent or more of the specified minimum yield stress of the pipe, or transports gas within a storage field. (See 49 Code of Federal Regulations 192)
Trap. pipeline facility for launching and receiving tools and pigs.
Yield Pressure. The pressure at which the nominal hoop stress in the wall of a pipe equals the specified minimum yield stress of the pipe grade.