Pipeline Pigging: Pig Types, Launchers, Receivers and Inline Inspection

Quick Answer

Pigging is the practice of sending a device through a pipeline, driven by the product flow, to clean it, separate batches, dewater it after hydrotest, or inspect it from the inside. Utility pigs do the mechanical work: foam pigs for light cleaning and drying, mandrel pigs with discs and cups for aggressive scraping and liquid removal, and spheres for continuous condensate control in wet gas lines. Gel pigs are viscous chemical slugs used alone or between mechanical pigs to carry debris and wet the pipe wall. Smart pigs — inline inspection tools — measure the pipeline: MFL (magnetic flux leakage) finds metal loss from corrosion, UT (ultrasonic) measures wall thickness directly and finds cracks, EMAT detects stress corrosion cracking and coating disbondment, and caliper/geometry tools find dents and ovality. A pipeline is only piggable if it was built that way: minimum 1.5D bends (3D for most ILI tools), full-bore valves with no obstruction in the through path, barred tees at every branch above one-third of the run diameter, no diameter changes without engineered transition, and launchers and receivers at both ends sized to the longest tool. Retrofitting piggability into an existing non-piggable line costs many times what building it in would have cost.

A 180 km crude gathering line in West Africa was built without pig traps. The decision was taken at FEED to save approximately 400,000 USD on two launcher and receiver stations and the associated valves.

Six years later the line's throughput had dropped 22%. Nobody could say why with any confidence: wax deposition was the suspicion, but the line had never been pigged and there was no inspection data. More urgently, the regulator required integrity verification, and the line had no means of inline inspection.

The remediation — hot tapping and installing temporary launcher and receiver facilities, replacing nine non-full-bore valves, cutting out and replacing eleven unbarred tees, and modifying four mitred bends — came to just over 3.1 million USD plus a 40-day partial shutdown. Before any pig had run.

Piggability is a design decision that cannot be deferred. Pipelines that cannot be pigged cannot be cleaned, cannot be inspected, and cannot be shown to a regulator as fit for service.

Why Pipelines Are Pigged

Commissioning and pre-commissioning. New pipelines carry construction debris — weld slag, electrode stubs, sand, offcuts, occasionally tools. Gauge plate pigs confirm there are no obstructions or excessive ovality before product is admitted. After hydrostatic testing, water must be removed; mandrel pigs with cups push the bulk out and foam pigs and dry-air or nitrogen swabbing bring the dew point down to specification.

Liquid removal from gas lines. Wet gas lines accumulate condensate and water in low points. The liquid reduces effective flow area and increases pressure drop, and water in low points is where internal corrosion concentrates. Regular pigging restores capacity and moves the water to a point where it can be removed and treated.

Wax and asphaltene control in crude lines. Paraffinic crude deposits wax on the pipe wall as temperature falls below the wax appearance temperature. Deposits of a few millimetres measurably reduce throughput; left long enough they can block the line entirely. Regular mechanical pigging keeps the wall clean. A line that has been allowed to accumulate heavy wax cannot simply be pigged aggressively — the pig collects a wax plug ahead of itself, stalls, and becomes a stuck pig, which is a far worse problem.

Scale and corrosion product removal. Iron sulphide, iron carbonate and mineral scale reduce flow area and shield the wall from corrosion inhibitor. Pigging removes the deposit so inhibitor reaches the metal.

Inhibitor and biocide distribution. A pig train carrying a batch of corrosion inhibitor between two pigs films the entire internal circumference, including the top of the line where a flowing liquid inhibitor would never reach.

Product batching. In multiproduct lines — gasoline, diesel, jet fuel — pigs separate batches and reduce the interface volume that must be downgraded.

Inline inspection. Smart pigs are the primary means of assessing pipeline integrity without excavation.

Dewatering and drying before return to service after maintenance or hydrotest.

Utility Pigs

Foam pigs

Open-cell or closed-cell polyurethane foam, usually bullet-shaped, with a polyurethane-coated rear base and optional wear-resistant coatings or wire brushes.

• Highly compressible — can pass through reduced-bore valves, short-radius bends and some diameter changes
• Light, inexpensive, disposable
• Densities from about 30 kg/m³ (very soft, for swabbing and drying) up to about 160 kg/m³ (medium-density, for scraping)
• Coating patterns: plain, criss-cross, spiral wrap, silicon carbide coated for abrasive cleaning, wire brush for scale
• Cannot be fitted with instrumentation and cannot be located if lost
• Typical uses: drying after hydrotest, light cleaning, first run in a line of unknown condition, lines with questionable geometry

Foam pigs are the right first choice in a line nobody is sure about. If something is wrong with the geometry, a foam pig is far more likely to pass through, or to disintegrate harmlessly, than a mandrel pig is.

Mandrel pigs

A steel body (mandrel) with replaceable polyurethane discs, cups, or both, plus optional brushes, blades and magnets.

Discs — flat polyurethane plates. Good sealing, good guidance, good scraping action.

Cups — cup-shaped seals that use differential pressure to seal tighter. Best for liquid displacement and dewatering.

Combination disc and cup — the general-purpose cleaning configuration.

Brushes — spring-loaded wire brushes for scale and hard deposits.

Scraper blades — hardened steel for heavy deposit removal.

Magnets — collect ferrous debris, particularly valuable in commissioning runs.

Bypass ports — allow a controlled fraction of flow through the pig, which jets debris forward and prevents a solid plug building ahead of the pig. Essential for wax removal.

Mandrel pigs are rebuildable, can be fitted with transmitters for tracking, and can be configured in progressively more aggressive stages across a cleaning campaign.

Spheres

Elastomer or polyurethane balls, sometimes inflatable with liquid to adjust diameter.

• Negotiate bends and tees in any orientation
• Can pass through full-bore ball valves and some tee configurations
• Used for continuous condensate control in wet gas lines, and for batch separation
• Lower sealing efficiency than cups
• Sphere tee arrangements allow launching without a conventional trap in some designs

Gel pigs

Viscous crosslinked polymer gels pumped as a slug, usually between two mechanical pigs.

• Debris-carrying gel suspends and carries solids out of the line
• Dewatering gel picks up residual water after mechanical dewatering
• Separation gel isolates incompatible fluids
• Hydrotest gel used in dewatering and drying sequences
• Pass through anything a liquid can pass through, including non-piggable features
• Cannot get stuck in the conventional sense
• Degrade or are broken on arrival and handled as liquid

Gel pigs are particularly valuable in lines with questionable piggability, in short-radius bends, and in cleaning campaigns where a mechanical pig alone would build a plug.

Gauge plate pigs

A mandrel pig fitted with a thin aluminium or mild-steel disc, typically 95% of the nominal internal diameter. On arrival, the condition of the gauge plate reveals whether the line has restrictions: an undamaged plate confirms the bore; a bent or notched plate records a restriction and its approximate severity.

Standard practice on every new pipeline before admitting product, and before any ILI run — an ILI tool is far more expensive to lose than a gauge plate.

Smart Pigs (Inline Inspection Tools)

MFL — Magnetic Flux Leakage

Powerful permanent magnets saturate the pipe wall with magnetic flux. Where metal is missing, flux leaks out of the wall and is detected by sensors between the poles.

• Detects: general and pitting corrosion, metal loss, gouges, mill defects, some weld anomalies
• Resolution: standard, high and extra-high resolution tools available; modern high-resolution tools detect metal loss from about 5-10% of wall thickness
• Strengths: works in gas and liquid, tolerant of debris and wall coating, well-proven, relatively inexpensive, no couplant needed
• Limitations: poor at detecting axially oriented cracks (flux runs along the crack rather than across it), reduced sensitivity in thick wall, cannot distinguish internal from external metal loss without additional sensors
• Variants: axial MFL (standard), circumferential/transverse MFL (better for axial defects and long seam anomalies), spiral MFL
• The workhorse of pipeline inspection — the large majority of ILI runs worldwide are MFL

UT — Ultrasonic

Piezoelectric transducers send pulses into the wall and measure echo timing.

• UT wall measurement (UTWM): measures remaining wall thickness directly, with very high accuracy — typically ±0.3 mm
• UT crack detection (UTCD): angled shear-wave probes detect planar, crack-like defects
• Strengths: direct quantitative wall thickness, clearly distinguishes internal from external defects, excellent accuracy, detects cracks and laminations
• Limitations: needs a liquid couplant, so UT tools generally cannot run in dry gas lines without a liquid batch. Sensitive to internal debris, wax and loose scale — the line must be thoroughly cleaned first. More expensive than MFL.

EMAT — Electromagnetic Acoustic Transducer

Generates ultrasonic guided waves electromagnetically in the pipe wall itself, with no couplant required.

• Detects: stress corrosion cracking (SCC), long seam weld cracking, coating disbondment
• Strengths: works in dry gas without couplant, the principal tool for SCC threat assessment
• Limitations: less mature than MFL and UT, more complex interpretation, lower resolution for simple metal loss

Caliper and geometry tools

Mechanical arms or electromagnetic sensors measuring internal geometry.

• Detects: dents, ovality, wrinkles, buckles, bore restrictions, bend radii, and in combined tools, mapping of the pipeline route
• Often the first intelligent run on an older line, because it confirms that larger and less flexible tools can pass safely
• Frequently combined with an inertial measurement unit (IMU) for route mapping and detection of ground movement over successive runs

Combination tools

Modern campaigns commonly run combined MFL plus caliper plus IMU in a single tool, so metal loss, geometry and position data are inherently aligned. This matters for assessing dents with associated metal loss, which are far more severe than either feature alone.

Launchers and Receivers (Pig Traps)

A launcher is a pressure vessel offset from the pipeline that allows a pig to be loaded and introduced into the flowing line without shutting the line down.

Components

• Barrel — usually one nominal size larger than the pipeline, so the pig can be inserted and the kicker flow can get behind it
• Closure — a quick-opening end closure, usually a clamp or bayonet type, with a safety interlock that prevents opening under pressure
• Reducer — a long-radius eccentric reducer from barrel to nominal bore, with the flat side on the bottom so the pig does not step down
• Kicker line — enters the barrel near the closure end and provides the flow that pushes the pig out of the barrel into the main line
• Main line valve — full-bore, usually a through-conduit ball valve
• Kicker valve and bypass valve
• Pressure gauge, vent and drain connections
• Pig signaller — mechanical or electronic, confirms passage
• Pressure-relief or equalisation connections
• Trap support — barrel sloped slightly toward the closure in launchers and toward the receiving end in receivers, so liquids drain predictably
• Pig stop / holding device in receivers, to prevent the pig travelling into the closure at speed

Barrel length

Barrel length must accommodate the longest tool to be run, plus the kicker position, plus handling allowance. Utility pigs need relatively little: typically 2.5 to 4 times the diameter plus the pig length. ILI tools are the governing case — multi-module MFL and UT trains can be 3 to 6 metres long, and combined tools longer still. A launcher barrel built for utility pigs only will not accept an inspection tool, which is a common and expensive discovery during an integrity campaign.

Specify barrel length against the longest ILI tool you might ever run, with margin. Steel is cheap at the design stage.

Safety

Pig traps are pressure vessels with an opening designed to be opened by hand. Every documented pig trap fatality involves opening a closure on a pressurised barrel. Mandatory features:

• Pressure-indicating device visible from the closure operating position
• Safety interlock preventing closure operation while the barrel holds pressure
• Independent vent capable of fully depressurising the barrel
• Drain for liquid removal, routed to a safe location
• Written procedure and permit control for every trap operation
• Trap isolation valves of a type that can be positively confirmed closed

Piggability — Designing a Line That Can Be Pigged

This is the section that gets omitted from pipeline specifications and then costs millions.

1. Bend radius. Minimum 1.5D for utility pigs; 3D for most ILI tools; 5D preferred for long rigid tool trains. Mitred bends are not piggable. Field-cold-bent sections must be checked for actual radius and ovality, not assumed.

2. Valves must be full bore. Reduced-bore ball valves, gate valves with partially closing seats, globe valves, check valves with internal obstructions and butterfly valves are all pig stoppers. Use through-conduit full-bore ball valves on the pig path. Verify the actual bore, not the nominal size — some "full bore" valves have a bore slightly below pipe ID, which can damage a tool's sensors.

3. Barred tees. Any branch connection where the branch diameter exceeds about one-third of the run diameter must have bars (a grille) across the branch opening, so a pig cannot enter or jam in the branch. Bars must be properly designed and welded — a failed bar inside a line becomes a pig trap of the worst kind.

4. No unintended diameter changes. Dual-diameter pigs exist and work, but they must be designed for the specific transition. Wall thickness changes that alter internal diameter — common at road crossings, where heavier wall is used — change the bore and must be accounted for in pig and tool selection.

5. Minimum straight length between features: typically 3 to 5 diameters between bends, and more before and after launchers and receivers, so tools stabilise before entering a feature.

6. Pig signallers at both ends and at intermediate points on long lines, so pig position and arrival are confirmed rather than assumed.

7. Internal weld quality. Internal weld protrusion, backing ring remnants and misalignment at girth welds damage pig seals and tool sensors. Specify internal bead height limits on the welding procedure for piggable lines.

8. Flow velocity window. Utility pigs run best at 1 to 5 m/s. ILI tools have tighter windows — typically 0.5 to 4 m/s for MFL and 0.3 to 2 m/s for UT, because sensor sampling rate limits speed. A gas line running at 10 m/s cannot be inspected without reducing flow or using a speed-control tool with bypass. This constraint must be checked before the campaign is planned, not after the tool arrives.

9. Receiver capacity for debris. The first cleaning run in a line that has never been pigged can deliver a large volume of solids and liquid. Receivers and downstream handling need to be sized for it, and the slug catcher or separator downstream must be able to take it.

Running a Cleaning Campaign

The sequence matters, and getting it wrong creates stuck pigs.

Progressive aggression. Start soft and escalate:

1. Gauge plate pig or soft foam pig — confirm the line is clear
2. Low-density foam pigs — light swabbing, remove loose debris
3. Medium-density foam or disc pigs
4. Disc/cup mandrel pigs with increasing seal interference
5. Brush pigs, then bypass brush pigs
6. Scraper or blade pigs if required
7. Final cleaning run and gauge plate before the ILI tool

Never start with an aggressive pig in a line of unknown condition. An aggressive pig in a waxed or scaled line removes a large volume of deposit, which accumulates ahead of the pig as a growing plug. Driving pressure rises, the pig stalls, and the plug sets. Recovering a stuck pig from a buried pipeline typically means locating it, cutting the line, and a lengthy outage.

Bypass pigs are the protection against this. A bypass pig lets a controlled fraction of flow through itself, which jets forward, fluidises the deposit and carries it ahead in suspension rather than letting it pack. For wax removal, bypass is not optional.

Record everything. Driving pressure, differential across the pig, transit times between signallers, volume and composition of debris received, and the condition of each returned pig. The trend across runs is how you know whether the line is getting cleaner and whether the next step up in aggression is safe.

Common Specification Mistakes

1. Building a pipeline with no launchers and receivers. The West African example: 400,000 USD saved at FEED, 3.1 million USD and a 40-day outage to retrofit.

   Prevention: Include permanent pig traps at both ends of every pipeline that could ever require cleaning or inspection, which in practice means all of them.

2. Launcher barrel sized for utility pigs only. The barrel cannot accept a multi-module ILI tool, and the integrity campaign stops before it starts.

   Prevention: Size barrel length against the longest ILI tool train plausibly needed, with margin — typically 6 m or more of usable barrel for a transmission line.

3. Reduced-bore or non-full-bore valves on the pig path. The pig jams, and recovery means cutting the line.

   Prevention: Specify through-conduit full-bore ball valves on the pig path and verify actual bore against pipe ID on the valve data sheet.

4. Unbarred tees. A pig enters the branch, turns, and jams.

   Prevention: Bar every branch above one-third of run diameter, with a bar design and weld detail that is reviewed and inspected.

5. Mitred bends or bends tighter than 1.5D. Not piggable at all; 1.5D bends block most ILI tools, which need 3D.

   Prevention: Specify 3D minimum bend radius on any line intended for inline inspection, and prohibit mitred bends entirely.

6. Starting a cleaning campaign with an aggressive pig. The pig builds a plug and sticks.

   Prevention: Run the progressive sequence from gauge plate through soft foam to brush and blade, and use bypass pigs for wax.

7. No velocity check before an ILI run. The line runs at 8-10 m/s; the tool needs under 4 m/s; the data is unusable or the tool is damaged.

   Prevention: Confirm the operating velocity against the tool's acceptable window and plan flow reduction or a bypass speed-control tool in advance.

8. Attempting a UT inspection in dry gas. UT tools need liquid couplant.

   Prevention: Use MFL or EMAT in dry gas, or plan a liquid batch — which is a significant operational undertaking requiring its own design.

9. No safety interlock on trap closures. Opening a pressurised barrel is the classic pipeline fatality.

   Prevention: Specify pressure-interlocked closures, visible pressure indication at the operating position, and independent vent and drain.

10. Inadequate downstream handling for the first cleaning run. Decades of debris arrive at once and overwhelm the receiver and separator.

    Prevention: Estimate debris volume, size receiver and downstream handling accordingly, and plan disposal of oily solids and produced water before the run.

Supply from Kasko Makine

Kasko Demir Çelik Makine supplies pigging equipment and the pipeline components around it:

Pigs

• Foam pigs in all densities, plain, criss-cross, spiral, silicon-carbide coated and wire-brush configurations
• Mandrel pigs with disc, cup and combination configurations
• Brush pigs, scraper and blade pigs, magnet pigs
• Bypass pigs with adjustable bypass ports
• Dual-diameter pigs for engineered transitions
• Gauge plate pigs and calibrated gauge plates
• Spheres, solid and inflatable
• Pig transmitters and tracking equipment
• Spare discs, cups, brushes and mandrel components

Launchers and receivers

• Horizontal and vertical pig traps, DN 100 to DN 1200
• Design and fabrication to ASME B31.4 and B31.8 with ASME Section VIII vessel components
• Quick-opening closures with pressure safety interlocks, clamp and bayonet types
• Barrel lengths engineered to specified ILI tool requirements
• Eccentric reducers, kicker and bypass piping, vent and drain assemblies
• Pig signallers, mechanical and electronic, intrusive and non-intrusive
• Pig stops and holding devices
• Trap supports, saddles and skid-mounted assemblies

Associated pipeline supply

• API 5L line pipe, grades B through X80, seamless and welded
• Through-conduit full-bore ball valves for pig paths
• Barred tees, fabricated and forged, with bar design documentation
• 3D and 5D induction bends and elbows
• Flanges, fittings, gaskets and stud bolts
• External coatings: 3LPE, FBE, coal tar enamel
• Insulating joints, closures and field joint coating materials

Engineering support

Send pipeline data — diameter, wall thickness schedule, length, bend radii, valve types, branch connections, product, operating pressure and velocity range — and we will assess piggability, identify the features that would block utility pigs and ILI tools, and specify launcher and receiver sizing including barrel length against your intended inspection tools. For new designs we can review the line list for piggability before the drawings are frozen, which is the cheapest moment to fix it.

Certification

Material certificates to EN 10204 3.1, welding procedure and welder qualifications to ASME Section IX or ISO 15614, hydrostatic test certificates, NDE reports including radiography and ultrasonic examination, PED and ASME U-stamp documentation for traps where specified, and closure interlock function test records.

Logistics

Standard pigs and spares generally ship in 1-3 weeks. Launchers and receivers typically 10-18 weeks depending on size, material and certification. Line pipe and bends vary with grade and quantity. Shipping from Istanbul by road to Europe, the Caucasus and Iraq, and by sea to Gulf, African and Central Asian destinations.

Send your pipeline data and we will return a piggability assessment and trap specification within five working days. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading: Pipeline Series

• API 5L Line Pipe: Grades and Specifications
• Pipeline Coatings: 3LPE, FBE and Field Joints
• Industrial Valves: Complete Guide
• Pipe Fittings: Types and Standards

Frequently Asked Questions

Q: What is pipeline pigging?
A: Pigging is sending a device through a pipeline, driven by the product flow, to clean it, remove liquids, separate product batches, dewater it after hydrotest, or inspect it internally. Utility pigs made of foam or a steel mandrel with polyurethane discs and cups do the mechanical work, while smart pigs carry sensors that measure wall thickness, metal loss, cracking and geometry without excavating the line.

Q: What is the difference between MFL and UT inline inspection?
A: MFL saturates the pipe wall with magnetic flux and detects leakage where metal is missing, so it finds corrosion and metal loss, works in gas and liquid lines, and tolerates some debris. UT uses ultrasound to measure remaining wall thickness directly to around ±0.3 mm and detects cracks and laminations, but it needs a liquid couplant so it generally cannot run in dry gas, and it requires a thoroughly cleaned line.

Q: What bend radius does a pipeline need to be piggable?
A: Utility pigs require a minimum 1.5D bend radius, but most inline inspection tools need 3D, and long rigid tool trains are better served by 5D. Mitred bends are not piggable at all. Since inline inspection is usually a regulatory requirement eventually, specifying 3D minimum on any new pipeline is the safe choice.

Q: What is a barred tee and why is it needed?
A: A barred tee has a grille of bars welded across the branch opening so a pig travelling along the run cannot enter or jam in the branch. Bars are required wherever the branch diameter exceeds roughly one-third of the run diameter. Without them, a pig can turn into the branch and become stuck, which usually means cutting the pipeline to recover it.

Q: How long should a pig launcher barrel be?
A: Barrel length must accommodate the longest tool to be run, plus the kicker connection position and handling allowance. Utility pigs need only a few diameters of length, but multi-module MFL and UT inspection tools are commonly 3 to 6 metres long and combined tools longer, so a transmission line launcher usually needs 6 metres or more of usable barrel. Barrels sized for utility pigs alone cannot accept inspection tools.

Q: Why do pigs get stuck in pipelines?
A: The usual cause is running too aggressive a pig in a line with heavy wax or scale: the pig scrapes off more deposit than the flow can carry, the material packs into a plug ahead of the pig, driving pressure rises and the pig stalls. Other causes are reduced-bore valves, unbarred tees, bends tighter than the pig can negotiate and unexpected diameter changes. Starting with soft foam pigs and using bypass pigs prevents most of it.

Q: Can a pipeline be made piggable after it is built?
A: Yes, but at very high cost. Retrofitting usually means installing launcher and receiver facilities, replacing non-full-bore valves, cutting out and replacing unbarred tees and modifying bends tighter than the required radius, all with hot tapping or extended shutdowns. The work commonly costs several times what building piggability in at design stage would have cost, so the decision should never be deferred.