Types of Pipeline Pigs Explained: The Complete Guide

1. The Two Main Categories of Pipeline Pigs

Pipeline pigs divide into two fundamental categories based on their purpose:

Utility pigs perform physical work inside the pipeline — cleaning, removing liquid, separating products, or checking bore dimensions. They are the most commonly used pig type in day-to- day pipeline operations across Australia.

Inspection pigs collect data about the internal condition of the pipeline — recording wall thickness, detecting corrosion and metal loss, identifying cracks, dents, and deformations. They are used as part of formal Pipeline Integrity Management Programs (PIMPs) and are typically run less frequently than utility pigs.

★ Royal Poly Products manufactures

Royal Poly Products manufactures the full range of utility pigs — foam pigs, disc pigs, cup pigs, solid cast pigs, dual diameter pigs, and pipeline gels — from its facility in Jandakot, Western Australia. The company also provides inline inspection services using third-party ILI
tools.

2. Foam Pigs

Because foam pigs are flexible, they can be slightly oversized relative to the pipe bore (typically 5–10% oversize) to ensure a good contact seal without generating excessive differential
pressure. This makes them ideal for pipelines that are not "fully piggable" in the traditional sense.

Foam pig density

Foam pigs are available in four standard densities, each suited to different operational requirements:

• Low density (16–32 kg/m³) — line proving, drying, light liquid removal after dewatering

• Intermediate density (40–56 kg/m³) — light cleaning, batching, dewatering operations

• Medium density (80–96 kg/m³) — general cleaning, debris and silt removal

• High density (128–160 kg/m³) — heavy scale, wax, and corrosion product removal

Foam pig coatings

In addition to density, the performance of a foam pig is significantly affected by its coating.

Royal Poly Products manufactures foam pigs in the following coating configurations:

• Bare foam (BR Series) — uncoated open-cell foam, ideal for initial line proving runs and drying passes

• Criss-cross coated (XX Series) — polyurethane applied in a spiral criss-cross pattern, creating a continuous wiping action ideal for general cleaning and water removal

• Fully coated (FC Series) — a uniform polyurethane shell over the entire body, providing improved liquid sealing and extended pig life in abrasive conditions

• Silicon carbide coated (SC Series) — an abrasive grit coating bonded to the foam body for aggressive scale, rust, and corrosion product removal

• Nylon wire brush (NW Series) — nylon wire filaments embedded in the foam surface for light mechanical cleaning without risk of sparking or pipeline damage

• Carbon steel wire brush (CW Series) — aggressive steel wire brushes for heavy mechanical cleaning of scale and hard deposits

• Stainless steel wire brush (SW Series) — used where contamination risk from carbon steel is unacceptable, such as potable water and food-grade pipelines

★ Key advantage of foam pigs

Foam pigs can pass through pipelines that are not fully piggable — including pipelines with non-full-bore valves, tight bends, weld intrusions, and gradual diameter changes. This makes them the first choice for new pipeline commissioning and for pipelines where the piggability has not been verified.

3. Disc Pigs (Bi-directional Pigs)

Disc pigs — also called bi-directional pigs or mandrel pigs — consist of a central steel mandrel body fitted with multiple polyurethane sealing discs. Unlike foam pigs, disc pigs generate a positive seal against the pipe wall using rigid disc contact rather than foam compression. This gives them superior liquid removal and product separation capability.

The term 'bi-directional' refers to the pig's ability to operate effectively in both directions of pipeline flow — making them particularly useful in pipelines where a dedicated pig launcher and receiver at opposite ends are not available.

Types of disc pigs

• Swabbing pigs (2-4 configuration) — two sealing discs and four support discs, used for liquid removal and light cleaning

• High seal pigs (2-6 configuration) — two discs and six support elements, providing an enhanced liquid seal for dewatering and product separation

• Long run pigs (4-4 configuration) — four discs and four support elements, designed for extended pipeline runs where disc wear is a concern

Disc gauging pigs

A disc gauging pig combines the sealing body of a standard disc pig with a metal gauge plate mounted at the leading face. As the pig travels through the pipeline, any restriction, weld bead intrusion, or deformation bends the gauge plate.

Inspecting the plate after the run reveals the internal bore condition and confirms the pipeline is clear for further pig runs or inline inspection.

Disc brush pigs

Disc brush pigs add wire brush elements to the standard disc pig body, combining the sealing and driving capability of the disc configuration with mechanical cleaning action. Available in body-mounted brush (brushes attached directly to the mandrel) and ring brush (brush rings between the disc elements) configurations. Wire material options include carbon steel, stainless
steel, and nylon.

★ When to choose a disc pig over a foam pig

Choose a disc pig when you need a positive liquid seal for effective dewatering or product separation, when the pipeline is fully piggable with full-bore valves and correct bend radii, or
when bi-directional operation is required. Choose a foam pig for non-piggable sections, first runs on an unknown pipeline, or when flexibility to negotiate tight bends is required.

4. Cup Pigs

Cup pigs are mechanical pigs that use a steel mandrel body fitted with polyurethane cup seals rather than flat discs. The cup shape — open at the rear and solid at the leading face — creates an extremely effective hydraulic seal against the pipe wall, generating high differential pressure across the pig for maximum driving force and liquid removal capability.

Cup pigs are used extensively in gas transmission pipelines and long-distance water mains where high differential pressure and effective liquid sealing are critical. The cup configuration is particularly effective in larger diameter pipelines (8" and above) where disc pigs may not provide
sufficient seal area.

Cup pig configurations

• 3-cup pig — three cup seals for general cleaning and liquid removal

• 4-cup pig — four cup seals for enhanced sealing in larger bore pipelines

• 2-cup with 2 support discs — combined cup sealing with disc support for longer runs

• 2-cup with wire brushes — cup sealing combined with mechanical brush cleaning action (available in carbon steel, stainless steel, and nylon wire)

★ Cup pig note

Cup pigs require a fully piggable pipeline — full-bore valves, correct minimum bend radii, and a consistent internal bore. They are not suitable for pipelines with bore restrictions or non-full- bore valves. Royal Poly Products cup pigs are available in 3-cup and 4-cup configurations from 4" to 24" diameter.

5. Solid Cast Pigs

Solid cast pigs are fully moulded from polyurethane — there is no mandrel or foam core. The entire pig body is cast as a single solid polyurethane unit, typically in a cup or disc configuration.
This makes them exceptionally durable and resistant to damage from aggressive pipeline conditions.

Solid cast pigs are used primarily for product batching and separation in multi-product pipelines,
post-hydrotest dewatering where the pig must withstand high differential pressures, and pipeline commissioning sequences where multiple pig runs are required under varying conditions.

Because the pig is fully cast, it has no components that can separate or be left in the pipeline — a significant safety advantage in critical commissioning operations. The solid construction also means the pig can withstand considerably higher differential pressures than foam or mandrel pigs before deformation.

Solid cast configurations

• 3-cup solid cast — three integral cup seals moulded into the body

• 4-cup solid cast — four integral cup seals for enhanced sealing in larger diameters

• Disc solid cast — flat disc configuration in solid polyurethane for bi-directional operation

6. Dual Diameter Pipeline Pigs

Dual diameter pipeline pigs are purpose-designed for pipelines that change bore diameter along their length. Standard pigs are manufactured to a single diameter and cannot effectively operate in a pipeline that transitions from one bore size to another — they will either lose contact seal in the larger section or become stuck in the smaller section.

Dual diameter pigs solve this by using a configuration that accommodates a specified range of bore diameters within a single pig body. This may be achieved through a specially designed foam pig body that compresses to fit the smaller bore and expands to maintain contact in the larger bore, or through a disc pig configuration with adjustable disc geometry.

These pigs are used in pipeline systems where a single pipeline run passes through sections of different nominal pipe size — common in distribution networks, meter station bypass sections, and offshore pipeline configurations where wall thickness changes result in varying internal
diameters.

★ Royal Poly Products dual diameter range

Royal Poly Products manufactures both dual diameter foam pigs and dual diameter disc pigs, custom designed to match the specific bore range of the client's pipeline. This capability — rare among Australian manufacturers — means operators can pig complex pipeline systems
without the cost and logistics of multiple pig types.

7. Gel Pigs

Gel pigs are not solid objects — they are slugs of highly viscous pipeline gel that are pumped into the pipeline between foam pig runs. The gel is a non-Newtonian fluid that behaves as a
solid under low shear stress (holding its shape in the pipeline) but flows freely under the higher shear stress generated by pig contact or pipeline turbulence.

Gel pigs are used in applications where a conventional solid pig cannot effectively remove contaminants — particularly for chemical cleaning, corrosion inhibitor application, and the removal of fine silt, hydrate, and wax deposits that a foam pig would push rather than capture.

Types of pipeline gel

• Cleaning gels — carry and suspend debris particles, transporting them to the pig receiver rather than leaving them redistributed in the pipeline

• Corrosion inhibitor gels — deliver a coating of corrosion inhibitor to the entire pipe bore
surface during a single pig run

• Dewatering gels — used ahead of drying pig runs to capture and remove residual water from low points and dead legs

• Batching gels — used as a separating medium between incompatible products in multi-
product pipelines

★ Gel + foam pig combination

The most effective pre-commissioning cleaning sequences often use gel pigs and foam pigs in combination — a gel slug pumped between two foam pigs suspends and carries debris that the foam pigs dislodge, resulting in a significantly cleaner pipeline than foam pigs alone could achieve. Royal Poly Products supplies both the gel and the foam pigs to execute the full sequence.

8. Gauging Pigs

A gauging pig is a utility pig fitted with a metal gauge plate — a circular aluminium or steel disc with a diameter slightly smaller than the nominal pipe bore (typically 95% of the internal
diameter). As the pig travels through the pipeline, any internal obstruction, weld bead intrusion, buckle, dent, or bore restriction that protrudes into the gauge plate's path will deform or mark
the plate.

After the pig is retrieved, the gauge plate is inspected. An undamaged plate confirms that the pipeline bore is clear to at least the gauge plate diameter — a mandatory check before running more valuable and sophisticated inspection tools. A damaged or deformed plate indicates an
obstruction that must be investigated before the pipeline is commissioned or before an inline inspection pig is run.

Smart Gauge Plate — Royal Poly Products' proprietary technology

Royal Poly Products offers a Smart Gauge Plate service as part of its pipeline services range. The Smart Gauge Plate is an instrumented gauging tool that records contact data electronically during the pig run, allowing the exact location of any bore restriction to be identified from the data download — not just detected from plate inspection after the run.

This significantly reduces the time and cost of identifying and excavating obstructions in new pipeline installations. The Smart Gauge Plate service is available as a standalone service or as part of Royal Poly's full commissioning pigging package.

9. Inline Inspection Pigs (Smart Pigs)

Inline inspection pigs — commonly called smart pigs, intelligent pigs, or ILI tools — are sophisticated electronic instruments that travel through the pipeline recording detailed data about the condition of the pipe wall. Unlike utility pigs, they do not clean or dewater the pipeline — their sole purpose is data collection.

ILI tools are used as part of formal Pipeline Integrity Management Programs required under AS
2885 and similar international standards. They identify and locate corrosion, metal loss, cracks, dents, buckles, and other anomalies that could affect the safe operating life of the pipeline.

ILI tool technologies

• Magnetic Flux Leakage (MFL) — the most common ILI technology. Magnetises the pipe wall and measures flux leakage at areas of metal loss or corrosion. Effective for detecting general corrosion, pitting, and wall thinning.

• Ultrasonic Testing (UT) — uses ultrasonic pulses to measure pipe wall thickness. Provides high-resolution wall thickness maps. Requires a liquid-coupled environment (not suitable for dry gas pipelines without special preparation).

• Caliper / Geometry tools — measure internal bore dimensions, detecting dents, buckles, ovality, and dimensional anomalies. Often run before MFL or UT tools to confirm the
bore is clear.

• Crack Detection tools — specialist tools using electromagnetic acoustic transducers (EMAT) or UT techniques to detect longitudinal and transverse cracks in the pipe wall.

★ Pre-ILI preparation is critical

Before an ILI tool run, the pipeline must be thoroughly cleaned using foam and/or mechanical pigs to remove debris, scale, and internal deposits that would interfere with the tool's sensors. Royal Poly Products routinely supplies foam pig pre-cleaning sequences ahead of ILI campaigns across Australian gas and liquid pipelines.

10. Full Comparison Table

The following table summarises the key characteristics of each pig type to assist with selection:

11. How to Select the Right Pig Type

Selecting the correct pig type for a specific pipeline operation requires consideration of several key factors. Use this quick-reference selection guide as a starting point — always consult with a
pigging specialist for complex or high-risk applications:

The most common mistake in pig selection is choosing a pig that is either too aggressive (risking the pig becoming stuck or damaging the pipeline) or too light (failing to achieve the cleaning or sealing objective). Royal Poly Products provides free technical consultation to help operators select the correct pig for their specific application and pipeline conditions.

★ Free pig selection consultation

Not sure which pig type is right for your pipeline? Contact Royal Poly Products at
royalpolyproducts.com/get-a-quote with your pipeline details — internal diameter, product, pipeline length, operating pressure, valve types, and bend radii — and the technical team will
recommend the correct pig type, density, and coating for your application.