What Are Piggable Pipes and How Do They Work?

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Piggable pipe is pipe which allows a device called "pig" to be sent through the pipe from a launcher to a receiver without getting stuck on the way. Pipeline pigging uses that tool to clean the line, separate products and inspect the pipe wall. Consistency of pipe inner diameter and existence of appropriate bends, full bore valves and fittings are among the factors that enable smooth pigging. The usage of long radius bends and well-designed tees ensures that the pig moves seamlessly with bends and joins along the pipeline. The tool is launched using a launcher and received by a receiver at the end of its trip inside the pipeline. Foam pigs clean the pipeline while intelligent pigs inspect for any defects in the pipes.

What Is Pipeline Pigging and How Does It Work?

Pigging of pipelines refers to the technique of pushing a specific piece of equipment known as a pig along the pipeline in order to clean, maintain, and check the inner surface of the pipeline. The pig travels inside the pipeline using the pressure of the flowing product, which could be oil, gas, water, and others. While doing so, the pig is able to clean any deposits from the pipeline, separate products flowing within the pipeline, remove liquids accumulating inside the pipe, and check that the bore is clear.

A typical pig run sequence

Operators rarely send an inspection tool into a line without preparing it first. A common pattern is shown below. The order and number of runs depend on the operator and the tool vendor.

Step	Pig Run	Purpose
1	Foam pig	Prove the line can pass a pig; remove loose debris
2	Cleaning pig	Remove scale, wax and deposits
3	Gauging pig	Check the bore, dents and ovality against the inspection tool limit
4	Intelligent pig	Record metal loss, cracks and geometry
5	Review and repair	Compare the report with the pipe and fitting records

The logic is simple. Start with the softest, lowest risk tool. Then work up to the instrumented tool, so an expensive inspection pig is never the first thing to meet an obstruction.

Pipeline Pig Types

There are many kinds of pig, but most fall into a handful of groups. The table shows the main pipeline pig types, what each is built for, and the tightest bend each can typically pass.

Pig Type	How it is Built	Main Job	Typical Minimum Bend (Confirm)
Foam pig	Polyurethane foam body, bare or coated, often bi-directional	Cleaning, swabbing, dewatering, drying; a low-risk first run in an unknown line	~1D to 1.5D
Mandrel pig	Steel body with replaceable polyurethane cups, discs or brushes	Cleaning, batching, wax and scale removal	~1.5D
Solid cast pig	One-piece cast polyurethane with cups or discs	Cleaning and batching; durable for long runs	~1.5D
Sphere	Solid or inflatable polyurethane ball	Batching in liquid lines; liquid removal in gas lines	~1.5D
Gauging pig	Standard pig carrying a metal gauge plate	Proves the bore; shows dents and obstructions	~1.5D to 3D
Intelligent pig(Pipeline Inspection Pig)	Instrumented tool: magnetic flux leakage (MFL), ultrasonic (UT), geometry or caliper	Finds metal loss, cracks, dents and ovality	~3D minimum; some rigid tools 5D

Radius figures are typical and differ by tool and vendor. The pig, not the pipe, sets the limit, so always confirm with the tool vendor. In this guide, D means the nominal pipe diameter, so a 3D bend has a centreline radius of three times the diameter.

Pig Launcher and Receiver

A pig launcher is a pressure-rated barrel installed at the beginning of a pipeline section to insert a pig into the line. It typically includes a quick-opening closure, isolation valve, kicker line, and pressure gauge. The pig is loaded into the barrel, the closure is secured, and the barrel is pressurised to introduce the pig into the pipeline using the flowing medium.

A pig receiver is installed at the other end to collect the pig after its journey through the pipeline. Before opening the receiver, operators must isolate it, release the pressure, and drain any remaining fluid. Both systems require adequate working space, lifting access, and a pig signaller to confirm the pig's passage.

Safety note: Pig launching and receiving must follow approved operating procedures and safe-isolation requirements. Never open a launcher or receiver closure while the barrel is pressurised.

Foam pig

A foam pig is the softest and most forgiving pig. Its body is compressible, so it can squeeze through bends, small restrictions and slight bore changes that would stop a rigid tool. That makes it the usual first run in a line of unknown condition. Foam pigs are used for cleaning, swabbing, dewatering and drying, and because they can pass tight spots, they also help show whether a line is likely to be piggable.

Intelligent pig and pipeline inspection pig

An intelligent pig, also called a smart pig, ILI pig or pipeline inspection pig, is an instrumented tool that records the condition of the pipe as it travels. The main sensor types are:

• Magnetic flux leakage (MFL): magnetises the pipe wall and detects metal loss, such as corrosion.
• Ultrasonic (UT): uses sound waves to measure wall thickness and detect cracks.
• Geometry or caliper: measures dents, ovality and bore changes.

These tools are long, rigid and costly, which is why most need bends of 3D or more, and why a gauging pig is run first. Note that a gauging pig does not measure wall thickness. It carries a metal plate that proves the bore is clear. Wall thickness is measured by an intelligent pig using MFL or UT.

Piggable Pipeline Design

Designing a piggable pipeline means checking every feature on the route against what the pig needs. The table below sets out the main items and the values commonly used in practice. These are typical industry values, not code limits. The governing code, the project specification and the pig vendor decide the final numbers.

Item	What a Pig Needs	Typical Design Practice (Confirm)
Bore	Constant internal diameter	Keep ID changes and bore reduction within the pig vendor limit (about 10% is often quoted)
Bends	Long radius, smooth	3D minimum for most intelligent pigs; 5D where rigid tools run; 1.5D can suit utility pigs
Tangents	Straight run at each bend end	At least about 1D of straight pipe at each end
Branch connections	Pig must not enter a side branch	Barred or flow tees where the branch is large relative to the main line
Valves	Fully open, no step or cavity	Full bore ball or gate valves; check valves chosen to pass the pig (API 6D)
Wall thickness changes	Gradual transitions	Taper heavy wall to line pipe; avoid abrupt ID steps
Internal weld profile	No heavy weld bead or high-low mismatch	Controlled root bead and alignment
Ovality and roundness	Near-round pipe	Ovality kept low (about 3% of OD is a common ceiling for intelligent pigs)
Launcher and receiver	Space and a way to handle the pig	Barrel, closure, kicker line, crane or lift access, signallers

Two points are easy to miss. First, the tightest feature sets the limit for the whole line, so one tight bend or one reduced bore valve is enough to make a long line unpiggable. Second, future inspection tools are often longer and more rigid than the ones used today, so designers who want flexibility choose generous bend radii from the beginning.

Bends, Tees and Valves for Pigging

Bends

Bends are where most piggability problems start. A pig needs room to turn, so the larger the radius, the easier the passage. The table shows which pigs usually pass which bend radius.

Pig Type	1D to 1.5D Bend Radius	3D Bend Radius	5D Bend Radius
Foam pig	Usually passes	Passes	Passes
Mandrel, solid cast, sphere	Usually passes at 1.5D	Passes	Passes
Gauging pig	Tool dependent	Usually passes	Passes
Intelligent pig (MFL or UT)	No	Usual minimum	Safe for rigid tools

Values are typical. Confirm with the vendor of the tool you plan to run. Piggable pipelines commonly use induction bends, which are made by heating a straight pipe and bending it to a set radius. They are covered by ASME B16.49, which sets requirements for radius, ovality and wall thinning. Factory-made buttweld pipe bends and long radius elbows are also used on some lines. For pigging service, the bend radius has to be chosen against the tool you plan to run, so specify piggable bends of 3D or 5D where intelligent pigs will pass.

Tees

When a pig passes a branch connection, it can be drawn into the side branch if the opening is large. A barred tee has bars across the branch opening, so the pig carries on along the main line. Branches that are small compared with the main line may not need bars, but this should be checked for each case.

Valves

A valve in a piggable line must be fully open with no step or cavity that can catch the pig. In practice this means full bore ball or gate valves, in line with API 6D for pipeline valves. Check valves and any other valve that cannot be fully cleared must be chosen specifically so the pig can pass.

Choosing Line Pipe for a Piggable Pipeline

The pipe itself matters as much as the bends. A pig travels on the internal surface, so internal diameter, roundness, wall thickness and weld profile all affect how smoothly it runs. Most pipelines use line pipe to API 5L or ISO 3183, in seamless, welded (LSAW or SSAW) or ERW form. Our range of API 5L line pipe includes API 5L seamless pipes, LSAW pipes and SAW pipes.

Choice	Options	What to Specify
Line pipe	API 5L / ISO 3183 seamless, SAW (LSAW or SSAW), or ERW	Grade (X52, X65, X70), PSL2 where required, wall thickness, ID or OD tolerance
Pipe tolerances	Standard or tightened	OD, wall, ovality, and straightness tight enough for the intelligent pig
Bends	Induction bends to ASME B16.49; factory buttweld bends	Radius (3D or 5D), tangents, wall thinning limit, ovality
Fittings	Reducers, tees, flanges	Barred tees where needed; matched ID and wall thickness
Valves	API 6D full bore ball or gate	Full bore, piggable design
Coating	External coating; internal lining or coating if used	Smooth, pig-compatible internal surface

Grade selection depends on the design pressure, pipeline requirements, and applicable code. Higher grades such as API 5L X52 PSL2, X65 PSL2, and X70 PSL2 can allow thinner walls for the same pressure. Whatever the grade, match the wall thickness and internal diameter across pipes, bends, and fittings to prevent internal steps that could obstruct a pig. Use API 5L buttweld fittings with compatible bores to maintain a smooth passage. Our guide to forged vs buttweld fittings explains the differences between these fitting types. 

Key Standards for Piggable Pipelines

The standards below come up most often. Verify the current edition of each before you rely on it, and treat the pipeline codes and inspection standards as references only. The owner of each standard is the authority on its wording.

Standard	What it Covers	Why it Matters Here
API 5L / ISO 3183	Line pipe for oil and gas pipelines	Defines pipe grade, chemical composition, and strict manufacturing tolerances
ASME B16.49	Factory-made induction bends for transportation and distribution systems	Specifies bend radius, ovality controls, and wall thinning limits for pig passage
ASME B16.9	Factory-made wrought steel buttweld fittings	Covers dimensional tolerances for standard elbows, tees, and reducers
MSS SP-75	High-test wrought butt-welding fittings	Essential for high-strength pipeline fittings matching API 5L pipe grades
API 6D	Pipeline and piping valves	Covers full-opening valves that can pass pigs when specified by the purchaser
ASME B31.4 / B31.8	Liquid (B31.4) and gas (B31.8) pipeline transportation systems	Pipeline design codes covering launchers, receivers, and inspection facilities (Note: Consult local regulations such as 49 CFR 192.150 / 195.120 for specific jurisdictional mandates on tool passage capability)
API 1163 / AMPP SP0102	In-line inspection (ILI) systems and pipeline pigging practices	Details operational performance and validation criteria for inspection runs

Sourcing Line Pipe and Piggable Bends

We do not supply pigs, launchers or inspection runs. What we supply is the steel that makes a line piggable: line pipe, bends and fittings made to the standards above. Amardeep Steel has been supplying pipes and fittings since 1982, to customers in more than 40 countries.

Item	Range & Specification Details
Line Pipe	API 5L Seamless (1/2" to 26") & SAW / LSAW / SSAW (16" to 100"), Grades B through X52, X60, X65, X70, X80 (PSL1 & PSL2)
Induction & Buttweld Bends	Radii: 3D, 5D, 6D, 8D, 10D & custom long-radius bends; Sizes: 2" to 56" NB
Tolerances	Tightened OD, wall thickness, and ovality limits (< 1.5%); custom straight tangent lengths (1D to 3D typical)
Standards	ASME B16.49, ASME B16.9, MSS SP-75, MSS SP-43, API 5L
Certificates & Testing	EN 10204 3.1 / 3.2 MTC, NDT (UT, RT, MPI), Hydrostatic testing, Hardness & Charpy V-Notch impact testing

If you are planning a piggable pipeline, tell us the line size, grade, design pressure and the pig you expect to run, and we can advise on bend radius, wall thickness and tolerances. See our carbon steel pipes, our piggable bends, or request a quote.

Why pig a pipeline? 

Regular pigging clears wax, scale and water that would otherwise reduce flow, supports corrosion control by removing the deposits that corrosion hides under, separates different products in the same line, and supplies the inspection data needed to manage integrity. How often a line is pigged depends on the product, the deposit rate and the operator's integrity plan, from weekly cleaning runs to inspection runs every few years.