Designing pig launchers and receivers: key technical parameters

Pigging operations play a crucial role in the maintenance and optimisation of pipeline systems in the oil and gas industry, where pig launcher and receiver (L&R) systems are the equipment used to insert and retrieve pigs, the specialised devices employed for cleaning, inspecting and maintaining pipelines. This article covers the key technical parameters for designing a reliable and safe pig launcher and receiver system.

Applicable design code

Since the pigging station and pig traps are pressure equipment, they can be designed as pressure vessels under an international standard, mainly ASME Section VIII Division 1. However, the pipelines connected to the pig traps are designed under pipeline design rules, which creates incompatibilities due to different material classes, design factors and MAWP — above all, the barrel thickness is calculated differently from the pipeline thickness. This is a common problem, so the main design requirement is that the pig trap minor barrel ID must match the pipeline ID.

The most appropriate code for the pig traps is usually the same design code as the pipeline they connect to:

• ASME B31.3 (USA): governs the design of process piping.
• ASME B31.4 (USA): governs the design of liquid pipelines.
• ASME B31.8 (USA): governs the design of gas pipelines.
• ISO 13623:2009: petroleum and natural gas industries — pipeline transportation systems.
• BS EN 14161:2011 (Europe): a MOD version of ISO 13623:2009 for petroleum and natural gas industries.
• ISO 13703:2000: design and installation of piping systems on offshore production platforms.

Other pipeline design codes not listed above may also apply.

Quick opening closure design

The quick opening closure must be designed in accordance with ASME Section VIII Division 1 or 2, and ASME UG-35 must be fully complied with to ensure safe operation.

Design pressure and temperature

Design pressure and temperature are critical parameters for the structural integrity and safety of the pig launcher and receiver system. They must be selected based on the pipeline's maximum operating pressure (MOP) and temperature, taking into account safety margins and applicable regulatory requirements. Proper selection ensures the L&R system can withstand the pipeline's operating conditions without risking system failure or compromising safety.

Pig trap components to consider in the design

Pig trap design should account for five groups of components:

• Connection to the pipeline: welded or flanged (main connection flange).
• Main barrel: made up of the minor barrel, the reducer and the major barrel.
• Quick opening closure: located at the end of the major barrel, for inserting or removing the pig from the trap.
• Branch connections (nozzles): kicker, bypass, balance, purge, PSV connection, vents and drains, pig signaller and pressure and temperature gauging connections.
• Saddles and supports.

1. Connection to the pipeline

Two types of connection can be designed. For a welded connection, the main design consideration is that the minor barrel ID matches the pipeline ID, as explained above. For flanged connections, the flange rating and standard must match, also considering an equivalent flange ID.

2. Main barrel

The pipeline diameter and wall thickness are decisive factors in sizing and configuring the pig launcher and receiver system. These parameters determine the pig size and, in turn, its ability to travel through the pipeline and perform its intended task effectively. The L&R system must be designed with enough clearance for the pig to pass without jamming or damaging the pipeline or the pigging equipment.

The minor barrel size should equal the connecting pipeline ID, to prevent damage to the pig tool during launching and receiving.

For major barrel sizing, common engineering practice specifies a 2-inch oversize versus the pipeline for lines smaller than 20", and a 4-inch oversize for lines over 20". This practice does not release the designer from calculating and considering special process conditions, such as the expected sludge volume that will be collected from the pipeline and removed by the pigging operation, together with operation and process conditions — especially for pipeline sizes whose nominal diameter differs from the actual size (for example, a 12" line with an actual size of 12.75").

Pig trap length must also be designed considering process and operation parameters; the most important factor for the designer is the maximum pig tool length that will be used. As a general rule:

• Launcher: the minor barrel length should equal half of the maximum pig tool length, and the major barrel length should equal the maximum pig tool length.
• Receiver: the minor barrel length should equal half of the maximum pig tool length, and the major barrel length should equal the maximum pig tool length.

3. Quick opening closure

The closure type of the pig launcher and receiver system is a critical design decision, as it affects ease of operation, safety and maintenance. Common closure types include quick-opening closures, threaded closures and bolted flange closures. The chosen closure type must provide a reliable seal, be user-friendly and meet the necessary safety and operational requirements.

It is located at the end of the major barrel, for inserting or removing the pig from the trap. The main design-code and safe-operation requirements are:

• The closure must have two independent mechanical interlocking systems that prevent it from opening while under pressure.
• It must be a quick-acting closure (fast opening and closing).
• It must be operable by a single operator.
• It must provide full bore in the open position.

4. Branch connections (nozzles)

Kicker, bypass, balance, purge, PSV connection, vents and drains, and pressure and temperature gauging connections.

Well-designed branch connections and nozzles are essential for the safe and efficient operation of the pig launcher and receiver. The system must allow controlled venting of pressure and fluid to ensure safe pig insertion and retrieval. The bypass system should also enable a smooth flow diversion, minimising pressure surges and potential damage to the pipeline or the pigging equipment.

The size and location of the branch connections should be defined based on the process and operation of the pigging station, as reflected in the P&ID.

5. Pig signaller

A device used to indicate the pig passing through set control points. On the launcher it is located at the end of the minor barrel (connection point to the pipeline); on the receiver, at the connection point to the reducer.

Pig type and function

The pig's specific type and function must also be considered when designing the launcher and receiver system. There are various pig types: utility pigs (for cleaning and debris removal), in-line inspection (ILI) pigs (for assessing pipeline integrity) and specialty pigs (for specific tasks such as sealing or batching). The L&R system must be designed to accommodate the particular pig type and its function, ensuring optimal performance and efficiency.

Pig tools are mainly categorised according to their function:

• Inspection.
• Maintenance and repair.
• Renovation / rehabilitation.
• Decommissioning.

Safety features

The pig launcher and receiver system must incorporate comprehensive safety features: pressure relief devices, interlocks and emergency shutdown systems. These features protect operators and equipment from the hazards associated with pigging operations, such as overpressure, pig jamming or accidental release of pipeline contents.

Conclusion

Designing a pig launcher and receiver system requires careful consideration of multiple parameters to ensure efficient, reliable and safe pipeline operations. By accounting for factors such as design pressure and temperature, pipeline diameter, pig type and function, barrel length, closure type, bypass and venting system, and safety features, engineers can develop a robust and effective L&R system tailored to each pipeline's specific requirements.

Related terms

• Pig: a device that travels through the inside of a pipeline to clean, inspect or maintain it.
• Pig launcher: equipment used to insert the pig into the pipeline.
• Pig receiver: equipment used to remove the pig from the pipeline at the end of its run.
• Pig trap: the assembly made up of the minor barrel, the reducer and the major barrel where the pig sits before or after its run.
• Quick opening closure: a closure system that allows the trap to be opened and closed quickly and safely, with safety interlocks.
• MAWP (Maximum Allowable Working Pressure): the maximum pressure the equipment is designed to withstand.
• MOP (Maximum Operating Pressure): the pipeline's maximum operating pressure.
• Kicker: the trap nozzle through which the propelling fluid that drives the pig is introduced.

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