Function of Pig Launchers and Pig Receivers

Launchers and receivers also commonly referred to as pig trap assemblies are used to introduce and remove in a safe and effective manner, scraper cleaning pigs, spheres and inspection tools (commonly referred to as Smart Pigs or Intelligent pigs) through liquid, gas and multi-phase hydrocarbon pipelines. The main purpose of a pipeline pig trap system thus is to provide, in a safe manner and without flow interruption, the means to either: 

  • Insert and launch a pig into a pipeline at Pig Launcher End
  • Receive and retrieve a pig from a pipeline at Pig Receiver End

The overall dimensions of the pig trap assembly is dependent on the type of pig to be handled. Pig Trap stations for intelligent pigging will occupy more space due to larger dimensions of the intelligent pigs.

Parts of a Pig Launcher or Pig Receiver

A typical pig launcher or pig receiver also commonly referred to as pig trap comprises of the following components :

  • Major barrel
  • Minor barrel
  • End closure
  • Pig signaller
  • Kicker line connection
  • Pressure gauge connection
  • Vent and drain connection
  • Utility connections

Major and Minor barrel

As a rough guideline, for pipelines less than 20 inches diameter, the major barrel diameter is 2 inches greater than the pipeline diameter. For pipelines with a diameter of 20 inches upto and including 46 inches, the oversize is 4 inches. For 48" pipeline and above the oversize is 6 inches. This guideline may vary from Organization to Organization. The barrel is sloped towards the end closure for a launcher and towards the pipeline for a receiver. Typically a slope of 1:100 is maintained on the pig traps. For bi-directional pig launchers and receivers no slope is required on the barrel.

The barrel should be designed to accommodate the longest pig that may be used. If the pipeline is designed for intelligent pigging, the length of intelligent pig will dictate the barrel length. During the early stages of piping study the type of intelligent pigs that will be used are agreed with COMPANY operations and documented in the pipeline pigging philosophy. The most conservative dimensions of pig trap are selected to develop the plot plans and detailed piping layouts. The reducer connecting the major and minor barrel is of eccentric type for horizontal pig trap assemblies. This ensures that the pig trap bottom is maintained over its entire length. For vertical pig traps the reducer is normally of concentric type.

End Closure

End Closure

The pig launchers and receivers and equipped with doors which are called end closures. The end closure is welded to the major barrel and hence its material and end wall thickness should be compatible with the barrel material. End closures are generally of quick opening type and are fitted with safety interlocks to prevent opening when the barrel is pressurized. The safety mechanism on the end closure may be specified to comply with the requirements of ASME Section VIII Division 1, UG-35. The safety feature in the end closure is important because the launching and receiving operation is complex and inadvertent opening of closure door while the pig trap is in a pressurized condition is not uncommon. The hinge position of the end closure and the maximum swing position should be checked for any obstructions. The clearance envelope for the door should be either modelled in 3D plant design system or shown on 2D piping layouts to ensure clear area is available for opening of the end closure. All the hinges should be preferably oriented on the same side in a pig trap area. Some of the reputed end closure manufacturing companies are GD Engineering and SHOLTZ.

Pig signaller

The pig signalers are located on the minor barrel. Pig signalers can be of intrusive and non-intrusive type. The pig trap shall have one signaler located on the minor barrel. Additionally, one more signaller must be suitably positioned on the line to allow the longest specified pig to pass completely through the pig trap isolation valve before activating the signaller.

Kicker line

The kicker line tapping is taken from the bypass line of pig trap. During the launching or receiving operation the pipeline fluid is diverted through the barrel to launch or receive the pig. For a pig launcher the kicker line connection should be connected towards the end closure on the major barrel. For a pig receiver the kicker line connection should be as close as possible to the reducer (i.e. away from the end closure). For a bi-directional pig trap the kicker line should be located at the center of the major barrel. Alternatively, two kicker connections can be provided to facilitate launching and receiving of pigs. 

Typical configuration of Pig Launcher

Pig Launcher

Design code

The pig trap assembly may be designed to pressure vessel code or the relevant pipeline or piping code. Most companies prefer to design the pig trap system to the piping code. The end closure is designed to ASME section VIII, Div.1.

Pig Launcher and Pig Receiver Layout

  1. Pig Launchers and Pig Receivers are generally grouped together in a dedicated scraper trap or pig trap area close to the plant boundary and preferably lined up along the primary roads to allow easy maintenance and provide adequate access for fire fighting. The orientation of the end closure shall be such that any projectile of the pig from the end closure will not be directed towards critical plant facility which may affect the integrity of the installation in case of pig or scraper colliding with the installation. The end closure shall also be oriented away from main access ways or roads with heavy traffic. Some organizations allocate an overall 20 to 30 degree sector clear envelope from the center of the trap end closure extending over a length of 40-50m.
  2. Pig Launchers and Pig Receivers are generally installed in horizontal direction. They may be installed in vertical orientation in offshore platforms where space limitations do not permit horizontal installation. When the pig trap is installed in vertical direction, there is a possibility of the debris falling and accumulating on the valve seat thereby damaging the valve.
  3. Adequate room shall be provided around the traps for lifting and handling of pigs. The lifting facilities are provided predominantly for handling of pigs and pigging tools.
  4. The clearance between the bottom of pig trap end closure and the finished grade is maintained between 700mm to 1000mm to facilitate easy handling of the pigging tools. The minimum elevation of the pig trap should allow effective draining of the hydrocarbon inventories without any pockets.
  5. Where pig launchers and receivers are located adjacent to each other a minimum access clearance should be maintained for operation of the valves around the pig trap assembly.
  6. A surface drainage system should be provided to collect any spills from the trap during pig receiving or launching and for collection of wash water.
  7. For large pipelines operating platforms will be required adjacent to the pipeline to conveniently access the valve actuators and the end closure. The layout should be arranged such that all the valves are accessible from the platform from one side of the pig trap.