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Horizontal bi-directional pig traps features

asked Oct 14, 2014 in Piping by Normandy (21,040 points)

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+1 vote
answered Oct 14, 2014 by Normandy (21,040 points) | selected May 8, 2015 by odadmin
 
Best answer

Features for a typical horizontal bi-directional pig traps:

  • For pipe 12" and smaller, the launch/receive barrel should be oversized by a minimum of 2" and preferably by 4".  For larger pipe, the barrel should be oversized by a minimum of 4" and preferably 6".  The barrel length should be at least the length of the pig, plus the distance from the reducer to the kickout line outlet. The oversized barrel is necessary to reduce the velocity of the incoming pig and facilitate pig installation and removal.
  • The pig trap closure should have a hinged, quick opening design with a pressure lock safety device to prevent opening under pressure.  A more elaborate design, with a built-in pig tray, should be considered for large sizes.
  • Larger size closures should include an integral davit or other device, for ease of opening and closing.
  • The kickout lateral should be located as near as possible to the reducer; however, it should not be closer than the distance between the pig's front and back drive cups.
  • The reducer should be the eccentric type, installed flat side down, to facilitate sphere launching and pig handling.
  • Two bi-directional pig signal indicators are required.  The receiver indicator should be located at the reducer end of the trap nominal pipe section.  The launch indicator should be located one pig length past the mainline bypass tee. The receiver indicator indicates receipt of an incoming pig.  The launch indicator confirms that the departing pig has cleared the launcher.
  • A 0.5" pressure relief valve for thermal expansion and 1" minimum blow down connections, located on top of the trap, should be provided.
  • A mainline surge relief valve should be required.  It should be located on the mainline, between the mainline block valve and the mainline bypass tee.
  • An equalizing line and valve should be required.  It should be located on top of the trap and connect the nominal pipe section to the oversized pipe section.
  • A pressure gauge located near the closure should be mounted on top of the oversized pipe section.  This gauge should be clearly visible to the operator from the operator's normal working position(s).
  • A pig drain tray and drip pan (piped for proper disposal) should be required.
  • Two 2" drain lines should be installed at each end of the trap and piped for proper disposal.  They can be used as purge and hydrostatic fill lines.
  • Except for drain and purge lines, all outlets should be on top of the trap.
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answered Oct 14, 2014 by Normandy (21,040 points)

Pig Trap Figure:

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