Prudent pigging

Jack Rankin, PPSA member and Manager of Engineered Solutions at T.D Williamson, provides guidelines for successfully tracking and locating pipeline pigs.

“Communication is critical. Everyone involved in the tracking process must have accurate information at all times to know when the pig is expected to arrive at a particular location”
-Jack Rankin

Tracking and/or locating a pig stuck in a pipeline can present a challenge. A little preparation and proper tracking techniques however, help ensure success. There are man applications in which it is important to track the progress of a pig as it travels through a pipeline, including:

• Running a smart pig
• Conducting a nitrogen purge with pigs
• Running a pig with a transmitter to track a smart pig

There are also several situations that can result in a pig getting stuck in the line such as:

• Excessive by-pass when the pig is in a bend
• Excess debris build up in front of the pig
• An obstruction such as a buckle in the pipe or a partially-closed valve

Manpower
First, plan to have an adequate number of two-man crews with each crew consisting of a pipeline operator who knows, and has access to, the pipeline right-of-way (ROW), as well as a contractor who is experienced in tracking equipment and procedures. The number of crews needed depends upon a variety of factors, including:

• Is the ROW accessible by vehicles?
• How long is the run from launcher to receiver?
• What is the velocity of the pig under expected conditions?
• Is the pig propelled with gas or liquids?
• Is there a contingency plan if the pig gets stuck and can, or can’t be located?

Job preparation and training
The pipeline operator should provide suitable maps and alignment sheets, and be thoroughly familiar with the pipeline ROW and access to various tracking locations. The contractor should possess an operating manual and be thoroughly familiar with the operation and maintenance of the tracking equipment. Crews should practice with the equipment so the signal can be observed, recorded and interrogated before every launching the pig. For practice purposes, the transmitter should be positioned a few meters away from the electronic receivers and moved parallel to the receivers at various velocities to demonstrate what the signal will sound and look like. For training, the transmitter should be placed out of sight. The trainee, following the instructions in the operator’s manual, should walk along a line that is parallel, but about three metres from the transmitter at its closest point. This exercise should be conducted in a field with overgrow vegetation where conditions are less favourable.

Equipment
Electronic tracking systems are an electromagnetic-pulse transmitter (mounted on the pig) and an electronic receiver system. The transmitter should be selected, based on the specific application considering size and wall thickness of the pipeline, and the amount of time that it may take to locate the pig should it get stuck. Lithium batteries will provided extended life (though there may be some restrictions on the use of lithium batteries in some areas). The tracking equipment should provide audible, visual and recorded indication of the pig passage. In addition to the electronic receiver, a geophone is recommended as it amplifies the sound being made by the cups, discs and brushes as the pig travels through the line, allowing the crew to hear the pig coming well in advance of its scheduled arrival time at the tracking location. Once the crew or crews are in place, confirm that all mainline valves are fully opened and that flow is going through the receiver barrel. Each crew should have spare batteries as needed, and a laptop computer with variable project inputs and a spreadsheet for recording data and notes. When positioning the tracking system receiving antenna and geophone probe, each crew should have a pipe locator to confirm it is over the pipeline. A spare receiving system should be carried by one of the tracking crews. If the pipeline goes through a casing, the receiver antenna should be positioned a bit upstream or downstream of the casing pipe so that the signal doesn’t have to travel through two pipes. Where possible pigs should be tracked at approximately two-kilometer (1.5 mile) intervals. Avoid areas with a lot of traffic, railroad crossings, and high voltage power lines as these may induce ‘noise’ in the tracking system receivers.

Communication
Communication is critical. Everyone is involved in the tracking process must have accurate information at all times to know when the pig is expected to arrive at a particular location. Should a pig pass a given tracking station (station 73 for example) but not arrive in a timely manner at the next station (station 74), the crew at station 74 should wait for the late-arriving pig. Perhaps the pig was damaged and is still moving but is by-passing flow, or one of the units (compressor or flow) may have shut down, causing it to be late. The crew should proceed as though nothing has changed, assuming that the signal was simply missed for some reason.

If after diligent tracking efforts all the way to the receiver, the crew has not heard/recorded pig passage at any location, including the receiver barrel and associated valves and fittings, it would be assumed that the pig is stuck somewhere between station 73 and 74. At this point, one person equipped with an antenna and receiver would start at each station walking toward each other until the stuck pig is found. If the ROW can be cleared in this area it will make the job easier and success more likely. If there are any fittings, valves etc, between the two stations, they should be searched first. The receiver and associated valves and fittings should be checked on a regular basis (every few hour is recommended) until the pig is located.