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Blog: How do I increase my chances of pig detection?

Sales and Service Manager, Alan Tulloch has written a blog about how to increase chances of pig detection:

This depends on the task in hand; is it simply to signal safe passage of a pig or tool past a fixed point (detection) or locate a pig that has not arrived or passed a known point (location)?

Pig detection relies on two main factors, the item(s) within the pig and the item outside the pipeline.  It is always useful to consider the former during the pig design such that any changes required are made early on and can be incorporated into the final pig.

One of the most reliable methods of detection of pig passage is the magnetic signaller, either in ATEX form top-side or subsea

For best results use a decent grade of magnet, the type used to gather debris can be used to trip the signallers however a neodymium (NdFeB) magnet has around ten times field strength per size and can easily be buried within the packer disc, this permits the re-work of an existing pig.

Ideally the magnetic signaller should be able to be easily transported and installed onto the line with little effort.  Sensitivity is a key feature which needs to be adjusted to suit the line/pig/conditions to prevent false alarms

For topside use then the most appropriate technology for location is usually Electro-Magnetic (EM) as this will work regardless of the medium or line type etc.  If you know if the line is exposed at all areas of its length, then detection is much easier as access is simple and signal strength will always be at its maximum.  In such cases a smaller transmitter could be specified, although the small saving in cost of transmitter can quickly be lost if the detection of the stalled pig takes an additional day or more to eventually locate!

Regardless of whether the line is above or below ground a larger transmitter will always improve the chances of detection as signal strength is usually linked to transmitter size.

If the line is buried then always opt for the largest transmitter that can fit within the pig as there may not be any above ground clues where the line actually traverses the ground, ‘note that ‘as planned’ might not be equal to ‘as built’ and the line could be several metres away horizontally from where it should be.  These few metres of horizontal error can make the difference between detecting the pig or failing to detect it when working at the margins of what is detectable.  This is especially true if a stationary detector is expecting to pick up a pulsing signal from a moving pig, the EM pulse may not occur whilst within detection range and for fast moving pigs (typically in gas) this type of detection may not be adequate if a slow pulsing transmitter is used.

Battery life might not be a concern for routine pig runs but when pig runs are infrequent then it is prudent to make sure that there will be sufficient battery life if the whole line needs to be checked. In worst case no signalling was planned or undertaken and the only known facts are that the pig has left launcher and that it has not arrived!

So in essence ‘bigger is better’