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In this first post in our Electromagnetic Pig Tracking for Newbies series, our Senior Application Engineer Alan Tulloch highlights the impact pig design has on an electromagnetic signal and provides recommendations on how to achieve an optimum signal level.

Although pig tracking may not be the most critical thing to consider when designing a pig or pig train, it should still be taken into consideration. Pig design can make a huge difference to confirmation of a pig’s location or failure to detect when using any Electromagnetic (EM) Transmitter.

Any signal will be absorbed to a greater or lesser amount by the nature of the metal either as part of the transmitter housing or the actual pig body. Aluminium and carbon steel are the worst offenders, 316 Stainless is the best of the commonly used metals. If possible, avoid any transmitter holder made from metal - both nylon and delrin have been used by some companies and consider the use of PU discs/cups to centralise the transmitter within the pig body.

When mounting the transmitter in the pig, it is best if it can be held such that as much of the transmitter is protruding from the rear of the pig as possible. Obviously, this will depend on the construction of the pig and the number of pigs in the pig train.

To confirm which pig has passed a location or is within the launcher/receiver it is often useful to have the option to provide a unique transmission frequency for each pig that can be detected using a multi-frequency EM receiver. This will depend on how many pigs are within the train and what the wall thickness of the line is.

The pig train and factors such as pig run length and speed should also be taken into account. For EM pig tracking, pulse rate, signal strength and battery life are critical and in most cases are mutually exclusive, ie for best results then the signal strength should be set at maximum, but this will shorten the battery life. This increased signal strength is often not possible given the expected run length and/or the run length might be quite short, but the pigs are pre-deployed into a launcher many weeks prior to the actual pigging operations.

For confirmation that a pig has passed a given point then a very fast pulse rate is required which will also result in a shortened battery life, especially where the pigs are travelling at a higher speed, eg in a gas line.

Through collaboration and discussion, pig and pig tracking manufacturers can strive to achieve a design that can carry out its primary function efficiently without compromising on EM signal detectability.

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