A Pig Tale…In Two Parts

By Jim Hunter, Hunter McDonnell Pipeline Services Inc., Edmonton, Alberta, Canada | February 2013, Vol. 240 No. 2
Buyer's Guide

People usually laugh when I tell them I chase pigs for a living. But the truth is that it’s very serious business - one which I have been perfecting for more than 25 years. I’ve tracked pigs in all kinds of pipelines, all over the world, and over the years I have seen all kinds of crazy things happen with pigs in pipelines. Probably the most important thing I’ve learned would be to expect the unexpected.

This tenet was never truer than during a recent pig run where a surprise awaited us at the trap after what had appeared to be another perfect tracking job. We discovered after opening the pig trap door that only the drive section of an inline inspection tool was in the barrel. How could this be? We had listened to this pig for the last few days and no one could recall a change in sound that would indicate a change in the pig’s configuration; it had triggered the above-ground marker (AGMs) flawlessly the length of the run.

Backing up 72 hours earlier…Hunter McDonnell Pipeline Services (HM) was contracted to track and benchmark a cleaning pig and an inline inspection tool through a crude oil pipeline in western Canada. The ILI vendor was providing its own AGM boxes to be used at all the benchmark sites. As part of our own R&D field testing for HM’s Armadillo AGMs, we also brought Armadillo AGM boxes to deploy concurrently with the ILI vendor’s.
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We launched the pig early in the day; it was my shift that tracked the pig out of the launch barrel and past the first few sites. It takes a few sites to determine what type of sound a pig is generally going to produce as you listen to it travel through the pipeline. The first three sites were valves. Nothing seemed to be out of line and both the vendor’s and the Armadillo AGM boxes were triggering like clockwork. In fact, we tracked the pig and recorded passages all the way to the trap without incident. Or so we thought.

Somewhere in the 200+ mile segment of pipe, the front section and the rest of the tool had parted ways. This particular pig was configured with a 22-Hz transmitter in its nose. That explained why it triggered AGMs all the way to the end. But it also eliminated any chance of finding the pig with standard locating methods. A rescue pig was one solution that could find the missing section; however, this could also seal off the line if the pig was stuck somehow. This was not a good option.

I polled the trackers to see if anyone could recall hearing anything abnormal or perhaps noticed a sound change during the run. No one could recall anything significant. Our initial inclination was that it must have happened near the end of the run, otherwise we would have noticed the change. I had the Armadillo AGM boxes collected as we downloaded the pig passage information from every site and looked for hints as to where the pig might have separated. 

This is where the significance of the Armadillo AGM boxes comes in. Unlike the ILI vendor’s AGMs, or any other AGM for that matter, the Armadillo AGM boxes record a continuous log the entire time that they are on and deployed. That includes all the sensors, which is also unique with two axis of 22Hz, three axis of magnetic sensors, and the unique acoustic sensor. It was the acoustic sensor that we eventually used to determine where the pig had separated. Through analysis of the recorded geophone data we could identify sound events that even the most experienced tracker would - and did - miss during the pig run.

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