However, the article doesn't say what the "PIG" is (but talks at length about how the "PIG" is "launched" or "received"). Wikipedia says it's basically a passive device that gets inserted into the pipeline and pushed along by the pressure to clean or inspect the inside of the pipe.
In the drinking water industry the pig is a large foam block that is shoved in the pipe, and the weight of the fluid behind it drives it along. It is used to physically loosen the accumulated debris on the inside of the pipe. This debris concentrates behind the pig, and when the pig arrives at it's destination you remove the pig and allow the fluid (and debris) to discharge to waste for a period of time until the fluid runs clear.
Some advancements include "ice pigs" which is just crushed ice. The advantage of an ice pig is you can hook up to a fire hydrant and pump the ice in, no need to access the mainline pipe itself. An ice pig will also disintegrate on its own, no need to remove it, just allow it to flow out of a downstream hydrant, any ice left behind isn't a problem.
Nowadays, they also have "smart pigs" that have sensors to detect gouges, dents, pipe wall that is too thin, etc. as the pig moves through the pipe, so that repairs can be made before the pipeline is filled with gas.
I’m guessing those are usually “dumber” ones.
Inside the tank terminals I had to witness and certify the pigging after each parcel loaded, when one chemical was done and the line needed to be cleared and volumes accounted for before filling with a different chemical. Among many other more or less toxic things. Measurement training was not easy in the full-scale industrial environment but you can't really lead as well in the micro-scale activities without it.
https://en.wikipedia.org/wiki/Pigging
> Some early cleaning "pigs" were made from straw bales wrapped in barbed wire[4] while others used leather.[5] Both made a squealing noise while traveling through the pipe, sounding to some like a pig squealing,[6] which gave pigs their name.[7][8]
We have a natural gas line running through one of our agency properties, and it was recently repaired due to the pig's findings.
Basically the engineers running the pig mark sections of the pipe that need physical inspection. The crews come out, dig it up, and repair or replace a section depending on how bad it is. Or do nothing if the engineers see that it's nowhere near as bad as they thought.