Kind of a tough question, Term.
I have worked around these "Pipe Layers" for years.
I have helped out in the trenches, handed the guys bolts and flanges and helped tighten them to make connections.
Watched in amazement while some old Italian guy cut a section of 24" ductile iron pipe with a cutoff saw....and it was perfect.
I've seen guys "hot tap" water mains. Cut in saddles on sewer pipe.
I've seen them fret cause they could not get all the air out of pipe so it could be tested properly.
When it can finally be tested, they have to find out why, and where, they are loosing pressure, dig it up and fix it.
I have worked in some fashion or other, around, and with the pipe crews for almost 30 years, and it is not a trade I would approach sheepishly.
If you intend to take on this type work you will have to be bold, move quickly and efficiently. Most of the work requires specialized tools to some extent.
These old boys make it look easy, that's part of their job, but it takes time, money and mistakes to learn the in's and out's of the pipe work business, same as it would take time, money and mistakes, for one of us who does not handle hot mix asphalt, to venture into your field of expertise.
How you would learn this craft without working it for about a decade or so is beyond me. I don't think it is something you can just "take on" as a fill in for your slack time.
Where are you located?