How do you cut threads in plastic coated steel pipe?

Question

I'm doing a home improvement project, and I want to bury 10' of 1/2" pipe. I've been to the city and understand the codes to do this legal. In my area, buried pipe has to be either plastic coated or buried within a protective plastic pipe (typically PVC). I've got a couple of pieces of pipe that will need to be cut and threaded.

My local big box hardware store (no names mentioned) sell the coated pipe but refuse to cut threads on their expensive Rigid pipe threading machines. They claim the coated pipe clogs up their threading machines, have a nice day.

I was looking at using a ratcheting pipe threader tool, but I notice from the Rigid catalog that they recommend a different die set for coated pipe? ref: dies here and ratchet handles here. That reference shows part # 51897 for 1/2 inch "high speed for plastic coated pipe".

The whole threading of plastic coated pipe sounds odd to me. I don't understand why plain 'ol pipe threading dies don't just cut right thru the stuff. Anybody know any details here?

If I'm careful with plain 'ol dies for black iron pipe work on the coated stuff?

Many thanks...

Answer 1

I spent hundreds of hours on a Rigid pipe threading machine and used the same dies for black iron, galvanized, and green coated iron gas pipe. The only issue was the green coated pipe is slightly larger on the O.D. (due only to the coating) so is a bit difficult to get the threads started. With the machine, I could grind a bit of the coating off by levering the dies open a bit, to get the thread started. With hand dies you may have to use a different method to scrape a bit of the coating off the end of the pipe, maybe just use a sharp knife or a file. Once the dies bite they will grind right through the coating, no clogging.

The official response will still be "follow the manufacturer's instructions", but I think you will be fine.

Answer 2

If this pipe line is for natural gas, I would check with the local gas company for recommendations. Where I live, near Pittsburgh, Pa. the steel connection that the threading procedure produced must itself be covered with a protective coating that wraps around the pipe connection. This is so all the piping is protected from the elements. There are strict codes for running pipe underground. Sometimes, running the new plastic pipe is more economical. Crap, I say, give me the old ways since I am from the old school.

Answer 3

Get a die for coated pipes and also a jaw for coated pipes, otherwise you might butcher the coating and that's not what you want to do with a pipe going under ground.