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Old 04-09-09, 03:19 AM   #10
AC_Hacker
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Default Welding Polyethylene Pipe...

I've been wracking my brain, trying to figure out how to join the pipe that will eventually become my ground-source heat exchanger.

I know that PEX is pretty good stuff, but because of the way the PEX plastic is made, it can't be welded.

PVC and CPVC is out of the question because it gets brittle.

I've noticed that in all the sources I have read, High Density Polyethylene (aka: HDPE) is the pipe of choice, with 3/4" being the size often used for small, home-heating applications. If the Ph of your soil is not acidic, copper would be good too, but very expensive. So in practice, HDPE seems to be the choice, with life-spans of 50 years guaranteed, and life-spans of 200 years expected!

The only catch is that many states require that the HDPE have all joints & couplings being welded. Since I'm going to be doing this myself, I have considered many alternatives to welding, including barbed connectors and stainless steel hose clamps... should last a good long while.

So, I was at the local gigantic home-improvement store, looking over various kinds of plastic pipe, and I saw big rolls of black polyethelyne water pipe. I zeroed in on the 3/4 pipe and saw that they have two grades, schedule 40 (100 psi) and schedule 60 (160 psi). The schedule 40 was too thin to consider, looks like it could be crushed by the force of the earth above. The schedule 60, however looked really pretty good.

So I bought a short length of the schedule 60 and went looking for possible joining solutions. At a high quality (professional) plumbing store, I did find some very nice looking brass barbed joints which would use stainless hose clamps. I also did some asking about as to welding tools. Turns out that there's a company named McElroy that makes a tool called MiniMc (pronounced 'mini-mac'), that consists of a teflon-faced heating tool, a ratcheting facing tool, and a gripper/slider tool that holds the pipe while it is being faced, heat-melted, and fused. See photos, etc here: (McElroy MiniMc Fusion Machine Overview). Also check out the manual, photos, animations, movies, etc. Quite an education! The local outfit sells the tools for nearly $2000 (OUCH!) they'll also rent them for $45/day or $180/week (gasp). But this doesn't really look like rocket science...

So, on the way home, I stopped at my favorite junk store and got a teflon skillet, to try a wee bit of free-style polyethelyne welding. I put a chunk of aluminum plate on the stove burner, and put the teflon skillet on top of that and set the gas flame as low as it would go (my stove has 35,000 burners). I used an infra-red thermometer and set some short lengths of Polyethelyne upright on the skillet. When the heat got up to about 300 degrees, I noticed a small bead forming on the pipe end, where it met the skillet. I picked up the pipe in my hands and pushed the hot ends together, and to my amazement, welding was happening!


Photo of my first try



Photo of my second try

This stuff ain't rocket science. I mean if I can get this close on two tries with a teflon skillet, this is possible!

Now, can anyone think of a way to make a heater tool and a device to hold the pipe securely while it is fusing?

This welding problem is sort of the missing link in the ground source loop field phase of the GSHP project.

Quote:
EDIT (11/29/2011): There are two types of HDPE fusion welding being done, butt welding and socket welding. In pages that follow, I demonstrate how I successfully made a butt welding paddle out of a heavy teflon skillet ($4), a removable electric skillet heat-controller ($3), and a heating element from a mini-panini maker ($4), all parts from a local thrift store. The electric welding paddle worked very well, and I am still using it.
The second type of HDPE welding, socket welding, requires Teflon coated parts of a precise size, that cannot be found on the second-hand market. Thanks to rhino 660 a reader and persistant EcoRenovator from Florida, a source for these parts has been found at a reasonable price, making socket welding also possible.


Source for socket Faces...

...the persistant EcoRenovator will still have to solve the heater and heater-controller problems, but therein lies the fun.
Regards,

-AC_Hacker
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Last edited by AC_Hacker; 11-29-11 at 11:41 AM.. Reason: In-Line images...
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