Reducing Resistance in Electrofusion Couplings for Steel Pipes

[mghdpe]

I have 6" Carbon steel pipe

Question. I am working on a project. I have 6" Carbon steel pipe which I am going to use 10" High Density Polyethylene Pipe(HDPE) to sleeve and protect 6" pipe from corrosion. This pipe will be buried. I am trying to use electrofusion coupling to connect HDPE. The couplings are install by using an Electrofusion(EF) box. It sends current to the coupling and melts/bonds O.D. of pipe to I.D. of coupling. My problem is that when the EF Box is ready to melt the coupling, a resistance problem occurs. It seems like the metal from the 6" pipe will not allow the EF Box to work Properly. I can take the coupling off the 6" Pipe and it works fine, but as soon as I place it back on the steel pipe I get a resistance error. The EF box Runs on 240VAC 30A. I manually operate it EF Box and set to run 40V for 6Min(the EF Coupling have internal wiring and 2 leads where I connect my EF Box.

My question is, is there and way the resistance on the metal pipe can be eliminated or reduced so my EF Box can operate.

Thank You

 

[Graham T]

Hi - the resistance of the fitting is set, and the wire is either ploughed into the plastic, or formed into the plastic, so the steel pipe has no influence at all on the fitting resistance. The problem is most likely the fitting's wound wires are shorting when pushed onto the plastic pipe (very common problem) probably becuse the fit is too tight. Normally, the circumference of the pipe is scraped (if using a rotary scraper the scrape depth is a uniform 0.2mm depth) before placing the fitting onto the pipe, to remove oxidation and detritus, and this reduction in diameter can help slide the fitting onto the pipe. You need to measure the insertion depth of the coupler (half the width less 5mm), mark the pipe halves with te dimension + 10mm, and scrape the pipe clean. Make sure the fitting slides on easiliy (use a new fitting as the one you have mentioned herein may be damaged as described) - insert the pipe halves fully and exqually to the stop in the center. The pipes MUST be secured and aligned properly and preferably clamped so they cannot move when the plastic becomes fluid - the fitting can move, and the winding resistance wires can move also and short-out, giving you the error you already have or fail altogether.
I hope this helps you.
Regards
Graham