Instructables
Picture of Welding EMT Conduit
I use EMT (Electrical Metallic Tubing)  conduit in a lot of my projects. EMT is cheap, smaller sizes are bendable and it is readily available at local home supply stores.

There are potential health problems welding EMT however. Please read this (and other Instructables warnings) before you consider welding EMT.

The biggest problem is that toxic fume are given off when the welding arc heats up the galvanized coating on the EMT. These fumes (mostly zinc oxide) are toxic, as in poisonous to breathe!

See this Instructable for a description of the risk: http://www.instructables.com/id/Bicycle-cargo-trailer--200-lb-capacity%2c-%2430-for-pa/step11/Safety-considerations/

NOTE: DO ALL OF THESE STEPS OUTDOORS IN A WELL VENTILATED AREA!

I am an amateur welder (not even close to an expert!) and to minimize the risk as much as possible I use these three steps when welding EMT.

BE CAREFUL. BE EXTRA SAFE. DON'T BREATHE IN ANY FUMES EVER. DON'T GET IN A HURRY AND SKIP ANY SAFETY PRECAUTIONS. USE A RESPIRATOR IF YOU ARE NOT POSITIVE YOU ARE AVOIDING THE FUMES.


 
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Step 1: Vaporize the Coating

Picture of Vaporize the Coating
1. Heat the EMT to vaporize as much of the galvanized coating as possible. I use a MAPP torch (I don't know if propane would work.) to thoroughly heat the area(s) where I will be welding. Do this outside. (Photo #1) The galvanized coating will vaporize and leave a brown residue (Photo #2 arrow)

Step 2: Grind the Surface

Picture of Grind the Surface
DSC04449line.jpg
2. Grind the area that you heated. I use a flap-pad in an angle grinder, a wire wheel in an electric drill or an abrasive paint remover for this step. Do this outside. (Photo #1) The result is a bright and shiny steel surface (Photo #2 below the yellow line)

Step 3: Move the Air While Welding

Picture of Move the Air While Welding
3. Weld with a fan (usually on the low setting) gently moving air over and away from the weld zone. Do this outside. (Photo #5) Move the fan around until the air flow moves the fumes away but doesn't blow the shield gas away from the weld arc. This position can change depending on whether it is windy or calm outside.
davidsaradin4 months ago

Or, follow Hackett's video to strip away galv, inside and out:

bukwessul8 months ago
sola0005, You can grind it off, but if it the galvanization done correctly, it actually seeps into the metal. The etching won't ever remove all of it, but it will be "cleaner" to weld. Fume wise, if you do get a mild bout of zink poisoning you can drink milk and it will minimize the nausea.
sola00059 months ago
Any reason I couldn't skip the heating part and just grind the zinc coating off?
Thanks!
Susan
andersonhdj2 years ago
Most anythng galvanised can be welded using a stick welder and 316 stainless electrodes, there's no spatter or striking problems and an excellent weld is obtained. As usual, BEWARE OF THE FUMES!!
valveman2 years ago
If using any acid to dissolve the galvanized coating, don't forget to wash the tubing well or the acid will keep working. Another option is to grind off the galvanized area you want to weld. As an extra precaution, buy a half face respirator like the 3M 3600 with 2097 filters. These fit well and can be used with practically any welding helmet.
Phil B3 years ago
I am guessing you are using a MIG welder. Do you need to weld in short bursts to avoid blowing holes in the tubing, or are you able to run a continuous bead? I have used a stick welder on EMT. The heat was about as low as I could go without sticking the rod. Starting an arc was difficult, so I used a piece of carbon rod. See my previous Instructable on that. I used 1/16 inch 6013 rod and welded in short bursts. There was some grinding to be done afterward to make the welds look decent. For me, the difficult thing was to weld "T" joints like you have in your photo. The butted piece heats up faster at the end than the continuous piece does at the joint. It is very easy to blow holes.
i use a stick welder too 1/16 7018 works better though
purplewg3 years ago
A method I use is dipping the ends to be welded in Muratic acid. Yeah, the same stuff they use in pools. It etches the galv right off.
Thanks, I love this hint. I have some sort of acid around and it'll keep me from using up Mapp. Very cool.