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PostPosted: March 31, 2018, 2:26 pm 
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I'm considering using 1" o.d. thin-wall EMT tubing (i.e., electrical conduit) for some non-structural body-skin framing. This would allow using a conduit bender to easily form several required 8" outside-radius bends. The problem is EMT tubing has an electro-galvanized exterior coating and the framing requires welding, creating toxic fumes. :ack:

Using non-galvanized 16 gauge 1" exhaust tubing isn't a good option because EMT tubing has oversize outside diameters which make the conduit bender dies a poor fit for the exhaust tubing.

So how to safely remove the galvanized coating from the EMT tubing? A chemical or electrical (reverse plating) approach would be preferred. Sanding it off would create zinc dust. A forum search suggested using possum pee, but I don't have a pet possum. A web site suggested heating with a torch while wearing a hazmat suit. :shock:

I'll to need cleanse about three 3' pieces of tubing, so the quantity isn't large and a chemical or electro-plating bath would be easy to make.

EMT tubing also has an anti-corrosive coating on the inside of the tube, but it's organic and should cook off safely.

Your thoughts on safely removing the galvanized coating ? Thanks!

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PostPosted: March 31, 2018, 2:54 pm 
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Pool acid ("muriatic acid", hydrochloric acid), though note that it'll produce hydrogen, so keep it away from flames.

Also, the parts will obviously have to be well cleaned, maybe with a dash of baking soda thrown in for good measure.

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PostPosted: March 31, 2018, 3:03 pm 
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Hi Tom! Personally, I would just weld it. Do it with some ventilation, like at least an open garage door or in the driveway if it's not windy. Avoid putting your face in the rising plume of smoke from the welding. I did this with Home Depot chainlink fence tubing to make a large run area for my families chickens. The tubing your talking about is zinc plated with a thin layer, it's not hot dipped galvanized. Some caution is in order, but we're not talking lead pipe, arsenic sandwiches or stacking bricks of plutonium.

I think vinegar would take the plating of tube ends, over the space of a few hours, maybe overnight. Perhaps you would have luck with a paper towel soaked in vinegar for places in the middle of a tube.

I think you could hold your breath for most of the work your talking about because it's small tubing and it probably takes 3 or 4 beads to make it around the tube. With some ventilation you would be OK, as opposed to a closed space. Don't blow a fan on the work which removes the inert gas.

Good luck!

We did use to brush our teeth with gasoline though so maybe I'm just old fashioned...

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PostPosted: March 31, 2018, 8:13 pm 
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I have read many internet "stories" about this. Everything that I have read from technical publications says that welding galvanized steel does not create "toxic" anything.
Quote:
tox·ic
ˈtäksik/
adjective
adjective: toxic
1.
poisonous.


Some people are sensitive and get flu-like symptoms. That can last for a day or so. There are no known long term effects i.e. it is not "toxic". See this from the CDC.

https://www.cdc.gov/niosh/docs/81-123/pdfs/0675.pdf

Personally, I weld galvanized and have never suffered any ill feelings. I have welded EMT and galvanized sheet steel. I feel it is a lot more safe than dealing with muriatic or hydrochloric acids. Good ventilation or a respirator will help if you are one of the sensitive ones, although I've never personally used one while welding EMT.

Just remember that any breeze at the weld will remove the inert (AR/CO2) gasses used. if you insist on forced ventilation, it might be a good application for flux core wire. YMMV

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PostPosted: March 31, 2018, 9:37 pm 
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Muriatic acid/pool cleaner works great. It leaves a sort of sandblasted surface that welds nicely.

The plastic jugs the local hardware store sells seem to be slightly permeable; I put the jug in the lawn shed instead of keeping it in the shop. A few weeks later everything within a few feet of it was rusty.


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PostPosted: March 31, 2018, 9:41 pm 
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rx7locost wrote:
Personally, I weld galvanized and have never suffered any ill feelings.


A great many people do. I got a good whiff once and had to sit down Right Now on a dirty shop floor and concentrate on breathing for a while.

Even if I'd looked up the safety stuff first, I would have thought nothing of firing up the welder; OSHA and the MSDS cry wolf about so many things, any real hazards are lost in the noise.

One of my favorites is the MSDS for "SAND, WASHED AND DRIED." Holy moly, it's dangerous! *How* dangerous... they kind of skip over that.


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PostPosted: April 1, 2018, 12:53 am 
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It's a real thing, Google " Silicosis"

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PostPosted: April 1, 2018, 8:47 am 
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TRX wrote:
rx7locost wrote:
Personally, I weld galvanized and have never suffered any ill feelings.


A great many people do. I got a good whiff once and had to sit down Right Now on a dirty shop floor and concentrate on breathing for a while.

Even if I'd looked up the safety stuff first, I would have thought nothing of firing up the welder; OSHA and the MSDS cry wolf about so many things, any real hazards are lost in the noise.

One of my favorites is the MSDS for "SAND, WASHED AND DRIED." Holy moly, it's dangerous! *How* dangerous... they kind of skip over that.


Like I said, some people are sensitive. You must be one of them. While there may be many who are affected, and the temporary effects are not minimal, there are no reputable precautions about long term health risks that I can find regarding "Monday Morning Fever", Metal Fume Fever", "Zinc Oxide Fever" etc. This is what I was trying to focus on.

I too, am not a fan of OSHA's over-cautious limits on just about everything. I did link to the CDC paper. I think they are fairly unbiased in this subject.

Some welders' tales suggest drinking a glass of whole milk before welding. I'm not sure if that helps or not. I've never tried it myself. It may just be a myth, or not. It certainly can't hurt.

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PostPosted: April 1, 2018, 3:20 pm 
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In general you should avoid welding fumes. The handbook that came with my welder specifically mentions making an effort not to be directly above the work area so that you are in the plume. Welderers are susceptible to getting live or kidney cancer, I don't remember which.

Tom, give the vinegar a try. The whole point of zinc plating is that it is so willing to sacrifice itself in the face of attack...

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PostPosted: April 1, 2018, 8:37 pm 
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Thanks all. I much appreciate your insights and suggestions. My lungs fall into the "sensitive" category so think I'll go ahead with the de-galvanization. I'll give vinegar (+ extra time) a try and if that doesn't do it then step up to muriatic acid with its complications. After the acid does its job and the bubbling stops, then the pieces will get a water rinse plus a second, neutralizing rinse with either a baking soda solution or a household ammonia solution. One more rinse plus a light sanding should clean them up ready for bending and welding.

I couldn't find the right size conduit bender on craigslist so ordered a 1" bender head from amazon and will use a piece of NPT pipe for the handle, a locost solution. Under the Benfield System, 1" conduit benders produce an 8" stub height (the outside radius of the bend.) 1" EMT tube is 1.163" o.d. x 0.057" wall (a 10' section of 1" EMT costs a little over $9 at HD.) 3/4" EMT tube is 0.922" o.d. x 0.049" with a 6" stub height. 1/2" EMT is 0.0706 o.d. x 0.042" with a 5" stub height. Not all benders use the Benfield System so one has to chose their bender wisely. But this approach makes for cheap and easy bends if the tube size and radius match. and EMT tubing should work for non-critical structure.

So that's the theory. By the end of the week I should have some non-galvanized bends made. I'll report the results. Thanks again for your input.

Horizonjob wrote:
We did use to brush our teeth with gasoline though so maybe I'm just old fashioned...
Geez, and I always thought Jack Daniels was the go-to mouthwash... :cheers:

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PostPosted: April 2, 2018, 3:40 pm 
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Personally, I just use my fight-angle grinder & a flap disc to remove the galvanizing within a 1/2" or so of points to be welded. With a MIG, at least, the heat doesn't travel further than that, so it never attacks the galvanizing nearby.

I figure that the galvanizing that remains is a good thing.

I never get gassed this way, and I get nice, clean, uncontaminated welds.

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PostPosted: April 3, 2018, 3:53 pm 
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I also used some EMT for areas I wanted rounded. Just held my breath and kept the air circulating with a fan. I'd be more concerned if I were doing a lot of it. As far as toxic metals go, I think zinc is down the list a ways.

One thing you'll find out though is that it is REALLY EASY to blow holes through the stuff. It is not nearly as forgiving as the normal 16ga tubes.

All in all, if I were to do it again, I'd figure out a way to use the 16ga tube and forget the EMT.


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PostPosted: April 4, 2018, 6:54 am 
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Geez, and I always thought Jack Daniels was the go-to mouthwash...
Tom, are you SURE you ain't a Southerner???

:cheers:
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PostPosted: April 5, 2018, 1:20 am 
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GonzoRacer wrote:
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Geez, and I always thought Jack Daniels was the go-to mouthwash...
Tom, are you SURE you ain't a Southerner???]
JD, my heart may be in Dixie when it comes to whisky, but my Southerner credentials would probably get disqualified for opting to use vinegar instead of possum pee to remove the galvanizing.

Well, the vinegar worked, albeit a bit on the slow side. I used Cleaning Vinegar (6%) and soaked the cut EMT tube lengths. It took about a day and a half and a refresh on the vinegar to remove all the plating. I set the vinegar soaks outside so my eyes wouldn't water and the garage wouldn't rust up worse than it is. The outside temperature was 40*F - 50*F, which probably lengthened the removal process. The organic anti-corrosive lining on the inside of the EMT tubes came off as well. When the plating was off, I hosed off the tubes followed by a short soak in a weak ammonia solution to neutralize the vinegar and then a final rinse. Result: nice shiny steel tubes ready to bend, fishmouth and weld.

There will be several welds on the tubes, some in really awkward positions. No way I could avoid the welding plume on all of them. And I turn blue in the face if I hold my breath too long. But now no worries, other than blowing holes through the thin-wall tube.

Hmmm, does JD stand for Jack Daniels? A curious world want to know... :?:

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PostPosted: April 5, 2018, 2:41 pm 
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Yo, Tom-
I feel certain possum pee would be damned hard to harvest. I might also totally dissolve the conduit on contact. I don't really know and do not wish to find out. You ever seen a possum up close?
Attachment:
Angry Possum.png
Angry Possum.png [ 1.09 MiB | Viewed 2006 times ]

With regard to "fumes" and such, I agree with you about taking care, not just "hold your breath" as a safety procedure. Like Chuck pointed out, the info about zinc and zinc fumes and welding fumes in general is rather "varied" and I'm not sure how much to believe. But removing the stuff and welding in a well ventilated area surely can't hurt. Good on ya, Tom!
:cheers:
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