territorialmillworks

Advise on removing hot dip galvanize from large piece of steel

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I've read lots of warnings about the toxicity of galvanize so I wanted some input before doing myself harm...Need to weld on to one leg of a hot dipped galvanized triangular shaped piece of steel that measures 24 X 24 x24 and 6" in depth. My thought was to stand it up in a plastic tub with vinegar on the leg that I need to weld to. The piece is made from 1/2 X 6 plate and will require multiple fillet welds, a lot of heat so I'm assuming that I'll need to remove a larger area. Will vinegar eat deep enough to remove the hot dip? Can I do this with acid instead? I have a carbon filter respirator and arm length rubber gloves. Thanks for your help, Keith

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you didn't say how many inches of weld.....grind the galv away and use 6011 for the root pass and go over with a 7018 but use good ventilation
grinding is no worse than the weld, the galv will burn away anyway so get used to it. Alum. paint over it

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I do not recall "get used to it" as being anywhere near safe.

Grinding galv puts lots of Zinc dust into the air which is NOT GOOD. Use LOTS of ventilation. BIG FANS both when grinding and when welding. You want any zinc fumes to be moved as far away from YOU as possible.

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I meant get used to the fact that the galv goes away, and you have to paint it or it will rust. I've been welding galv pipe for thirty years...don't like it, but if thats the job..... you have to know how to do it, safely

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Muriatic acid will remove it quite quickly in minutes. (vs hours with vinegar) You may try washing instead of dipping since it is potent. It will gas off hydrogen, and may aerosolize the acid, so take precautions. Wash well with soap and lots of water to neutralize.

Melting point of zinc is 787F, there will be vapor at that point too. You can wrap with wet rag (water) to stop heat from moving to the unstripped areas, but need to strip a suitable amount. Re-wet the rag as it dries out.

There are "cold galvanizing" and Zinc sprays that work fairly well, they are a paint vehicle with a high zinc load in them There are other steel protecting paints that can be used in place of galvanization. Sadly they are not generally as good as hot-dip.

Grinding is probably safer than heating because the dust can be more easily protected against with a mask than the fumes.

Phil

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Smithy-1
As long as it is done safely, Thanks for clearing that up.

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Grind it off.

Acid etching has just as many negatives as grinding, ... PLUS disposal of the HAZ-MAT acid.


.

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Another thing concerning galvy is the very popular "turkey in a garbage can" method of cooking a turkey.

Are there any health concerns associated with cooking food with a galvanized garbage can? Seems to me that there would be.

http://www.google.com/imgres?imgurl=http://www.scoutingthenet.com/Cooking/Turkey/images/near_end.jpg&imgrefurl=http://www.scoutingthenet.com/Cooking/Turkey/index.php&h=242&w=250&sz=15&tbnid=1U8e6aavd44bhM:&tbnh=97&tbnw=100&prev=/search%3Fq%3Dturkey%2Bin%2Ba%2Bgarbage%2Bcan%2Bpictures%26tbm%3Disch%26tbo%3Du&zoom=1&q=turkey+in+a+garbage+can+pictures&docid=PPBrDNP6KZeskM&hl=en&sa=X&ei=oUgKT-SeBcjx0gHe6ajQAQ&sqi=2&ved=0CEQQ9QEwCQ&dur=3272

http://www.google.com/imgres?imgurl=http://elpasotimes.gannettonline.com/gns/thanksgiving/tfoto-tcan2.jpg&imgrefurl=http://elpasotimes.gannettonline.com/gns/thanksgiving/20041110-53075.html&h=331&w=240&sz=30&tbnid=50XR1LLSrdgomM:&tbnh=93&tbnw=67&prev=/search%3Fq%3Dturkey%2Bin%2Ba%2Bgarbage%2Bcan%2Bpictures%26tbm%3Disch%26tbo%3Du&zoom=1&q=turkey+in+a+garbage+can+pictures&docid=RIpFsGVByzGuSM&hl=en&sa=X&ei=oUgKT-SeBcjx0gHe6ajQAQ&sqi=2&ved=0CEAQ9QEwCA&dur=481

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Another thing concerning galvy is the very popular "turkey in a garbage can" method of cooking a turkey.

Yikes! First time I've seen that, don't want to try it.

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Grind it off.
... PLUS disposal of the HAZ-MAT acid.



Grinding probably would produce a better local area removal of the galv for welding than acid.
.......But mild muriatic acid isn't high on the haz scale......I've seen stone masons and crete heads wash down their work many times with HCL and it runs off into the ground after a good hosing down.....OSHA/EPA would be all over this widespread practice if it was that detremental to the enviroment or the workers........Use with caution and do it outdoors..... B)

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Grind it off and use a wheel made for aluminum on the galvy, it wont load up or use coarse grit sanding disc like 36 or so. Get back about 1/2" from the weld should be enough.

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Grinding probably would produce a better local area removal of the galv for welding than acid.
.......But mild muriatic acid isn't high on the haz scale......I've seen stone masons and crete heads wash down their work many times with HCL and it runs off into the ground after a good hosing down.....OSHA/EPA would be all over this widespread practice if it was that detremental to the enviroment or the workers........Use with caution and do it outdoors..... B)


Anything with a pH of 2 or less is a Characteristic Hazardous Waste by the characteristic of corrosivity, 40 CFR Part 261. Waste Muratic Acid falls into that category. The penalty for illegal disposal of a hazardous waste is a fine not to exceed $50,000 and or 5 years in prison. Cement being on the alkaline side of the pH scale would tend to neutralize the acid although to what extent could only be determined by testing. Myself, I would be careful about advising people to just dump something on a public forum that has world wide access.

There are several stickies on this site on the effects of Zinc fumes I would suggest that you read them. If one uses proper respiratory protection with adequate ventilation, grinding and welding should not be a problem.

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Zinc chloride is the classic tinner's flux used to solder sheet metal, so your toxic waste is actually a useful commodity. If you want to dispose of it and if your used acid still has too low a ph, add lime until it's neutralized. (just regular lime unslaked is NOT needed!)

If the original was hot dipped galvanized you should probably look into doing the same for the repair/modification!

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Honestly, the turkey in the trash can oven amuses me more than disturbs me. Zinc is a dietary requirement. (edit: I looked, my daily multivitimin has 12mg of zinc)

Phil

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Honestly, the turkey in the trash can oven amuses me more than disturbs me. Zinc is a dietary requirement. (edit: I looked, my daily multivitimin has 12mg of zinc)

Phil
Zinc, ingested is a necessary mineral... fumed zinc in the resperatory system is toxic. Handling zinc isn't a problem either... it really is just a matter of how it is getting into the body, and of course, the quantity.

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Well the thread is about advice so I'll limit this response to some don't and facts.....Dont ever mess with acid if you aren't knowedgeable with handling it, as with fire, machinery and paint etc.......working with acid indoors is especially dangerous, don't do it...............Fact: Stone masons, bricklayers and concrete workers routinely wash their finished work with muriatic acid they get from places like Home Depot,Lowes,Ace etc......It's available in the section where concrete and such is sold for that purpose. They spray the stuff on mostly and never have I seen them take any special precautions other than diluting it with water for disposal ..........They do on occasion wear protective clothing,goggles and resperators. They can be real inconsiderate when other trades are present and are roundly cursed at times when they give no warning.Those fumes and airborn droplets are NASTY!
Kieths project with it's large surface will make a lot of fumes if doused with the stuff so wear the protective clothing and resperator if you choose to do so Keith, myself I would simply get upwind of it but that's a risk I'm personally willing to take..... :)

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When cleaning masonry we would dilute the muriatic acid down to about a 5% solution. Muriatic acid for the construction/masonry industry is typically bottled in a 20%-30% solution with 70%-80% water. When you rinse down the wall after washing you are further diluting the solution down many times. The result in the soil would be a fraction of a % solution. Not saying it's OK, just providing info.

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As old as this topic is I want to tell you a couple of things about muratic acid. First, muratic acid is the acid used in swimming pools to adjust the pH. Another place it's used in in Murine eye drops. However in both the pool and in Murine the acid is VERY diluted. Just looking into a bottle of swimming pool muratic acid can get some fumes in your eye and damage it. Always use goggles. Anyway disposal isn't really damaging if it's diluted enough, just like if you were to drain a swimming pool. 

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You will need to use the amount of acid needed to remove the amount of zinc, which leaves you with a large amount of hazardous zinc compound material to dispose of properly.

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True. I was thinking about the acid not the zinc. I'm not sure how to dispose of zinc properly. Of course zinc is in the ground and even ocean water naturally. It's even in vitamin supplements so it must not be too dangerous. Still, I don't know what form the zinc removed from steel is in compared to these.

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Arsenic is also a necessary nutrient found in sea water but in very small amounts, dont want too much or it causes problems

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Wow; all the early poisons were found "naturally".  For instance Botulism is a naturally occurring thing that makes one of the deadliest poisons out there. Arsenic, mercury, asbestos, cyanide, digitalis, the list goes on and on not to mention all the naturally occurring diseases---want some tetanus?---I don't!  Even water will kill you if too much is consumed and it's a necessity to the body.    So "naturally occurring" has no bearing on what's actually tolerated by the human body. 

I had a friend who got metal fume fever that progressed to pneumonia and DIED.  Please don't follow in his footsteps.

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