Are you sure you want to weld that?  Let's talk about galvanized.

  2017 July 12    Metal & Shop  


Introduction


This article is about galvanized metal, and some safety concepts if you're thinking of welding it. 

Hopefully you'll find it helpful;  it could even keep you from doing something dangerous.

Please read the Disclaimer

So, here we go. 


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Silvery, Gray, or Bluish-Gray


You look at a piece of sheet metal and notice light patches amid the dark.  They're like irregular snowflake patterns, frozen in the surface.  This is called "spangle". 

You will see this often, but not always, on hot-dip galvanized metals.



Galvanized pipes are usually hot-dip, not the thinner electro-galvanized.

Arc welding can easily vaporize zinc.  With temperatures of 10,000 Fahrenheit or more, it can vaporize a lot of other things, too.

When the zinc vapor meets air, it quickly forms tiny particles of zinc oxide.  These are basically "fumes";  the particles are so small that they form a colloid.  Unless there's a breeze, the fumes will just hang on the air.



Look closely at the rust.  It might be rust staining over a layer of galvanizing. 


Too much metal-- even zinc or iron-- is bad for you. 

Traces of other, more toxic metals are common in the environment, but especially in things made of metal. 

"Spangled" galvanizing may have around 0.1% of lead, aluminum, cadmium, or other metals.  Normally that's not a big deal;  the thing is just sitting there on a shelf or something.  But an electric arc would vaporize the metals. 



Metal Fume and Other Maladies


Can metal-fume fever cause lasting effects?  Well, the basic mechanism appears to be cytokine-related.  There's an inflammation response. 

In extreme cases, it might lead to a "cytokine storm", which could be fatal.  That's a lasting effect.  But even aside from that, zinc overload is probably not good for you.  Repeated bouts might eventually throw off the redox balance in your cells. 



Galvanized pipes have zinc on the inside, too. 

Magnesium, calcium, antioxidants, and certain other things would probably offer some protection.  This is one of several reasons to eat good food, rather than a constant diet of funnel cake and pork rinds. 

I wouldn't be too quick to dismiss the old welder's tactic of drinking milk (if you're not allergic).  It should not be the only measure taken, but it could have some merit.  Drinking milk can increase serum proteins, sort of indirectly but it still seems to happen.  Perhaps by slowing the breakdown of serum albumin.  (You need your serum albumin to help deal with cadmium and other metals.)  And the milk definitely supplies calcium. 

It could also be that cow's milk changes the cytokine response, or it could be something else.

Another traditional remedy is milk of magnesia;  this would supply magnesium.  Some toxic metals compete for magnesium, and probably calcium, at enzyme binding sites;  deficiency of these would make it worse.  There are probably multiple reasons why magnesium could help.  (Once again, read the disclaimer.)

Most of all:  wear a respirator when you weld.  Get a respirator that fits under a welding helmet, so you will wear it when you need it most. 

One advantage of stick welding is that it works in a strong breeze, unlike MIG.  So you can use a shop fan to keep the air moving.  (DON'T try to make a breathing system with your air compressor;  the oil will kill you.)  Just use a shop fan.  It will decrease the fumes that get to your respirator.  Get in the habit of using both of these where possible.




Conclusion


If you can help it, try not to weld through galvanizing.  Zinc fumes can cause metal fume fever.  Traces of other impurities-- very common in things made of metal-- could worsen it. 

Yes, there are probably certain foods which could decrease some of the damage from toxic metals.  And I wouldn't dismiss those.  But the surest thing is to use proper safety gear and welding technique to reduce the chance of harm in the first place. 

If for some reason you have to weld galvanized, first remove the coating as much as possible near the weld area.  Then when you weld, don't rely on the direction of the wind.  Use a shop fan or fume extractor, and be sure to wear a P100 respirator under your helmet.  This may sound obvious, but many people say "Ah, it's only a quick repair, I'll just weld right through that coating." 

Get the right gear and use it. 


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