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Anonymous Poster #1

Welding on Galvanizing

02/09/2014 10:28 PM

I have done galvanizin of 32mm thick plate, now I have to do lot of welding on one side of this plate, is there will be any effect of thi welding on other side of this plate where galnizing is there?
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lyn
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#1

Re: welding on galvanizing

02/09/2014 10:36 PM

Yes, don't do it without a respirator.

Yes, don't do it without a respirator.

Yes, don't do it without a respirator.

Yes, don't do it without a respirator.
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SolarEagle
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#2

Re: Welding on Galvanizing

02/10/2014 12:01 AM

It depends....

http://www.galvanizeit.org/design-and-fabrication/fabrication-considerations/welding/welding-after-hdg

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#3

Re: Welding on Galvanizing

02/10/2014 2:31 AM

How big of stuff are you going to weld to it? Up to maybe 15-20mm, the heat might not affect the opposite side. More than that could be a problem.

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#4

Re: Welding on Galvanizing

02/10/2014 7:13 AM

Welding onto things that are galvanised does two things:

  1. It causes the zinc to vaporise, producing fumes and smoke that are harmful to the individual doing the welding and any others that are nearby, and
  2. It removes, in the fumes, the protective effect that the galvanising was applied to provide.

So generally don't do it.

  • If a thing needs to be galvanised, then do it after all the fabrication by welding is complete.
  • If a galvanised thing needs to be welded then in addition to the operative wearing welding PPE, a supply of fume-free air needs to be forced into the operative's location so as to protect that individual and any bystanders from the effects of the smoke that will be produced. Whatever the thing is, it will need re-galvanising after the welding is all complete.

Next time, the work needs better planning so that the galvanising is done after all the welding is complete.

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#5

Re: Welding on Galvanizing

02/10/2014 9:29 AM

Depends on the heat(temperature) on the other side of the plate.

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#6

Re: Welding on Galvanizing

02/10/2014 2:13 PM

Here is a link to safety in welding galvanized metal. It gives evaporation temp of the zinc.

http://www.sperkoengineering.com/html/articles/WeldingGalvanized.pdf

Note it's not the zinc you have to worry so much about. It's the impurities like lead.

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#7

Re: Welding on Galvanizing

02/10/2014 6:09 PM

It is preferable that galvanization be removed everywhere temperatures are likely to exceed 750 F and then reapplied after all welding has been completed.

.

Heating galvanized steel to over 750F increases the risks of a number of problems from mere separation of galvanizing layer, to more severe problems like catastrophic failure via LME (liquid metal embrittlement).

.

You definitely should respect the advice several others hhave given you concerning breathing safety precautions, even with the removal of galvanizing material, there is likely to be some you missed that will vaporize.

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old salt
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#8

Re: Welding on Galvanizing

02/12/2014 9:41 AM

From a strictly welding standpoint it all depends upon the amount of welding being done, the current being used, the number of passes, the length of time for each pass, the wait time between consecutive passes and the type of rod being used. These all determine how hot the opposite side gets and therefore how much galvanizing becomes airborne. They all determine how hot the back side of the plate will get. They are also not everything that influences the temperature.

At 32mm, approx. 1-1/4", the root pass is going to be very deep, which increases the heat. The root pass rod will probably be something like a 6010 which is hotter than many others. This rod is slower than many and this will increase the heat. The closer this root pass is to the other side the hotter it will get. The more time between passes the cooler it gets. The higher the current the hotter it gets. Higher current is higher heat. As you can see there isn't a yes or no answer to your question. Management of these factures to keep the steel as cool as possible will not heat the back side very much, less than a 100 deg change. Not controlling them could raise the temperature well over 1,000 deg or more and destroy the galvanizing on the back side.

For a good demonstration of how much airborne materials is released when welding galvanized steel, watch someone do it in such a manner that you don't have to wear the shield. I think it will greatly increase your appreciation for the PPE.

Good Luck, Old Salt

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