Welding galvanized carbon steel 5

[spike]

Is there any reason why a mill galvanized carbon steel assembly can not be welded if the steel is to be used in a very cold environment? I know that normally the galvanizing should be removed prior to welding, but what if it is not removed.

 

[unclesyd]

It is welded all the time, i.e. fence post, small structural, and so on. The zinc should vaporize or melt in front of the melt pool and not cause much trouble. . It will take a little getting use to welding it. After welding you have to clean the weld area with a wire brush and apply a "cold galvanize material/coating".
For maximum strength or structural code welds it is advisable to clean the galvanize off prior to welding. It will still require a "cold galvanize". Stay with 6010 welding electrode. Some of the maintenance consumable manufacturers make a special rod (flux) for welding galvanize on non-critical connections.

Any welding on galvanized should be done it the open or well ventilated (exhausted) area and the welder needs a respirator suitable for metal fumes. You will hear people say that's not necessary it is and is required in some areas.
Metal fume poisoning is very pleasant for anyone and especially to some.
Be careful!

 

[sayee1]

A star for ur reply unclesyd, to the point and succinct.
But one confusion "Metal fume poisoning is very pleasant for anyone and especially to some." ??? pleasant ::typo??? or intended ?

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[unclesyd]

sayeeprasadr,
Thanks!
The last 2 sentences should read:
Metal fume poisoning is very unpleasant for anyone and especially to some.
Be Careful!

The "some" was a reference to myself and what is now called an industrial hygienist who had argued with me about the hazards of welding galvanize.

 

[Nate101]

Check this out.

http://www.hdgasa.org.za/welding.htm

There are some galvanizing paints available that take care of the exposed area's, if the rust is an issue.

 

[Rich2001]

I agree that welding of galvanized steel is done all the time. On critical welds one needs to be assured that the galvanizing is removed. Zinc is very ductile material and will smear over the surface. To check to see if it is removed heat the cleaned(sic) steel to around 500 F, the steel will turn brownish while any galvanizing will be silver in color.

Zinc forms brittle intermetallic compound with iron. Cross section some welds on galvanized steel, polish the surface using kerosne as the lubricate and etch with a Cro3 solution. It is not uncommon to find zinc pipes starting at the root of fillet welds.

As one know along the the is aone can observe the HAZ in the steel. There is aloso a HAZ in the galvanizing. Depending on the galvanizing alloy strange intermettalic compound can form (many very brittle) and could cause solid metal embrittlement of the steel. This is time at temperature dependent, therefore watch interpass temperatures, keep as low as possible.

Commercial galvanizing is generally 98% zinc, 2% of aluminum, tin, bismuth, lead, nickel. Several low melting temperature eutectoids can form that could wet the columnar type grain boundaries in the weld's solidifcation zone.

Because of the galvanize coating common low cost NDE methods to locate discontinuities do not exist, with the exception for the limited use AC Dry Yoke magnet particle inspection. ACFM (AC Field Measurement), though realtively new (ASTM standard approved last year)and fairly expensive can detect dicontinuites beneath coating at realtive quick speeds and provide a permanent record.

 

[JoeTank]

Just a word of caution. You should remove the galvanizing material if the weld is being made to a stainless steel component. Otherwise you end up with cracking.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[Weldmedic]

Another method to restore the galvanizing are zinc alloy solder bars that can be wiped over the heated surface of the welds to hot coat exposed steel surfaces. I have used this method on hot dipped galvanized handrails where changes were made in the shop or field. I believe they are called Galva-guard rods about 1/4" in cross section. Clean the weld or damaged surface, heat with a propane torch and "tin " the suface and build up as needed wire brush to smooth it out and presto! There are other products too with similar or modified techniques as above.

Concur on the SMAW 6010...the digging action makes it go better but welding galvanized is a messy, foul proposition especially if you use flux core. Wear an appropriate respirator, stay upwind and make especially sure that your protective clothing is adequate. Use leathers if you have them. Sometimes you will get violent eruptions of molten material while welding.

Good luck,
Weldmedic

 

[HgTX]

We just took zinc-rich paint (a.k.a. "cold galvanizing") out of our spec for repair of welded areas on galvanizing because it turns out that it offers pretty poor corrosion protection, even when applied in accordance with manufacturer's instructions (as opposed to just spraying till it looks silver). Our spec lists the solder "crayons" (and metallizing, but that's rather more difficult).

Hg

 

[Rich2001]

The problem that you will run into with metallizing is obtaining the correct surface preparation for good adhesion.

The crayons have somewhat of a steep learning curve to obtain a good looking finish. Use lots of ammonium chloride flux and a tool and scotch-brite to finish the repair.