Welding Galvanized Steel with Stainless Steel

[Metcorr]

If under certain extreme constraints of materials availabiltiy, one is forced to weld galvanized steel with stainless steel. Keeping in view the potential danger of Liquid Metal Embrittlement (LME), if NDT is passed after welding, is it okay to put the vessel in operation? Comments and advice will be greatly appreciated.

 

[strider6]

I'm thinking to Galvanic corrosion.
You'll have to consider what kind of service you have in the vessel, fluid composition, presence of water, or the environment in which is placed the vessel, if the weld will external and exposed to the atmosphere.
SS coupled with galvanized steel can be a serious issue if there is the possibility of galvanic corrosion.
Hope this can help
regards

Vitt

http://xoomer.alice.it/corrosion

http://corrosionist.blogspot.com

 

[metengr]

What type of NDT did you perform? Was this a pressure vessel that was code stamped? Did you remove any of the zinc from the weld region before welding?

You may not detect the extent of liquid metal embrittlement to stainless steel weld deposit. I would not place the vessel into service w/o further determination/evaluation of the weld region. If you are unsure, go back, remove the weld, locally remove the zinc, NDT using liquid penetrant (PT), re-weld and locally repair the galvanized steel at the weld region.

 

[Metcorr]

Dear Metenger,

We can only perform Dye Penetrant Test. Is it possible to detect cracks if LME is happening? Or, it will only happen in service.

 

[metengr]

If you welded with the stainless over the galvanized layer, you need to locally clean the surface and check for cracks in the weld region. I would not trust a PT on a welded surface without proper surface preparation. If after cleaning, the PT is acceptable, you should be ok. However, you will need to locally re-coat this region to avoid corrosion in service.

 

[stanweld]

If you did not remove the galvanize layer prior to welding the galvanized steel part to the stainless steel part, process as metengr states.

I truly cannot understand why one would not remove the galvanize prior to welding. It is so easy to remove from steel. All you have to do is dip it in muriatic acid, which is commonly available in swimming pool supply stores, hardware stores, Home Depot, etc.

 

[unclesyd]

I've done a bit of welding SS to HDG for components on boats with out any problems. As posted above the better way is to remove the existing zinc on the CS and then weld.

I would not normally do any testing but again as posted PT would give you peace of mind. If I were going to PT it would be accomplished while the part is part is still warm either from welding or grinding after welding. I would use a dwell time of 20-30 minutes, with the same for the developer.

After the joint is cleaned up we always coat the steel with ZRC. I've have found this to be very good for marine enviroments.

http://www.zrcworldwide.com/index.asp

 

[BenThayer]

i replaced a few hundred feet of 304L stainless piping after we "saved" money by reusing some galvanized steel for insulation supports.

the zinc got into the stainless and it cracked at every weld. every 10 feet we had a leak.

i would not trust any means of zinc removal except starting with something that did not was not galvinized in the first place.

not worth it, imho.