Welding before galvanizing 5

[RHTPE]

I am preparing a detail that uses a bracket (resistance-welded assembly) which will be welded (in the steel shop) to a bridge plate girder prior to hot-dip galvanizing.

Has any experienced any problems with welded connections after galvanizng?


Ralph
Structures Consulting
Northeast USA

 

[Ron]

Welding after galvanizing presents a host of problems. Off-gassing that creates a fume issue for the welder is one. Porosity and inclusions in the welds is another as a result of the galvanizing being included in the weld. Fusion and penetration issues can also result from welding over galvanizing.

Weld first, galvanize after if you can.

 

[RHTPE]

Thanks Ron. I'm aware of the fume issue when welding thru galvanizing. I'm concerned about any possible loss of strength of the welds when exposed to the molten zinc.


Ralph
Structures Consulting
Northeast USA

 

[Ron]

The loss of strength comes from the potentially poorer quality weld. Zinc will mostly diffuse through the weld metal, but in so doing, creates quality issues.

 

[BAretired]

I agree with Ron.

BA

 

[hokie66]

The OP's question was whether there are strength problems associated with galvanizing after welding. That is the way it usually is done, and the answer is NO.

 

[BAretired]

I thought the question was "Has anybody experienced problems with connections which were welded after galvanizng?" My response would be yes, indeed.

BA

 

[darthsoilsguy2]

you're in USA so it's worth noting that welding galvanized steel is an essential variable change which means the contractor won't be able to use "AWS Pre-qualified Welding Procedures". that being the case, you run the very real risk (i would guess certain risk) that whoever wins the work will not be qualified to do it by code. they will need a qualified welding procedure that was ran and tested. they will also need all the welders to have been certified to this exact procedure via testing. their procedure, if it exists, may be with a different electrode than what you specify too.

some welders will crank up the juice on the welds to get through the galv. this results in undercut and even overheating of the member to the point that galvanization flakes off in places away from the weld area. if they keep it set too low, there are plenty of nasty things that can occur (low penetration, porosity, inclusion).

just specify that the contractor shall grind off the galvanized coating in the weld area and cold-galv paint all the welds afterwards. and make sure that the contractor and the field inspector know you mean it at the pre-con discussion.

or you could just not give a crap and let them weld the galv. plate knowing this inferior work happens all over the place. i suppose i shouldn't judge....maybe egrs are oversizing weld lengths to account for decreased weld quality....

 

[BAretired]

I have read the OP one more time. I misread it before. If the weld is done prior to galvanizing, no harm is done. That is to say, galvanizing has no effect on a weld done before galvanizing.

BA

 

[apsix]

Embrittlement and cracking due to the galvanising process can occur but is not generally a problem with normal structural steels.
More information here;

http://www.ingal.com.au/IGSM/38.htm

 

[hokie66]

Liquid Metal Assisted Cracking (LMAC). A new one on me. But this seems to be related more to the steel itself than to any welding done on the section. Interesting that it has occurred mostly on electric arc furnace produced sections, where scrap steel is used, rather than on blast furnace steel.

Thanks for the post, apsix.

 

[doct9960]

RHTPE,

Lots of galvanizing info in AGA's website (

http://www.galvanizeit.org)

Here are some articles that relate to welding & HDG...

http://www.galvanizeit.org/images/uploads/drGalv/silicon_welding.pdf

http://www.galvanizeit.org/aga/desi...elding/welding-before-galvanizing-fabrication

http://www.galvanizeit.org/images/uploads/publicationPDFs/T_WHDG_02.pdf

http://www.galvanizeit.org/images/uploads/publicationPDFs/D-PGAF-05.pdf

 

[doct9960]

RHTPE,

I'm concerned about any possible loss of strength of the welds when exposed to the molten zinc.

Hot-dip galvaning, if done properly, shouldn't affect weld strength.

If HDG or welding is not done properly, crack formation in welds is a possibility. See articles below...

http://www.slv-duisburg.de/fileadmin/user_upload/pdfs/GSI_News_engl_04_2007.pdf

http://files.aws.org/itrends/2004/07/it0704-29.pdf

 

[csd72]

hokie66,

Australian blast furnaces also use a lot of scrap metal, so its not the scrap metal content that does it. Maybe more to do with the carbon content.

 

[Zambo]

The title of this thread is "welding before galvanising" but the question is about "welded connections after galvanising"

But on re-reading it is clear that the threadstarter is worried that galvanising will damage previously welded joints. If the welds have been carried out correctly to a WPS backed up with a WPQR then there should be no problem with the weld.

 

[apsix]

If you read the whole sentence it is clear enough;
"Has any experienced any problems with welded connections after galvanizng?"

It's the problems which may occur after galvanising, not the welding.

 

[RHTPE]

It's amazing how so many of us engineers respond to what we think the question is and not to what the question REALLY is.

The welding will be done BEFORE the galvanizing. My inexperience with the process, combined with ancillary knowledge of problems of embrittlement associated with the process, is what led me to ask the question.

My conclusion is specify that proper post-pickling procedures be followed (ASTM A143), which is likely if this welding occurs in the same shop, and with the same welders, where the plate girder is being fabricated. My notes include that requirement.

Thanks to all who commented (even if you didn't get the question correct).


Ralph
Structures Consulting
Northeast USA

 

[Ron]

RHTPE...the last sentence of the post can be interpreted in two ways....

is there a problem with a welded connection as a result of galvanizing after welding, or...

is there a problem with a welded connection that is made after the galvanizing.

Thanks for clarifying your intent. Both interpretations have been correctly responded to in the thread, but obviously only one fits your intent.

In the event that you run into the other conditions, you have some answers for that as well...two for the price of one!

 

[darthsoilsguy2]

my bad.


whatever possible problem galvanizing could cause... it's nothing compared to weather and road salt.

 

[graybeach]

Galvanizers will generally know this but you should be careful with welded lap splices and such. These should be seal welded all around because the galvanizing compound wont be able to get into the interface.