welding before galvanizing

huangyhg

welding before galvanizing
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
check out our whitepaper library.
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.
thanks ronfff">.  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
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.
i agree with ron.
ba
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.
  
i thought the question was "has anybody experienced problems with connections which were welded after galvanizng?"  my response would be yes, indeed.
ba
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   
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
embrittlement and cracking due to the galvanising process can occur but is not generally a problem with normal structural steels.
more information here;
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.