Welding hot dip galvanized A588,weld crack problem 1

[intimidator3]

We are welding hot dip gal. 7/8 - 9 nuts,A325,to hot dip gal. 7x4x1/2 A588 angle and are having a problem with cracks in the welds.
The process we are using is FCAW,gas is Co2,wire class is E80T1(8100 dual shield).Volts are 30,amps are 280 resulting in over 50k joules as required by NY state for bridge work.
We have been advised to use an E6010 stick,or solid 70 series wire with a gas coverage of at least 80% argon.
Is there a more cost and labor effective solution to this problem,as we have thousands of this type of weld to do?

 

[metengr]

The thickness of the zinc coating will have a significant affect on weldability. I would agree with the advice that you received, and would try an E6010 or even an E6011 weld electrode. You need to use a welding process that does not rely on shielding gas because of the volatility of zinc. FCAW relies totally on gas shielding to protect the weld puddle. If you need to stick with FCAW for various reasons, you will probably have to locally remove the zinc coating (by grinding) where you want to place the tack weld.

The E6010 or E6011 are electrodes are deep penetrating and are forgiving in terms of environment. You do realize that the area that is being tack welded will be exposed to corrosion attack because there will be no zinc coating. Do you plan to hand apply or spray some type of corrosion resistant coating after tack welding? I really do not think tack welding galvanized nuts to galvanized structural steel is good design.

 

[deanc]

FCAW-"Flux Core" Should work. Do you have crater defects? Perhaps try a smaller diameter wire.
This is "nasty at best. I would choose the 6010 if no option. Can you use ungalvanized parts and hot dip later?

Take care of your welders. Zinc chills!!!!

 

[metengr]

As a follow-up, the web site below contains some general information on welding pre/post galvanized structures,

http://www.galvanizeit.org/showContent,48,80.cfm

 

[stanweld]

intimidator3,
You did not state whether cracking is in the weld metal, nut HAZ or A-588 HAZ. You may have to preheat to approximately 200 F to avoid cracking due to the relatively high carbon content of the nut. Note, welding over galvanize generally produces highly porous welds.

 

[intimidator3]

Thanks everyone for the input.
A special thanks to METENGR for the accurate info. once again. I do agree strongly that this design is NOT the best way to go.
Unfortunatly my concerns,this being one of them, were ignored by managment.
To METENGR, the coating,which was supposed to be .020 to .030 thick, is actually turning out to be closer to anywhere from .050 to .071. As you stated,part of the prob.Quite a variance in my opinion. We have removed the coating by grinding and it has not helped. And we have pre-heated to the specified temp. as this is a NY State on-site inspected contract. We do have an approved method of hand coating the affected HAZ.
To DEANC & STAN, crater defects do not apply,the entire weld does not pass Mag-Part testing. We are bound by the WPQ sheets we have approved.
And yes,I am taking care of my welders,positive pressure hoods,and outside,local vent.with on site fume filters.
Using prior un-gal. parts is not an option per contract.
It would appear 6010 (too slow!) will have to do at this point.
Thank you all for the advice!