Hi tensile strength.

 

That makes no sense, since a friend of mine welds high tensile crane steel with gas mig all the time, both in the shop and in the field. Steels with tensile strengths that often exceed 140 ksi. regularly. About 60% of his stuff is gas mig, 35% is stick, and the rest is subarc. He doesn't use FC at all, so I doubt tensile strength is the real reason.

 

You can weld structural steel any way you want if you have enough money to spend on testing your welding procedure and having it approved by engineers.
Alternatively you follow existing codes that qualifiy certain welding processes and procedures. A "prequalified" process might be something like using E 7018 electrode. Some structural codes do not prequalify solid wire yet so the company has to do a set of tests to prove the process.
For example I worked in a pressure vessel shop that used solid wire in their procedures for pressure tanks. They had gotten approval for using solid wire on structural jobs since they chose to continue to use the same process in the shop rather than changing all the time.
I believe that Canadian and American structural codes prequalify SMAW with E xx18 and also many flux core wires.
Engineers are very cautious. I attended a presentation about updates to the Canadian code and the presenter mentioned that finally CWB recognised spray transfer processes. Spray transfer had been around for over 20 years and we all started asking.... What about pulse transfer?? It will be another 10 or 20 years before they will recognise pulse transfer as a prequalified process. In the mean time companies who want to use pulse must do all the expensive tests to get approval.
Note that solid wire is a low hydrogen process simply because there is no flux to carry moisture.

 

Spray transfer had been around for over 20 years and we all started asking.... What about pulse transfer?? It will be another 10 or 20 years before they will recognise pulse transfer as a prequalified process. .

That's been the subject of interesting debate recently, the main point that being is that the mode of transfer isn't being changed (pulsed spray is still spray transfer), its the waveform. Since the waveform isn't an essential variable, it should not require re-qualification.

 

GMAW in its basic form is known as a cold process and doesn't have the heat input as FCAW or GMAW-S .

 

I think this would be advantageous to the final product, Less heat input into the base= less warpage and a smaller HAZ. The welds are every bit as strong with proper fitup and joint prep.

 

So, Jay O, is the issue the metallurgy or simply a matter of penetration? I've never used fluxcore but I've heard it has better penetratrion and know that you can weld thinner metal with solid wire than fluxcore but because it's considered a hot process is the metallurgy of the surrounding metal affected differently than from solid wire? I recognize that the processes are different but what is the rationale behind one being allowed and not the other?

 

You have to look at the voltage that the other processes use, which is going to be higher volts then GMAW. More volts more heat input more fusion/penetration. Like other have said that the welding proceedure has to be proven and that where GMAW gets stopped. I'm not saying a weld test can't be passed with GMAW but say you get your best welder to pass the test and prove the proceedure but all your other welders can't pass, the process is then useless.

ironmangq,

Less heat input would be ideal but if it doesn't allow you proper fusion to do the job then what? If everything were prepared with proper fit and prep then things should be equal but since every weld process has to be proven, you have to get buy that first.

 

lotechman, thanks, you said what I was thinking better than I did.

 

All pretty good here;

lotech is right with the quallies. Hard wire in short circuit without preheat "higher than used for most structural", along with significant CO2 in the mix usually won't get down to the 16ppm max needed for low-hydrogen. With low CO2 and spray the deposit should always get below 4ppm (preheat correct also).

The cored wire carries a large portion of the arc energy on the outside (solid part) of the tube and has a predictable penetration profile. Cored wire if set very far out of parameter works and looks like sewage...

Solid wire if given all the possible ways it can be used gives penetration profiles all over the place IE: nipple shaped with shallow mixing at the toes (spray) to deep and narrow (high power pulse) to finger shape (high CO2 or sub-arc).

Hard wire is like having one gun that shoots a lot of different caliber bullets... You want to make sure there isn't a 22 in the chamber when a bear shows up.:gunsfirin

Matt

 

"blanket statements" are almost always wrong.

Different welding/fabrication codes call for or 'allow' several different processes.

Solid wire GMAW certainly is an 'allowed' procedure. Sometimes. And with the proper welding parameters and procedures.

Cause you're not going to weld a structural beam using some 0.025 wire in short-circuit transfer! :laugh:

Same as using SMAW. Some SMAW procedures (electrode size and type and amperage and so forth) are 'allowed' and others are not.

Same for FCAW (both FCAW-S and FCAW-G).

Same as preheat and interpass temperature limits (high and low).

As well as possible electrode exposure limits.

All part of the WPS and the 'Codes'.

As to a 'practical' reason why someone might not want to use a solid GMAW electrode in the field, it might be because of possible problems of wind or other air flow blowing away or otherwise disrupting the 'blanket' of shielding gas and thus cause the weld to turn to crap.

So the answer is :

It depends.

:drinkup:

 

Jason,

Well your right, I thought that GMAW-S stood for spray transfer but looking in my book the really isn't a clear designation for spray mode.

My book also shows FCAW-G for gas shielded flux and FCAW-S for self shielded flux core. This is from a AWS Welding Inspection Handbook so are processes noted differently up north?

 

AWS and CWB Nomenclature are fairly close, but not always exact. I will snoop around in my books when I get home, and get back to you. I might be off as well - I usually say it, as opposed to writing it. lol

EDIT: I checked the Lincoln Electric (Canada) site while I am at a 'puter and they use the same designations as you FCAW-S and FCAW-G so I will sit corrected.

I got so used to saying Self Shielded or Dual (Gas) Shielded when talking about Flux Core to fellows at the shop that obviously I started to type it that way.

It is always good to have a "Refresher"

Thanks and Have a Merry Christmas.

 

The issue is speed. I was an ironworker in Boston for years and innershield was used most of the time for that reason. A lot of metal deposited and fast setup time. With dual shield we would have to put up screens to block the wind and it was never fast. Flux core wire size was 5/64 " so it would weld moment connections quickly.

 

GMAW-S is Short-Circuting transfer
AWS D1.1 has had GMAW listed as a pre-qualified process for many years. GMAW-S requires qualification. GMAW spray is used by many structural companies. In theory, GMAW globular is pre-qualified, but probably not a good idea.

 

What is interesting to me is that most stationary structural welding over 3/4 inch is flux cored wire feed. But if you look to the marine fabrication world, almost all work over 1/4 inch is done with dual-shield. Sub-arc and ceramic tape welding dominate on 1"+ in the marine construction world. But why is dual shield so rare on stationary construction? Dual shield is a spray transfer process. Is it simply because of costs? Boats are very dynamic structures and any reduction in hydrogen embrittlement is a plus.

 

YES $$$$, no bottle to hump around, store & lock up, regulators & hoses to replace from damage, AND the WIND to blow the gas away. K.I.S.S. -- there's $ to be made with speed :cool2:

 

several reasons. First and for most is speed. FCAW lays down fast in big full pens.

Second is Charpy V notch property's. As far as i know no solid core mig wire meets the charpy V notch requirements of AWS D1.8 for welding of structures in seismically active areas.

Here in CA you would get walked off a job for using solid core MIG on anything thicker than 1/4"

We run some Dual shield in the shop on full pens and fillets all the time. The 0.052" Lincoln Ultra core 71C. Its a very nice running wire with a wide operating window and easy operator appeal.

On anything over 1/4" in the field its damn near ALL 0.072" NR-232, NR-233, or Esab Coreshield-8.

Having to deal with a Co2 cylinder and hoses on a jobsite is nothing i want to deal with, or anyone else in the area either.

you can run the self shielded flux core in some pretty nasty winds and it wont care. with the gas shield you have basically build a blind or a building around your building to weld. In this game time is money.

 

Hi we are welding the largest field and shop welded job in the USA Tower 1 &4 and the transportaion hub at the World Trade Center . Up to 7 " full pen welds 7 tons of shop weld in 1 piece Lincoln Ultracore 71-C 1/16 CO2 flux core , Lincoln LA--75 860 flux 5/64 sub arc , Esab core shield 8 in field self shielded .