FCAW for site welding of structural steel 3

[djwright]

Is flux cored arc welding a good process for site welding of structural steel?

Has there been any history of weld cracking associated with this process?

Thoughts and experiences would be appreciated.

 

[sayee1]

Which flux cored welding variety are you asking about, self shielded or gas shielded(also referred to as dual shield sometimes)...Lotsa experience...Which grade of structural steel? Which grade of consumables? Thickness(es) of base material(s)? Type of cracking which is a concern to you?
Please provide more data

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
The whole of science is nothing more than a refinement of everyday thinking!!!

 

[evelrod]

Flux Core, Innershield, whatever---Is now and has been for ~30 years the "standard" for field and shop welding of structural steel. Cracking problems? Of course but, all well defined and with procedures for preventing and/or corecting them. "Wire" and "stick" will be found on almost every job in the country these days. Less common is the "mig" GMAW welders (often using 'flux core' wire) that are becoming more and more popular among the "miscellaneous" contractors (at least here in the L.A. area). Makes welding handrail and such a real 'breeze'!
I don't quite know how to "take" your question. The process is so common that I am curious why you are not familiar with it.

Rod

 

[CWIC]

djwright:
FCAW-S (flux core arc welding-self-shielded) is the most common welding process for field welding of structural steel. It is portable, equipment and consumables are readily avaiable. I've only seen FCAW-G (gas-shielded) used locally once. The contractor switched to self-shielded electrodes about half way through the job when wind overcame the tents and they got tired of lugging gas cyliders around the job site.

There is a substantial amount of info available on weld failures for this process used in structural applications. Most include incorrect selection of electrode classification, workmanship and technique. Notch toughness (or lack thereof) of electrodes proved to be a major factor after the Northridge earthquake. Technique (bead width, thickness, etc.) were also noted to be major factors.

This process may be specified provided the above concerns are addressed in the welding specifications; strict adherance to a WPS and/or PQR if required, QC does their job and monitors parameters with a calibrated meter, etc. It is the fastest and most economical process for most structural steel field welding.

Many designers are not welders nor welding engineers. There is justified concern on their part with regards to this process. Many designers, owners and contractors now retain welding consultants or engineers for complex structural applications. Check out faq 725-513.

 

[sayee1]

Evelrod
You hit the rod, I mean nail on the head ;-) . The reason why I asked all those queries is that FCAW ss and GS are so common in our site that I could not fathom what sort of cracking djwright could be worried about. The most common consumables I have used are the common E61T8K6 used for the S355/2H Gr 50/API X52 grades. The only problem associated with these consumables are the clasification which shows 60 ksi, whereas the actual strengths are typically~70 ksi. As a result of the materials being welded with these consumables, many specs/clients ask for Tensile testing(AWT) of every batch of consumables... Remember Lincoln generally gives type certificates. Also the second problem is that these consumables, actually the weld with these consumables are not low hydrogen as per most specs. The diffusible H2 in weld metal is typically 8+ ~10-15 ml/100gm. As a result some clients/specs would insist on H2 test for weld metal. There is also some problems when fracture notch toughnes required....but like CWIC says...Nothing new about the problems associated and the applications of the process. Good post from CWIC.... Finally I would like to say that unless you are in a extremely cold/windy country like say Azherbaijan where the oil and gas happenings concentrated nowadays, I would still make a decent attempt to use FCAW-GS for welding using wind breakers, because of the deposition rates/properties/quality achievable with FCAW-GS!!!

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
The whole of science is nothing more than a refinement of everyday thinking!!!

 

[djwright]

Thanks for helpful posts.

In our application we have used gas-sheilded process to weld 60ksi structural steel. Welding environment was offshore / windy but full protection and monitoring was provided.

Some "cracking" was reported. Various theories have been put forward (lack of pre-heat, fatigue of partially completed connections). However, latest reports have made reference to LOF (it would be nice to get a straight story from our offshore guys!).

I will post final diagnosis if its interesting.

 

[stanweld]

Lack of Fusion could result from manipulation of the torch by the welder in conjunction with the use of constant voltage power supplies when welding thick members. As the contact tube to work distance increases, amperage decreases and weld penetration decreases. LOF problems have been reported in the past when welding thick sections.

 

[intimidator3]

Once again I totally agree with sayeeprasadr with the suggestion that a "decent" attempt be made to use FCAW-GS.If getting a "stright story" is a concern, getting a CWI on site would prob. be the answer so an independant opinion is presented.
I would also have to agree with stanwelds post that lack of fusion could ,and in my opinion,does, result from improper torch manipulation,more so in thicker materials. The optimum torch angle that should be used is a bit shallower than other processes, around 20 degrees or so.As sayeeprasadr has stated,the yield rating of any wire usually surpasses what they say,if used correctly.
We use 8100 W (dual shield) wire ,as required in New York as we make expansion systems for bridges.It's a very "operator friendly" wire.
We have never had any cracking problems when used in parameters. Ours are (.045) 30v- 290a.