Mr. Shashank,
FCAW has some limitations no doubt, as every welding process does. However if one know the process then good results are achievable. Typically:-
the advertised benefits of FCAW were:
• High quality weldments,
• Increased tolerance for scale and dirt when compared to GMAW
• Higher deposition rates when compared to manual processes(SMAW)
• Multi-position potential
• Optimization of weld joints thru active flux alloying
• Good Bead Appearance
• Better penetration than obtainable from SMAW
• Smooth, Stable Arc
Common problems
• Undercutting
• Incomplete joint penetration
• Porosity
• low impact (CVN) test results
• local brittle zones in weldments HAZ
• reheat cracking in 300 series stainless steels
• poor wire quality (incomplete filling)
• lack of small diameter wires
• lack of fusion (need to stay on leading edge of puddle was not appreciated, leading to LOF)
I have seen that oil refineries / owners allowing FCAW for pressure parts, however calls for a lot more control, due to propensities of defect. However note defects in gas shielded process could be due to many factors. Some examples are cited below from the welding specifications of various large oil giants:-
1. A North American Oil Giant (Largest in the world):- Flux cored arc welding (FCAW) either with or without external gas shielding may be used for either groove or fillet welds. For pressure boundary welds and welds with impact test requirements, only electrode classifications or types which are identified as multipass and which have specified minimum impact test requirements shall be used.
2. Large Oil Giant from Middle East :-Flux-Cored Arc Welding (FCAW).—
• The FCAW process shall not be used for the root pass on full penetration, groove joints that are welded from one side only without backing (backing may be used if it is removed after welding).
• Self-shielded FCAW shall not be used without the specific approval of owner. FCAW electrode shall be restricted to the specific brand, type, and maximum size as used for the PQR.
3. Another Larger Oil Company in North America (Now part of the largest Company as under 1):-
The flux cored arc welding process(FCAW) may be used, subject to owners review & approval. Proposal to use FCAW must be submitted prior to order placement, provided:-
1. Gas shielding is used
2. Material to be welded is carbon steel or for application of weld overlay on carbon steel or low alloy steel.
3. The FCAW process is not "short arc".
4. The FCAW process is not used for the root pass in single sided welding.
5. Production consumable are restricted to the manufacturer and grade qualified.
6. Only EXXT-1 or EXXT-5, (flat or horizontal position only) welding wires are used.
7. Service is not hot hydrogen (over 2600 C--500 0F), wet hydrogen sulphide or hydrogen fluoride.
8. Primary flange rating is class 300 or lower.
9. At least five percent of the individual welds are 100% radiographed or ultrasonically tested
10. Ten percent of the nozzle-to shell or head welds (including at least one of each size) shall be 100% radiographed or ultrasonically examined.
11. For all other applications not meeting the above conditions, FCAW process may be considered on a case-by case basis. The review will include the evaluation of the specific application, verification of fabricator's experience, additional qualification and/or NDE requirements and owners witnessing of welding procedure and/or welder qualification.
Generally due to past records of this process many clients provide conditional acceptance and additional NDE. But the process, equipments, consumables, gases have improved leaps and bounds in last 2 decades, and with availability of skilled welders, this process helps the fabricators a lot and is lot reliable than before. For pressure vessels this process would give good reliability with premixed mixed gases (Ar+CO2, Ar+O2) from good suppliers .Refer AWS-SFA 5.32, specification for shielding gases for good selection criteria.
I hope this would be some food for thoughts. If you have access to NACE , you may download the attached article, which is very informative.
Thanks.
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Shashank Vagal
Sent: Friday, April 23, 2010 3:44 AM
To: materials-welding@googlegroups.com
Cc: Shamesh Lotalikar
Subject: RE: [MW:4939] FCAW welding for pressure part
| Can anyone explain to me why one goes for FCAW - manual? As I see it, it is intended for automated welding (like SAW). But then again, while SAW is relatively safe and efficient mode of welding, FCAW seems to plentily flawed. So, why FCAW? And if it HAS to be FCAW, what are the pros and cons - meaning how to get the best out of it?
Its true that LOF is not easy to detect by RT if its not preferentially oriented. But no NDT method can be replaced by other since each method has its own advantage & disadvantage over each other. So decision of change of RT with UT is depend on so many other factors such as time, economics, skill, retention of records and last but not least recommendation of code of construction. Bharat B. Gole Subject: Re: [MW:4917] FCAW welding for pressure part From: "sachin sankhe" [sachin.sankhe@rediffmail.com]
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