Hi
We are continuously facing problem of Poak marks on the SAW Welding surface. Welding Consumable L-61 (wire) with 865 (flux) combinations. Any body has idea to prevent this. Please share.
Best Regards
M.Masthan
K.S.A
Here is an extract from lincon catalogue, they recommend L50
wire to avoid this or change the flux to 860
865… is a general purpose
flux designed to weld butt joints and flat and horizontal fillets. 865 produces
70,000 psi tensile strength as welded or after short or long term stress relief.
865 flux should be used with L-50 electrode for optimum impact properties,
resistance to rust porosity, and resistance to pock
marking. L-61 may be used on steel free of scale and
rust.
.
Poak marks in SAW due to following,
a)Excessive height of flux
b) Small Grain size or fines
Both the factors would contribute poaks particularly on capping ,
The gases evolved during flux and metal reactions may not escape, because of
a) & b)
You can avoid the poaks by optimum grain size or avoid using fines or usage
of recycled flux on the capping
Regards
K.Babu
----- Original Message -----
From: "limesh M" <lime...@gmail.com>
To: "Materials & Welding" <material...@googlegroups.com>
Sent: Thursday, June 10, 2010 5:08 PM
Subject: [MW:5514] Re: POAK MRKS ON SAW WELDING
Dear Mr. Masthan,
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Dear Mr.Sreevalsan, Thanks for providing the details. I have faced the same problem. In SAW weld I have observed surface dippression. What is the root cause? Can we take any precaution at welding stage? Who is responsible for this type of defect? flux mfr/ wire mfr./ user? How to avoid it. I am not sure, this problem may be due to excessive heap of flux on molten weld pool. can you enlighten us. With Regards, Rutvik Sr.Surveyor TATA Projects Ltd. --- On Sat, 12/6/10, sreevalsan sreedharan <sreeva...@gmail.com> wrote: |
Hello Mr. Masthan,
Te correct word is "Pock Mark". It's commonly found with high Mn-silicate low basicity fluxes.Lincolnweld- 865 is a general purpose flux,with basicity of 1.0-1.3
High quality, and highly basic fluxes (Basicity 2.7 and above) will hardly produce this defect, unless they are properly baked,or reused or recycled.Recycled fluxes will have too many fine particles which will hinder the passage of gases on the flux layer. Ideally the gas pockets should all be entrapped in SAW flux layer. Following is the illustration from ASM Metals Handbook on this problem.The SAW slag must be fluid enough so that it flows and covers the molten weld pool but must be viscous enough so that it does not run away from the molten metal and flow in front of the arc, leading to possible overlapping by the weld metal. It has been reported that if the manganese silicate flux viscosity at 1450 °C (2640 °F) is above 0.7 Pa · s (7 P), a definite increase in weld surface pocking will occur. Pock marks have been associated with easily reducible oxides in the flux, which contribute oxygen to the weld pool. The weld pool reacts with carbon to form carbon monoxide, which cannot be transported through a high-viscosity flux and is trapped at the liquid-metal/flux interface. The result is a weld metal surface blemished by surface defects or pocks. Because viscosity is sensitive to temperature and thus heat input, pocking can be the evidence that a flux formulated for high-current welding is being used at too low a current or too great a travel speed.
A few suggestions to reduce this problem:-
I attached a few illustrations to the above problem.Hope this would help you.
Thanks
Dear Mr. Rutvik,
Finally I received Lincoln Letter from our welding group regarding the Pock Mark issue. (Photos & Letter attached). Now we qualify the PQR L61 with 860 (flux) combinations. It’s ok. Further we took some precaution at welding stage like proper cleaning of bevel edges and controlled travel speed for the L61+865 combination. Some time it’s ok but not all the time. We cannot explain who’s responsible for this type of defect; ultimately it is the responsibility of vessel manufacturer even though pock marks are not affecting weld integrity.
If anybody having more details please share.
Thanks
M.Masthan
K.S.A
From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of rutvik dixit
Sent: Saturday, June 12, 2010
11:01 AM
To: material...@googlegroups.com
Cc: lakshma...@gmail.com
Pock marks are not truly a “defect”. These typically are cosmetic surface blemishes which have no effect on the actual quality or functionality of the weld.
John
From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of rutvik dixit
Sent: Saturday, June 12, 2010 4:01 AM
To: material...@googlegroups.com
Cc: lakshma...@gmail.com
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
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