POAK MRKS ON SAW WELDING

[masthan]

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

 

 

[limesh M]

Dear Mr. Masthan,

Which company product you are using?We faced such kind of problem with
ESAB filler and flux combination and eliminated the problem by
introducing Lincoln products.The problem we faced only on surface
profile of the weld bead(Radiography was OK).There was no
metallurgical problem with ESAB products during SAW process.

[Bathula Raghuram (Mumbai - PIPING)]

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.

.

[Kathalingam Babu]

Dear Mastan,

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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[lakshman]

hi,
dear all,

shall i know what is a poak mark,
anybody having the photo of the same.

Thanks & Regards,
Lakshman

On Jun 9, 11:18 pm, "masthan" <sabreenbah...@hotmail.com> wrote:

[sreevalsan sreedharan]

HI

 

POCK MARKING OR SLAG STICKING

FOR MORE DETAILES PLS CHECK ATTACHMENT

 

S.SREEVALSAN

ABUDHABI

 

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[rutvik dixit]

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:

[pgoswami]

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:-

• Reduce travel speed, to allow more time for solidification and gas entrapment at the same operating current. You may need a few trials to get the correct operating parameters.
• Remove surface scales or dirt, because they also generate gases.
• Check the condition of fluxes, if it's too old with a lot of fines, sieve, and get rid of the fines.If fluxes have too many fines, talk to manufacturer.
• Last of all, if all solutions fail, change to basic fluxes (which generally have more deoxidizers). However welding productivity may be hampered, because basic fluxes are not high speed fluxes.

I attached a few illustrations to the above problem.Hope this would help you.

Thanks

Pradip Goswami,P.Eng.

Welding & Metallurgical Engineer/Specialist

Ontario Power Generation Inc.

Email-pgoswami@sympatico.ca,

pgos...@quickclic.net

 

---

From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of sreevalsan sreedharan
Sent: Saturday, June 12, 2010 1:12 AM
To: material...@googlegroups.com
Cc: lakshma...@gmail.com

Subject: Re: [MW:5548] Re: POAK MRKS ON SAW WELDING

[masthan]

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

[John Henning]

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

[Rajesh Reddy]

Hi,

Increase heat input to the maximum extent (by reducing travel speed & increasing wire speed/current).  it solves the problem

Regards,

Rajesh Reddy

[Kannayeram Gnanapandithan]

Decrease current

Decrease travel speed

Increase Voltage

Reduce flux burden

change over to high manganese rod

Check the flux sizes

THANKS & BEST REGARDS,

KG.PANDITHAN, IWE,  AWS-CWI, CSWIP 3.1,

CONSULTANT-WELDING & QUALITY

Mobile no: +919940739349

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[Saulo MU]

Reduce the proporción of recycled flux.Ensure no moisture in flux by keeping and baking properly and in case situatión continúes.increase the proporción of new flux (100%).