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Re: Fw: [MW:21134] Poke Mark observed in thin wire SAW

By Materials & Welding

Respected Sir,,

Sorry to use wrong word and thanks a lot for your reply and solution.

Regards
Mohit

On 16-Jun-2014 1:55 AM, "'c sridhar' via Materials & Welding" <materials-welding@googlegroups.com> wrote:

The correct word is "Pock Mark or Gas Flattening". It's commonly found with high Mn-silicate low 
Basicity fluxes 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 ASTM 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  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.
  
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, get a mixture of more coarse (60 to70 %) and balance  in fine type.
Last of all, if all solutions fail, change to basic fluxes (which generally have more de-oxidizers). 
However welding productivity may may be hampered, because basic fluxes are not high speed fluxes..
 

C Sridhar.
Mobile no: 0 94449 71097.

 
From: Mahendra Arya <mkarya.delhi@gmail.com>
To: materials-welding@googlegroups.com
Cc: pgoswami <pgoswami@quickclic.net>
Sent: Saturday, 14 June 2014 2:10 PM
Subject: Re: [MW:21113] Poke Mark observed in thin wire SAW

Kindly use baked flux....
On 14-Jun-2014 2:08 pm, "Mohit Aggarwal" <aggarwalmohit05@gmail.com> wrote:
>
> Respected Experts,,
> We are doing thin wire SAW ON Ss material pipe to pipe joint observing poke mark often. Kindly let me know how can it be eliminated because it effecting over all.productivity due to grinding of poke marks observed in weld metal layer!!
>
> Best Regards
> Mohit Aggarwal
>
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