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Re: [MW:13343] What is Marangoni Effec and its relation with

By Materials & Welding
Hi Anil,

Marangoni effect is related to the amount of sulfer present in metals to be welded.
At low levels of sulfur (less than about 0.007 weight percent ),  the temperature coefficient of surface tension becomes negative i.e. 
surface tension of liquid metal decreases with increase in temperature. So, liquid metal at outer edge of weld pool has high surface
tension compared to liquid metal under the arc which results in outward flow of liquid metal carrying heat to the outer edges, it is called
Marangoni convection. Weld pool size increases and depth of penetration decreases (high width to depth ration) due to the outward flow 
of heat and this large weld pool is difficult to be managed in orbital welding.

Reverse Marangoni convection takes place as sulfur level is raised (about .014 weight percent) and weld metal flows from outer edges to
center thereby increasing depth of penetration, which is favorable condition for welding. Below right fig. indicates Marangoni convection and
left one for reverse Marangoni convection.


Regards
Gogulu Kumar


On Tue, Dec 27, 2011 at 4:55 PM, anilkumar <anilb2000@gmail.com> wrote:
>
> Respected All,
>  I found the ollowing lines in an welding article on orbital
>  welding, that for a  cryogenic fluid carrier, inner pipes
>  were chosen of 4306 stainless steel, diameters between 84
>  to 273 mm.L = 11,5 m / 6 m).Thickness (mm) 2.9 .Inner pipes
>  were supposed to be  in contact with cryogenic fluid. With
>  different cryogenic temperatures: 1.8 to 80 K .xxxx
>  Conlcuding remark was "Practioner should pay attention about
>  Chemical composition to avoid "Marangoni effect" during welding.
>
>  Plz. educate me, what is Marangoni Effec and its relation with
>  weld material composition.?
>
>  Regards.
>  ANIL BARIK
>
>
>
> --
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--
  -Gogulu Kumar

--
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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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