Re: [MW:4797] how to avoid hollow bead

Dear Gulam,

 DC-ve polarity should be used to prevent.

It generally occours when using pipe steel containing over 0 .1 silicon.

Lower curent to be used.

Hot passes and all other passes should run by DC +ve.

Itmay be caused by poor joint preparation and or cleanlines.

On Mon, Apr 12, 2010 at 8:38 AM, Yadav Shiva <luvshiv2002@gmail.com> wrote:

Dear Gulam kader,

 

Problems with hollow beads begin in the root pass when the primary causes, very high welding currents and travel speed are used. One additional contributor is the high cellulose electrode such as your 6010.

 

The parameters which affect the formation of hollow bead are,

1. High levels of welding current and travel speed were found to have a mojor influence on hollow bead.

2. The silicon content of the parent metal and the flux moisture content of the electrode had a minor effect on the occurrence of the defect.

3. The dimensions of the joint geometry, the presence of rust and paint on the joint and the concentration of aaluminium and carbon in the parent metal had no significant effect.

The most important factor for the occurrence of Hollow bead defects was a fast weld travel speed combined with hight welding current. The major gas in the Hollow Bead pore is hydrogen, which has been rejected from the super-saturated liquid ahead of the solid-liquid interface. on the basis of these findings postulated that the hydrogen gas rejected by the saturated liquid ahead of the solid liquid interface accumulates in one single gas bubble, which is enclosed by columnar grains growing parellel to the welding direction.

 
Some times Segregation associates with Hollow bead defect.

 

 To control the HOLLOW BEAD DEFECT, CONTROL THE WELDING CURRENT AND TRAVEL SPEED.

Regards,

 

Yadav Shiva Chelliya,
Inspection Engineer,
Doha Qatar,
+974-6166465

 

 

On Sun, Apr 11, 2010 at 6:35 PM, Gulam kader <armvasi@gmail.com> wrote:

Hai to all,

In our project we are facing continuos hollow bead. Can any one explain reason for hollow bead and how to control this .

WPS Details ;

Process : SMAW

Electrode : E 6010 For root & E 8010 for remaining

Direction of welding : All Down hill 

Size : 68" , 60" 

Expecting your earliest reply

Regards,

Gulam Kader

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Yadav Shiva Chelliya,
Inspection Engineer,
Doha Qatar,
+974-6166465

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