Re: [MW:14745] unbaked flux during LSAW welding.

Mr. Meghwal,

 

The basic welding flux is treated as equal to Low hydrogen ( E 7018 or E xxx6/8) type electrodes.

If they are not baked prior to use for welding and its exposure to atmosphere for more than one hour,

may allow it to pick up moisture according to relative humidity in the air, resulting in the formation of hydrogen in the arc as a result of flux decomposition. The hydrogen is absorbed by the weld metal in the molten state and released under pressure as the weld metal cools and contracts. All the hydrogen may not be  released, but a part of it  may collect at suitable voids  causing minute invisible cracks in such regions.

There is consequently  an overall reduction in ductility and toughness of the weld metal and the phenomenon is termed Hydrogen Embrittlement. This problem is more, if the steel is hard and brittle

or if the stress system does not permit plastic deformation or  if the joint has high degree of restraint.

This type under bead cracks may occur  at heat affected zones. Apart from cracks, hydrogen pick up  may also induce pores in the weld bead.

Hence, SAW fluxes should be spread uniformly in the flux drying oven and dried at 350- 400 deg.C for two hours and used within one hour after removal from the oven.

sridhar.

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From: B R Meghwal <br.meghwal@fernas.co.in>
To: materials-welding@googlegroups.com
Sent: Monday, 2 July 2012 10:12 AM
Subject: [MW:14739] unbaked flux during LSAW welding.

 

Dear All,

 

Please note that the Manufacturer used without baking flux during LSAW welding.

You are requested to clarify the matter indicating up to what extent it could affect strength of weld quality.

 

 Appreciate on your prompt reply.

 

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