Re: [MW:4839] RE: 4827] cellulose electrodes.

Dear all,

Advantages:

Cellulose electrodes are good for vertical down welding.

- Deep penetrating welding in every position,
- Vertical down welding capability,
- Weld metal with good mechanical properties.

Cellulosic manual electrodes with vertical-down progression has been used for decades. It offers fast travel speeds and can accommodate poor fit-up.

Pipe strength: While cellulosic electrodes are suitable for low strength pipe, higher strength pipe and weld metal require low hydrogen electrodes to minimize cracking.

However, past experience has shown that high strength steel pipe can be successfully welded using a cellulosic root and hot pass with proper preheat and filling the remainder of the joint with a low hydrogen electrode.

disadvantage

However, there main drawbacks:

1) It leaves deep undercut grooves along the edges of the weld face, commonly referred to as wagon tracks; and

 2) it usually is necessary to expose these wagon tracks so they can be consumed by the next weld pass — the "hot" pass. This is done by removing the weld crown by grinding.

3)Thus, using cellulosic electrodes requires extra time after welding the root pass to remove part of the weld and then replace this with new weld metal.

4) Also, cellulosic electrodes produce weld metal with relatively high levels of weld diffusible hydrogen, rendering it crack sensitive when used on higher strength pipe grades.
welding.Its drawbacks 

5) Diffusible hydrogen: Some requirements specify only electrodes that meet a certain maximum weld metal diffusible hydrogen level may be used. In these cases, cellulosic electrodes are usually prohibited.

6)This increase in strength has caused some issues, especially when using cellulosic electrodes which are sensitive to cracking on higher strength steels. It is usually recommended to weld high strength steel with low hydrogen electrode for all passes.

 

Regards,

 

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

On Wed, Apr 14, 2010 at 7:51 PM, John Henning <jhenning@deltak.com> wrote:

The primary advantage to cellulose electrodes (EXX10 and EXX11) is that they form a thin slag cover and are what Lincoln electric called "fast freeze".  They produce a deeply penetrating arc but because of the thin slag, solidify rapidily.  Therefore they are very good at bridging gaps and were used for making root passes in piping/pipe lines.

 

The major disadvantage is that the cellulose, a hydrocarbon, breaks down in the heat of the arc and produces copious hydrogen which is absorbed into the molten weld pool.  These electrodes produce the highest weld metal hydrogen of all common practices/processes.  Therefore they may cause hydrogen assisted cracking if the other required factors are present.   

 

A minor disadvantage is that the weld is coarse in appearance due to the high solidification rate and therefore may lack visual appeal.

 

John

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of prashant pansare
Sent: Wednesday, April 14, 2010 8:55 AM
To: mat wel
Subject: [MW:4827] cellulose electrodes.

Dear all, What r advantages & dis-advantages of cellulose electrodes. Pl. reply. psp

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