Cellulosic Electrodes

Cellulose is the principal substance in this type of electrode and comprising typically ~ 40% of the flux constituents.
Cellulose is an organic material (naturally occurring) such as cotton and wood, but it is wood pulp that is the principal source of cellulose used in the manufacture of electrode coverings.
The main characteristics of Cellulosic electrodes are:

1. Cellulose breaks down during welding and produces carbon monoxide & dioxide and hydrogen
   
2. Hydrogen provides part of the gas shielding function and gives a relatively high arc voltage
   
3. The high arc voltage gives the electrode a ‘hard’ and forceful arc with good penetration/fusion ability
   
4. The volume of slag formed is relatively small
   
5. Cellulosic electrodes cannot be baked during manufacture or before welding because this would destroy the cellulose; the manufacturing procedure is to ‘harden’ the coating by drying (typically at 70 to 100ºC)
   
6. Because of the high hydrogen levels there is always some risk of H cracking which requires control measures such as ‘hot-pass’ welding to facilitate the rapid escape of hydrogen
   
7. Because of the risk of H cracking there are limits on the strength/composition and thickness of steels on which they can be used (electrode are manufactured in classes E60xx, E70xx, E80xx & E90xx but both lower strength grades tend to be the most (commonly used)
   
8. High toughness at low temperatures cannot be consistently achieved from this type of electrode (typically only down to about -20ºC)

Application of Cellulosic Electrodes
Cellulosic electrodes have characteristics that enable them to be used for vertical-down welding at fast travel speed but with low risk of lack-of-fusion because of their forceful arc.
The ‘niche’ application for this type of electrode is girth seam welding of large diameter steel pipes for overland pipelines (Transco (BGAS) P2, BS 4515 & API 1104 applications). No other type of electrode has the ability to allow root pass welding at high speed and still give good root penetration when the root gap is less than ideal.
Because of their penetration ability these electrodes have also found application on oil storage tanks – for vertical and circumferential seam welding of the upper/thinner courses for which preparations with large root faces or square edge preparations are used.