Sandvik's root flux is used for root protection when joining tubes and pipes where it is impractical to use a shielding gas or access is limited. However, the root flux does not give the same degree of protection. It can, therefore, only be used when the parent metal has enough margin of corrosion resistance for the actual application.
The use of root flux reduces the risk of porosity, surface oxides and burn through and is always better than no root protection.
Root flux is a powder, which is mixed with water or methanol to form a paste. It is brushed on to the root side, about 20 mm (0.787 in.) on each side of the joint. During welding the paste reacts with the heat of welding, forming a thin protective slag.
The slag is washed away by the process medium when the pipe is taken into service.
The root flux, which can be used for root passes made by the MMA, TIG or MIG welding methods, is available in plastic bottles containing 0.5 kg (1.1 lbs), sufficient for about 50 m (164 ft) of root weld.