The document discusses how scale formation can be prevented during welding of pipes. It explains that REDOX pipe uses vapor phase inhibition (VSI) oils to create a reduction reaction when heated during welding, preventing oxidation and scale formation on the inner pipe surface. In contrast, pickled and oiled pipes are more prone to scaling through oxidation reactions when welded. The document provides tips for controlling reduction reactions when welding REDOX pipe, such as spraying WD-40 inside the pipe and sealing the ends to prevent oxygen from entering and disrupting the reduction environment needed to prevent scaling.

1. SCALE RESISTANT WELDING
© REDOX 2011
Fig. 1 REDOX scale resistant weld Fig. 2 Scale from pickled pipe weld
Scale formation on the ID of the pipe as a result of welding does not have to occur. In
understanding reduction reactions you can easily obtain results like Figure 1. Figure 2 is
the result of oxidation reactions.
REDUCTION REACTIONS
REDOX pipe uses a reduction reaction to resist scale. As the pipe is being welded, the
VSI oils on the ID of the pipe are turning to gas and the exposure to the hot metal
disassociates the hydrocarbon into hydrogen and carbon. Carbon is higher on the
electromotive scale so it is more aggressive then iron in attracting oxygen. Instead of
forming scale it forms carbon dioxide which also acts like a purge as the metal cools.
OXIDATION REACTIONS
Pickled and oiled pipe forms scale through an oxidation process. When the pipe is
heated by welding it turns the trace amounts of water found in the grain of the metal and
oil to steam. The metal is highly active when it is in the red hot state. The metal
oxidizes the steam and the result is scale. This is very similar to the way scale is formed
during the manufacture of pipe.
It is quite easy to achieve scale resistant welds:
Avoid metal that has been pickled and oiled
Control the reduction reaction
PICKLED AND OILED PIPE
This product is the result of an oxidation process. The metal is highly reactive and prone
to scaling when welded. AW 46 is hydrophilic so it always has trace amounts of water
in it consequently forming scale.
CONTROLLING THE REACTION
All oxidizing reactions must be avoided. These would include avoiding water based

2. coolants for cutting, anti splatter compounds that contain Tri Chlor, and making certain
that the pipe ends are sealed to avoid a stove pipe effect that will draw oxygen into the
weld zone.
After the pipe has been cut and assembled for welding:
Spray WD 40 into the ID of the pipe
Seal the ends with plastic plugs or aluminum tape
Strike the weld on the shoulder of the fitting
WD 40 is also a VSI oil and is compatible with REDOX VSI oils. Sometimes through
fabrication processes at the jobsite the VSI oil may be marginalized and require a quick
refresher. WD 40 does a good job and is readily available at a nominal price.
Avoiding a stovepipe effect will keep the reduction reaction from being blown away by
fresh oxygen entering the weld zone. Plastic plugs perform well for plugging the pipe
but do not tolerate high heat near the welding. Aluminum tape found at most auto
supply stores can withstand the heat and provides good sealing.
Striking the arc on the shoulder of the pipe is important. That fraction of a second that it
takes to move the arc to form a fillet weld gives the VSI oil on the ID of the pipe an
opportunity to turn to gas. Once the gas is formed the reduction environment is in place
to resist scaling.
Scale formation with welding is not unavoidable. The use of REDOX pipe with its clean
ID and VSI protection opens new possibilities to deliver a more reliable system at a lower
installed cost. Additionally, your customer will also enjoy a lower operating cost.