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Cracking concerns with cellulosic electrodes are addressed
with proper preheat and interpass temperature control, and by
using procedures which insure adequate ligament in the root pass.
Preheat and interpass temperatures are dictated by steel chemistries
which today are more forgiving than previously. Use of the correct
electrode size run in the middle to lower portion the range for
that electrode helps insure a proper ligament. Root bead cracking
can also be minimized by not moving the lineup clamp until the
second pass has been completed.
Self shielded flux cored arc welding, Figure 2, has the advantages
of shielded metal arc welding with cellulosic electrodes including
high arc force, high penetration and excellent puddle control
when welding with a vertical down progression. In addition,
this process has the advantages of automated processes including
high deposition rates, high travel speeds, high arc on times,
and controlled hydrogen levels. Frequently self shielded is
used over root passes made with shielded metal arc welding.
This is one approach to the welding of X80, where hydrogen cracking
in the parent steel is not a concern for the root pass, but
weld metal hydrogen cracking could be a concern on subsequent
passes.
In shielded metal arc welding shielding is generated
by the decomposition of the flux at the arc. In self shielded
flux cored arc welding a continuous tubular electrode contains
are stabilizers and core materials which will generate shielding
when they reach the arc. Both processes work outside under severe
weather conditions including temperature extremes and high winds.
Likewise, both shielded metal arc welding with cellulosic electrodes
and self shielded flux cored arc welding are easily learned by
welding operators already skilled in other forms of shielded metal
arc welding. For example, one instructor was recently able to
train and qualify to API 1104 over ninety welding operators unfamiliar
with self shielded flux cored arc welding.
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