TDW PIG-SIG V, Operating And Maintenance Instructions Manual

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Section IV – Pipeline Under Pressure
1.0 Continued
D. For proper weld penetration, a root gap should be
introduced between the weld-end of the nipple
and the surface of the pipe. A 3/32-inch (0.094)
root gap is recommended. Do not weld inside of
the nipple and be careful to prevent excessive
weld penetration inside the nipple to help avoid
tapping problems. The length of the nipple varies
according to pipe wall thickness. For installation
on six-inch and larger pipe, the sum of the nipple
length, root gap, and pipe wall thickness should
be 4-1/4 to 4-1/2 inches. If that combination
would exceed 4-1/2 inches, grind some off the
weld-end of the nipple to obtain a shorter nipple
or decrease the amount of the root gap.
E. Upon completion of the welding, remove the cap
from the nipple.
F. Clean internal and external threads of the nipple.
G. Inspect the welded area inside the nipple.
Remove any loose weld spatter or bread.
H. Before tapping the line, allow the weld area to
cool. Normally, it will cool sufficiently while the
tapping equipment is being prepared.
⚠ WARNING
Follow established welding standard
when welding the nipple onto the
line. Improper welding can cause
rupture of the pipeline during or after
welding.