20 In
a weld-backed joint, the first weld pass (made by submerged are, gas metal-arc
or shielded metal-arc) forms
the backing for subsequent passes made either from the opposite side or from the
same side. Manual
welds are often used as backing for submerged arc welds (Fig. 8.) when it is not
convenient to use other
backing methods because of inaccessibility, poor joint preparation or fitting,
or difficulty in turning the weldment.
The manual weld may remain as a part of the completed joint if it is of suitable
quality, or it may be
removed by gouging, chipping, or machining after the submerged arc weld has been
made. When the manual
weld is removed, it is replaced by a permanent submerged arc weld.
FIG. 7 - Root Backing and Weld Backing
(Root backing for first weld, weld backing
for finishing weld.) If
a shielded metal-arc weld must be used for submerged arc weld backing, a low hydrogen
electrode such as
E-7016 or E-7018 is recommended. The E-6012 and E-6013 electrodes and their
iron powder equivalent are
not recommended because they tend to cause porosity in the finished submerged
arc weld. Continued
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