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 WELDING & NON-DESTRUCTIVE TESTING
CASE W1 - Distortions in Welded Structures, J. Cecilio
Problem: Structures such as POL tanks and radio shielded rooms require large
areas to be covered by steel plates and connected by welding to insure
tightness. These facilities require a great deal of planning, preparation,
and care in fabrication to insure proper fit and to minimize warpage and
distortion.
Collection of Facts: When improper welding methods are used excessive
buckling and warpage occur requiring additional rework and increased cost.
Solution: Distortions and warpage in welded plates can be minimized and
satisfactory results can be obtained, if the proper methods are used.
Distortion and warpage can be minimized by adherence to the following:
Don't overweld.
a.
Control fitup.
b.
Use intermitted welds where possible.
c.
Use the smallest size of weld permissible.
d.
Use minimum root opening, including angle and reinforcement.
e.
Select joints that require minimal weld metal, for example, a
f.
double "V" joint instead of single "V" joint.
Weld alternately on either side of the joint when possible with
multiple pass welds.
Use fewer weld passes/ high deposition rate.
h.
Use higher speed welding methods (iron powder coated electrodes
i.
or mechanized welding, etc.)
Use welding methods that give deeper penetration and thus reduce
j.
the amount of weld metal and heat needed for the same strength.
k.
Use welding positioners to achieve maximum amount of downhand
welding, allowing the use of larger diameter electrodes or higher
deposition rate welding procedures with faster welding speeds.
Balance welds about the neutral axis of the member.
l.
Distribute the welding heat as evenly as possible through planned
m.
welding sequence and weld position.
Weld toward the unrestrained part of the member.
n.
Use clamps, fixtures and strongbacks to maintain fitup and
o.
alignment.
Prebend the members or preset the joint to let shrinkage pull
p.
them back into alignment.
Weld those joints that cause the most contraction first.
Weld the more flexible section first so they can be strengthened,
if necessary, before final assembly.
Sequence subassemblies and final assemblies so that the welds
s.
being made continually balance each other around the section's
neutral axis.
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