Page 248 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 233

Minimize the amount of weld metal: Any reduction in the amount of
weld metal will result in a decrease in the amount of distortion:
Use the smallest acceptable weld size
Use intermittent welds where acceptable
Utilize double-sided joints versus single-sided joints where
applicable
Use groove details that require the minimum volume of weld per
metal per length

Fabrication practices that minimize distortion. Fabricators can use tech-
niques that will minimize distortion. These include the following:
Use as few weld passes as possible: Fewer passes are desirable inas-
much as they limit the number of heating and cooling cycles to
which the joint will be subjected. The shrinkage stresses of each
pass tend to accumulate, increasing the amount of distortion when
many passes are used. Note that this is in direct contrast with the
criterion of maximizing notch toughness.
Avoid overwelding: Overwelding results in more distortion than is
necessary. Holding weld sizes to print requirements will help avoid
unnecessary distortion.
Obtain good fit-up: Poor fit-up, resulting in gaps and larger included
angles for bevel preparations, means more weld metal is placed in
the joint than is required, contributing to excessive distortion.
Use high-productivity, low-heat input welding procedures:
Generally speaking, high-productivity welding procedures (those
using high amperages and high travel speeds) result in a lower net
heat input than low-productivity procedures. At first, high-amperage
procedures may seem to be high-heat input procedures. However,
for a given weld size, the high-amperage procedures are high travel-
speed procedures. This will result in a decreased amount of heat-
affected zone and reduced distortion.
Use clamps, strongbacks, or fixtures to restrict the amount of distortion:
Any tooling or restraints that avoid rotation of the part will reduce
the amount of distortion experienced. In addition, fixturing may be
used to draw heat away, particularly if copper chill bars and clamps
are used in the vicinity of the joint. The arc should never impinge
on copper as this could cause cracking.
Use a well-planned welding sequence: A well-planned welding
sequence is often helpful in balancing the shrinkage forces against
each other.

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