6 BASIC WELDING GUIDE
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© ESAB AB 2021
Figure 66: Parent metal expansion
1 Weld
4 Cool
2 Upsetting
5 Hot
3 Expansion with compression
Figure 67: Parent metal contraction
1 Weld
3 Contraction with tension
2 Permanent upset
Overcoming distortion effects
There are several methods of minimizing distortion effects.
•
Peening
This is done by hammering the weld while it is still hot. The weld metal is flattened slightly
and because of this the tensile stresses are reduced. The effects of peening is relatively
shallow, and it is not advisable on the last layer.
•
Distribution of stresses
Distortion may be reduced by selecting a welding sequence which will distribute the
stresses suitably so that they tend to cancel each other. see the figures below for various
weld sequences. Choice of a suitable weld sequence is probably the most effective
method of overcoming distortion, although an unsuitable sequence may exaggerate it.
Simultaneous welding of both sides of a joint by two welders is often successful in
eliminating distortion.
•
Restraint of parts
Forcible restraint of the welded components is often used to prevent distortion. Jigs,
positions, and tack welds are used.
•
Presetting
It is possible in some cases to tell from past experience or to find by trial and error (or less
frequently, to calculate) how much distortion will take place in a given welded structure. By
correct presetting of the components to be welded, constructional stresses can be made to
pull the parts into correct alignment. A simple example is shown in the figure below.
