Page 76 - SSAB Welding Handbook Edition 2

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13.0 Distortions in joints Welding handbook

The actual geometry and size of the distortions in Example 2:
a welded structure is complex and can take various If feasible, a balanced welding sequence that
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forms. Their appearance depends on a combination of alternates between each side of the joint is favorable
effects from several factors such as: since this measure reduces the distortion in the joint.

4Joint geometry In this case, each weld pass counteracts distortions
4Heat input applied from the previous weld pass. A symmetrical joint
4Locations of the joints in the structure supports these types of welding sequences. This
4The planning and execution of weld sequences issue is mainly addressed for the first weld passes,
4The level of restraint in the joint see fig. 13.3.
4If presetting of the joint is carried out

The exact directions and levels of the distortion in a 3 4
structure are normally difficult to predict before 1
welding actually takes place. However, the following 2
issues address general measures that can reduce 5 6
distortions in a welded structure.
Fig. 13.3: Favorable welding sequences for a double-V joint. The
Appearance of the joint geometry number of each pass indicates the weld sequence. A double-V joint
is often suitable for thicker joint sections where a number of weld
Reducing the volume of the joint geometry decreases passes are to be performed.
the general distortion of the joint. This is because
the weld metal naturally shrinks during the cooling
process of welding, consequently, smaller volumes of The effect of heat input
weld metal lead to less distortion compared to larger A lowered heat input can lower the distortion levels
volumes. in the joint as long as the number of weld passes in
the joint does not increase. The reasons are that:
Example 1:
4 The volume of the weld metal from each weld pass
Unsymmetrical joints typically lead to angular decreases with a lowered heat input. The weld metal
distortions. This issue is exemplified for a single-V from each pass shrinks during cooling leading to
butt joint. In this type of joint, there is more weld less distortion because a smaller amount of weld
metal at the upper section compared to the lower metal deforms less than a larger amount
section. Since larger volumes of weld metal contract 4 Parent metals that are thermally affected around
more than smaller ones during welding, an angular the weld metals can shrink and cause distortions.
distortion will occur. If the groove angle is increased, A reduced heatinput causes a narrower zone of
then larger levels of angular distortions are further thermally affected parent metals, which thereby
promoted, see fig. 13.2.
supports lowered distortions.

1 A common way to decrease distortions using this
measure is to increase the welding speed. However,
if a reduction in heat input leads to additional weld
passes in the joint, this technique might not be
Increasing joint angle advantageous and may instead cause increased levels
2 of distortions.

2 1
Fig. 13.2: Influence of different groove angles in single-V butt joints

76 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.