Page 29 - SSAB Welding Handbook Edition 2

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Welding handbook 4.0 Hydrogen cracks

4.12 Measures that reduce the 4 Tack welds and root passes are more sensitive to
residual stresses in joints during hydrogen cracking than other passes. This is
©SSAB
welding because there are often very high residual stresses
at these locations. It is, therefore, essential that
There are many measures that can be taken in order special attention is paid to our recommendations
to reduce the levels of residual stresses in the joint. for these types of welds. When tack welding is
The measures discussed in this context are those that performed, it is recommended that each individual
are recommended in order to minimize the risk for tack is at least 50 mm long in order to reduce the
hydrogen cracks. stresses in the joint. For plate thicknesses up to
4 Large root gaps facilitate stress concentrations. 8 mm, shorter tack lengths than 50 mm may be
SSAB recommends that the size of the root gap applied.
in joints made in the Hardox and Strenx grades
should be a maximum of 3 mm in order to reduce 4.13 Recommendations for
stress concentrations, see fig. 4.10.
consumables for welding of the
Hardox grades
Max. gap of 3 mm
4 Joints made in the Hardox grades are welded using
consumables with yield strengths of up to approx-
imately 500 MPa. This requirement can be fulfilled
when welding with unalloyed, low alloyed and
stainless consumables. The reason for this limita-
tion is that it further limits the residual stresses
since they can not exceed the local yield strength in
Fig. 4.10: Allowable gap sizes in joints. the joint. The Strenx grades can, however, be
welded using consumables with yield strengths higher
than 500 MPa since the measures for minimizing the
4 The residual stresses from a welding procedure risk for hydrogen cracks is, to some extent, less
can be lowered if start and stop sequences are not compared to the case for the Hardox grades.
placed directly in the corners. If possible, SSAB
recommends that start and stop sequences are made
50 mm-100 mm away from a corner of a joint, see 4.14 A suitable measure for welding a
fig. 4.11. multi-pass joint in the Strenx grades
4 The first few weld passes in a multi-pass joint
normally have a higher sensitivity towards
hydrogen cracks than the remaining passes. When
welding joints in Strenx 700-Strenx 1300, it is
particularly beneficial to weld with consumables of
different strengths. Tack welds and the first passes
can be welded with low strength consumables and
then high strength consumables can be used for the
remainder of the passes. This technique increases
the resistance to hydrogen cracks since the residual
stresses are lowered for the welding passes that are
Fig. 4.11: Avoid start and stop sequences in corners when possible. most prone to hydrogen cracks, see fig. 4.12. Note
that this kind of measure in not mandatory but
it results in an extra high resistance to hydrogen
cracks.

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. 29
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.