ssc-367 - Ship Structure Committee

Fatigue strength of a tubular joint is shown to improvedue to weld
profiling (References 7.12 and 7.13). Weld profiling (including
grinding of weld toe) has two primary benefits:
● It can minimize the potential for crack propagation by
removing inherent crack-like flaws.
● It can reduce stress concentrations by improving local weld
profile.
However, grindingto remove flaws and to provide a smooth transition
between the weld and parent material is not universally accepted as
quantifiable benefit unless the weld toe undercut is sufficient.
Both AWSand API do not require a correctivemeasure if the undercut
of weld toe is less than 0.01 in. (See Figure C 10.7.5, Reference
4.14). DnV (Section3.3.1 , Reference 1.7) states, “the effect of
weld profiling giving the weld a smooth concave profile compared
with the typical triangular or convex shape~ improve the fatigue
properties.”Although DnV accepts the use of an X-curve (in lieu of
a T-curve) provided weld profiling is carried out, it also
stipulates that the effect of profiling on the S-N curves will be
considered for each case separately.
The weld profiles applicabletoAPI XandX’ S-N curves are shown on
Figure 7-3. However, to ensure that the flaws at weld toe are
removed, grinding or AWJ process should result in sufficient
undercut at the weld toe. The minimum undercut recommended by the
DEn Guidance Notes (Reference 1.6) is shown on Figure 7-4.
Further discussion and an excellentoverview of the effects of weld
improvementtechniques is provided by Bignonnet (Reference7.14).
7.2.3
Environmental Parameters
The environment in which fatigue cracks initiate and propagate
substantiallyaffectsfatiguelife. The amplitude,distributionand
7-1o