ssc-367 - Ship Structure Committee

Maddox (Reference 7.11) provide the basis for assessment of
misalignments.
Weld Quality
A significant scatter of fatigue life test data is expected and
appropriatelyaccountedfor. Acharacteristic strengthrepresenting
a 95% confidence level in test data may be used to assess data
points falling substantiallybelow the S-N curve. Such data points
are likely to be due to a problem with the welding procedure or the
welder qualification. Weld quality degradation (and therefore
fatigue life degradation) due to incomplete penetration and poor
weld root quality can be minimized by developing a welding
specification applicable to the specific configuration and closely
adhering to it during fabrication. Weld quality degradation due to
undercut at the weld toe can be similarly minimized.
Weld Toe Profile
The significance of weld profiles on joints subjected to fatigue
loading is controversial. Substantial time and expenditures are
necessary to prepare a favorable weld profile, and weld profiling
may increasewelding costs by as much as 20%. Thus, weld profi1ing
is limited to specific tubular joints of discrete marine systems.
While API RP2A does “not recognize and quantify plate thickness
effects, theAPI S-N curves recognize and quantifyweld profile. As
illustrated on Figure 4-3 in Section 4.1.2, API (Reference 1.5)
recommends the use of an X-curve for welds with a favorable profile
while the X’-curve is reconnnendedfor welds without such a profile.
As il1ustrated on Figure 7-3, substantial preparation, weld bead
shape, applicationof extra weld beads and grinding may be necessary
to allow the use of an X-curve.
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