ssc-367 - Ship Structure Committee

not three but five Charpy specimens from the low-toughness HAZ
region to more accurately predict brittle fracture.
On the other hand, crack-toughness levels implied in the impact
tests required in design guidelines may be overly conservative.
Pense’s work (Reference 3.2) indicates that the ship hull strain
rates during crack initiation,propagationand arrest are lower than
those estimated, confirming higher levels of crack-toughness.
Fabrication Specificationsand Procedures
Degradation of root toughness extending into the parent material
beyond the HAZ can be caused by procedures used in the fabrication
yard. Loosely specified fabrication tolerances often result in
fabrication and assembly distortions and may cause strain aging
embrittlement. Unnecessarily tight tolerances could result in
repair work that might contribute to degradation of material.
Fabrication procedures contribute to the pattern of local weldment
defect distribution, residual stress pattern in the HAZ, and
material properties. Since these factors in turn directly affect
crack growth, fabrication procedures should be carefully developed
for each design.
3.1.2
Fabrication and Post-FabricationParameters
Activities in the shipyard or fabricationyard directly impact the
fabricatedmarine structure. These activitiescan be categorizedas
either fabrication or post-fabricationparameters (Figure3-3).
Fabrication Parameters
The primary fabrication parameters can be defined by the questions
who, what, when and how. Each of these parameters affects the
fabricationquality, in terms of residualstresses,defects,repairs
and post fabrication processes. These variables, which determine
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