ssc-367 - Ship Structure Committee

elsewhere). Both thermal stress relief and weld material straining
to set up desirable compressive stresses at the weld toe are used.
Typically, a node subjected to PWHT experiences both stress and
strain relief and should exhibit improved fatigue performance.
However, the efficiency of PWHT needs further verification. Some
experts in the field consider it difficult to justify any
improvement of fatigue performance as a result of stress relief.
Corrosionprotection is necessaryto ensure as-designedperformance
of the structure, including achieving the desired fatigue life.
Post fabrication work on corrosion protection systems varies from
installation of anodes for cathodic protection to coating and
painting.
3.1.3 In-Service Parameters
The environment in which fatigue cracks initiate and grow
substantially affects fatigue life. The environment affects
corrosionand crack growth due to both the nature of the environment
(i.e., sea water properties, including conductivity, salinity,
dissolved oxygen, pH and temperature) and the magnitude and
frequency of the applied loading (i.e., wind, wave and current
characteristics).
Environmental loads that cause reversal of stress on a marine
structure component are primarily caused by wave and wind
action. While the loading directionality and distribution is often
carefully accounted for, the sequence of loading usually is not.
The other in-serviceparametersreflect inspection,maintenance and
repair philosophy and have a major influence on corrosion and the
rate of crack growth. The in-serviceparameters are summarized on
Figure 3-4.
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