ssc-367 - Ship Structure Committee

after
a given number of stress cycles, the stress range to cause
failure is practicallyconstant for a wide range of mean stresses.
The undesirable tensile residual stresses at the weld can be
modified by the following methods to set up desirable compressive
stresses at the weld toe:
●
Stress Relief
Various fatigue tests on simpleplate specimens indicate that
an improvedfatigue strength can be obtained by stress relief
due to post-weld heat treatment (PWHT). However, PIate and
stiffening elements of continuous systems rarely require
stressrelief. Thick tubularjointswith residual stressesas
a result of fabrication work can often benefit from stress
relief. Yet, it is not clear that a complex joint with builtin
constraints can be effectively stress relieved. It is
1ikely that substantial residual strains and stresses wil1
remain at a joint assembly after PWHT.
Localized stress relief may be very beneficial in an
embrittled heat-affected zone (HAZ). Typically, high
localized heat input in a HAZ alters the material properties
and causes reduced fatigue life due to unstable fracture. A
PWHT carriedout to improvetoughnessof the HAZmay partially
restorethe fatiguestrengthof welded joints, as the residual
stresses have an influence in the development of fatigue
cracks. Previous investigations on this subject (Reference
1.8) document influence of PWHT on fatigue.
●
Compressive Overstressinq
Compressiveoverstressingis a technique in which compressive
residual stresses are introduced at the weld toe.
Experimental results and analytical work demonstrate
effectivenessof prior overstressing,but the procedure to be
implementeddoes not appear to be practical for most marine
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