Pressure Vessel Peak Stresses
Peak stresses in pressure vessels are generally the highest stresses that exist in the various separate components of a vessel. They are distinguished from primary and secondary stresses in that they do not produce significant distortion, but they need not be localized nor necessarily self-limiting. They are developed at locations of high stress concentration (i.e., acute structural discontinuities) and by certain types of thermal stress. Peak stresses are of consequence only with regard to the possible initiation of fatigue failure under cyclic loading conditions, and brittle fracture if the material lacks adequate toughness. The stress limit for peak stresses is three times the allowable design stress for the material of construction.
Examples of peak stresses in pressure vessels are:
1. Stresses at corners and fillets of nozzles.
2. Thermal stresses in the shell related to cladding or weld overlay.
3. Thermal stresses in the shell due to rapid change in temperature of vessel contents.
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