Pressure Vessel Primary Stresses
Primary stresses are those developed in each component of a vessel due to sustained internal and external loads. The fundamental characteristic of primary stresses is that they are not self-limiting. In other words, no redistribution of load or reduction of stress will occur despite yielding within the component; primary stresses are not reduced by the deformations they produce. Therefore, primary stresses that exceed the yield strength of the material will cause failure either by gross plastic deformation or by bursting.
Primary stresses are the most significant stresses that occur in pressure vessels, and their limits for design are set both to prevent plastic deformation and to provide a factor of safety against bursting.
Primary stresses are further divided into primary membrane stresses and primary bending stresses because different stress limits are applied for design, depending on the type of primary stress.
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