Primary Stress
Primary Stress
(OP)
For calaculation of wall thickness of a pressure vessel, what means "primary stress" and "primary membrane stress" ?
Thanks,
Thanks,
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RE: Primary Stress
Primary stress = maximum stress, usually the hoop stress in a cylindrical vessel.
RE: Primary Stress
The definition of a primary stress appears simple in wording, but is quite complex in the consequences: it is that part of the stress due to the external loads that is necessary to satisfy the equations of equilibrium (hence they are not required to be compliant).
The consequences of this definition might seem unrelated to strength calculations, but they are, as a primary stress is not self limiting: if the load increases, the stress will increase till rupture.
The commonest source of primary stress in a pressure vessel is pressure: however not all the stresses due to pressure are primary (e.g. continuity stresses at the junction between a cylinder and a head).
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RE: Primary Stress
At the joint between head and shell, membrane stress is primary (local), bending stress is secondary.