We design pressure vessel for longitudinan and circumferencial stresses. Now whats that?
Ok, longitudinal stresses comes on circumferencial joints, where as circumferencial stresses comes on longitudinal joints.
And to add cherry on top circumferencial stresses are twise that of longitudinal stresses.
If you are not yet twisted your tongue, and to avoid that we generally call them c’seam and l’seam and c’stress and l’stress.

In below pictures, one can identify types of Seams and Stress.

here p is design pressure, R is internal Radius, L is Length of shell, t is thickness of shell.

Hence with the basic mechanical formula,
t for Hoop stresses = pL (2R)/2 xStressx L = pR/Allw. Stress
t Longitudinal stresses = px3.14xR^2 / (2×3.14xRxAllw. Stress) = PR/2 Allw. Stress

& what ASME Says..
t for Hoop Stress = PR/(SE – 0.6P)
Where S > All. Stress, E > Joint Eff. or factor of safety
why 0.6 P, because, its factor of safety set by ASME People

t for Longitudinal Stress = PR/(2SE+0.4P)

Note the ‘2’ in denominator..

if E remain the same for both cases, then thickness given by Hoop stress will be twice that of by Longitudinal stresses

For Calculation Sheet Visit http://sumitmechsoftware.blogspot.com/


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