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Stress in Ellipsoidal Head Seam Equations and Calculator

Structural Design and Analysis
Pressure Vessel Design and Engineering

Stress in Ellipsoidal Head Seam Equation and Calculator

The stress in the girth seam will govern only when the circumferential join efficiency is less than one - half the longitudinal joint efficiency, or when the internal pressure additional loadings (wind load, reaction of saddles) are causing longitudinal bending or tension . The reason for it is that the stress arising in the girth seam pound per square inch is one - half of the stress in the longitudinal seam.

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Stress in Ellipsoidal Head Seam Calculator:

Required minimum wall thickness

t = [ P (D + 2CA) ] / ( 2SE - 0.2P) + CA

Maximum allowable working pressure
P = 2SEt_a / ( (D + 0.2t_a)

Head height:

h = D / 4

Where:

P = Design pressure or max. allowable working pressure, psi
S = Rated stress value of the material
E = Weld Joint efficiency
R = Inside radius, inches
D = Inside diameter of vessel , inches
t = Thickness of shell (wall), inches
t_a = Wall thickness used in actual design, inches
CA = Corrosion allowance, inches

1. For heads without a straight flange, use the efficiency of the head to shell joint if it is less than the efficiency of the seams in the head.

Example:

Given:

P = 100 psi design pressure
S = 17,500 psi stress value of SA 515-70 plate @ 650°F
E = 1, efficiency of seamless heads.
D = 96 inches
R = 48 inches
CA = 0.125 in

Shell thickness requirements:

t = ( 100 psi x 96.25 in.) / ( 2 x 17,500 psi x 1.00 - 0.2 x 100 psi) + 0.125 in.
t = 0.400 in.

Probably use 0.4375 in. plate for design = t_a

Maximum working pressure

t_a = ( 2 x 17,500 psi x 1.00 x 0.4375 in) / ( 96.00 in + 0.2 x 0.4375in)
t_a = 159 psi