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Stress in Cylindrical Shell Long Seam Equations and Calculators

Structural Design and Analysis
Pressure Vessel Design and Engineering

Stress in Cylindrical Shell Long 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 Cylindrical Shell Long Seam Calculator:

Required minimum wall thickness

t = [ P (R + CA) ] / ( SE - 0.6P) + CA

Maximum allowable working pressure
P = SEt_a / (R + 0.6t_a)

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. Usually the stress in the long seam is the governing design feature
2. When the wall thickness exceeds one half of the inside radius or P exceeds 0.85 the above design equation are not applicable.

Example:

Given:

P = 100 psi design pressure
S = 17,500 psi stress value of SA 515-70 plate @ 650°F
E = 0.85, efficiency of spot-examined joints of shell.
D = 96 inches
R = 48 inches
CA = 0.125 in

Shell thickness requirments:

t = ( 100 psi x 48.125 in.) / ( 17,500 psi x 0.85 - 0.6 x 100 psi) + 0.125 in.
t = 0.450 in.

Probably use 0.500 in. plate for design = t_a

Maximum working pressure

t_a = ( 17,500 psi x 0.85 x 0.500 in) / ( ( 48 in+ 0.6 x 0.500 in)
t_a = 154 psi