Stress in boiler drums

Circumferential

L=Length of cylinder
t= Material thickness
D= Diameter
F_p= Force acting on cylinder due to pressure
F_h= Resolved horizontal component of force
Equal forces act on all surfaces. If a vertical section is cut then the forces may be considered to be resisted by the longitudinal seam for the horizontal direction.
i.e. horizontal forces to left=Horizontal forces to right
= resisting force in seam
Pressure x projected area = stress x C.S.A of joint
By using projected area the horizontal component of the pressure force is automatically resolved
p x dia x L = stress x 2 x t x L
(p x dia x L)/ 2 x t= Stress ( longitudinal joint)

Longitudinal

Similarly
Horizontal forces to left = Horizontal forces to right
Pressure x end plate area = Resisting force in circumferential joint
P x (pi x d²)/4 = stress x csa (circumferential joint)
= stress x pi x d x t
(p x d)/ 4 x t = stress ( longitudinal)
Hence, circumferential stress is twice that of the longitudinal stress and hence seams in the longitudinal axis must be twice as strong.