HEAT EXCHANGER E-BOOK (MECHANICAL DESIGN)
SHELL CYLINDER, FRONT HEAD CYLINDER (CHANNEL), SHELL COVER CYLINDER
Shell thickness:
Required wall thickness of cylinder, greater of
Circumferential stress
t = (P*OR / (S*E+0.4*P)) + cai + cao + Tol (From ASME Appendix. 1-1 A) - 01
Longitudinal stress
t = (P*IR / (2*S*E+0.4*P)) + cai + cao + Tol (From ASME UG-27(C) (2)) - 02
Where,
P – Design pressure in psi.
OR – Outer radius of the shell in inches.
IR – Inside radius of the shell in inches.
S – Allowable stress for the corresponding material in psi.
Cai – Inside corrosion allowance in inches.
Cao – outside corrosion allowance in inches.
Tol – Under tolerance allowance in inches.
Thus from equations 1 and 2 fix the thickness value whichever is greater.
tnom – greater of equation 1 or 2
But according to TEMA standards the minimum shell thickness for classes RCB is
shown in tables below
Now compare the values of tnom and the thickness value from the above table for the respective shell diameter. Take the greater value.
Required thickness of the shell cylinder = Greater of tnom or table value.
Maximum allowable external pressure for Shell cylinder:
Pa = 4*B/ (3*(Do/t)) - 03
Where,
B – Factor from ASME section 2 D (Refer from page 747)
Do – Outer diameter of the shell in inches.
t – Required thickness of shell cylinder in inches.
Pa – Maximum allowable external pressure in psi.