Tube thickness:
Required wall thickness of tubes, greater of
Circumferential stress
t = (P*OR / (S*E+0.4*P)) + cai + cao + Tol (From ASME Appendix. 1-1 A) - 08
Longitudinal stress
t = (P*IR / (2*S*E+0.4*P)) + cai + cao + Tol (From ASME UG-27(C) (2)) - 09
            P – Design pressure in psi.
            OR – Outer radius of the tube in inches.
            IR – Inside radius of the tube 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
Maximum allowable external pressure for tubes:
Pa = B*((2.167/ (Do/t))-0.0833) - 10
            B – Factor from ASME section 2 D (Refer from page 747)
            Do – Outer diameter of the tubes in inches.
            t – Required thickness of tubes in inches.
            Pa – Maximum allowable external pressure in psi.
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