S = [2P(1.3D2 + 0.4d2)]/[E(D2 - d2)]
Where:
S = wall stress, psig;
P = service pressure, psig;
D = outside diameter, inches;
d = inside diameter, inches; and
E = joint efficiency of the longitudinal seam (from paragraph (d) of this section).
49 C.F.R. §178.61