In this paper the line-spring model (LSM) developed by Rice and Levy is used to obtain an approximate solution of the stress intensity factor for a partial circumferential, externally cracked tube under axial tension and four point bending. The calculation is based on the work done by Delale and Erdogan for cylindrical shells containing a circumferential or an axial semi-elliptical, part-through crack. The range of utility of their analysis is enlarged to thicker wall tubes with nonelliptic and longer part-through circumferential cracks. Values of Kl calculated by the LSM are compared with those from a finite element analysis for remote tensile loading and bending cases, which shows fairly good agreement. The calculations are also applied to a fatigue crack growth test in a tube in four point bending to correlate the da/dN vs AKl data. NOMENCLATURE a, a, = crack depth at the deepest penetration point a(x) =crack depth of surface crack C, = local compliances corresponding to the SEN specimen da/dN = crack growth rate F, , F2 = geometry functions for the SEN specimen KO = stress intensity factor for a corresponding SEN specimen under tension and bending L =half length of surface crack K I , AKl = stress intensity factor M , M" =bending moment per unit length on a plate N, N" = membrane force per unit length on a plate r = plate thickness or pipe wall thickness P,, = compliances of the SEN specimen 6 ( x ) , 6, = axial displacement of the plate at mid-surface O ( x ) , 0, = rotation on plate at mid-surface 5 = dimensionless crack depth 1, = shape factor of the cylinder shell v = Poisson's ratio u = fiber stress of pipes 24 =crack angle for a surface crack in a pipe

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