http://www.documentbays.org/89951-bs-7910-2013a1-2015.html

P.9 Reference stress and/or limit load solutions for pipes/cylinderswith axial flawsP.9.1 Through-thickness flaws in thin-walled pipe/cylinder undermembrane stress and through-wall bending [277] and [358]See Figure M.13 for the definition of geometry. The reference stress is calculatedfrom Equation P.17:σ ref = 1.2MTPm +2Pb3(1− 2a W) (P.17)where:MT = 1+1.6a2riB⎛⎝ ⎜⎞⎠ ⎟⎡⎣ ⎢⎢⎤⎦ ⎥⎥0.5Pm is the hoop (membrane) stressPb is the bending stress transverse to the flawNOTE 1 The multiplier of 1.2 is an empirical multiplication factor introduced in thisBritish Standard based on experimental experience gained from large-scale pipe tests.NOTE 2 See M.7.2.1 for the stress intensity factor solution for this geometry.P.9.2 Internal surface flaw in thin- and thick-walled pipe/cylinderunder membrane stress and through-wall bending, [277], [358],[359] and [360]See Figure M.14 for the definition of geometry. The reference stress is calculatedfrom the following equation:σ ref = 1.2MsPm +2Pb3(1−α ′′)2