ESDU 74043 gives curves@ calculated by a theoretical method that assumes a pure bending moment and that initially-plane sections stay plane when under bending@ for the flexibility of@ and the maximum shear stress in@ a pipe bend with or without internal pressure. The curves can be used for bends connected to long straight pipes (length exceeding three diameters@ say).
ESDU 74043-1974 history
1974ESDU 74043-1974 Flexibilities of and stresses in unrestrained pressurised thin pipe bends subjected to in-plane bending.