I have to design an external stiffening ring for a 60 " Pipe. Besides checking as per SEC VIII Div 1 for external pressure,I want to check for the effects of the local stress on the pipe wall.. Can someone suggest where in Roarks Formulas for stress and strain, I can get the necessary relations for the same.

ASME VIII Div.1 UG29~30 extenal pressure design does not say anything about local stress. I do not feel the necessity of local stress check for it.
Do you really need to check local stress on the junction of stiffener ring and pipe wall ?
Are there any significant external loads applied on stiffener other than external pressure ? If so, you may use one of 17 equations on Roark's Formulas Table 29 with appropriate stress conception for primary and secondary loads.
However, I am not sure you will find it satisfactory. FEA is best solution

Sun Wee