A method for evaluating wellbore conduit condition includes using measurements of at least one of (i) inelastic gamma rays made during emission a burst of neutrons into the conduit from within the conduit at at least one spaced apart location from a position of the emission and (ii) epithermal neutrons or capture gamma rays therefrom detected at at least two spaced apart locations from the position of the emission within a selected time after the emission. The at least one of the measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts are characterized to estimate an amount of loss of iron in the conduit.