Topological insulator nanowires provide a versatile platform for studying the interplay between disorder, quantum interference, and symmetry-protected transport. We investigate quantum transport in disordered topological insulator nanowires threaded by an axial magnetic flux. From the length dependence of the conductance, we extract the localization length and characterize the flux-driven delocalization transition near half-integer flux quanta. We determine a localization-length exponent $\nu \simeq 2$, robust against variations of chemical potential and disorder strength, and relate this scaling to the asymptotic dominance of the protected helical channel. This value differs from the localization-length exponent of the integer quantum Hall transition, indicating that the transition is not described by integer quantum Hall critical scaling. Near integer flux quanta, we uncover an unexpected crossover from weak localization at low chemical potential to weak anti-localization at higher chemical potential, followed by a splitting and eventual suppression of the interference peak as the system enters the strongly localized regime.