  We compute instantonic effects in globally consistent T^6/Z2xZ2 orientifold
models with discrete torsion and magnetised D-branes. We consider fractional
branes and instantons wrapping the same rigid cycles. We clarify and analyse in
detail the low-energy effective action on D-branes in these models. We provide
explicit examples where instantons induce linear terms in the charged fields,
or non-perturbative mass terms are generated. We also find examples where the
gauge theory on fractional branes has conformal symmetry at one-loop, broken by
instantonic mass terms at a hierarchically small energy scale.
