We consider the expulsion of proton fluxoids along neutron vortices from th
e super fluid/superconductive core of neutron star with weak (B < 10(10) G)
magnetic field. The velocity of fluxoids is calculated from the balance of
buoyancy, drag and crustal forces. We show, that the proton fluxoids can l
eave the super fluid core sliding along the neutron vortices on a timescale
of about 10(7) years. An alternative possibility is that fluxoids are alig
ned with the vortices on the same timescale. As the result, non-aligned sur
face magnetic fields of millisecond pulsars can be sustained for <greater t
han or similar to>10(9) years only in case of a comparable dissipation time
scale of the currents in the neutron star crust. This defines upper limits
of the impurity concentration in the neutron star crust: Q less than or sim
ilar to 0.1 if a stiff equation of state determines the density profile.