  We analyze possible nodal superconducting phases that emerge from a doped
nodal-line semimetal. We show that nodal-line superconducting phases are
favored by interactions mediated by short-range ferromagnetic fluctuations or
Hund's coupling. It is found that the leading pairing channels are
momentum-independent, orbital-singlet and spin-triplet. In the pairing state,
we show that the Bogoliubov-de Gennes (BdG) Hamiltonian hosts a pair of
topologically protected nodal rings on the equators of the torus Fermi surface
(FS). Using a topological classification for gapless systems with inversion
symmetry, we find that these nodal rings are topologically nontrivial and
protected by integer-valued monopole charges $\nu = \pm 2$. In the scenario of
pairing driven by ferromagnetic fluctuations, we analyze the fate of
superconductivity in the magnetically ordered phase. Based on Ginzburg-Landau
free energy analysis, we find the energetically favored superconducting state
is characterized by the coexistence of two pairing orders whose $\bf d$-vectors
are perpendicular to the magnetization axis $\bf M$ with their phases unfixed.
In this case, each nodal loop in the pairing state splits into two, carrying a
$\pm 1$ monopole charge. For bulk-boundary correspondence, these nodal rings
enclose flat-band Majorana zero modes on top and bottom surface Brillouin Zones
with distinct $\mathbb{Z}$-valued topological invariants.
