  The mass of $^{31}$Cl has been measured with the JYFLTRAP double Penning trap
mass spectrometer at the Ion-Guide Isotope Separator On-Line (IGISOL) facility.
The determined mass-excess value, -7034.7(34) keV, is 15 times more precise
than in the Atomic Mass Evaluation 2012. The quadratic form of the isobaric
multiplet mass equation for the T=3/2 quartet at A=31 fails ($\chi^2_n$=11.6)
and a non-zero cubic term, d=-3.5(11) keV, is obtained when the new mass value
is adopted. $^{31}$Cl has been found to be less proton-bound with a proton
separation energy of $S_p$=265(4) keV. Energies for the excited states in
$^{31}$Cl and the photodisintegration rate on $^{31}$Cl have been determined
with significantly improved precision using the new $S_p$ value. The improved
photodisintegration rate helps to constrain astrophysical conditions where
$^{30}$S can act as a waiting point in the rapid proton capture process in type
I x-ray bursts.
