Please try this :
select a.orion_tank, b.OrionCrude, a.prop_modified_value,
a.DayInserted, SEQ5_CRDINV.nextval, sysdate, user
from ps_staging_data a, ps_crude_map b
where a.Orion_tank = b.OrionTank
and to_char(a.dayInserted,'dd/mm/yyyy') = to_char(sysdate, 'dd/mm/yyyy')
and a.validated = 1
and...