Do your homework and you will find that virtually every standard category aircraft on Australian register has an Australian imposed life, no such equivalent in US.
The Cirrus aircraft SR20 and SR22 have an airframe life limit of 12000 hrs on their FAA issued Type Certificate Data Sheet (TCDS). This is not the case for the PA31. (Old)Piper may have issued guidance on spar life early on, Newpiper wants nothing to do with the PA31, although I have heard rumors that if you order a fleet (20 or more) of them at the right price they may consider new builds. There is no life limit figure for the PA31 other than the main spar assembly.