>30 is the best guess I can find...

>From my notes:

Ultrium cleaning cartridge              The IBM LTO Ultrium Cleaning Cartridge
                                        is valid for 50 uses only: the
                                        cartridge's LTO-CM chip tracks the
                                        number of times that the cartridge is
                                        used.  If you insert a cleaning
                                        cartridge when the drive does not need
                                        to be cleaned or if you insert a
                                        cleaning cartridge that has expired, the
                                        drive will automatically eject the
                                        cartridge.
                                        Ref: 3580 Ultrium Tape Drive Setup,
                                        Operator, and Service Guide

  Richard Sims, Boston University Office of Information Technology