The load on the seal faces can be too high causing excessive heat. The lapped seal faces can deform and go out of flat. The seal can push off the set screws. High shaft speed. Greater than 5000 fpm.
Axial movement causes changes in the seal face loading.
Radial movement can separate the lapped faces. Not listed in the above categories. The Mc Nally Institute 1986 S. Belcher Rd.