Scoring or wear of the hard face is the most common symptom of this failure. The scoring occurs because the solids imbed into the softer carbon face after they open. The seal faces must stay in contact, but there are all kinds of conditions that are trying to force or pull them open. This is normal at start up. Operating off of the pump's best efficiency point.
Centrifugal force tries to separate the faces in a rotating seal application.
Hydrodynamic forces generated between the lapped faces. Pressure distortion caused during pressure peaks such as water hammer and cavitation. A failure to provide equal and opposite clamping across the stationary seal face will cause distortion. A hardened sleeve can cause the seal set screws to slip. A wrong initial setting of the face load.