You are trying to seal a halogen like chlorine, fluorine , bromine, astintine or iodine. Some forms of de-ionized water will pit and corrode carbon faces Cracked or damaged carbon face. The product is solidifying between the faces. Carbons are strong in compression but weak in tension or shear. This problem is common with intermittent service or standby pumps each time they start up.
Excessive vibration can bang the carbon against a metal drive lug.
A cryogenic fluid is freezing a lubricant that was put on the face. The elastomer is swelling up under a carbon face. The shaft is hitting the stationary face or the rotating seal face is hitting a stationary object. The fluid, containing solids, is underneath the carbon face. Centrifugal force is throwing solids or abrasive material into the soft carbon.