Evaporation causes expansion and the seal faces separate. Seal springs push the faces back together, causing chipping. This damage can happen on either the inside or outside diameter. The seal faces in Photo 7 have been pitted. Strain occurs from thermal expansion and is released by cracks.
Material is wiped away by face contact.
Figure 1 shows a seal face that has been fractured. High startup torque in viscous service can cause unprotected ceramics to fracture in this way. Tension due to very high inside diameter pressure can also cause this kind of damage. An automobile or truck traveling down a dirt or gravel road will eventually wear two ruts in the road surface. The wear is indicated by the tire's contact with the ground.