It takes a film thickness of at least one micron at operating temperature and face load to be classified as a lubricating fluid. Carbon graphite can easily be inserted into a metal holder. Most oils coke between the seal faces and can pull out pieces of carbon , causing fugitive emissions problems. If the product tends to stick the faces together. Some DI water applications can attack any form of carbon.
Halogens can attack all forms of carbon.
If the product you are sealing is an oxidizer that will attack all forms of carbon, including black O-rings. If you are pumping a slurry and you cannot keep the two lapped faces together by flushing, suction recirculation, a large diameter stuffing box or some other method usually employed to seal a large percentage of solids. If nothing black is allowed in the system because of a possible color contamination of the product you are pumping. The cause is not fully understood, but hydrogen embrittlement is suspected as the main cause. Cracks have been observed after seven to eight temperature cycles.