Plated and coated hard faces are subject to heat checking and cracking if improper bonding methods have been used. I do not recommend plasma spray processes for this reason. Pressed in carbons and hard faces can become loose in their holders. This has caused some seal manufacturers to glue in seal faces and as you can imagine, not a very satisfactory solution. Some seal face designs can go out of flat with very little temperature differential.
Water becomes steam.
Glue, paint and all kinds of polymers with odd sounding names can solidify. Oil changes its viscosity, caustic and sugar syrups crystallize and the list goes on and on. Centrifugal pumps and mechanical seals can handle liquids, they have problems with vapors and solids. If a Cryogenic evaporates across a mechanical seal face it can freeze any lubricant that might have been put on the face and either tear up the carbon or break the hard face. The easiest product to pump or seal is a cool, clean, lubricating liquid.