Check to see if your design does it efficiently. The seal face load should be adjustable to compensate for open impeller adjustments and axial growth of the shaft. Cartridge seals do this very well. All of the seal materials should be clearly identified by type and grade. You will need this information if you have to analyze a premature seal failure.
Pressures can reverse in dual seal applications.
The elastomers, especially the dynamic elastomer Excessive corrosion of the seal components. It can change with heat. It can vaporize, solidify, crystallize, coke or build a film with an increase in the product's temperature. Internal tolerances of the seal especially face flatness and elastomer squeeze. Heat causes thermal growth of these components that will alter their critical tolerances.