Seat-to-body sealing prevents bypass leakage around the seat pocket. The best designs use press-fit carbide seats with secondary O-ring backups in lower temperature classes (K, L, P). For X and Y classes above 350°F, pure MTM pressed-fits eliminate elastomers entirely. API 6A Annex G de-rates pressure ratings for high-temperature service. Inconel 625 or 718 overlays enhance corrosion ... https://globalsealstech.com/