Gate Valves for Chemical Processing

API 600 covers steel gate valves with bolted and pressure-seal bonnets in flanged and butt-welding ends — the primary standard for carbon steel (WCB), alloy steel (WC6, WC9) and carbon-moly gate valves in process plant and pipeline service. API 603 covers corrosion-resistant gate valves — specifically CF8M (SS316) and CF3M (SS316L) austenitic stainless steel — with the same general design provisions as API 600 but addressed to the specific considerations of stainless steel castings (lower allowable stresses, different hardness limits). For chemical service: carbon steel isolation uses API 600; stainless isolation uses API 603. Compact small-bore forged gate valves (DN15–DN50) are covered by API 602 (threaded and socket weld ends) regardless of material.

Flexible wedge gate valves have a disc with a split or thin-section allowing the two gate faces to flex independently to conform to the seating surfaces — preventing the thermal lock-up that affects solid wedge gates when a valve closes hot and cools, causing the wedge to jam (thermal binding). Flexible wedge is preferred for: steam service (closes hot); chemical process lines with frequent temperature cycling; sizes DN200+ where thermal binding risk increases. Solid wedge is simpler and stronger — preferred for: low-temperature chemical service without thermal cycling; slurry service where the solid wedge is more resistant to wedge face erosion; high-pressure service where body casting is simpler without the split disc. For most chemical plants above DN100 in steam or process service with temperature variation: specify flexible wedge.

Yes. PTFE-lined gate valves provide economical chemical resistance for Class 150 (PN10/16) service in highly corrosive chemicals including chlorine, fluorine, HF (dilute), chlorinated solvents, and strong acids. The PTFE liner covers all wetted metal surfaces — body, gate, and bonnet — with continuous PTFE; the underlying carbon steel body provides structural strength. Limitations: maximum operating temperature typically 150°C (PTFE softens above 200°C but the liner may deform under load at lower temperatures); maximum pressure Class 150 / PN16 (higher pressure ratings not available due to PTFE liner thickness constraints); not suitable for permeating gases (some gases permeate through PTFE at elevated temperature and pressure). For higher pressures (Class 300+) or temperatures above 150°C in corrosive chemical service: solid Hastelloy C-276 or Alloy 20 gate valves are required.