Gate valves for steam: materials, wedge, packing and operating rules
Steam is one of the hardest services for a gate valve: high temperature, thermal cycling, condensate and water hammer risk. A wrong choice leads to leaks, binding and sometimes failure. These are the points to check.
TAZ Engineering Team · · 6 min
Body material
Steam calls for steel gate valves. Cast carbon steel (25L, WCB) suits temperatures up to about 425 °C, which is the limit of the 30s41nzh and 30s15nzh valves. Higher temperatures need alloy steels such as chromium-molybdenum grades. Grey iron is acceptable only at very low steam parameters, and many operators prohibit it on steam altogether.
Wedge and seats
A flexible wedge is preferred on steam because it accommodates distortion during warm-up and reduces thermal binding. Seats are stainless steel or hardfaced. Resilient rubber wedges are not suitable for steam.
Packing and gaskets
Packing and bonnet gaskets must handle steam temperature and pressure; flexible graphite is usual. The gland normally needs an even retightening after the first heat-up.
Operation
Warm the downstream section through a bypass or drain and remove condensate before opening; opening suddenly onto a cold line causes water hammer. Do not close a hot valve with excessive force, and do not throttle with a gate valve; use globe or control valves instead.
What to state in the RFQ
Steam pressure and temperature, saturated or superheated, DN, end connection (flanged or butt-weld), test standard and documents. TAZ will select the steel grade, wedge type and sealing materials.
Checklist
- steam pressure and temperature
- saturated or superheated
- steel grade
- flexible wedge
- seat material
- graphite packing
- warm-up bypass or drain
- end connection
- test standard