Valves and Valve Equipment

High Pressure and High Temperature Valves: Material and Rating Selection

Learn how pressure class changes with temperature, which body material to choose and which seat and packing options suit superheated steam and thermal oil lines.

ORFA Technical TeamUpdated: Oct 30, 20263 min read

High pressure and high temperature valves – cast steel industrial valves

On superheated steam, thermal oil or high pressure process lines, a valve failure means not only lost production but a serious safety hazard. When selecting high pressure and high temperature valves, the body material, pressure-temperature rating, seat (trim) and packing design must be specified as carefully as the valve type itself.

This article explains which criteria to check when choosing valves for severe service, how the pressure rating changes with temperature and which valve type is used for which duty.

Evaluate Pressure Class Together with Temperature

A valve’s pressure class (ASME Class or PN) reflects its strength at ambient temperature. As temperature rises, material strength falls and so does the pressure the valve can safely carry. According to ASME B16.34, the allowable working pressures for carbon steel bodies (A105 forged / WCB cast, material group 1.1) are:

Temperature	Class 150	Class 300
Up to 38 °C	19.6 bar	51.1 bar
200 °C	13.8 bar	43.8 bar
300 °C	10.2 bar	39.8 bar
400 °C	6.5 bar	34.7 bar
425 °C	5.5 bar	28.8 bar

For example, on a line carrying 10 bar saturated steam (about 184 °C) a Class 150 carbon steel body is sufficient in terms of pressure, but with superheated steam above 300 °C the same pressure requires Class 300.

Material Selection

Carbon steel (WCB cast, A105 forged): The standard choice for steam, thermal oil and general process lines. Carbon steel is not recommended for prolonged service above about 425 °C.
Chromium-molybdenum alloy steels (WC6/F11, WC9/F22): For superheated steam and power plant lines at higher temperatures.
Stainless steel (CF8M / F316): For corrosive media, food and chemical processes and low-temperature service.
Ductile iron: Used on steam and thermal oil lines at moderate pressure and temperature, within the limits of the material.

Seat, Trim and Packing

Stellite hard-faced seat and disc: Resists erosion and wear at high temperature and high flow velocity.
Soft seats (PTFE etc.): Excellent tightness, but the temperature limit is set by the seat material; metal-seated designs are needed at high temperatures.
Graphite packing: Widely used for stem sealing at high temperatures.
Bellows seal design: On thermal oil and steam lines a metal bellows replaces or backs up the packing to prevent stem leakage.

Valve Types by Duty

Valve type	Duty	Note
Gate valve	Full on-off isolation	Low pressure loss; not for throttling
Globe valve	Flow regulation, frequent operation	Common on steam and thermal oil lines
Ball valve	Fast, tight shut-off	Metal-seated type at high temperatures
Check valve	Backflow prevention	Swing, lift or dual plate
Butterfly valve	Compact isolation in large sizes	Eccentric metal-seated at high temperatures
Control valves	Automatic flow, pressure and temperature control	With actuator and positioner

Tip: When ordering high pressure and temperature valves, state the medium, operating and design pressure, maximum temperature, connection standard (EN or ASME flange, weld end) and required certificates together. This prevents the wrong class being chosen because of missing information.

Applications

Boiler rooms, main steam and superheated steam lines
Thermal oil heating systems
Power and cogeneration plants
Petrochemical, refinery and chemical plants

Frequently Asked Questions

Can a Class 150 valve be used at 19.6 bar at any temperature?

No. For a carbon steel Class 150 valve the allowable pressure is 19.6 bar at 38 °C but falls to 13.8 bar at 200 °C and 5.5 bar at 425 °C. Selection must always be based on the value at the operating temperature.

Which valve is preferred on a thermal oil line?

Bellows-sealed globe valves with cast steel or suitable ductile iron bodies are generally preferred. The bellows prevents leakage along the stem, reducing fire and environmental risk.

Can a soft-seated ball valve be used on a steam line?

Only if the temperature limit of the seat material covers the operating temperature. At higher temperatures, choose a metal-seated ball valve or a globe valve.

Conclusion

The key to safe selection of high pressure and temperature valves is to evaluate the pressure class together with the operating temperature, choose the body material for temperature and medium, and specify suitable seat and packing designs. Explore gate, globe, ball, butterfly and check valve options in our High Pressure and High Temperature Valves product group.

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