Key Takeaways
- “High temperature” for valves typically starts around 200°C and extends to about 650°C; above that, special alloys or alternative designs are required.
- Body and bonnet material is the first decision: ASTM A217 cast low-alloy (WC6/WC9) and A351 austenitic stainless cover most thermal-service needs.
- Trim and seat facing — not just the body — control wear and leakage; Stellite or hardfacing is common above 425°C.
- Pressure-seal bonnets outperform bolted bonnets for high-pressure, high-temperature lines because the seal tightens as pressure rises.
- Specify the standard: API 600 (cast), API 602 (forged) and ISO 10434 define the acceptance criteria buyers should write into the purchase spec.
Short answer: A high temperature gate valve is engineered to keep a tight shutoff and retain structural strength when process temperatures run above roughly 200°C (392°F) and up to about 650°C (1200°F). The performance is set by three decisions — body and bonnet material grade, valve trim and seat facing, and bonnet sealing design — not by pressure class alone. At Sedelon we have manufactured API 600 cast and forged steel gate valves since 1998 for refineries, power plants and petrochemical lines, and this guide breaks down exactly how material and design choices determine performance in thermal service.
What Makes a Gate Valve “High Temperature”?
In everyday plant language, a valve enters “high temperature” service once sustained process heat climbs past the range where standard carbon-steel (A216 WCB) and standard packed bonnets stay comfortable — roughly 200°C (392°F). From there, thermal expansion, graphite oxidation and creep become the dominant failure modes, and material selection takes over from pressure class as the deciding factor. For a closer look at the boundary with cryogenic duty, see our comparison of low temperature vs high temperature valves.
| Service band | Typical temperature | Usual body material |
|---|---|---|
| Elevated | 200–425°C | A216 WCB / A217 WC6 |
| High | 425–540°C | A217 WC6 / WC9, A182 F11/F22 |
| Very high | 540–650°C | A217 C5/C12, A351 CK20, A182 F91 |
| Extreme | Above 650°C | Special alloy (consult manufacturer) |
Body and Bonnet Material Selection
The body and bonnet carry the pressure and the heat. For the bulk of refinery and power applications, two ASTM families do the work: A217 low-alloy cast steel (WC6, WC9, C5, C12) for strength and creep resistance up to the high/very-high bands, and A351 austenitic stainless (CF8, CF8M, CF3M) where corrosion or oxidation control matters as much as heat. Forged A182 grades (F11, F22, F91) are specified on smaller, high-integrity branches. Review the full Sedelon cast and forged gate valve range for available sizes and pressure classes.
| Material | Form | Practical max temp | Best-fit service |
|---|---|---|---|
| A217 WC6 | Cast, 1.25% Cr-Mo | ~540°C | Refinery / steam, moderate alloy |
| A217 WC9 | Cast, 2.25% Cr-Mo | ~565°C | Higher-temp steam, hydrogen service |
| A217 C5 / C12 | Cast, 5% / 9% Cr | ~650°C | Severe high-temp, oxidation resistance |
| A351 CF8 / CF8M | Cast austenitic SS | ~540°C (oxidation-limited) | Corrosive + hot media |
| A182 F22 / F91 | Forged alloy | ~565–650°C | Small-bore, high-integrity branches |
The seating-surface materials behind these bodies are covered in detail in our notes on API 600 seating surface material classification. Note that the body alloy sets the ceiling, but the seat facing sets the leak-tightness.
Valve Trim and Seat Design for Thermal Service
Trim is the collection of internal wear parts — stem, gate, seat rings and backseat — and in thermal duty the seat facing is where galling and oxidation start. Below about 425°C, 13% chrome (F6a) trim is adequate. Above it, hardfacing such as Stellite 6 or 21 on the seat surfaces is the norm because it resists both wear and high-temperature oxidation. The differing stainless grades are explained in our guide to stainless steel material properties.
| Trim / facing | Typical limit | Use in thermal service |
|---|---|---|
| F6a (13% Cr) | Up to ~425°C | General-purpose trim |
| Stellite 6 / 21 | Up to ~650°C | Hardfaced seats, anti-galling |
| Solid solution SS | Corrosion-limited | Hot corrosive media |
The backseat — the secondary seal that lets packing be changed under pressure — is another thermal-service detail often missed; our note on why gate valves need a backseat covers why it matters for safe maintenance.
Bonnet and Sealing Design
The bonnet joint is the second place high-temperature valves fail. A bolted bonnet with a spiral-wound gasket is fine for moderate conditions, but as temperature and pressure climb, the pressure-seal bonnet becomes the better design: its ring seal is energised by line pressure, so it tightens rather than relaxes as the system heats up. Packing choice matters too — flexible graphite with live-loading (constant-load belleville washers) keeps the stem seal tight through thermal cycling and avoids the “hot pass” leaks that plague plain gland packing. For lines that must hold heat in rather than shed it, our jacketed (insulated) gate valve is built for traced, thermally managed service.
| Bonnet type | Seal behaviour under heat | When to specify |
|---|---|---|
| Bolted bonnet | Bolts relax as it heats; needs re-torque | Lower temp / pressure classes |
| Pressure-seal bonnet | Seal tightens with line pressure | High temp + high pressure |
Where tight shutoff with frequent operation is needed instead of isolation, globe valves or ball valves are often compared against gate valves — each has a different thermal and wear profile.
Standards, Compliance and Proven Manufacturing
For buyers, the standard is the contract. API 600 governs cast steel gate valves for refinery service, API 602 covers small forged steel gate valves, and ISO 10434 is the international equivalent. Specifying one of these forces the supplier to meet defined wall thickness, stem design, testing and marking rules. Sedelon has held API 6D, CE, ISO 9001 and TS system certificates since the late 1990s and reinforces valves against fugitive-emission limits; our API and ISO certificate list and our company profile describe the quality system and the technical team behind every valve.
How to Select a High Temperature Gate Valve
A practical selection sequence keeps the spec honest:
- Fix the sustained and peak temperature, not just the design temperature.
- Pick the body/bonnet alloy from the temperature band above, then the trim facing.
- Choose pressure-seal over bolted bonnet once pressure and temperature are both high.
- Specify the standard (API 600 / 602), pressure class, end connection and any NDE.
- Confirm the supplier can document material certs and seat-leak tests.
Our longer gate valve selection guide walks through application trade-offs, and the API vs DIN valve standards explain marking and test differences. Browse the complete Sedelon gate valve catalogue to match a standard configuration to your line.
Need a High Temperature Gate Valve Quoted to Your Spec?
Send us your line conditions — sustained and peak temperature, pressure class, media and end connections — and our engineering team will recommend the right ASTM material grade and bonnet design, with full API/ISO documentation. We manufacture cast and forged steel gate valves to order and hold stock for fast delivery.
Common Specification Mistakes
The failures we see in the field are rarely the valve — they are the spec. Three recur: quoting only the design temperature and ignoring thermal cycling; specifying a carbon-steel body above 200°C; and specifying a gate valve for throttling, which it cannot do without rapid seat erosion. A high temperature gate valve is an isolation device — it is not a control valve, and it should not be used to regulate flow in thermal service. Getting the material grade and bonnet type right up front is far cheaper than an unplanned shutdown.
Frequently Asked Questions
What temperature is considered “high temperature” for a gate valve?
A gate valve is generally classed as high temperature when continuous service exceeds about 200°C (392°F), the point at which standard carbon-steel bodies and conventional packed bonnets begin to lose margin. From 200°C up to ~650°C, material grade and bonnet design — not pressure class — govern service life, and above 650°C special alloys are normally required.
Which materials are best for high temperature gate valves?
ASTM A217 low-alloy cast steel (WC6, WC9) is the workhorse for high temperature gate valves up to roughly 540–565°C, with C5/C12 (5%–9% chrome) extending toward 650°C. A351 austenitic stainless suits corrosive hot media, and forged A182 F22/F91 is used on small, high-integrity branches. The body alloy defines the temperature ceiling; the seat facing defines leak-tightness.
How does bonnet design affect high temperature performance?
A pressure-seal bonnet outperforms a bolted bonnet in high temperature, high pressure service because its ring seal is energised by line pressure and tightens as the system heats, whereas bolted joints relax and need re-torquing. Paired with live-loaded graphite packing, a pressure-seal design is the reliable choice for thermal duty with frequent heating and cooling cycles.
What is valve trim and why does it matter in thermal service?
Valve trim is the internal wear parts — stem, gate, seat rings and backseat — and in thermal service the seat facing must resist galling and oxidation. Below ~425°C, 13% chrome (F6a) trim is sufficient; above it, Stellite or other hardfacing on the seats is standard to prevent seizure and leakage during repeated thermal cycles.
Are API 600 gate valves suitable for high temperature service?
Yes. API 600 is the primary standard for cast steel gate valves in high temperature and high pressure refinery and power service, and it defines wall thickness, stem, seat, testing and marking requirements. For small forged valves, API 602 applies; both are the acceptance criteria buyers should write into the purchase specification.
Can a high temperature gate valve be used for throttling?
No. Gate valves are strictly on/off isolation valves; using them to throttle in thermal service accelerates seat erosion, stem damage and leakage because the partially open gate vibrates and suffers uneven wear. For flow regulation in hot lines, specify a globe or control valve instead — a gate valve should only be fully open or fully closed.
Related Resources
- Low Temperature Valve vs High Temperature Valve
- Gate Valves: Differentiation and Selection for Different Applications
- API 600 Valves: Seating Surface Material Classification
- The Feature of Different Stainless Steel Materials
- Sedelon Jacketed Gate Valve for Thermal Service
Talk to a Sedelon Valve Engineer
If you are specifying thermal-service valves and want a second opinion on material grade, trim or bonnet design, our engineering team can review your operating envelope against API 600 and ASTM requirements. Download our technical data sheet or start a quote today.
Specifying a high temperature gate valve is less about picking a pressure class and more about matching material grade, trim and bonnet design to your actual operating envelope. Start with the sustained and peak temperature, then confirm the body and bonnet alloy, seat facing and bonnet seal before you issue the purchase spec. If you would like a second opinion on a live project, our engineering team can review your line conditions against API 600 and ASTM requirements and recommend the right configuration. Explore Sedelon’s full range of cast and forged steel gate valves, or reach out to discuss thermal-service valves built to your specification.
