Valves for Hot Oil (Thermal Heat Transfer Fluid) Service
Hot oil or thermal fluid is used as a heat transfer medium in indirect heating systems — circulated through heaters and heat exchangers to transfer heat without generating steam. Common fluids: Therminol VP-1, Dowtherm A, Marlotherm SH, Mobiltherm 605. Operating temperatures reach 300–400°C at relatively low gauge pressure (1–10 bar).
Pressure Range
1–15 bar (circulation system pressure)
Temperature
150–400°C (design temperature drives alloy steel selection above 370°C)
Industries
Chemical plant indirect heating, Textile processing, Food processing (frying, drying)
Key Properties — Hot Oil (Thermal Heat Transfer Fluid)
- Operating temperature: 150–400°C at 1–10 bar gauge
- Thermally stable synthetic or mineral oil base
- Low vapour pressure at operating temperature — low pressure despite high temperature
- Degrades over time — TAN (Total Acid Number) and viscosity must be monitored
- Flash point typically 150–200°C — fire hazard if leaked onto hot surfaces
Material Compatibility — Hot Oil (Thermal Heat Transfer Fluid)
Ratings are indicative. Actual compatibility depends on concentration, temperature, velocity, and presence of contaminants. Always consult corrosion tables or a materials engineer.
| Material | Rating | Notes |
|---|---|---|
| Carbon Steel (WCB/A105) | Excellent | Standard material for all hot oil service up to 400°C at Class 150–300. |
| SS 316 | Excellent | Acceptable but not normally required unless process contamination is a concern. |
| A217 WC6 (1¼Cr-½Mo) | Excellent | Required above 370°C for long-term creep resistance per ASME B16.34. |
| PTFE seats | Not Recommended | PTFE has a 200°C maximum — metal seats required for hot oil above 200°C. |
| Cast Iron | Poor | Not recommended — brittle at thermal cycling; use carbon or alloy steel. |
Recommended Valves
Gate Valve (OS&Y, cast steel, metal seated)
Standard isolation for hot oil mainline — low pressure drop, suitable to 400°C.
Globe Valve (cast steel, metal seated)
Flow control and modulating service on hot oil supply to heat exchangers.
Ball Valve (trunnion, metal seated, extended stem)
Fast isolation with fire-safe capability and low-emission graphite packing.
Check Valve (swing or tilting disc, cast steel)
Pump discharge non-return on hot oil circulation pumps.
Valves to Avoid
PTFE-seated ball valves (temperature limit exceeded)
Cast iron body valves (thermal shock and brittleness risk at high temperature)
Plastic or elastomer-sealed valves
Standard ANSI 150 flanged connections above 370°C (check P-T ratings — A216 WCB limits)
Special Considerations
Applicable Standards
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