Valves for Heavy Fuel Oil (HFO / Bunker C / Fuel Oil No. 6) Service
Heavy fuel oil (HFO), also known as bunker fuel, residual fuel oil, or Fuel Oil No. 6, is the thick, viscous residue remaining after lighter fractions are distilled from crude oil. With a kinematic viscosity of 180–700 cSt at 50°C, HFO must be heated to 120–150°C to achieve pumpable viscosity for marine engines and power plant burners. It contains high levels of sulphur (0.5–3.5%), vanadium, sodium, and asphaltenes. Valve selection must account for high viscosity, high temperature, and potential plugging on cooling.
Pressure Range
3–25 barg (fuel oil system operating pressure)
Temperature
50°C (minimum pumpable) to 150°C (burner inlet temperature)
Industries
Marine power plants (bunker fuel), Power station fuel oil systems, Cement kilns (fuel oil firing)
Key Properties — Heavy Fuel Oil (HFO / Bunker C / Fuel Oil No. 6)
- Extremely high viscosity: 180–700 cSt at 50°C — must be heated for pumping and atomisation
- Pumpable at 50–60°C, burner atomisation requires 120–150°C
- Solidifies below 20–30°C (pour point) — all lines and valves must be heat-traced
- High sulphur content (0.5–3.5%) — SO₂ dew point corrosion risk in exhaust circuits
- Asphaltene precipitation risk in valve bodies and in flash conditions
Material Compatibility — Heavy Fuel Oil (HFO / Bunker C / Fuel Oil No. 6)
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) | Excellent | Standard for HFO pipelines and tank connections with heat tracing. |
| Ductile Iron | Good | Acceptable for lower-pressure HFO service in marine applications. |
| SS 316L | Good | Optional — adds corrosion resistance where sulphur compounds are present. |
| Cast Iron | Fair | Acceptable only for low-pressure utility HFO service. |
| Bronze | Good | Common for marine HFO service valves. |
Recommended Valves
Gate Valve (carbon steel, flanged, heat-traceable body)
Main isolation for HFO tank connections and fuel oil headers — full-bore for pigging
Globe Valve (WCB, Stellite trim)
Control of HFO flow to burners — Stellite seat resists wire drawing at partial open
Ball Valve (full-bore, jacketed/heat-traceable body)
Quick isolation for HFO service lines where fast shutoff is required
Y-Type Strainer
Essential upstream of every HFO control valve and burner gun to remove scale and char
Safety Relief Valve
Overpressure protection on HFO heaters and steam-traced systems
Valves to Avoid
Butterfly valves for high-viscosity HFO — disc creates excessive pressure drop
Non-heat-traceable valve bodies for HFO — asphaltene deposition on cooling
Special Considerations
Applicable Standards
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