Weld Preheat Energy and Fuel

Heat needed, fuel energy after efficiency, and propane in pounds and gallons to bring a steel mass to a preheat temperature. The preheat temperature comes from carbon-equivalent or the WPS; hot-work hazards govern.

Heat needed = mass x specific heat x (preheat temp - start temp); fuel = heat needed / efficiency; propane lb = fuel / 21,600 Btu/lb; propane gal = fuel / 91,500 Btu/gal.

Specific heat of carbon steel (about 0.11 Btu/lb-degF) and the heating value of propane (about 21,600 Btu/lb, 91,500 Btu/gal), by name; sensible-heat first principles.

The sensible-heat relation and the property values are public.

Math aid for personal verification. Stop work and consult the qualified person on site if any number does not match the field condition.

Field names used by the API: steel_lb, start_temp_F, preheat_temp_F, efficiency_pct, c_steel, propane_btu_lb, heat_needed_btu, fuel_btu, propane_lb, propane_gal

• Steel specific heat 0.11 Btu/lb-degF default; editablecarbon-steel property tables
• Propane heating value 21,600 Btu/lb and 91,500 Btu/gal default; editablepropane property tables
• Open-torch efficiency 25% default (roughly 15 to 30% for an open torch on a plate); an enclosed heat, blanket, or induction is far higher; hold the preheat through the weld and verify the interpass temperaturewelding preheat practice