It is highly recommended that a new boiler should be boiled-out before being utilized. This can be done right before or immediately after the primary start-up.

The inner surface of a new boiler will contain residual deposits of grease, oil, and protective coating from the manufacturing process. It’s crucial that these elements are removed from the boiler’s surface as the deposits will lower the transfer rate of heat and could even result in overheating of pressure vessel metal. A boil-out can clear away any oil or grease that might have remained in the waterside of the boiler after the installation. A pristine waterside is vital in the establishment and maintenance of a durable waterside condition.   

Procedure for a Boiler Boil-Out

  • All tubes should be checked for obstructions and the required hydrostatic tests have been conducted. Make sure that all debris is removed from the drum. After ensuring that all safety measures are in place, close the boiler (except for the drum vent), the inspection doors and all other access points.
  • Take off the manhole on the steam drum. Fill up the boiler with water.
  • Dissolve the right amount of chemicals. This typically consists of 0.3 kilograms of H2SO3, 4 kilograms of Na3PO4.12H20, and 2 kilograms of NaOH for every 1,000 kilograms of water. These chemicals should be carefully placed into the drum to prevent injuries.
  • Add the chemical solution via the steam drum manhole and close it. Increase the drum’s water level to the appropriate working level after the chemical solution has been put in.


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  • Close superheater vents and drains except for the outlet header drain. This should remain open for the whole duration of boiling out process. Drum vents should also be kept open.
  • Purge the furnace of all combustible gases. Once the furnace has been cleared, burners and torches should be lighted in a way that they will deliver heat as evenly as possible. The drains, vents, firing equipment, settings, etc. should be run normally.
  • Fire the boiler to take approximately 10 kg/cm2G pressure for eight hours. This pressure should also be maintained for four hours to check circulation. Close the drum vents as the drum pressure raises to 2 kg/cm2G. Make sure to check out the unit’s expansion regularly.
  • Shut down burners after four hours. Allow the pressure of the boiler to decrease. Once the pressure is reduced to around 4.5 kg/cm2G, increase the water level until the gauge glass is nearly full.
  • Blow down the boiler using the lower blowdown valves. Don’t let the level to move out of the gauge glass sight. Return the water to normal levels after the blowdown.


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  • Repeat the process of firing the boiler and reducing the pressure three times. Increase pressure every cycle but make sure water levels are also set to be concurrent.
  • Don’t forget to take solution samples regularly during the boil-out. Add more boil out chemicals when the alkalinity and phosphate concentration of the boiler water has been decreased to half. This is to ensure that the water remains at the primary chemical concentration.
  • Continue the boil-out until the solution sample reveals that the oils and grease have been removed.