Interview questions & answers on Boiler Alkali Boilout


1-Why do you carry out an Alkali boil out of a Boiler?

Alkali Boil out is done for

  • To remove oil & grease
  • To remove rust, scale  

2-When you will carry out alkali boil out on Boilers?

Alkali boil out is carried out for new boilers or Boiler where maintenance works like Bank tubes replacement, SH coils replacement are done.

3-List down the chemicals required for Alkali boil out of a Boiler

  • Hydrous Tri-Sodium Phosphate (Na3PO4.12 H2O)
  • Anhydrous Di-Sodium Phosphate (Na2HPO4)
  • Wetting agent (Surfactant / Detergent)

4-What is the ratio of selection of Disodium phosphate & detergents for alkali boil out

Quantity of Anhydrous Di-Sodium Phosphate (Na2HPO4) = Hydrous Tri-Sodium Phosphate X 20-25%

Quantity of Wetting agent (Surfactant / Detergent) = Hydrous Tri-Sodium Phosphate X 5-6%

 5-What are the two conditions for newly erected boilers for carrying out Alkali Boil out?

Boiler’s Hydraulic test should be completed

Boilers’ refractory dry out procedure should be completed

6-What are the pre-checks to be carried out before carrying out Alkali Boil out?


1-Ensure Boiler erection work is completed & its all auxiliaries trials taken & found okay

2-Ensure Fuel handling & fuel feeding system is okay & trial is being taken with respect to Mechanical, Electrical & instrumentation

3-Ensure Deaerator & related pumps are ready & can be taken into line readily

4-Ensure DM water is available

5-Ensure sufficient quantity of fuel is available at yard or at bunker

6-Ensure all equipment are hooked up to DCS

7-Ensure sufficient local PG & TG are avail be at Boilers

8-Ensure competent team is available

9-Ensure chemicals required for boil out & testing are available

10-Ensure all sample points are identified & competent person/team is there to collect the sample as per per decided frequency.

11-Ensure chemical dosing system is available

12-Ensure drain lines/flushing lines sample/sample lines are extended to safe location

7-Write down the procedure of Alkali Boil out in detail?


  1. Maintain the drum level just 6” -8”below the drum man hole door
  2. Initially, collect the required chemicals at drum platform as per dosage quantity decided
  3. Dissolve all the chemicals into water & then pour the chemical mixture into the drum from man hole
  4. After pouring, close the manhole door & raise the drum level up to normal operating level or just 2” below the normal operating level.
  5. Light up the boiler as per Boiler start-up & light up SOP
  6. Raise the Boiler pressure & temperature as per Boiler pressurizing curve
  7. Ensure thermal expansion of Boiler is happening & is uniform at all the headers
  8. Give IBD when drum pressure reaches 5 to 6 kg/cm2
  9. Raise the boiler pressure slowly & bring it to 50% of normal operating pressure or 40 kg/cm2, whichever is lower.
  10. Boil the chemical at same pressure for 10-12 hours.
  11. During boil out keep crack open CBD valve to avoid line & valve chocking
  12. During boil out period, operate the IBD for 15-20 second at every one hour & ensure water is replenished every time you give blow down.
  13. Note: Do not take drum level gauge glass into line during alkali boil out, keep one set of drum level transmitter on line
  14. At the end of the boiling period, collect the sample of IBD sample & test for oil traces. If the oil level is not in the allowable limit, then again add the chemicals & start boiling until the sample oil parameter meets the desired value.
  15. In order to decide the boil out is completed, the oil traces of 3 samples collected at 15 minute span should be < 5 ppm (Ensure consistency in results)
  16. After boil out, stop the boil out procedure & Box up the boiler & allow to cool the Boiler.
  17. During cooling period operate the blow down valves of drum & water wall panel bottom headers at least 2-3 times throughout the cooling period. And ensure normal water level in drum every time.
  18. Open the drum & super heater vents at pressure 2 kg/cm2
  19. Start rinsing the boiler, until the drain water pH equals to feed water pH
  20. After rinsing, drain the boiler completely & at the same time start to make up the boiler with DM water until the drain water pH becomes equal to feed water pH
  21. For flushing the super heater coils, raise the boiler pressure up to 40 kg/cm2 by Boiler feed pump (Hydraulic test of boiler at 40 kg/cm2 pressure) & then flush the water with from drain valve present before MSSV.This rinsing procedure is continued until the drain water pH becomes the makeup feed water
  22. Open the drum manhole doors & clean the internal surfaces with wire brushes
  23. Cut the stub ends/inspection caps of bottom headers & put wooden block in cut caps tightly.
  24. Again fill the boiler with feed water up to normal operating level & remove the wooden blocks one by one to remove the debris, scale or any other foreign materials from headers.
  25. Repeat above procedure for all bottom headers, then inspect all bottom headers for any debris, scale & foreign materials.
  26. After ensuring, everything is okay, then inspection caps should be welded subsequently radiography & hydraulic test should be done.

No comments:

Post a Comment

Hi all,
This article is written based on practical experience..If liked, share with others, or any suggestions leave in comment box.

15-Emergencies in power plant operation

Most visited posts