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Boiler Boilout Procedure

     As a general rule of thumb, a boiler boilout procedure needs to occur when a new boiler is installed, but what does the process entail and why?

     It is typically the case that oil and grease from the manufacturing processes are still present within a new boiler, from tube rolling lubricants and threading to other various components beyond the manufacturer's control. Often a boilout procedure is recommended either when a new boiler is installed, a large percentage of the boiler tubes have been replaced, or a boiler is transferred to a new location. The boilout process not only improves thermal efficiency but increases the boiler’s reliability. Residual oil, grease, or paint not removed can result in tube failures and turbine damage as these materials help insulate the heat transfer surfaces which can increase internal temperatures. Debris present can accumulate within the boiler during shipping or installation. This material may lead to plugged tubes which could lead to failure on the waterside and restricted gas flow on the fireside.

Figure 1: Water Capacity (normal and flooded) of several Cleaver-Brooks Boilers

     Most boiler manufacturers and high-pressure boilers will include their recommended boilout procedure which is important to note as there may be subtle differences. Also included in most operation manuals will be internal water volumes important for calculating the correct amount of boilout chemicals (Figure 1).



Typical Boilout Procedure


     1.) Prior to commencing, clear the boiler for firing by taking all safety and standard precautions. This would include isolating the boiler so that it is valved off properly and has been hydrostatically verified.

     2.) Flush and rinse the waterside thoroughly with water to initially remove as much debris and oil as possible. Although the boiler will not reach the max firing rate during the procedure, this will aid in avoiding any material getting baked onto internal metallurgy.

     3.) Using the manufacturer’s recommendations, compute the quantity of alkaline cleaner necessary to perform the task. This can be accomplished by obtaining the volume of water (flooded) within the boiler and calculating the required ppm of cleaner. Sometimes chemical quantities can be estimated based on boiler HP if internal volumes can’t be obtained. Another ‘Rule of Thumb’ used in boilout procedures is that 1 HP is construed as being equal to 10 ft2 of heat exchange surface.

     4.) An overflow pipe should be attached to one of the boiler openings and routed to a safe discharge point. Remove relief and steam safety valves before the boilout chemical addition to avoid contamination.

     5.) Introduce the recommended dose of alkaline cleaner into the boiler while the boiler is being filled. Of course, wear the recommended PPE as mixing caustic solution with water is an exothermic reaction. Ideally, cleaner is added in a way to promote it being mixed and dissolved.

     6.) Close the boiler, fire lightly to raise the pressure no less than 10-15 PSIG, and boil out for at least 12 hours. Slightly increase the pressure if good circulation cannot be obtained. The boiler should be fired intermittently to hold the solution just at the boiling point. While boiling out, open each blowdown connection for a short duration hourly to help remove debris and oil. Typically hydrate alkalinity should be maintained above 150 ppm.

     7.) When the overflow water appears clear, the burner can be stopped, and the boiler can be drained when sufficiently cooled (internal water should be cooled to around 140°F). The manhole and handholes can then be removed for internal inspection. It is recommended to wash the interior until there is no evidence of debris, oil, and impurities.

     8.) If at this point the internal surfaces do not appear to be clean, the boilout procedure can be repeated.

     The boilout procedure is a necessity when it comes to new boilers and ensuring the longevity of their use. As previously mentioned, the boilout process not only improves thermal efficiency but increases the boiler’s reliability. This process can be quite rewarding as visual improvements can be made quite rapidly. Regardless, make sure to adhere to operational manuals and a professional water treater!


    Jed Kosch












List of Resources:


[1] Boil-Out Procedure Watertube Steam Boilers. (n.d.). Bond Water. Retrieved September 18, 2021, from


[2] Smith, J. (2016, March 3). Typical Firetube Boiler Boil-out Procedure. Industrial Boiler & Mechanical.


[3] Alkali Boil Out of Steam Boilers. (2019, December 15). Collaton Consultancy Limited.


[4] New Lattner Boiler Boil-Out Recommendations. (n.d.). Lattner Boiler Company. Retrieved September 18, 2021, from


[5] Cleaver-Brooks. (2009, December). Cleaver Brooks Model CB, CL-LE Packaged Boiler Operation and Maintenance Manual.

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