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Descaling steam boilers

ttekushan_3 Member Posts: 958
so descaling steamers is a regular part of what I do if the boiler's been neglected.

I go for a good inhibited hydrochloric acid product. I've had good results with the Nu-Calgon acid descaler. The "inhibited" part of the name indicates that it will not attack the boiler metal for a given period of time, usually about 8 hours. If the descaler is still working after 8 hours, get it out of there and start over. Wear protective gear and a mask. Plan carefully how the product is introduced. The pump method is the safest. Most acid descalers will indicate how much scale each gallon will dissolve by weight before becoming neutralized. The Nu-Calgon dissolves 3lb of scale per gallon neutralized. You can get a good indication of how much scale has been removed and make inferences on scale thickness by looking at the heating area in square feet. That thickness can be cross referenced to a chart to tell you how much efficiency is being restored by scale removal.

If I'm not positive that all the scale has been removed (and I never am), it has at least been sharply reduced in thickness. Flushing until the pH is about neutral is essential. Then I use a water treatment product of an alkaline nature to complete the descaling task. Alkaline water treatments can remove accumulated scale over time, but the aggressive acid treatment at the beginning is still necessary. There's a good reason. Badly scaled boilers might have enough mineral content to combine with the alkalinity of the water treatment to cause Caustic Attack. Thats bad. So keep an eye on that pH.

My supplier carries stewart-hall/rectorseal 8-Way additive. Its an alkaline cleaner and oxygen scavenger. A modest amount of this kind of a cleaner will liberate all kinds of remaining glop from the boiler. Its one of those "lather rinse repeat" deals. About 3 times does the trick. Be aware that skimming and/or surface blow-off should be considered at this step, and definitely so if the boiler starts surging. The surging is a temporary condition caused by liberated "stuff" from the near boiler piping and other nooks and crannies within the boiler. Endless surging can indicate that the water pH is too high. Use less additive. The last treatment, leave in there. For CI heating boilers I add some at the beginning of each season for regular customers. This seems well enough to prevent future scale build up and minimizes the blowdown requirements.

Larger scale steel steam heating boilers require a regularly scheduled water treatment program if you don't want scale accumulation and erosion of the tubes.

Hope this helps.



  • will smith_4
    will smith_4 Member Posts: 259
    What have YOU had to do to descale your worst boiler ever?

    Hey folks-I'm currently working on descaling a steam boiler that has been a bit, well, ignored through the years. I've been sent out citric acid to pump through as a descaler, but so far, due to the mountain of scale I'm up against, I would politely describe my endeavor as urinating up a vertical rise of tightly wound hemp. What's your worst case/best solutions? Thanks!
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