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Alkalinity In Boiler Water

When it comes to Alkalinity in boiler water it is important to test its levels. If it gets outside of safe operating ranges; it will cause corrosion, embrittlement, and carryover with cooling water systems. where it has a significant effect on chemical treatments for scale and corrosion inhibition.

The Three Basic Forms of Alkalinity

Alkalinity can occur in three different forms depending on the pH levels of the water. These can come in the form of carbonate (CO3), bicarbonate (HCO3), or hydroxide (OH). Total alkalinity occurs from the sum of these three forms. You can determine Alkalinity levels by measuring water sample with a standard acid to a designated pH and is recorded as P, M, or T alkalinity. P alkalinity is titrated with phenolphthalein to pH 8.3, M alkalinity with methyl orange indicator to pH 4.6, and T alkalinity with total alkalinity indicator to pH 4.5. Once you know the values for P, M, or T alkalinity you can use the table of relationships below to determine treatment control and effectiveness.

How is Alkalinity Maintained?

When you’re maintaining a boiler, treatment specialists must maintain M (or T) alkalinity below a maximum level prescribed by the boiler’s manufacturer to help prevent foaming and carryover. If boiler operating pressure then higher purity water must match. A minimum level of OH must be maintained (generally, over 150 ppm as CaCO3) to prevent scaling tendencies and ensure that that alkalinity levels don’t damage or hinder other components. Water treatment professionals aim to treat control alkalinity in cooling water to prevent corrosion and scaling. If alkalinity should drop below acceptable levels, corrosion will occur. Though it should be noted that the higher the pH level detected the more alkalinity will be present and can lead to calcium forming and causing scaling. If you’re in need of products for pH treatment, check out our pHREADY to help maintain alkalinity levels.

Alkalinity Testing Interference

When managing alkalinity titrations, highly turbid or colored samples will mask the color change at the endpoint. Chlorine may also interfere with the sample as well, so we recommend sodium thiosulfate to counteract any interference. Suspended solids can be filtered out of the sample using paper filtration, and colloidal colors may require syringe filtration. Treatment polymers will titrate as M and T alkalinity. In waters using polymer treatment, OH alkalinity needs to be directly titrated using the barium chloride method. Using a 2P-M method to determine OH alkalinity will result in a negative interference for the calculation of OH. Absorption of CO2 will depress alkalinity in water samples. To prevent this situation, analyze samples at the point of collection. When on-site analysis is not practical, collect samples for off-site testing in overflowing containers and cap them tightly. If acid is being added to adjust pH, it will also alter the P/T alkalinity relationship. If you notice foul smells during your testing, our pHREADY for Odor Control can help you treat the issue at the source while balancing the alkalinity in your system.

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