Proper Condensate Treatment and Monitoring

Proper treatment of your plants steam condensate is essential for two reasons:

1. To protect the integrity of your valuable equipment.
2. To minimize the amount of condensate corrosion byproducts that are returned to the boiler feedwater.

Corrosion occurs in steam condensate systems due to carbonic acid attack and oxygen pitting. Carbonic acid attack occurs due to CO₂, which is the breakdown product of carbonate alkalinity in the boiler, condensing with water to form H₂CO₃. This results in the "grooving" of condensate piping, which usually shows up first in leaks at threaded sections. Oxygen pitting occurs as steam condenses and the vacuum created pulls air into the system. Because of the localized nature of oxygen pitting it can cause relatively quick failure in a condensate system.

The most common method of addressing carbonic acid attack is through the use of neutralizing amines. These chemicals, such as morpholine and cyclohexylamine neutralize the carbon acid, and increase the pH of the condensate. Corrosion of mixed metallurgy condensate systems is minimized when the pH is maintained between 8.8 and 9.2. Due to high alkalinity in boiler feedwater elevating the pH to this level may not be economical. In this case the pH should be maintained at 8.3 or higher, or a filming amine applied. A filming amine, such as octyldecylamine, provides a non-wettable protective barrier against both carbonic acid and oxygen. When utilizing a filming amine, the pH is usually maintained between 6.5 and 7.5, so a neutralizing amine may still be required. Additionally, filming amines can be difficult to apply and generate fouling of the system, particularly in systems where they have not been applied previously.

In order to minimize oxygen pitting one can utilize a filming amine or a volatile oxygen scavenger such as DEHA (diethylhydroxyamine.) In the author’s opinion utilizing DEHA provides better results as it scavenges oxygen and passivates the condensate system, making it less susceptible to corrosion. For a comparison of DEHA vs. 

Depending on the treatment method chosen, condensate monitoring can vary. In all cases the following tests should be performed.

1. Soluble and insoluble iron levels.
2. pH levels at various points in your steam condensate system. It is extremely important that pH measurements be made on cooled ("unflashed") samples. If the sample is taken hot, carbon dioxide will flash, which results in artificially high pH measurements.
3. Condensate corrosion coupons.

If a filming amine is utilized, the residual should be measured. The same is true if DEHA is used as an oxygen scavenger. In the latter case, a residual of 100 to 150 ppb is usually targeted. Note that this may take time (as much as 3 to 6 months) since much of the DEHA will be consumed passivating the system. These are some general guidelines. For specific recommendations please contact our staff through our Ask the Experts functionality.