Steam is the life blood of many buildings and manufacturing operations. When companies are looking for ways to lower operating costs and ensure reliability, the steam boiler system is a good place to start. After steam does its work, it becomes condensate, which is often referred to as “liquid gold” due to its low dissolved solids and high heat content. Maximizing the recovery of condensate reduces utility costs and conserves natural resources. As a rule of thumb, every gallon of condensate that is returned to make more steam saves a cubic foot of natural gas.
Figure 1: Corrosion in Condensate Pipe
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Without proper treatment, condensate can destroy the return system piping causing leaks that waste both water and heat. The damage typically results from the corrosive carbonic acid that forms due to the breakdown of makeup-water alkalinity in the boiler. Oxygen intrusion can also contribute to the corrosion. Water treatment professionals typically employ neutralizing amines and filming amines to help protect the steam and condensate return system piping.
In most applications, neutralizing amines are added to neutralize the carbonic acid and raise the pH of the condensate to reduce corrosion. Morpholine, cyclohexylamine and Diethylaminoethanol are commonly used neutralizing amines.
Filming amines or film forming amines (FFA) have been around for decades with new-generation products now being applied to a wide range of boiler and cooling water systems. Filming amines can be a better choice for condensate corrosion protection in applications where the makeup water alkalinity is very high, making it difficult to add enough neutralizing amine, or where oxygen in-leakage is a concern. It is important to understand how filming amines work to avoid problems associated with improper use and start-up.
Figure 2: Filming Amine Treated Pipe
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Filming Amines
Filming amines work by laying down a protective monomolecular film on the system piping minimizing corrosive condensate and dissolved gasses from reaching the metal surface. Their strong affinity for metal is caused by the free electron pair on the nitrogen in the amine. The “tail” of the filming amine is hydrophobic which makes the metal bond that much stronger by pushing the amine further away from the water and closer to the metal surface.
Since filming amines have such a strong affinity to metal, they may actually penetrate existing deposits and corrosion byproducts in the condensate return lines. It is critical that filming amines are fed slowly into condensate systems with deposits. If they are fed too rapidly into a fouled system, the existing deposits will slough off and may plug strainers and collect in low flow areas. It is best to start feeding filming amines at a low feed rate and gradually increase the feed rate to avoid potential issues. A good starting point for feeding filming amines is to feed one third of their final feed rate at start up and gradually increase the feed rate over time. Most filming amines are fed in conjunction with neutralizing amines for better distribution and complete protection of the steam system.
Testing
Filming amine levels should ideally be tested in the steam rather than the condensate. Another way to monitor protection is to install a spool piece in condensate return line. Spool pieces can be removed during service calls to see how well the condensate beads up on the metal surface that is protected by filming amines. As a general rule of thumb, water should bead up on piping that is protected by filming amines in a similar fashion to how water beads up on a freshly waxed car. (See Figure 2 of a treated pipe section.)
Corrosion coupons can also be utilized in a similar fashion as spool pieces to check the performance of the filming amine program. Dropping water on a removed coupon should show the same beading effect.
As a global leader in custom-designed water treatment programs, Chem-Aqua has the experience, knowledge, and technology to effectively protect your boiler and all components of your steam system. Since 1919, our success has been built upon our Total System Approach providing solutions for water treatment problems and improving water system efficiencies. To learn more, contact Chem-Aqua today!