What are the two chemical used to prevent corrosion in condensate return lines and explain how they provide protection?

Answer 1

There are two different materials on the market today which are being used with good results. These are the neutralizing amines, and the filming amines.

The neutralizing amines are volatile alkaline materials. They are primarily effective against carbon dioxide corrosion, but have very little value in combating oxygen corrosion. In your raw water are naturally occurring bicarbonates. As these pass through the heater and into the boiler they are converted to caustic soda. Carbon dioxide gas is given off as a result of this conversion and it passes out of the boiler with the steam. Carbon dioxide is an acid and it dissolves in the condensate as it is formed. This lowers the pH of the condensate to a point where actual acid attack of the pipe occurs. The neutralizing amines simply neutralize this acid.

If soda ash is used for boiler water treatment it too breaks down in the boiler to form caustic soda and carbon dioxide. This simply increases the corrosion problem, and, if you are using a neutralizing amine it increases your cost. Inasmuch as caustic soda is already reverted to the final pro- duct, no carbon dioxide is given off in the boiler. This is of course the ad- vantage of caustic over soda ash.

Filming amines actually protect the pipe by forming a thin, non-wetable coating on the surface. This separates the pipe from the corrosive condensate and offers excellent protection from both carbon dioxide and/or oxygen corrosion. The filming amines represent a far better material in almost every case. Not only do they provide better protection, they usually cost less as well!

The filming amines cannot be mixed with other chemicals, and pure condensate must be used to prepare the feeding solution. However, the filming amines can be fed to the boiler by means of the boiler feed water. it is not necessary to feed it into the steam line.

The filming amines have a strong affinity for iron. Therefore they will clean off all of the corrosion products, dirt, and oil that might be inside your condensate return system. This may give some trouble with plugged traps and strainers until the system is cleaned out.

Answer 2

Sodium sulfite and hydrazine are commonly used chemicals to prevent corrosion in condensate return lines. Sodium sulfite acts as an oxygen scavenger, removing oxygen from the system to prevent oxidation reactions that lead to corrosion. Hydrazine also removes oxygen and forms a protective layer on metal surfaces, acting as a passivating agent to inhibit corrosion.