Deaerators – Oxygen Pitting Prevention

| Edward McKellar

Oxygen present in boiler feed water is a killer for the tubes of a boiler. Water contains many elements that can either accumulate or erode the metal surfaces inside of a firetube boiler. Oxygen and Carbon Dioxide are present in most water sources and, when heated, the corrosive nature of these dissolved gases increases. As the temperature (and operating pressure) of a boiler increases, the destructive ability of O2 and CO increases as well.

Corrosion due to Oxygen causes severe metal breakdown. Opitting increases by a factor of two for every 18°F rise in temperature. Once pitting has started, tube failure can occur even with minimum metal loss. Dissolved gases present in systems cause havoc from the feedwater entering into the boiler all the way through to the condensate recovery system

Oxygen pitting can begin to erode the tubes of a boiler rapidly and it is imperative to ensure that all dissolved gases are removed prior to entering the boiler. This can be accomplished by chemicals, however, chemicals alone can create other issues to deal with namely increased blowdowns.

While chemicals themselves are important in a steam system, higher temperature and pressures systems need further mechanical treatment. High-pressure steam applications rely on deaerators for maximum removal of dissolved gases from their steam systems. A deaerator can remove nearly 98% of the harmful dissolved gases present in boiler feedwater.

While there are a few different designs and features of various deaerators, each works on the same basic principle: heat, agitation, and liberation. Softened makeup and return water enters the deaerator where the surface tension of the water is broken up by either spray heads, perforated trays, or a combination of both.

During this agitation stage, low-pressure steam is simultaneously being introduced to the vessel and heats this incoming water. The water is essentially flashed and releases the non-condensible gases where they are vented (liberation)  into the atmosphere. The deaerator relies on a balanced state where the incoming steam pressure and the vent valves are set precisely and maintained. Due to the nature of the systems working principle, deaerators typically work best when they are brought online and run continuously.

Along with the removal of dissolved gases, deaerators provide heated feedwater storage. This helps to prevent cold water from shocking the boiler along with increased efficiency. Deaerators require very little maintenance aside from daily monitoring and annual inspections. Daily monitoring ultimately means that the temperature and pressure are being recorded. A decay of pressure could indicate a faulty pressure-reducing valve or problems with installed traps. Temperature drops from the normal range could indicate a problem with the vent valve. The deaerator relies on this balanced state between the steam inlet and vent valve outlet for optimum deaeration.

Deaerators are essential for high-pressure steam boiler operations. Tubes can rapidly begin to pit and lead to failure resulting in increased maintenance costs and extended downtime. Contact Power Mechanical Inc. today for more information on deaerator rentalssales, and services to ensure your systems are running their best.  1-877-764-7832


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