Corrosion Inhibitors

Boiler systems can be very complex, and an intimate knowledge of the system’s purpose and components is a prerequisite to properly treating a given system. They must be treated with a comprehensive approach beginning with the preboiler section, then the boiler, followed by the condensate system. Corrosion can lead to pitting and metal loss that can cause critical system failures – sometimes catastrophic. It is estimated that corrosion in boiler systems cost the industry billions of dollars every year.

Oxygen Scavengers

Corrosion is most commonly caused by dissolved gases (primarily oxygen and carbon dioxide), low pH, the attack of mechanically stressed areas, and under-deposit attack. To avoid the corrosion of vital (and costly) metal components throughout boiler systems, external treatment of the feedwater is performed in order to remove dissolved oxygen (DO) and other contaminants such as iron and copper. The majority of the DO removal, along with other dissolved gases, is done by mechanical deaeration. In order to remove the remaining oxygen and provide the boiler with high-purity feedwater, the application of an oxygen scavenger is utilized. Additionally, applying chemical oxygen scavengers indirectly leads to passivated metal surfaces and lower amounts of metal oxide that is transported to the boiler. Multiple factors such as system design, pressure and temperature, and the quality of the make-up water play a key role in determining the proper O2 scavenger to be applied (Non-volatile, Volatile, Organic or Inorganic).

Bio-Source provides the following Oxygen Scavengers for boiler water applications – external (preboiler), internal, and condensate treatment:

DEHA (Diethylhydroxylamine)

DEHA is an excellent chemical product used to prevent corrosion by exhibiting characteristics that have gained it widespread use in industrial water treatment. It is highly effective at removing dissolved oxygen from boiler systems, and it also provides excellent metal passivation. It has a higher volatility than other common oxygen scavengers, which allows it to be distributed throughout the entire steam system; thus, protecting the system from oxygen corrosion. In addition to its metal passivating and oxygen scavenging properties, DEHA degrades (thermal and oxidative degradation) to form neutralizing amines that protect condensate piping from carbonic acid attack, and to maintain proper pH. DEHA reacts with oxygen to form acetate, nitrogen and water; therefore, it does not add any dissolved solids to the system.

Hydrazine (35%)

Hydrazine is an organic O2 scavenger and metal passivator, and is not considered “volatile”. However, it can be added to boiler return lines to scavenge oxygen in the condensate. Hydrazine does not contribute solids to a boiler system, so sludge removal via boiler blowdown is reduced. It can be utilized in all boiler systems, but it is the oxygen scavenger of choice in high pressure and supercritical boilers where absolutely no solids can be tolerated. It does not produce corrosive gases at high pressures and temperatures, and it reacts with oxygen to form nitrogen and water. Additionally, hydrazine also aids in the protective filming formation of magnetite on the boiler drum and tubes.

Erythorbic Acid (Solid)

Erythorbate is an organic non-volatile metal passivator, and contributes no solids to the boiler system. The standard recommended dosage level is 11 parts per 1 part of oxygen (as O2). In addition, Erythorbic Acid is a vegetable-derived food preservative, and is a stereoisomer of ascorbic acid (Vitamin C). It is generally recognized as safe (GRAS) by the FDA and is widely used as an antioxidant in food processing applications.
Carbohydrazide (6% and 12%) – Carbohydrazide is a volatile, passivating oxygen scavenger; and it contributes no solids to a boiler system. It reacts readily with oxygen at low pressures and temperatures, but in its reaction with O2, carbon dioxide is produced.

Neutralizing and Filming Amines

Due to the complexity of steam generating boiler equipment and design, a systematic holistic approach must be utilized to effectively treat each system, and its individual components. Corrosion control begins by effectively removing contaminants in the feedwater, and then by controlling deposition within the boiler. The final phase of boiler system corrosion control occurs in the Condensate System. Because of carryover, iron and copper corrosion is not limited to the piping and equipment of the condensate system. Corrosion products and process chemicals can return to the boiler causing damaging boiler deposits, and deposits on steam-driven equipment. If this happens, the boiler’s system performance is reduced and operational, maintenance and repair costs are increased.

From the reaction between heat, water, and sodium carbonate and bicarbonate, carbon dioxide (CO2) is liberated in the generated steam; and is distributed throughout the entire system. As the steam is used and then condensed, the CO2 dissolves in water and drives down the pH, resulting in the formation of carbonic acid (H2CO3). The resultant carbonic acid formation further lowers pH, and will corrode condensate piping and equipment. In order to prevent acid attack corrosion, and to maintain proper pH, neutralizing amines such as morpholine and cyclohexylamine are used. When added to water, neutralizing amines hydrolyze and generate the required hydroxide ions for neutralization.

Bio-Source offers the following amines for boiler water and condensate treatment:

Cyclohexylamine

An amine with a high neutralizing capacity, which is extremely important in treating systems where the feedwater has a high alkalinity. Cyclohexylamine is an organic chemical that offers superior thermal stability at high pressures, and it characteristically distributes into the steam.

Morpholine

Morpholine is an organic neutralizing amine that primarily distributes into the liquid phase. It offers superior thermal stability at high pressures, and is one of the most common amines used in condensate systems. In steam systems containing multiple condensation sites, optimum protection can be achieved by blending amines with differing steam/liquid distributions, such as blending Cyclohexylamine and Morpholine.

DEAE (Diethylaminoethanol) / DEEA (Diethylethanolamine)

DEAE is a chemical product that has neutralizing and oxygen scavenging characteristics, and is used as a corrosion inhibitor for steam and condensate lines. As an alkanolamine, it maintains a constant alkalinity in boiler water and condensate, and it does not contribute solids to the boiler system. DEEA is utilized in the water treatment, gas treating, water-based and solvent-based coatings, and pharmaceutical industries, among others.

DEHA (Diethylhydroxylamine)

DEHA is an excellent chemical product used to prevent corrosion by exhibiting characteristics that have gained it widespread use in industrial water treatment. It is highly effective at removing dissolved oxygen from boiler systems, and it also provides excellent metal passivation. It has a higher volatility than other common oxygen scavengers, which allows it to be distributed throughout the entire steam system; thus, protecting the system from oxygen corrosion. In addition to its metal passivating and oxygen scavenging properties, DEHA degrades (thermal and oxidative degradation) to form neutralizing amines that protect condensate piping from carbonic acid attack, and to maintain proper pH. DEHA reacts with oxygen to form acetate, nitrogen and water; therefore, it does not add any dissolved solids to the system.