Corrosion inhibition vapor-phase inhibitors

Vapor phase inhibitors (VPIs), also called volatile corrosion inhibitors (VCIs), are compounds that are transported in a closed system to the site of corrosion by volatilization from a source. In boilers, volatile basic compounds such as morpholine or octadecylamine are transported with steam to prevent corrosion in condenser tubes by neutralizing acidic carbon dioxide (Boles et al. 2009). Compounds of this type inhibit corrosion by making the environment alkaline. In closed vapor spaces, such as shipping containers, volatile solids such as the nitrite, carbonate, and benzoate salts of dicyclohexylamine, cyclohexylamine, and hexamethyleneimine are used. 

Detailed data have been presented for dicyclohexylammonium nitrite [31], which is one of the most effective of the vapor-phase inhibitors. This substance is white, crystalline, almost odorless, and relatively nontoxic. It has a vapor pressure of 0.0001 mmHg at 21°C (70°F), which is about one-tenth the vapor pressure of mercury itself. One gram saturates about 550m (20,000ft ) of air, rendering the air relatively noncorrosive to steel. The compound decomposes slowly nevertheless, in properly packaged paper containers at room temperature, it effectively inhibits corrosion of steel over a period of years. However, it should be used with caution in contact with nonferrous metals. In particular, corrosion of zinc, magnesium, and cadmium is accelerated. 

Volatile corrosion inhibitors (VCls), also called vapor phase inhibitors (VPIs), inhibit corrosion by being transported as a vapor from a permeable container to the site susceptible to corrosion. In boilers. 

Inhibitors can also be classified on the basis of their functions. For instance, chromates and nitrates are called passivating inhibitors because of their tendency to passivate the metal surface. Some inhibitors, such as silicates, inhibit both the anodic and cathodic reactions. They also remove undesirable suspended particles from the system, such as iron particles, by precipitation. Certain types of inhibitors make the surrounding environment alkaline to prevent corrosion. Such inhibitors in the gas phase are called vapor phase inhibitors, and they consist of heterocyclic compounds, such as cyclohexylamine. These inhibitors are used within packing crates during transportation by sea. 

Vapor phase inhibitors, like dicyclohexy-lamine, inhibit the corrosion most importantly by... 

Volatilization has already been discussed under vapor phase inhibitors in connection with boilers and closed containers. Another application is the inhibition of gas condensate corrosion. However, the treatment here is essentially the same as used in batch or squeeze treatments. 

Inhibitor No. 3. [Oxidinc.] Metalwmk-ing coolant arWtive, vapor phase corrosion inhibits. 

Metals exposed to humid atmosphere corrode by an electrochemical mechanism due to the formation of a thin electrolyte layer on the metal surface (Chapter 3.1, this volume). This type of corrosion can be controlled by Vapor-phase Corrosion Inhibitors (VCIs), that is, volatile inhibiting substances that allow vapor-phase transport to the corroding surface (examples are amines, benzoates, imidazoles, or triazoles [3]). The vapor pressure should be sufficiently high to ensure a protective surface concentration of the inhibitor, but low enough to prevent premature depletion of... 

Gaseous environments include the open atmosphere, the vapor phase in tanks, natural gas in wells, and the empty space in packaging containers. Here again, water and oxygen are the principal corrosive agents, but the main problem in providing inhibition is to transport the inhibitor from a source to the sites where corrosion may occur (Faessler et al. 1989). 

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