Where is sodium nitrite predominantly used as a corrosion inhibitor?

Sodium nitrite is predominantly used as a corrosion inhibitor in closed water loops due to its effectiveness in reducing corrosion rates in systems that contain ferrous metals. Closed loop systems, such as those found in heating and cooling processes, often have limited water exchange and can lead to the concentration of corrosive agents. Sodium nitrite works by providing a layer of protection on metal surfaces, mitigating the effects of oxygen and other corrosive elements present in the water. It effectively forms a passive film on the metal surfaces, which helps to prevent oxidation and subsequent corrosion.

In contrast, other options like cooling towers and air washers operate with different dynamics, such as continuous water exchange and evaporation processes, which may not benefit from sodium nitrite in the same way. Moreover, galvanized evaporative condensers typically use specialized coatings to protect against corrosion, making sodium nitrite less applicable in those scenarios. Therefore, its specific application as a corrosion inhibitor in closed water loops is well suited to maintaining system integrity and extending the lifespan of the equipment.