Corrosion engineering is the field dedicated to controlling and preventing corrosion. Addition of chromium produces stainless grades resistant to corrosion. Wrought iron is more corrosion resistant than steel. However, it is not impervious to corrosion or rust. This increases the corrosion or oxidation of components exposed to phosphoric acid. Surface attack includes oxidation, hot corrosion, and thermal fatigue. Pollutants may cause visible deterioration, including discoloration of surfaces and corrosion. It also demonstrates remarkable protection against corrosion and oxidation. Corrosion and heat resistance makes iridium an important alloying agent. These metals are used in applications where corrosion resistance is important. It is resistant to many forms of corrosion. Insufficient hardness can lead to corrosion and water foaming. Chloride anions induce both localized corrosion (pitting corrosion) and generalized corrosion of steel reinforcements. Besides cooling system corrosion, biological fouling also occurs. There are many mechanisms behind that corrosion resistance.