Nitric acid corrosion

Biocorrosion in well-oxygenated cooling systems can also involve other types of bacteria, such as nitrifying bacteria, which are commonly found where ammonia is present (say from refinery or fertilizer plant leaks). They are principally aerobic and oxidize ammonia to nitrate, causing serious local falls in pH that result in nitric acid corrosion. Examples are Nitrosomonas sp. and Nitrobacter sp. 

Using 95% confidence interval, determine whether the mean nitric acid corrosion rate of metal A is different from that of metal B. The data on 10 runs for each metal under identical conditions are ... 

Sand, W. Bock, E. (1991a). Biodeterioration of mineral materials by microorganisms -Biogenic sulphuric and nitric-acid corrosion of concrete and natural stone. Geomicrobiology Journal, 9, 129-38. 

When some metals or alloys are immersed in an oxidizing solution, corrosion does not occm, although it is favored thermodynamically. For example, iron will dissolve in dilute, but not in concentrated nitric acid. Corrosion is prevented because of the formation of a protective oxide film on the metal surface. This loss in chemical reactivity of a metal is known as passivation. Metals which readily undergo passivation in damp air include Fe, Al, Cr, Ni, Ti, and Pt. 

PERSONAL PROTECTION wear full gas-tight clothing or rubber overclothing rubber gloves are recommended wear chemical safety goggles and self-contained breathing apparatus equipment should be resistant to nitric acid corrosion. 

Corbett, R. A., "Using Multisample Test Apptiratus for the ASTM A 262, Practice C Nitric Acid Corrosion Testing of Types 304 and 304L Stainless Steels, Corrosion Testing and Evaluation, Silver Anniversary Vohime, ASTM STP 1000, R. Baboian and S. W. Dean, Eds., ASTM International, West Conshohocken, PA, 1990, pp. 335-347. 

A similar procedure was also successful in the case of biogenic nitric acid corrosion... 

The stay in a reactor, materials can undergo various changes (phase precipitations and dissolution, occurrence of irradiation defects, internal and external corrosion, etc.) likely to reduce the cladding resistance to nitric acid corrosion. 

The dissolution conditions, especially the concentration in nitric acid and temperature. The more these conditions are severe (concentration and high temperatures), the more extensive is the nitric acid corrosion of the cladding. 

First corrosion tests were conducted on 9/18 Cr ODS grades on CEA alloys [87]. They confirmed that chromium content plays a major role in nitric acid corrosion (Fig. 10.41). It is shown in particular that the ODS grade containing 9% chromium is the most unfavorable with respect to dissolution. Therefore, it is probably for this grade that the dissolution operating conditions selected will have to be the mildest possible in order to meet the recycling plant constraints. 

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