Nitrate solutions, stress corrosion cracking

Fig. 8.21 Current density dilTerences between fast and slow sweep rate polarisation curves and stress corrosion cracking suspectiblity as a function of potential for a C-Mn steel in nitrate, hydroxide and carbonate-bicarbonate solutions...

For carbon steels, however, a full stress-relief heat treatment (580-620°C) has proved effective against stress-corrosion cracking by nitrates, caustic solutions, anhydrous ammonia, cyanides and carbonate solutions containing arsenite. For nitrates, even a low-temperature anneal at 350°C is effective, while for carbonate solution containing arsenite the stress-relief conditions have to be closely controlled for it to be effective . 

Originally, the reactor failed due to stress corrosion cracking from nitrates. The source of the nitrates was water sprayed from an external hose used for supplemental cooling. The inadequate cooling capacity was resolved with a less than adequate technical solution that caused unexpected and unwanted consequences. Management of change was not properly applied. 

Stress-corrosion cracking of copper-zinc alloys can occur in environments other than ammoniacal solutions (Ref 114, 147, 151, 152). Included are nitrogen-bearing compounds such as amines and aniline, as well as sulfates, nitrates, nitrites, acetates, formates, and tartrates. These environments can produce tarnish films of Cu20 similar to the films formed in ammoniacal solutions. Both the rate of formation and... 

Flis J. (1991). Stress corrosion cracking of structural steels in nitrate solutions. In Corrosion of Metals and Hydrogen-Related Phenomena. Materials Science Monograph, Vol. 59 (ed. J Flis). Amsterdam Elsevier, pp. 57-94. 

Normal anodic stress corrosion cracking is caused by a combination of mechanical tensile stress and loeal eleetrolyte dissolution processes when certain conditions are met. First, the corrosive medium must have a specific effect on the respective alloy, and in addition, the alloy in contact with the electrolyte in this material/corrosive medium system must be prone to stress corrosion cracking. The tensile stress must also be suffleiently high. Susceptible systems, for example, are stainless austenitic steels in chloride-eontaining solution or unalloyed and low-alloy steels in nitrate solutions. In contrast, unalloyed and low-alloy steels are not susceptible to stress eorrosion eraeking in ehloride solutions. 

Stress corrosion cracking in alkali-metal hydroxide solutions shows a number of variations. Whereas in nitrate solntions the grain bonndary breakthrough potential only means a restriction of... 

In addition to the known corrosive effects of alkali-metal hydroxide and nitrate solutions, intergranular stress corrosion cracking in unalloyed and low-alloy steels in contact with ammonium carbonate and crude methanol (methanol with low concentration of impurities) has also been observed (Matsukura and Sato 1977 Wendler-Kalsch 1983). When this group of materials comes into contact with various othCT aggressive substances, stress corrosion cracking occurs, primarily with transgranular characteristics. 

The high nitrogen content of Bessemer steel makes it more sensitive than open-hearth steels to stress-corrosion cracking in hot caustic or nitrate solution. For this reason, open-hearth steel is usually specified for boilers. 

Figure 8.3. Effect of heat treatment of mild steel after quenching or cold rolling (70% reduction of thickness) on resistance to stress-corrosion cracking in boiling nitrate solution [15], (Reprinted with permission of ASM International. All rights reserved, www.asminterna tional.org.)...

Annealed brass, if not subject to a high applied stress, does not stress-corrosion crack. Whether residual stresses in cold-worked brass are sufficient to cause stress-corrosion cracking in an ammonia atmosphere can be checked by immersing brass in an aqueous solution of 100 g mercurous nitrate [Hg2(N03)2] and 13 mL nitric acid (HNO3, specific gravity 1.42) per liter of water. Mercury is released and penetrates the grain boundaries of the stressed alloy. If cracks do not appear with 15 min, the alloy is probably free of damaging stresses. 

Method for Mercurous Nitrate Test for Copper and Copper Alloys. Practice for Use of Mattsson s Solution of pH 7.2 to Evaluate the Stress-Corrosion Cracking Susceptibility of Copper-Zinc Alloys. 

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