Stress corrosion cracking nitrate

Unfortunately, the water contained nitrates, which caused stress corrosion cracking of the mild steel reactor. The reactor was removed for repair, and the temporary pipe that replaced it later failed and caused the explosion (see Section 2.4). 

Certain environments containing nitrate, cyanide, carbonate, amines, ammonia or strong caustic, due to the risk of stress corrosion cracking. Temperature is an important factor in assessment of each cracking environment ... 

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 . 

Low-carbon and chromium-nickel steels, certain copper, nickel and aluminium alloys (which are all widely used in marine and offshore engineering) are liable to exhibit stress-corrosion cracking whilst in service in specific environments, where combinations of perhaps relatively modest stress levels in material exposed to environments which are wet, damp or humid, and in the presence of certain gases or ions such as oxygen, chlorides, nitrates, hydroxides, chromates, nitrates, sulphides, sulphates, etc. 

An environment containing HjS, cyanides, nitrates or alkalis may produce stress-corrosion cracking in highly stressed structures and these should be first stress relieved by heating to 650°C. 

Yet another problem associated with ammonia is stress corrosion cracking (SCC or caustic embrittlement) of brasses (such as brass valves and other stressed components). Stress corrosion cracking of brass may develop in systems where ammonia steadily becomes available from a suitable source (such as the breakdown of sodium nitrate when it is added to inhibit SCC of steel) because it can concentrate in the steam. 

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. 

R.G.I. Leferink and W.M.M. Huijbregts, Nitrate Stress Corrosion Cracking in Waste-Heat Recovery Boilers, Anti-Corrosion Methods and Materials, 49(2), 118-126 (2002). 

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. 

---