Methodology based on potential measurement for predicting corrosion behaviour of SS 304L in boiling nitric acid containing oxidising ions

Abstract

Austenitic stainless steels like SS 304L are prone to intergranular corrosion (IGC) in boiling nitric acid media. A major cause is sensitisation induced in the heat affected zone of the weldments. Developments in sensitisation resistant materials have lead to the minimisation of degradation due to IGC. Corrosion in nitric acid medium is essentially controlled by oxidising potentials in the transpassive potential regime. The corrosion potential of stainless steel in nitric acid is a function of the concentration of acid, temperature and concentration of specific oxidising ions. In this work, a 'master curve' for the dependence of corrosion rates on the applied potentials was generated for type 304L stainless steel (nitric acid grade) in 6M nitric acid at near boiling (95uC) condition. The master curve was validated by measuring the corrosion rates at 48 h exposure in 6M near boiling nitric acid, in which various oxidising ions had been added. It was illustrated that there is a threshold potential (at transition to transpassivity) above which the non-sensitised stainless steel also undergoes IGC. A methodology for the prediction of corrosion rate has thus been proposed that can be applied to austenitic stainless steels at any given operating condition/component in operating plants where nitric acid media are used as process fluid. The effect of the temperature/ area ratio of stainless steel on corrosion has been illustrated.

Effect of metal ions in a heated nitric acid solution on the corrosion behavior of a titanium–5% tantalum alloy in the hot nitric acid condensate

“…They show, however, severe intergranular corrosion in certain instances due to transpassive dissolution resulting from an increase in the nitric acid concentration in the presence of certain corrosion products [1], TRU [2,3] and FP [4] with high oxidizing potentials. This is because the corrosion of austenitic steels in nitric acid medium is essentially controlled by oxidizing potentials in the transpassive potential regime [5]. Some alternative materials for nitric acid applications, such as Ti base alloys [6,7] and Zr base alloys [8], were developed and have been investigated for utilization in actual plant components.…”

Intergranular corrosion in evolving media: Experiment and modeling by cellular automata

“…All these experimental and modeling approaches allowed studying the influence of different metallurgical and chemical parameters on IGC. It appears that IGC could be dependent on the surface exposed to corrosive medium regarding the rolling direction [29,30,39,49], on the chemical composition of the SSs, which in turn influence the chemical composition of the grain boundaries [15,18,24,25,30,38,42,43,50,51], on the grain size [40] and on the metallurgical treatment [35]. IGC of SSs was also studied in a pure nitric medium at different concentrations [38,42] but also with the addition of different oxidizing species at different levels [36,37,49,51].…”

“…It appears that IGC could be dependent on the surface exposed to corrosive medium regarding the rolling direction [29,30,39,49], on the chemical composition of the SSs, which in turn influence the chemical composition of the grain boundaries [15,18,24,25,30,38,42,43,50,51], on the grain size [40] and on the metallurgical treatment [35]. IGC of SSs was also studied in a pure nitric medium at different concentrations [38,42] but also with the addition of different oxidizing species at different levels [36,37,49,51]. However, these parameters were only correlated to the corrosion potential and corrosion kinetics, without further information about the material/solution interface in terms of chemical composition and morphology.…”

Aspects of intergranular corrosion of AISI 321 stainless steel in high-carbon-containing environments

“…Thus, a local active-passive cell is created, where chromium is leached from grains and chromium carbides are cathodes, and the anodes are localized in the chromium-depleted region. When the cell works, intergranular corrosion can take place (Lopez et al, 1997;Michiuchi et al, 2006;Singh et al, 2003;Bhise and Kain, 2012;Martin et al, 2012;Sahlaoui et al, 2004;Aydogdu and Aydinol, 2006;Kelly et al, 1993;Gaudett and Scully, 1993;Bruemmer et al, 1992).…”