CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 2
their segregation to the grain boundaries. The mechanism of attack is not understood fully,
however it is suggested that dissolution of weak passive film formed at the grain boundaries
causes the intergranular corrosion [15]. Increase in phosphorus content results in progressive
increase in intergranular corrosion. The effect of silicon is more complex, and no intergranular
corrosion attack is observed in low (< 0.1 %) and high (> 2 %) silicon levels. Maximum rate of
attack occurs at approximately 0.7 % silicon.
2.10.2 End-grain attack
This is an unusual form of localized corrosion in austenitic stainless steel that occurs in
nuclear fuel reprocessing plant as well as other chemical processing plant handling concentrated
nitric acid. End-grain attack otherwise known as tunnel corrosion occurs along the cross section
normal to the rolling direction, and is considered to have significant effect on the corrosion
resistance of austenitic stainless steel in highly oxidizing nitric acid solution. The schematic of
end-grain attack is shown in Fig. 2.8a and a typical example of end-grain attack in 18 Cr-10 Ni
austenitic stainless steel in simulated dissolver solution containing highly oxidizing nitric acid is
shown in Fig. 2.8b [43].
Fig. 2.8 (a)
Fig. 2.8 (b)
Fig. 2.8: (a) Schematic of end-grain (b) a typical end-grain attack in austenitic stainless steel [43].