Intergranular corrosion attack

Zinc alloys with addition of >0.03% aluminum are susceptible to intergranular corrosion attack [2, 39]. 

In RBMK reactors, oxygen (up to 0.2mg/kg) is injected into the feedwater circuit downstream from the condensate polishing system in order to prevent corrosive attack on the perlitic steels, and then removed from the water in the deaerator (Dragunov et al., 1992). Attempts have also been made to inject hydrogen as a remedy for intergranular corrosion attack on stainless steels. 

Figure 6.17 Stainless-steel cavernous pits formed on S30400 stainless steel following an intergranular corrosion attack. (Courtesy of Russ Green, TMI)...

Intergranular Corrosion Selec tive corrosion in the grain boundaries of a metal or alloy without appreciable attack on the grains or crystals themselves is called intergranular corrosion. When severe, this attack causes a loss of strength and ductility out of proportion to the amount of metal actually destroyed by corrosion. 

Evaluation of Results After the specimens have been reweighed, they should be examined carefully. LocaHzed attack such as pits, crevice corrosion, stress-acceleratedcorrosion, crackiug, or intergranular corrosion should be measured for depth and area affected. 

At temperatures above 300°C, low-carbon nickel (0-02% C) is preferred to avoid the possibility of intergranular attack developing after long exposure if material of higher carbon is employed it should be annealed after fabrication and before exposure to caustic alkalis to prevent stress-assisted intergranular corrosion. 

Intergranular corrosion of Fe-Ni-Cr alloys has been the subject of a comprehensive review by Cowan and Tedmon who summarised the various tests used for determining susceptibility (Table 19.3). Of these tests. Nos. 1-5, which are regarded as reliable test procedures by the ASTM, have been incorporated into ASTM A262 1986 Recommended Practice for Detecting Susceptibility to Intergranular Attack in Stainless Steel as follows ... 

Practices for detecting susceptibility to intergranular attack in austenitic stainless steels Recommended practice for detection of susceptibility to intergranular corrosion in severely sensitised austenitic stainless steel (intent to withdraw)... 

Streicher s work indicates how useful the potentiostat has been in studying intergranular corrosion. Ideally, future data would be expanded to provide Pourbaix-type diagrams that also contain kinetic information showing various rates of attack within the general domain of intergranular corrosion. (Similar data for cases other than intergranular attack would be equally valuable.)... 

Localised Corrosion (or localised attack) accelerated corrosion at certain sites only of a metal surface, usually induced by spatial separation of the anodic and cathodic sites. Examples include pitting corrosion, stress-corrosion cracking and intergranular corrosion. 

CORROSION EMBRITTLEMENT. The or loss of ductility of metals due to corrosion, usually as a result oF intergranular embrittlement attack, which may not readily be visible. 

Pits are found to develop particularly in the region of grain boundaries which themselves are readily open to attack ( intergranular corrosion ). Thus, it is the Cu-depleted regions that are the major cause of the intergranular damage of Al-Cu alloys. The A1 itself remains passive for a certain time and potential, but even when... 

The intergranular corrosion of Zn-Al alloys may be attributed to the preferential attack at the Al-rich phase present in the grain boundaries. 

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