Corrosion inter-granular

The electrochemical examination of fusion joints between nine pairs of dissimilar metal couples in seawater showed that in most cases the HAZ was anodic to the weld metals" . Prasad Rao and Prasanna Kumarundertook electrochemical studies of austenitic stainless steel claddings to find that heat input and 5Fe content significantly affected the anodic polarisation behaviour under active corrosion conditions whilst Herbsleb and Stoffelo found that two-phased weld claddings of the 24Cr-13Ni type were susceptible to inter-granular attack (IGA) as a result of sensitisation after heat treatment at 600°C /pa was unaffected by heat input. 

It has been established that low-antimony alloys are susceptible to inter-granular corrosion. At high antimony content levels (above 8.0 wt%), an overall (general) corrosion pattern prevails, whereas between 4.0 and 8.0 wt% Sb content both general and inter-granular corrosion occur [19,20]. 

If the data in Figs 4.12 and 4.14 are juxtaposed, it can be noted that antimony increases the corrosion rate of lead, whereas silver not only neutralises this influence of Sb, but even improves the corrosion resistance of Pb—Sb—Ag alloys. Silver suppresses the inter-granular corrosion and hence overall corrosion is the main process in Pb—Sb—Ag alloys. Silver affects... 

When a grid with such a structure is subjected to anodic polarization, the corrosion attack is faster along the inter-dendritic and grain boundaries. This leads to deeper inter-granular corrosion, which may eventually result in grid bar damage. 

Penetration of liquid metal into solid materials causing frontal and inter-granular corrosion. 

The development of corrosion resistant structural materials is apparently the main problem in lead cooled reactor technology. Lead exhibits strong erosion-corrosion effect on structural materials, such as material dissolving, embrittlement, thermal transport of mass and inter-granular penetration of lead. 

Figure 10.1 Examples of different forms of corrosion are (a) uniform corrosion, (b) non-uniform corrosion, (c) inter-granular corrosion, (d) stress corrosion cracking, (e) crevice corrosion, and (f) selective corrosion.

Many cases of cracks in piping have occurred (especially in welds, although almost all have been discovered before the pipes have broken). The most common causes are inter-granular stress corrosion cracking, and thermal fatigue from the movement of variable temperature fluids. 

A small leak grows by a combination of corrosion and erosion. Although a high velocity jet of steam or water blows out of the leak, there is back-diffusion of sodium round the jet into the hole, where it reacts with water and corrodes the metal. Grains are loosened by inter-granular corrosion and swept away by the jet. 

IGSCC inter granular stress corrosion cracking... 

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