Stress assisted intergranular corrosion

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. 

As with alloys of other metals, nickel alloys may suffer stress-corrosion cracking in certain corrosive environments, although the number of alloy environment combinations in which nickel alloys have been reported to undergo cracking is relatively small. In addition, intergranular attack due to grain boundary precipitates may be intensified by tensile stress in the metal in certain environments and develop into cracking. Table 4.28 lists the major circumstances in which stress corrosion or stress-assisted corrosion of nickel and its alloys have been recorded in service and also shows the preventive and remedial measures that have been adopted, usually with success, in each case. 

The PWS has been susceptible to intergranular stress corrosion cracking (IGSCC) and irradiation-assisted stress corrosion cracking (lASCC). The effects are assessed below. 

The chemical properties of the feedwater system should be maintained to minimize detrimental consequences (e.g. intergranular stress corrosion cracking and flow assisted eorrosion) for the internal structures and components, including tubes, of the steam generators. 

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