Studies of IGA intergranular attack/stress corrosion cracking related parameters and remedies Original Research Article

The parameters influencing the appearance of intergranular corrosion of steam generator tubes are examined: the sludge zone located above the tube sheet, the secondary system materials (copper alloys), the age of the unit and the design of the tube support plates, which plays an important role in the hide out and in the hide out return of chemical species. The occurrence of intergranular attack/stress corrosion cracking (IGA/SCC) as a function of chemical parameters is also examined. These parameters include the following: sodium hydroxide, partly brought by the cooling water condenser inlets or by makeup water pollution, calculations of pH at high temperature in zones of restructed flow show a generally alkaline tendency; lead, often found on cracked tubes at particularly high concentrations, and well known as an aggravating element; copper, found in abnormal quantities on tubes pulled from Fessenheim unit 1, thus the relation between the materials of the secondary system, the copper concentrations on pulled tubes and the presence of IGA is carefully studied too; phosphate pollution, generally brought by the intermediate cooling system. Finally, the remedies implemented by EDF to limit the degradations with time are described.