Corrosion of SG Tube Alloys in Typical Secondary Side Local Chemistries Derived from Operating Experience

In spite of strong industry improvements (new alloys, more stringent chemistry control…), Outer Diameter Stress Corrosion Cracking (ODSCC) still occurs in modern SG alloys, although at a lesser extent than it used to affect 600MA tubesTubes . Currently, alloy 600TT, and even 800NG, do indeed suffer from ODSCC. Since the chemistry of the secondary sideSecondary side of PWR NPPs improved, past tests do not enable to assess simply the risks for modern alloys (too extreme pH for instance). Thus, IRSN reviewed what typical chemical conditions could be met in actual steam generatorsSteam generators. Based on this review, IRSN performed corrosionCorrosion tests in these conditions to assess the potential risks for alloys 600TT and 690TT in “typical” top-of-tubesheet environments. This paper will present the safety, technical and industrial frames of these tests, as well as the first results. An emphasis will also be put on the scientific implications of these results.