Corrosion testing of laser welded sleeve mockups

A laser welded sleeving technique is used by Westinghouse to restore degraded PWR steam generator tubes to a condition that permits the continued safe operation of the steam generator. Prior to installing laser welded sleeves in operating steam generators, it was necessary to qualify the installation processes and to verify that the sleeved tubes had acceptable resistance to stress corrosion cracking (SCC) in the steam generator operating environment. Verification of the stress corrosion cracking resistance of sleeved tubes in an operating PWR plant was obtained through accelerated corrosion tests. The tests were performed on mockups of tubes sleeved by laser welding using prototypic field equipment and procedures. The SCC tests were conducted in autoclaves operated at 400 C with the ID of the sleeve and the ID of the tube exposed to a doped steam plus hydrogen environment that promotes cracking in materials with low resistance to primary water stress corrosion cracking. Tests were performed on sleeved samples stress relieved in the range of 760 to 871C as required by the sleeving process specifications, on samples stress relieved at temperatures below and above the specified range, and on sleeved samples without stress relief. SCC tests were also performed on mockups of the tube-to-tubesheet roll transition expansions. The stress corrosion cracking test results for the laser welded tubes stress relieved in the 760 to 871 C range verified that the sleeved tubes have acceptable SCC resistance at the operating conditions of the steam generator. Performance of the sleeves in these tests supported the installation of laser welded sleeves to permit continued operation of the steam generators