DAMAGE MECHANISMS FOUND IN GENERATOR ROTOR 18MN18CR RETAINING RINGS

摘要

This study focuses on damage to 18Mn18Cr retaining rings over a period of seven years. A total of seventeen (17) 18Mn18Cr ring metallurgical investigation reports were reviewed. Of all the 18Mn18Cr retaining rings damage, were due to SCC (Stress Corrosion Cracking). No ring material deficiency was found in case examined. The 18Mn18Cr material performed exceptionally well. All ring damage was due to external factors in an around the rings; melted Copper or Aluminum deposits, electrical arcing, pitting, fretting or just localized overheating. Damage on the rings that was severe enough to cause microstructural transformation or cracking in most cases resulted in the need for ring replacement. Deposits that did not affect the material's structure typically were able to be removed and the ring put back in service. Most of the damage areas occurred in the retaining ring shrink fit area, which makes repair of these rings more problematic. Damage to areas of the rings outside of the shrink fit area typically are due to Copper winding ground faults and deposits of melted material on the ring inner diameter.