The original superheater outlet headers on TVA's Cumberland Units 1 and 2 have been high maintenance items throughout the life of the units. Periodic assessment and maintenance have been required to minimize the units' forced outrage rate. The problem areas include the ligament and bore hole cracking, tube stub pull out, and circumferential weld defects. Failure mechanisms were identified and root cause analyses were performed. Replacement of the headers were justified based on lost generation from forced outages. The BLESS computer code was used to evaluate the new design. German Code TRD-301 was also used to investigate the impact of fast load ramping. Potential new header materials were considered Tube spacing and connecting piping were rearranged. Several fabrication details were revised to eliminate previous problems. Barkhausen Noise and X-ray defraction techniques were used to quantify the residual strain in the weldment and heat-affected zone from the fabrication process.
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