Analysis of Failure Modes Resulting in Stress Corrosion Cracking of 304N Tubing in a High Pressure Heater Desuperheater

Santee Cooper (South Carolina Public Service Authority) experienced twenty-three tube failures in a high pressure feedwater heater that was in service less than three years. The tube failures were located at baffles adjacent to both exits of the dual flow desuperheater. Metallurgical analysis of the failed tubes indicated that stress corrosion cracking of the 304N stainless steel was the primary failure mode (Rudin, 1994; Shifter, 1994). The investigation to determine the factors leading to the onset of stress corrosion cracking included analysis of heater acceptance tests, the heater manufacturer’s proposal and manufacturing procedures, operational data, eddy current reports, metallurgical reports, and a heater design review for vibration and wet wall potential (formation of condensation on the outside diameter (OD) of the tube prior to the desuperheater exit).