Handling Nine-Chrome Steel in HRSGs

摘要

Nine-percent chrome-moly steels (9Cr-lMo) have been used successfully in U.S. fossil boilers as far back as the 1980s. Early pioneers included Tennessee Valley Authority, Dayton Power & Light Co., Appalachian Power Co., and Hawaiian Electric Co. Inc. In recent years, the alloy (known as P91 in piping applications and T91 for tubing) also has been applied in large heat-recovery steam generators (HRSGs), in order to reduce thermal fatigue and creep damage in main-steam piping and superheaters. However, HRSG users generally have experienced more trouble with the alloy than their counterparts in the fossil-boiler sector have. Combined-cycle plants have been hit with problems in the fabrication, construction and repair of P91/T91 components. In fact. HRSG users have experienced failures in dissimilar metal welds and transition areas in less than 1,000 operating hours, and failures caused by poor weld geometry or inappropriate heat treatment in less than 5,000 operating hours.