Long Arc Shrouding—A Reliability Improvement for Untuned Steam Turbine Blading

Abstract

An approach to the design and modification of untuned variable speed steam turbine exhaust blading has been found to be highly successful in eliminating fatigue failures due to the first tangential in-phase mode resonance. The approach consists of butt-welding the shrouds on the short arc blade groups to form a substantially longer arc length. The result is a significant reduction in vibratory stress at resonant speeds. Because of the ease with which the approach can be implemented in the field, backfitting is highly attractive to turbine operators. Availability benefits to the marine, utility, petrochemical, refining, industrial and commercial fields are anticipated.