Blade Failure
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Phase Angle Continuous Monitoring Detects Blade Failure
by Damon E. Woodson and Thomas B. Lantrip
Abstract
This paper describes a case history on a turbine generator where significant damage to the turbine rotor was detected and later repaired due to continuous monitoring of the 1x rpm vibration phase angle. Using trend data and vector diagrams, the authors make the point that if only amplitudes were trended, the problem either wouldn’t have been detected or wouldn’t have been considered as significant as it truly was. Extensive photos of damage to the turbine rotor are provided along with trend plots before & after the damage occurred.
PREVIEW
“Introduction to FEA Method:
This case history is on a large, 3600 rpm steam turbine generator. The machine is a General Electric G3 machine with reheat. It is nominally rated at 818 Megawatts electric and operates as a load following machine (not constant loading). The turbine is in three steam path sections. The first section is the high pressure (HP) section. The HP section is not a tandem machine but steam enters one end and exits the other creating an unbalanced thrust loading. The outboard end of the HP section has a thrust bearing and radial sleeve bearing (Named # 1) and the inboard end has radial sleeve bearing (Named #2). The HP has seven stages of rotating buckets, and steam enters the high pressure section at 2400 psig and 1000 deg F. Full load steam flow is about 5.8 million lbs per hour. Each turbine stage removes energy from the steam, and the exhaust steam is at roughly 600 psig and 650 deg F. After leaving the HP section the steam is reheated in our coal fired boiler to approximately 570 psig and 1000 deg F. The steam then enters the intermediate pressure section of the G3 turbine. The intermediate pressure section is a tandem rotor and steam enters the center of the machine and exits each end. The machine has six tandem rows of buckets (six on each side of the machine center) and these stages are designated as numbers eight through thirteen.
The inboard side of the machine has a radial sleeve bearing (Named #3) and the outboard side of the machine also has a radial sleeve bearing (Named #4). The steam leaves the IP at about 200 psig and enters two twin tandem low pressure stages (Named A and B). The steam flow path is a parallel flow path from the IP. Each has its own inboard and outboard radial sleeve bearings (Bearings 7 through 8). The generator is next and it also has inboard and outboard bearings (Named 9 and 10) and the last machine on the common shaft is the exciter with inboard and outboard radial sleeve bearings (Named 11 and 12). All bearings have mounted proximity probes with a continuous monitoring system.
"Alarm Event:
On January 15th, 2003 our vibration monitoring group noticed a change in phase angle and 1x amplitude on the intermediate pressure section of our main turbine generator. The continuous monitoring system went into alarm from a phase angle change.”
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