Failure Knowledge Database / 100 Selected Cases

Fracture of Turbine Shaft in Wakayama
June 5, 1972 at the Kainan Thermal Power Station of the Kansai Electric Power Company
Masayuki Nakao (Institute of Engineering Innovation, School of Engineering, the University of Tokyo)
Turbine and generator shafts fractured during a test run of 600,000-kilowatt steam generator unit conducted at athermal power station. Fr agments of the tur bine, t he generator an d the exciter scattered in the area. Thegenerator caught a fire. Inadequately adjusted bearings caused turbine-blade vibrations, and resonance.
1. EventTurbine and generator shafts fractured during a test run of 600,000-kilowatt steam generator unit conductedat the Kainan Thermal Power Station of the Kansai Electric Power Company. Fragments of the turbine, thegenerator and the exciter scattered in the area. The generator caught a fire.
2. Course
The steam g enerator unit had a c oupling mechanism as shown in Figure 1, in which 9 co uplings and 11
bearings secure connections between the shaft of the generator and the shaft of a rotating object such as anaxle or wheel.

Figure 1. Schematic Diagram of 600,000-Kilowatt Unit [1]After en gineers adj usted the bear ing balance a t t he f actory, the e quipment was s hipped in April to th epower s tation t o ha ve them assembled and the c oupling m echanism affixed t o t he generator. Wh ile
engineers had adjusted the be aring balance 62 times by June 5 whe n the incident occurred; the engine had
been experiencing intense turbi ne-blade vibrations at bearing #1 1 s ince May 27 . After c ompleting thebalance adj ustment and th e te st run at the nor mal ope ration speed of 3,60 0 rpm , engin eers i ncreased theturbine spe ed to the maximum, 3 ,850 – 3 ,900 r pm to c heck the t urbine-blade vibrations. As engin eers
started decreasing the turbine speed from 3,850 rpm, the engine made a loud rasping noise. Within several
seconds af ter the generator vibration alarm activ ated the tr ip (emergency shutdown), the en d shaf t of th e
generator (#10) caught a fire. Engineers turned off the boiler to decrease the pressure when the turbine, thegenerator and the exciter fractured with heavy banging noises. Fragments scattered in the area, and the fire1Failure Knowledge Database / 100 Selected Cases
broke out from the g enerator. Figu re 2 and 3 show the d amaged turbine g enerator and r otor. One of thefragments flew 380 meters, the longest distance of all, as Figure 4 illustrates.

Figure 2. Damaged Turbine Generator Shaft [1]Figure 3. Damaged Rotor Shaft [1]Figure 4. Scattered Fragments and Flying Distances [1]3. Cause
The housing of bearing #11 failed to secure the bearing stand and the upper vibration-absorbing pad. The
vibration occurred during th e bearin g ad justment loosened th e upper vibration-absorbing pad (the upper
half of th e jo urnal be aring sea t), and the loosened pad f ell off ( Figure 5 a). This de creased t he criticalwhirling speed (resonant frequency) of the shafting, which influenced the bearing vibrations and resulted instructural resonance. The structural resonance caused abnormal vibrations, which led to loose or deformed
bearings, h ousing an d b olts (Figu re 5b ). Violent v ibrations at b earings d amaged th e ref ueling s ystem.
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Failure Knowledge Database / 100 Selected Cases
Bearing metal partially melted down because of the interrupted refueling. Violent vibrations also scraped
off or deformed the b earing metal. D amaged b earings fail ed to secure theshaft, which led to thedestruction of the r otating s haft d ue to abnormal axial di splacement b etween th e shaft and the housing(Figure 5c).

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Failure Knowledge Database / 100 Selected Cases

Figure 5. Turbine Failure: Sequence of Events
The d amaged generator bearing a nd se al all owed hydrogen gas to l eak out of the ge nerator. T he le aked
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Failure Knowledge Database / 100 Selected Cases
hydrogen gas was ignited, cau sing a fire (Figure 5d). Most power g enerating p lants use hydrogen gas tocool the electrical windings within the power generator. This i mproves operating efficiencies by lowering
the losses due to the resistance of the windings (windage loss).
4. Immediate Action
All devices were rebuilt at the factory. Engineers installed the bearing and performed vibration diagnostics.
5. Countermeasure
Instead of adjusting the bearing for e ach device and readjust bearings of the assembled turbine generator,
the be arings were adjusted as conn ecting devices so t hat the assembled tur bine g enerator do not r equire
bearing readjustment.
6. Summary
The in cident proved the magnitude of the des truction ca used by a hig h-speed r otating machinery. The
flying di stances of fra gments themsel ves sho w clear evidence of de structive cap abilities. Casualties ar e
inevitable if fr agments hit engineers. It was a pure luck that the incident did not result in casualties. It wasan oversight of eng ineers that they under estimated t he a bnormal vibr ations at th e bearing s tand #1 1
worsened on May 27.
7. Knowledge(1) A high-speed rotating shafting produces a whirling motion.
(2) When whirling magnifies from r esonance, the rotating body with centrifugal force can burst out andcause serious accidents.
(3) Every failure comes with an infallible indication of some sort. It is critical not to miss it and to take anappropriate action before an indication lead to a failure.
(4) Never stand near on the plane of rotation when one must be near a rotating machinery. Early propeller
aircrafts did not have see-through covers over the propeller blades’ plane of rotation.
8. BackgroundA steam turbine is a rotary engine that extracts energy from a steam flow. It is the main mechanical deviceof a power generation system that extracts thermal energy from pressurized steam by sending steam in highpressure and temperature to the blades attached to a shaft (the rotor assembly). The blades react to the flow
so that they rotate and impart energy to the rotor. The generator connected to the turbine convert the energy
into electricity, which is suppli ed to communities. Leading domestic manufacturers at ti me h ad technicalcollaboration with f oreign ma nufacturers suc h as Westinghouse ( U.S.), Gener al El ectric ( U.S.) andSiemens (Europe) to develop turbines. Domestic development of turbine technology was yet to come. The
industry did not have fully de veloped balance adjus tment tech nology for mul ti-bearing ro tor systems.
5Failure Knowledge Database / 100 Selected Cases
Turbines were shipped back to the factory to adjust bearings, if engineers were unable to adjust them after
assembling the turbine.
References[1] Yotaro Hatamura (Editor), Jissai-no Sekkei (Practical Design) Research Foundation (1996) Zoku-Zoku
Jissai-no Sekkei (Practical Design III), The Nikkan Kogyo Shimbun, LTD.

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