Failure Analysis of a Gas Turbine Marriage Bolt
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Failure Analysis of a Gas Turbine Marriage Bolt Mohsen Mohammadi Æ Hamid Reza Salimi
Published online: 4 May 2007 ASM International 2007
Introduction A gas turbine exploded after 3 h of ordinary operation. This type of gas turbine works at maximum 5,100 rpm angular velocity and 18 MW output power. The rotor of the turbine had undergone repair after 77,000 operating hours and was then assembled on another unit of the power plant. Total operating hours and number of starts were 95,000 h and 4,785 times, respectively. The operating hours are listed in Table 1. The catastrophic failure caused heavy damages to the rotor and the casing. The marriage bolts of the rotor, the second stage buckets, and the shaft experienced high degradation. Approximately all turbo-compressor components—including inlet casing, compressor casing, discharge casing, turbine shell, exhaust hood, exhaust diffuser, exhaust plenum, inlet plenum, ACC gear, reduction gear, generator, couplings, piping of turbine surroundings, and combustor—were damaged beyond repair. The overall view of the failed gas turbine is illustrated in Fig. 1. Based on the primary information and data collected, three possible scenarios could be presumed for the accident: Case 1: Failure originated from a marriage bolt. We assumed that one of the twenty-four marriage bolts was broken due to material degradation. This resulted in an
increase in the vibration of the system causing the failure of the other marriage bolts. In this situation compressor and turbine were separated from each other and finally the journal shaft no. 1 was broken by an overload. Case 2: Failure originated from the second stage bucket. In this case, initially one of the second stage buckets was damaged; therefore, the amplitude of vibration was increased in the unit and marriage bolts were broken one by one. Finally, the rotor was separated and the journal shaft no. 1 was damaged. Case 3: Failure originated from the journal shaft no. 1. We assumed that the journal shaft no. 1 was damaged suddenly or gradually. Therefore, marriage bolts were broken and compressor and turbine were separated from each other. Due to any of these scenarios, the piping of turbine surroundings was damaged and led to explosion of the unit. Two important reasons led us to the conclusion that the cause of the failure was Case 1. First, experience shows that if any accidents occurred on rotating parts, damages must only affect the moving blades. In other words, when some rotating parts in a gas turbine unit are failed, none of the marriage bolts of the unit is broken; but in this failure all twenty-four marriage bolts were broken. Secondly, maximum service time after which the marriage bolts should be replaced was 100,000 h. The explosion occurred after 95,000 operation hours of the system, so their
M. Mohammadi (&) Mechanical and Materials Engineering, The University of Western Ontario, 408 Coombs Ave, London, Ontario, Canada N6G 1J5 e-mail: [email protected]
Table 1 Operating Hours of the
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