Abstract
The present paper studies a root cause of failure analysis of lacing wire used in the last stage blade of low pressure (LP) steam turbine. The lacing wire is made of Stainless Steel Grade 17-4 PH with a diameter of 1.4 mm. The failure occurred after the unit had been operated for 4 years. The fault occurred several times during the operation periods. The failure location is near the tack weld which has functions as a stopper between the lacing wire and the stub. Macro fractography, light optical microscope and scanning electron microscope were used to examine the fracture surface and microstructure closed to the failures. The cyclic stress was evaluate using harmonic analysis simulation using FEA (finite element analysis) Ansys 2019 R2. The benchmark that is indication of fatigue failure was clearly visible. It is concluded that the failure mechanism is fatigue failure with crack initiation. Improper maintenance procedures especially welding procedures trigger an initial crack and then the initial crack gets a concentrated cyclic load causing lacing wire broken.
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