Probability Analysis in Predicting Creep Life of Power Plant Material Using High Power Ultrasound

Nonlinear ultrasonic (NLU) has been established as an effective method for the non-destructive evaluation
of power plant materials for various types of damage, including estimation of creep damage. However, the
information obtained through NLU measurement may not be sufficient to predict either the failure
probability or remaining creep life of any power plant component. A procedure has been formulated to
estimate the probability of failure vis-a-vis creep life of power plant materials through a two-parameter
Weibull analysis of NLU data. The investigation involved creep testing of P92 steel at 625 C for three
different applied stresses 120, 140, and 160 MPa. Subsequently, the extent of damage was estimated using
Weibull distribution analysis from NLU parameter b, measured in the same specimen at different interruptions.
The variation in cumulative distribution function (CDF) and the damage accumulation rate with
increased damage, were examined. Further, the behavior of predicted NLU parameter b obtained using
inverse CDF was evaluated with respect to measured b. Damage accumulation during creep deformation
was confirmed through significant microstructural changes such as the growth and coarsening of precipitates,
micro-crack formation, and their coalescence. Weibull distribution-based analysis established its
potential as an alternative method for predicting the failure probability and life of power plant components
under creep deformation from the NLU measurements.