Estimating the depth of intergranular attack in piping by ultrasonic time delay: A theoretical analysis

Abstract

Detection and sizing of intergranular attack in steam generator tubes by ultrasonic time delay measurements may be a viable alternative to the use of eddy currents. A model of the behaviour of ultrasound in intergranular attack is constructed based on the self-consistent elastic theories of O'Connell and Budiansky for media permeated by a random array of small cracks. The presence of intergranular attack causes velocity changes in the material. The model incorporates a non-uniform degradation of material properties with distance from the corrosive fluid and makes use of two parameters: ε, a crack shape parameter and D̄, a characteristic length associated with the particular corrosive environments. The parameter ε is metallurgical and is primarily determined by alloy content and heat treatment, whereas D̄ is controlled primarily by the chemical environment.