Many industrial machines have components which undergo case hardening to enhance surface resistance to wear and fatigue. The depth of the hardened layer, known as Hardened Depth (HD), is a critical design parameter that influences the lifespan of these components. A reliable Nondestructive Testing (NDT) technique capable of determining the HD is therefore essential for the quality control of hardened parts. To this end, a novel HD estimation system has been developed using the Phase Coherence Imaging (PCI) technique. PCI images are obtained from Full Matrix of A-scan Data (FMC) collected via a high-frequency; large-aperture linear array coupled to the component with a shear-refracting wedge. PCI images exhibit strong contrast between the induction-hardened case and the unhardened base material, allowing the CHD to be algorithmically determined by identifying the line that maximizes the statistical distance between image pixel intensities on either side. The accuracy and repeatability of the system has been validated through tests on multiple samples with destructively verified case depths. The imaging and HD estimation algorithms have been implemented as an inspection solution based on AOS hardware (Explorer 64) together with the SonoDepth software from Eclipse Scientific. In this talk an overview of the HD estimation process is provided, followed by a comparison between the non-destructive and destructive estimates of the HD.