Computed Tomography as an Alternative Method to Measure Crack Growth in Non-conventional Geometries

The computed tomography (CT) application presented herein aims at measuring cracks three dimensionally in a non-traditional fracture mechanics Superalloy 718 specimen exposed to supercritical CO₂ (sCO₂). Superalloy 718 is one material of choice for manufacturing components for Concentrated Solar Plant (CSP) units using sCO₂ power cycle. To quantify the low cycle fatigue (LCF) capability of the Superalloy 718 material exposed to sCO₂, at 550 °C, 200 bar internal pressure, hollow tensile specimens were designed and LCF experiments at different loading levels were conducted. The same hollow specimen was considered to monitor fatigue crack growth (FCG) while the crack surface is exposed to sCO₂ environment. By interrupting the LCF test procedure and conducting ex situ volumetric CT scans, the location, size and shape of several cracks were identified and, incremental crack advancement was measured.