Throughout the United States, there are cast iron water pipelines located underground that face corrosion. The oxides that form are quite detrimental to the mechanical stability of the cast iron. Thus, usable material diminishes and the pipes thin out. Corrosion Probe Inc. uses ultrasonic testing (UT) to measure the thickness of these pipelines, therefore allowing them to predict how long they will continue to be in service. Although ultrasonic testing is reliable on materials such as stainless steel, readings done on cast-iron pipes are very inaccurate due to the heterogeneous microstructure present. In our work, we are testing several variables on cast iron samples, such as graphite size, shape, concentration, and microstructure, to determine how to improve the accuracy of readings via UT gauges. This involves creating relationships between microstructural components and correlating how each variable impacts the UT error.