A Field Deployable Electrochemical Sensor to Nondestructively Evaluate De-alloying in Gray Cast Iron

Gray cast iron piping is the most common pipe material in North America. Based on the high carbon content, graphitic needles or flakes are a common feature in these alloys. As a result, these areas of super-saturated carbon will consistently establish galvanic attack of the adjacent iron matrix, especially when in the presence of most ionic liquids. The localized galvanic potentials create microscopic pits and fissures which can lead to macroscale corrosion and cracking. The nuclear power industry has identified the selective leaching or de-alloying in gray cast iron, as well as in copper alloys with concentrations greater than 15% zinc or 8% aluminum. Existing NDE technologies can assess changes in pipe wall thickness but not changes in the mechanical properties resulting from de-alloying. A need exists for a completely non-destructive method to assess de-alloying and help determine the useful life and/or necessary repair of these pipes. MFS Technovation Corp. (MFST) in collaboration with the University of Houston (UH) will demonstrate the feasibility of a field deployable electrochemical non-destructive evaluation (NDE) sensor for the quantification of de-alloying in gray cast iron. Based on Metal Fatigue Solutions’ patented electrochemical fatigue sensor (EFS), combined with the electrochemical impedance spectroscopy (EIS), and the porous electrode expertise of UH, the proposed NDE technique will enable real-time evaluation of a metals and alloys corrosion resultant damage condition. The key enabling innovation, developed by the University of Houston, is the use of porous electrode theory and EIS to electronically assess the severity of galvanic corrosion damage on metallic alloys. This technology will be combined with the advanced signal processing and sensor fabrication expertise of MFST to develop a modular sensor package to provide a fast, accurate, and robust technique to non-destructively evaluate pipe-structures, such as those found in large scale power plants. The methods and technology developed here may also be directly applicable to other alloys critical to our infrastructure such as copper-nickel alloys. MFST’s proposed EIS-based NDE will demonstrate a clear value proposition by providing several economic advantages including reduced cost and improved quality of the metal pipe inspection process, reduced maintenance/repair of power plants, by enabling early warning of impending failure and confidence in properly operating components, and overall reduction in cost of electricity produced by the power plant by reducing the cost of operation and increasing the plant output. Coupling these benefits with MFST’s low-cost system will enable rapid commercialization. The ability to retrofit the proposed NDE onto existing power plants opens a very large addressable market and will reduce existing operation & maintenance (O&M) costs.