Few in-situ corrosion monitoring techniques are available to use in high pressure and high temperature (HPHT) environments. This paper presents the outcome of the development of a technique based on optical ellipsometry that may be used to measure oxide film thickness growth in real time to better understand material degradation. Ellipsometry is an optical technique where the light from a laser is reflected off the specimen surface into a sensor to measure the polarization change (phase and amplitude changes). While this technique is used at ambient pressure and temperature, it is rarely used at HPHT. In this study, the laser light was radiated through a HPHT window attached on an autoclave. This technique was used to measure nanometer to micrometer changes in thickness of an oxide film in supercritical CO2. The oxide film thickness measurements were compared to measurements of the thicknesses using scanning electron microscope imaging of the cross section and to data found in the literature.
High pressure and high temperature processes are present in a wide variety of industries and are often pushing the limits of common materials. As a result, these applications have required advanced materials as well as an improved understanding of the in-situ conditions. Furthermore, those processes have become more and more present in a wide range of industries such as upstream oil and gas (O&G) and power generation (in supercritical CO2 or molten salt nuclear reactors). The corrosion performance of existing and emerging materials to the extreme environments present in next generation power must be well characterized to ensure material integrity and reduce the risk of catastrophic failures due to environmentally assisted cracking, homogeneous corrosion, thermal oxidation, or other mechanisms.
To respond to the ever-growing material needs, it is important to find new tools to study them. There is often a lack of data, for weight change, composition, oxide film thickness, hardness, etc., available for materials in HPHT environments because the properties of HPHT materials are usually only measured before and after exposing them to the environment of interest. This is usually done because of the technical complexity of performing measurements in-situ. However, the ability to measure corrosion of materials in real time in relevant environments would provide significant advantages including:
• Direct observations of corrosion or oxidation kinetics in response to transient conditions.
• Simplified understanding of corrosion processes uncompromised by changes in surface film properties resulting from analysis in lab air.
• Reduced overall exposure costs by avoiding shut-off/start-up procedures required for autoclave testing when examining samples at various time intervals.