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Measuring the severity of corrosion on a specific alloy is often accomplished via mass loss using ASTM G-1. These processes work well and provide high fidelity data for many materials, especially steels. However, recent internal findings and disclosures from other research groups have highlighted a potential issue with using mass loss techniques to measure the damage on some aluminum alloy surfaces.
Recent efforts have highlighted a potential issue in the currently accepted ASTM G-1 mass loss standard as an effective means for evaluating corrosion damage on aluminum alloy 7075-T6. It was found that the use of the current standard can result in users reporting mass loss values that are inconsistent with the visual corrosion assessment, including mass gain instead of loss on obviously corroded samples. It is hypothesized that the current method of repeated immersion in acidic solution followed by mechanical cleaning is not effective at dislodging corrosion product from the pits formed on a corroded aluminum surface. To address this issue, studies have been completed to evaluate a two-step method for corrosion analysis. First, ultrasonic cleaning of coupons in nitric acid more effectively removes corrosion from the corroded surface. Second, follow-on analysis of the cleaned coupons with both mass loss and optical profilometry demonstrated that there is significant amount of corrosion information which analysis via mass loss alone will not reveal. The present work focuses on the refinement of a new cleaning protocol for aluminum and the use of profilometry to assess coupons corroded in outdoor exposure and accelerated corrosion tests.
Geothermal Energy is currently engineered as an “always on” baseload supply, due to the limited flexibility to throttle the well without scaling and fatigue issues, and it is engineered for maximal efficiency at this output level. Scaling is a major problem in geothermal plants, particularly in cases where the geothermal fluid composition and plant operation make it difficult to control scaling. In such areas, particularly where scale inhibitors cannot be employed, the formation of scales can make the process less efficient and in extreme cases can lead to unexpected shutdown.
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Knowledge of the localized corrosion environment on a metal substrate can provide the critical link between atmospheric data and corrosion morphology and can enable the formation of a framework to predict service life as a function of environment. Over the last few decades the analytical characterization of bare metal surfaces undergoing atmospheric corrosion has improved, resulting in a more complete understanding and consideration of the environmental parameters involved. However, the corrosion processes and the role that the environmental parameters play in what is a multiphase system is rather complex involving chemical reactions and equilibria, ionic transport phenomena, and gaseous, aqueous and solid phases.
UNS S209101, also known as XM-19 by ASTM A2762, is a nitrogen-strengthened austenitic stainless steel with high strength and excellent corrosion resistance. Besides nitrogen (N) it also contains higher amounts of chromium (Cr), nickel (Ni), manganese (Mn), and a similar molybdenum (Mo) content compared with UNS S31603, as well as small additions of niobium (Nb) and vanadium (V). High contents of Cr, Mo and N confer this stainless steel high localized corrosion resistance. Mo, Mn and Cr increase the nitrogen solubility in iron alloys.