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Effect of Various Engineering Design Variables on Oxidation in High Temperature Supercritical CO2

Various type of specimens were exposed at 450°C and 1100 psi in pure supercritical CO2(sCO2) for over 1 month. The exposure was performed in order to assess the effect of various variables on the oxidation of materials used in supercritical CO2 at high temperature.Variable such as temperature and pressure are fairly well covered in the literature. Other identified variables such as contaminants and coatings have been partially addressed. Additional variables of interest such as welding stress corrosion cracking galvanic issues or crevices have not been studied.Welding changes the local microstructure due to the high temperature in the vicinity of the weld. The chromium will diffuse to the grain boundaries and the chromium concentration in the matrix will drop significantly. Consequently the corrosion resistance near the weld will drop. Since welding will likely be used in the manufacturing process it is recommended to test coupons containing the heat affected zone near a weld.Galvanic corrosion occurs when two materials with different electrochemical potentials are in contact with a corrosive environment. There is usually very little change in corrosion rates when materials with similar composition are in contact. However there may be some issue in the case of nickel alloys/stainless steel couples. It has also been suggested in the literature that galvanic corrosion may not be an issue because sCO2is not considered an electrolyte. However it may be of interest to electrically couple two samples of different material (stainless steel and nickel alloy) and measure the weight change of each sample individually after exposure to assess galvanic corrosion.Stress corrosion cracking combines the effect of applied stresses and corrosive environment leading to accelerated crack growth of a susceptible material due to its microstructure.Crevice corrosion may occur within the occluded site of two sandwiched specimens of identical material.Mass loss micro-hardness and SEM/EDS inspection of the specimen cross sections were used to measure the extent of oxidation. The welded specimens wee of both martensitic stainless steel 410 and austenitic stainless steel 310. The galvanic corrosion specimens were stainless steel 410 coupled to nickel alloy 625. The crevice corrosion specimens were two martensitic alloy 410 specimens coupled together. Stress corrosion cracking was studied using C-ring specimens.

Product Number: 51319-13243-SG
Author: Florent Bocher
Publication Date: 2019
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