Sub-surface corrosion research on rock bolt system, perforated SS sheets and steel sets for Yucca Mountain Repository
Friction type steel rock bolts are one of the most commonly used for reinforcing tunnels, since the late 1970’s due to their ability to sustain large rock mass displacements. These ASTM A607 steel rock bolts are tubes slotted along the length with one end tapered for easy insertion into a drill hole and the other end with a welded ring flange to hold the bearing plate. It is more commonly used these days to reinforce tunnels, and also being studied for underground support for nuclear repositories. We studied corrosion behavior of this A607 steel rock bolts using electrolytes in three different concentrations; 1X,10X,100X, in aerated (oxygenated) and deaerated (nitrogenated) conditions from 298 to 363K for nuclear repository applications. The corrosion behavior for 1X and 10X concentrations for this rock bolt were similar in both aerated and deaerated conditions except the corrosion rates were a order of magnitude higher in the aerated condition; ranging from ~30 to 200mm/yr for deaerated and 150 to 1600 mm/yr for aerated. The corrosion behavior using 100X electrolyte was quite different in aerated condition showing initial increases in the corrosion rate between 298 to 338K ( ~210 to 2400 μm/yr) and an unusual steep decrease from 338 to 348K(~2400 to 750 μm/yr). General as well as pitting corrosion were observed for these steels. In this paper we report results from potentiodynamic polarization and potentiostatic tests in simulated electrolytes as a function of concentration, temperature and environment. We also compare corrosion behavior of the A607 rock bolt steel with 1040 and A36 steels using the same electrolyte and similar environment.
Corrosion behavior of carbon steel rock bolt in simulated Yucca Mountain ground waters
Medium carbon steel (AISI 1040) was one of the candidate materials for rock bolts to reinforce the borehole liners and emplacement drifts of the high-level nuclear waste repository in Yucca Mountain. The corrosion performance of this structural steel was investigated by techniques such as linear polarization, electrochemical impedance spectroscopy (EIS), and laboratory immersion tests in simulated ground waters. The corrosion rates of the steel were measured for the temperatures in the range from 25 °C to 85 °C, for the ionic concentrations of 1 time (1×), 10 times (10×), and a hundred times (100×) ground water concentration. The steel corroded uniformly at penetration rates of 35 to 200 µm/year in the deaerated waters, and at 200 to 1000 µm/year in the aerated waters. Increasing temperatures in the deaerated waters increased the corrosion rate of the steel. However, increasing ionic concentrations influenced the corrosion rate only slightly. In the aerated 1×and 10×waters, increasing temperatures increased the rates of the steel significantly. In the aerated 100×waters, the corrosion rate increased from 25 °C to 45 °C and decreased at higher temperatures (65 °C and up) due to the formation of oxide/hydroxide films and salt scales on the surface of the steel specimen. The steel suffered pitting corrosion in the both deaerated and aerated hot ground water environments after anodic polarization.
Characterization of Fe-silicates and their catalytic properties for the selective reduction of nitric oxide by hydrocarbons
Abstract H-form Fe-silicate (H-Fe-silicate) catalysts having various Si/Fe molar ratios were synthesized and used for the reduction of NO by hydrocarbons. The results of the chemical analyses, NH3-TPD, X-ray photoelectron spectroscopy (XPS) and TPR, showed that the non-framework iron content increased with increasing content of iron. Olefins (C3H6 and C2H4) were more effective reducing agents than parafins (C3H8, C2H6). The active temperature region for NO reduction by C3H6, became lower with increasing iron content in the Fe-silicates, while both the number of acid sites and the NO conversion to N2 was approximately constant independent of the iron content. Therefore, the iron incorporated in zeolite framework provided acid sites that controlled the catalytic activity for selective reduction.