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.
X-ray photoelectron spectroscopic analyses of corrosion products formed on rock bolt carbon steel in chloride media with bicarbonate and silicate ions
The passivation behavior of Yucca Mountain Repository rock bolt carbon steel in deaerated 3.5% NaCl solution containing SiO{sub 3}{sup 2} and HCO{sub 3} ions was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopic methods. Polarization results indicate that combinations of silicate and bicarbonate anions decrease the passive current density and raise the pitting potential. XPS results indicate the enrichment of silica at passive potentials and the formation of mixed FeCO{sub 3} and silica film at lower potentials. This change in film composition was responsible for the changes in corrosion rate at lower and higher potentials. XPS results also support the thermodynamic data with regard to the occurrence of second oxidation peak observed in the polarization curves to be due to the oxidation of FeCO{sub 3} to Fe{sub 2}O{sub 3}.
The influence of pH on the inhibition of corrosion of iron and mild steel by sodium silicate
Abstract The inhibition of iron and mild steel in solutions of sodium silicate of different concentration and pH has been studied by means of potentiostatic and potentiokinetic polarization measurements. The mechanism of formation of protective layers formed in the presence of inhibitor has been discussed on the basis of experimental measurements and literature data. The difference in the protective action due to the presence of sodium silicate as distinguished from the effect of the alkaline media has been demonstrated. The influence of the metal corrosion products in the formation of the protective layers has also been investigated.