Validation of the Steinrath Index Predictions for the Degree of Soil Aggressiveness Toward Copper Corrosion in Soils Contaminated with Chlorides

Abstract

The main goal of this study is to validate the Steinhrath index predictions towards copper corrosion in two different soils (loamy and sandy) non−modified and modified with chlorides, reaching the typical levels of seawater and Steinrath indexes varying between (-3) and (-8). Average corrosion rates between 4.5±0.3 and 124.5±0.5 µm y -1 showed to be in good agreement with the predictions of the Steinrath index.The copper surfaces, covered with corrosion products, were analyzed by visual observation, scanning electron microscopy coupled to energy dispersive spectroscopy (SEM/EDS), powder X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Cuprite (Cu 2 O) has been identified, by XRD, as the main constituent on all the surfaces, with traces of atacamite (Cu 2 (OH) 3 Cl) on top of the Cu 2 O layer. FTIR spectra suggest that, sulfate, silicate and/or hydroxyls are likely to be present. and concluded that, for short time exposures, the mass loss decreases as the amount of water increases.Bech-Nielsen et al. [19] have studied the behavior of copper in moderately acid medium (pH 5.0) and non−deareated chloride aqueous solutions (3% NaCl). Using Auger spectroscopy, the authors identified the presence of a Cu 2 O layer on the surface of copper samples. The layer thickness was found to increase with the exposure time.Soil corrosivity is not a directly measurable parameter and corrosion is largely a random phenomenon, hence no explicit relationship exists between soil properties and soil corrosivity. The soil texture is a parameter that can influence its aggressiveness since the drainage and aeration are texture dependent. Gerwin and Baumhauer [31] have concluded that corrosion of buried iron objects decreased in loamy soils due to oxygen deficiency. On the other hand, a sandy soil results in comparatively good drainage and aeration.Correlation between the corrosion rate of pipeline made of steel and soil parameters has been investigated under both controlled laboratory and natural outdoor conditions by Murray and Moran [33]. They have found a good correlation between corrosion rates of laboratory and outdoor samples. In general, the moisture level appears to control the corrosion rate following a semilog law with water concentration ranging between low (typically 6 wt%) and near saturation (typically 20 to 25 wt%) concentrations. Wang et al. [34] have concluded that the decrease of dissolved oxygen contributes to decrease gradually the corrosion rate of X80 steel in acidic soil solution. In addition, Gardiner and Melchers [35] concluded that oxygen and proton ion (H+) as the most common cathodic depolarizers, both playing its role in the corrosion process of steel in soils.

Moisture content and chloride ion effect on the corrosion behavior of fitting brass (gate valves) used as a connection of PVC's conduits in aggressive sandy soil

“…The higher percentage of Cu and Zn,which was diffused into the corrosion layer because of Cu and Zn dissolution tendency into the corrosion layer. Also, the higher percentage of O suggests that thicker copper and zinc oxides films have been formed during the corrosion process under the form (Cu 2 O,CuO and ZnO) [53]. The presence of Clin the corrosion products indicates the formation of the passive salt layer that covers the surface (CuCl,ZnCl 2 ) [54].Moreover, Soil elements such as Fe, Si, Ca, S, Na, Mg, and K are detected in the corrosion products.…”