Silicon https://doi.org/10.1007/s12633-018-9821-4 ORIGINAL PAPER Corrosion and Corrosion Inhibition of Steel Pipelines in Montmorillonitic Soil Filling Material A. M. El-Shamy 1 · M. F. Shehata 1 · H. I. M. Metwally 2 · A. Melegy 2 Received: 6 November 2017 / Accepted: 26 March 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract Buried steel pipelines pass through different soils therefore; it could be subjected to dissimilar soil corrosion. A possible way to overcome this problem is using one kind of soil as filling material. The investigated filling materials were collected from Faiyum depression. XRD analyzes revealed that the soil composed mainly from montmorillonite, kaoilinite, illite and potassium chloride. The corrosion behavior of mild steel in the clayey soil was investigated by electrochemical techniques in correlation with moisture level. The results showed that, there are an increase of the corrosion rate with moisture content up to 40% by wt and a further increase in the moisture had no significant effect. Minor additions of CaO up to 0.5% by wt were added to the filling material to reduce its corrosivity. The results showed that the corrosion rate of steel is highly reduced with CaO. The reduction was related to the role of CaO in reducing moisture level and increasing clay alkalinity. Keywords Pipelines corrosion · Clay minerals · Filling materials · Moisture contents · Corrosion resistance · Montmorillonitie 1 Introduction 1.1 Clay Overview The clay materials constitute a broad-spectrum area from the earth surface and it is generally identified as fine-grained naturally occurring composed minerals. These materials are generally plastic at certain moisture contents [1–12] The grain size and the crystal structures give the filling materials a specific behavior against the corrosion of pipelines [13]. These properties include; the capabilities of cation exchange, plastic limit, swelling effect, the catalytic behavior and its low permeability [14, 15]. These unique features give the clay minerals many applications Such as in paper manufacturing to improve the absorption of ink, car tires to extend the rubber, improvement of concrete  A. M. El-Shamy elshamy10@yahoo.com 1 Physical Chemistry Department, Electrochemistry and Corrosion Laboratory, National Research Center, El-Bohouth St. 33, Dokki, P.O. 12622, Giza, Egypt 2 Geological Sciences Department, National Research Center, El-Bohouth St. 33, Dokki, P.O. 12622, Giza, Egypt mixtures, pharmaceuticals, ceramic and porcelains industry and as a catalyst especially in oils purification [16–19]. The montmorillonite is one of the important clay minerals and it is used in the treatment of chemical and nuclear wastes due to the capabilities of cation exchange, its low permeability and structural stability [20, 21]. 1.2 Corrosion Overview A wide variety of buried metallic structures such as trans- mission pipelines and bases of storage tanks are subjected to soil corrosion, which in turn could lead to serious eco- nomic losses and casualties. Therefore, soil corrosivity has to be taken into consideration when installing metallic struc- tures under the ground. Soil characteristics such as elec- tric resistively, moisture content, dissolved salts, pH level, porosity particle size and aeration are the key factors that can determine the degree of the soil corrosion processes [22–26] In general, the corrosivity of the soil increases with increasing moisture content dissolved salts pH value, poros- ity, particle size and aeration However; the corrosivity is reduced with increasing soil resistivity. For example, soil resistivity is strongly linked to moisture level, which has a strong impact on the degree of aeration and dissolution of the salts. The moisture itself is linked to porosity and par- ticle size of the soil. The corrosion rate of buried steels is