امل ومحمد وسارة2 Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. Corrosion control of Buried Low Carbon Steel Structure Alteration Medias method Amel S. Merzah* Mohammed H. *, *** Technical college ** Department of Petroleum Technology / University of Technology *Email: **Email: ***Email: (Received 1 September Abstract The aim of the present work is to control of metal buried corrosion by alteration the depended on the characteristics of each media. The corrosion rates in different media (soil, sand, porcelanite stone and gravel) for specimens of low carbon steel were measured by two methods weight loss method and polarization m weight loss measured by buried specimens in these medias separately for 90 days. The polarization method includes preparing of specimen and salt solutions have electrical resistivity equivalent electrical resistivity of these media. The corrosion rate of two method results in (soil > sand> porcelainte stone> gravel). The lower corrosion rate happened in gravel media because of characteristics of high electrical resistivity and lower porosity for gravel while the higher corrosion rate occurred in the soil. Keywords: Low carbon steel, corrosion rate, medias, electrical resistivity, soil, sand, porcelanite media, gravel. 1. Introduction The study of soil as a corrosive medium is important taking into account the large amount of buried structures .The deterioration of that kind of structures could represent economic, safety, and environmental problems through the years. defined is an aggregate of minerals, organic matter, water, and gases (mostly air). It is formed by the combined weathering action of wind and water, and also organic decay [1]. Then the corrosion process of buried metal structure is extremely variable and can range from rapid to negligible [2]. The corrosiveness of the soil can be defined as the capacity of producing and developing the corrosion phenomenon. Soil is defined as an electrolyte and can be studied by electrochemical methods [3]. The factors ef of corrosive in soil included: Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 65- 74 (2014) Corrosion control of Buried Low Carbon Steel Structure by Alteration Medias method Mohammed H. Hafiz** Sarah k. Mohammed *, *** Technical college- Baghdad Petroleum Technology / University of Technology Email:amelmerza@yahoo.com Email:Drmhh1962@gmail.com ***Email: Sarah_materials@yahoo.com 1 September 2013; accepted 15 April 2014) The aim of the present work is to control of metal buried corrosion by alteration the media method. This method depended on the characteristics of each media. The corrosion rates in different media (soil, sand, porcelanite stone and gravel) for specimens of low carbon steel were measured by two methods weight loss method and polarization m weight loss measured by buried specimens in these medias separately for 90 days. The polarization method includes preparing of specimen and salt solutions have electrical resistivity equivalent electrical resistivity of these media. The te of two method results in (soil > sand> porcelainte stone> gravel). The lower corrosion rate happened in gravel media because of characteristics of high electrical resistivity and lower porosity for gravel while the higher Low carbon steel, corrosion rate, medias, electrical resistivity, soil, sand, porcelanite media, gravel. The study of soil as a corrosive medium is large amount of buried structures .The deterioration of that kind of structures could represent economic, safety, and environmental problems through the years. Soil as defined is an aggregate of minerals, organic matter, water, and gases (mostly air). It is formed by the combined weathering action of wind and water, and also organic decay [1]. Then the corrosion process of buried metal structure is d can range from rapid to negligible [2]. The corrosiveness of the soil can be defined as the capacity of producing and developing the corrosion phenomenon. Soil is defined as an electrolyte and can be studied by electrochemical methods [3]. The factors effects • Electrical resistivity • Porosity • Dissolved salts including depolarizes or inhibitors • Moisture • pH. Each of these variables may affect the anodic and cathodic polarization characteristics of a metal in a soil [4]. Soil electrical resistivity is an important parameter in underground corrosion general, the lower the resistivity, the higher the corrosion rate as shown in (Table 1) Al-Khwarizmi Engineering Journal by Using Mohammed*** media method. This method depended on the characteristics of each media. The corrosion rates in different media (soil, sand, porcelanite stone and gravel) for specimens of low carbon steel were measured by two methods weight loss method and polarization method, weight loss measured by buried specimens in these medias separately for 90 days. The polarization method includes preparing of specimen and salt solutions have electrical resistivity equivalent electrical resistivity of these media. The te of two method results in (soil > sand> porcelainte stone> gravel). The lower corrosion rate happened in gravel media because of characteristics of high electrical resistivity and lower porosity for gravel while the higher Low carbon steel, corrosion rate, medias, electrical resistivity, soil, sand, porcelanite media, gravel. Dissolved salts including depolarizes or Each of these variables may affect the anodic and cathodic polarization characteristics of a . Soil electrical resistivity is an important parameter in underground corrosion In general, the lower the resistivity, the higher the corrosion rate as shown in (Table 1). mailto:amelmerza@yahoo.com mailto:Drmhh1962@gmail.com mailto:Sarah_materials@yahoo.com Amel S. Merzah Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 64- 73 (2014) 66 Table1, Corrosivity rating based on soil resistivity [1]. Soil resistivity Ω.cm Corrosion rating >20,000 10,000-20,000 5000-10,000 3000-5000 1000-3000 <1000 Essentially noncorrosive Mildly corrosive Moderately corrosive Corrosive High corrosive Extremely corrosive Ions from dissolved salts and minerals must migrate through the electrolyte in a soil to supply the metal surface with the electron donors or acceptors necessary for the corrosion reaction to proceed. Soil resistivity is a measure of the concentration of these ions and how easily they move through the soil environment [6]. Metals buried in low resistivity soils will generally be anodic, whereas metals buried in adjacent high resistivity soils will generally be cathode .While the completely free of water has an extremely high resistivity. For example, sandy soils that easily drain water away are typically noncorrosive; clayey soils that hold water have low resistivity and are typically corrosive. Alteration soil one method of corrosion control soil high in organic acids can be made less corrosive by surrounding the metal structure with limestone chips. A layer of chalk (CaCO3) surrounding buried pipes has been used in some soil formations likely to produce microbiologically influenced corrosion [4]. The resistivity indicates the probable corrosivity of the soil decreases with increasing water contents ions, thus nonporous soils. Exhibit relatively high value of resistance, since the water content is small; these include nearly all of the igneous and metamorphic rocks such as granite, plus much sedimentary rock such as dense limestone or sandstone. The resistivity of bedrock can vary considerably depending upon the type of bedrock and extent of weathering and fracturing .The resistivity of the sand and gravel deposits generally high and uniform, while many bedrock formations have high but erratic resistivity or in the other word Clay soils and shale layers generally have low resistivity values resulting from their inherent moisture and mineral content. Very dry sand, gravel or rock has a very high resistance. As empty pore space fills the water, resistivity decreases. Materials that lack pore space such as massive limestone, granite, and basalt have high resistivity. All other factors being constant, the degree to which crack and fissure are present controls the resistivity of rock [2].In (Table 2) typical resistivity values minerals and soils are given. 2. Experimental Work Corrosion rate was measured for specimen of low carbon steel in four different media (soil, sand, porcelanite stone and gravel). (Table 3) shows the chemical composition of the low carbon steel. The specimen prepared for corrosion and microstructure test included grinding, polishing, etching and examination processes. (Fig. 1) shows the microstructure of low carbon steel before it was buried in different media. Methods of measuring the corrosion rate: 1. Weight loss: In these method specimens was buried in (soil, sand, porcelanite stone and gravel) separately for 90days. The corrosion rate (CR), was calculated using the following formula: CR= Δ W/ AT …(1) CR: Corrosion rate in mdd. Δ W: weight loss in milligrams. A: Exposed surface area in dcm2. T: time exposure in days. The conversion of corrosion rate in units milepenetration per years (mpy) by following relationship [7]: C.R (mpy) =(1.44/S.G)C.R (mdd) …(2) Where: mpy: corrosion rate unit (mils penetration per year ) S.G: specific density of metal (for steel =7. 9 mg/cm3). 2. Electrochemical techniques called polarization method this method is carried and consisting with an instrument of an electrochemical cell. The electrochemical cell contain three electrodes immersed in the solution ,working electrode (WE) which represents the studied sample ,reference electrode (calomel) and an auxiliary (platinum) electrode, the cell is connected to a device ,which allows the changing in current range and measuring the output potential as a function of current ,at which the input and output data are controlled by computer program .the applied current is a linear function potential. Amel S. Merzah Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 64- 73 (2014) 67 The corrosion of metal in soil depends upon its resistivity. Electrochemical polarization methods are used for measuring corrosion rate using three solutions of resistivity of (20, 10000, 20000) Ω.cm, (20Ω.cm) for soil measurement by use device (soil box resistivity and DET5/4D Megger Digital Earth Tester) shown in (Fig. 2), (10000Ω.cm) for sand and porcelanite, and 20000 for gravel [2], Table (4) represents the equivalent values of the resistivity of this media depending on the standard value with varying the concentration of NaCl as shown in (Table 4) .The electrical conductivity of the solution was measured using digital electrical conductivity meter model (DDS- 307) which is shown in (Fig. 3). Table 2, Electrical resistivity of various minerals and soil [2]. Minerals and Soil Resistivity , Ω.cm Minerals Pyrite Magnetite Graphite Rock Salt(impure) Serpentine Igneoue Rock Granite Diorite Gabbro Diabase Metamorphic Rocks Garnet gneiss Mica chist Biotite gneiss Slate Sedimentary Rock Chattanooga Shale Michingan Shale Calumet and hecla conglomerates Muschelkalk sandstone Ferruginous sandstone Muschelkalk limestone Marl Glacial till Type of Soil sand oil sand Gravel Loam Clay Silt 0.1 0.6-1.0 0.03 3000-500 000 20 000 500 000-100 000 1 000 000 10 000 000-1 400 000 000 310 000 20 000 000 130 000 100 000 000 -600 000 000 64 000 -6 500 000 2000-130 000 200 000 200 000-1 300 000 7000 18 000 18 000 7000 50 000 10 000- 500 000 400 – 22 000 20 000 – 400 000 3000- 20 000 500 -2000 1000 -2000 Table 3, The chemical composition of the specimen. Alloy % C Si Mn Fe Component 0.16 0.15 0.7 Reme. Amel S. Merzah Al-Khwarizmi Engineeri Table 4, Equivalence of resistivity by NaCl concentration NaCl content g\L Concentration % .30 3 0.04 0.004 0.0187 0.00187 Fig.1. the microstructure of surface of low carbon steel specimen before it was buried in different media (200X). Fig. 2. Devices connected and the experiment of electrical resistivity measurement Fig.3. Digital electrical conductivity meter Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 68 Equivalence of resistivity by NaCl concentration. Resistivity Ω.cm Conductivity (µ 20 50 000 10000 100 20000 50 microstructure of surface of low carbon steel specimen before it was buried in different media Devices connected and the experiment of electrical resistivity measurement . electrical conductivity meter. ng Journal, Vol. 10, No. 2, P.P. 64- 73 (2014) Conductivity (µΩ/cm) microstructure of surface of low carbon steel specimen before it was buried in different media Devices connected and the experiment of electrical resistivity measurement. Amel S. Merzah Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 64- 73 (2014) 69 Fig.4. Shows corrosion rates of low carbon steel in different media the buried for 90 days. Table 5, Corrosion rates (mdd) and (mpy) for low carbon steel specimen at different medias. Media Corrosion rate (mdd) Corrosion rate (mpy) Soil 18.93628 3.4516 Sand 2.6717933 0.4870 Porcelanite stone 0.516 0.094055 Gravel 0.2231 0.040666 Table 6, The corrosion rate of specimen of low carbon steel by polarization method. Resistivity (Ω. cm) Corrosion potential Ecorr (mV) Corrosion current density icorr (µA/cm 2) Corrosion rate (mpy ) 20 -450.1 199.21 83.592 10000 -330.9 14.38 6.03413 20000 -268 13.16 5.522 Amel S. Merzah Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 64- 73 (2014) 70 Fig. 5. (A1, A2), (B1, B2), (C1, C2)and (D1, D2) photographs and the microstructure of the surface specimens buried in soil, sand, porcelanite and gravel respectively (200X). B1 A1 A2 B2 C2 D1 C1 D2 Amel S. Merzah Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 65- 74 (2014) 71 Fig. 6. Polarization curve of specimen of low carbon test in solution with electrical resistivity (20 Ω. cm). Fig.7. Polarization curve for specimen of low carbon steel in solution with electrical resistivity (10000 Ω. cm). Fig.8. Polarization curve for specimen of low carbon steel in solution with electrical resistivity (20000 Ω. cm). Amel S. Merzah Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 65- 74 (2014) 72 Fig.9. The relationship between corrosion rate and current density. 3. Results and Discussion ( Fig .4 ) and (Table 5) represents the corrosion rate of low carbon steel specimens in different media (soil ,sand ,porcelanite stone and gravel) calculated by weight loss (first method) , specimens buried in this media for 90 days. Note that the corrosion rates in (soil> sand >porcelanite stone> gravel), are the highest corrosion rates occurring in the soil and the less the corrosion rate occur in gravel because the highest electrical resistivity. (Fig.5) shows the photographs and the microstructure of the surface of low carbon steel specimens after buried in different media. So the corrosion on surface of specimen buried in soil and sand can be observed, the corrosion product seen here is rust, surface color was dark orange to brown. Those areas that are dark in color contain significant sediment on the surface as shown in (Fig. 5) at (A 1, A2) and (B1, B2).The corrosion product on surface of specimen buried in porcelanite stone and gravel show very low , surface color ranging light orange to dark orange, and the rust is not uniform as shown in Figure (5) at (C1,C2)and (D1,D2). Calculation of corrosion rates by the second method (polarization method) using three solutions with different electrical resistivity (20,10000,20000) Ω.cm repesenting the electrical resistivity of (soil, sand and porcelanite stone ,gravel) respectively. The solution resistances are very low as would be the case with a specimen having a high corrosion rate ,the effect of the solution resistance may be a significant portion of the corrosion current reading , where corrosion rate can by determined be the following relationship [8]: Corrosion rate (mpy) = 0.13*i Corr. e/D …(3) Where : icorr: Corrosion current density µA/cm 2 e :Equivalent weight (for steel= 25.5) D :Density of metal(for steel = 7.9 gm/cm3) The polarization gave us values corrosion potential (Ecorr) y-axis and corrosion current density (icorr) x-axis as shows in (Table 6) and (Fig. (6), (7), (8)). The result higher corrosion current density (icorr) at low electrical resistivity values (20Ω.cm) this indicates the high corrosion rate , while lower corrosion current density (icorr) in high electrical resistivity solution (20000Ω.cm) indicates the lower corrosion rate. Results show a propotional relationship of corrosion rate with current density, but inversily proportional with resistivity, this is due to the reduction of water content, the density increases (soil,sand,porcelanite and gravel) which reflects at the values of resistivities.In (Fig. 9) shows relationship between corrosion rate and corrosion current density . Show presenceis a difference in the rate of corrosion between two methods corrosion rate higher in polarization method than weight loss the reason , The corrosion behavior of iron and steel buried in the soil approximates , in some respects, the behavior of the iron and steel on total immersion in water [4]. When soil resistivity value (> 20,000Ω.cm) essentially noncorrosive [1], This point different corrosion between soil and water, very pure or very soft waters are often excellent solvents for metallic ions. If these waters are very pure or very soft waters are often excellent solvents for metallic ions [9]. Rates corrosion in media depended on the characteristics of the media buried metal structure , Many factors affected of corrosion rate, important factor affected electrical resistivity and porosity . Lower corrosion rate in media with high electrical resistivity and less porosity (more dense ) .Than gravel of these four media is best media protect from corrosion . Amel S. Merzah Al-Khwarizmi Engineering Journal, Vol. 10, No. 2, P.P. 65- 74 (2014) 73 4. Conclusions 1. Corrosion rates of structure metal buried in media depend on the characteristics of this media (electrical resistivity , porosity, hydraulic permeability which describes how pores are interconnected, etc.). 2. Electrical resistivity of media is important factor effect on corrosion rate for metal buried in it. 3. Select best media for buried metal structure with low corrosion rate. Sand , porcelainte stone and gravel have best corrosion resistance compared to soil. 4. Gravel is the best media with higher corrosion resistance. 5. Reference [1] Roberge P.R, "Handbook of Corrosion Engineering", McGraw-Hill,USA 2000. [2] Robert Baboian,"Corrosion Test and Standards: Application and Interpretation", Second Edition, ASTM Stock Number: MN120-20nd, 2005. [3] Córdoba V. C., Mejía M. A., Echeverría F., Morales M. and Calderón J. A. ,"Corrosion mitigation of buried structures by soils modification", Chilean Journal of Engineering, vol. 19,No.3,pp486-497, 2011. [4] Winston R. R., Herbert U. H., ‘’Corrosion and Corrosion Control’’, Fourth Edition, USA, 2006. [5] M. Romanoff, “Underground Corrosion,” NBS 579, NTIS PB 168,350, National Bureau of Standards, April 1957. [6] 6.“Standard Method for Field Measurement of Soil Resistivity Using the Wenner Four- Electrode Method,” G 57, Annual Book of ASTM Standards, American Society for Testing and Materials, 1995. [7] Naser Korde," Cathodic Protection of Steel Pipelines Using Solar Energy", MSc Thesis, Department of Production Engineering and Metallurgy, University of Technology, 2012. [8] Formerly EFM, Engineering Filed Handbook, Engineering Field Manual Notice NB-21, 1979. [9] ASM Handbook, “Corrosion Fundamentals, Testing, and Protection”, Vol .13A, ASM,2003. )2014( 65- 74، صفحة 2، العدد10دجلة الخوارزمي الھندسیة المجلم امل صالح مرزه 74 حمایھ التأكل للفوالذ الكاربوني المدفون بوساطة تغیر الوسط ***ساره كریم محمد** محمد ھلیل حافظ * امل صالح مرزه بغداد - الكلیھ التقنیھ*** ،* ةالجامعھ التكنلوجی/ قسم تكنلوجیا النفط** amelmerza@yahoo.com :البرید االلكتروني* Drmhh1962@gmail.com :البرید االلكتروني** Sarah_materials@yahoo.com :البرید االلكتروني*** الخالصة حیث . الھدف من ھذا العمل ھو السیطرة على تأكل المعدن المدفون بطریقة استبدال أوساط،وھذه الطریقة تعتمدعلى خصائص كل وسط اوساط مختلفة واختیار افضل وسط حامي من التأكل واألوساط تشمل حسبت معدالت التأكل لعینات من فوالذ منخفض الكاربون في قیس فقدان الوزن ،حسبت معدالت التأكل بطریقتین طریقة فقدان الوزن وطریقة االستقطاب ) . صخر البورسلینات والحصى،الرمل،التربة( ً ٩٠(بدفن العینات في كل وسط من ھذه االوساط لمده ستقطاب تضمنت تحضیر محالیل ملحیة تملك مقاومیات كھربائیة وطریقة أال) یوما صخر >الرمل >التربة(اظھرت نتائج معدالت التأكل على نحو التالي.مكافئة لألوساط المستخدمھ وحساب معدالت التأكل في ھذه المحالیل ص ھذا الوسط من مقاومیة كھربائیة عالیة اقل معدالت تأكل حصلت للعینات المدفونة في الحصى بسب خصا).الحصى >البورسلینات .ومسامیة قلیلة واقل معدالت تأكل حدثت للعینات المدفونة في التربة mailto:amelmerza@yahoo.com mailto:Drmhh1962@gmail.com mailto:Sarah_materials@yahoo.com