M. A. Doheima, S. M. Ahmedb and Y. M. Abdelrahmanc
Keywords: erosion-corrosion, Steel pipelines, reacted alumina
Abstract:
Field tests are specifically designed to monitor the deterioration behaviour of the Soderberg pipeline, to evaluate alternative materials of construction, to determine the effect of process conditions, and determining the most useful means for reducing the deteriorating rate. It was found that the change in steel composition affects both erosion and corrosion resistances. The results showed that increasing corrosion resistance is beneficial to decreasing synergistic mass loss rate. Steel with 1%Cr, 0.3%Si, and 1,35Mn was the most resistant. The corrosion rate of C-steels increases with C-content. The horizontal parts of pipelines are more deteriorated than the vertical parts.
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ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 Erosion-Corrosion Control in steel pipelines of Reacted alumina Transport M. A. Doheima, S. M. Ahmedb, Y. M. Abdelrahmanc a professor, Min.& Metal. Eng. Dept. Faculty of Eng. Assiut Univt., Egypt. b professor, Mech. Eng. Dept. Faculty of Eng. Assiut Univt., Egypt. c Engineer , Aluminium company of Egypt, Egypt. Abstract Field tests are specifically designed to monitor the deterioration behaviour of the Soderberg pipeline, to evaluate alternative materials of construction, to determine the effect of process conditions, and determining the most useful means for reducing the deteriorating rate. It was found that the change in steel composition affects both erosion and corrosion resistances. The results showed that increasing corrosion resistance is beneficial to decreasing synergistic mass loss rate. Steel with 1%Cr, 0.3%Si, and 1,35Mn was the most resistant. The corrosion rate of Csteels increases with C-content. The horizontal parts of pipelines are more deteriorated than the vertical parts. Keywords: erosion-corrosion, Steel pipelines, reacted alumina Corresponding author: mohdoheim@yahoo.com Tel.: ++2-01007041155 Fax: ++2-0882326134 - ++2-0882332553 1 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 1. Introduction Volume 16, Preprint 37 submitted 20 May 2013 The erosion-corrosion problem may result in serious deterioration of transport pipelines in various industries [1]. The synergistic effect of erosion-corrosion could cause more damage than the sum of both effects [2,3]. The system under consideration [4] involves recycling the enriched reacted alumina to the self-baked cells in Al-production plant. The system was analyzed and discussed in all its aspects [5]. It is known that the transport lines for fresh alumina or in the pre baked cell system suffer very little damage compared to the self-baked (Soderberg) cell system [5]. Such problems in industry are very annoying and are a threat to the production plant. It needs a good and expert effort for good design and material selection to control such deteriorating effect. The carbon content of the steel play an important role in the corrosion process, especially in the acidic solutions. The mechanism involved in this effect is not clear [6]. Low carbon steel materials showed high corrosion rates in NaCl 4.5%. The corrosion rates were found to be quite low for the low carbon steels but with higher corrosion rates for the medium and high carbon content steels in NaCl and CO2 gas. For the third aqueous solution which consists of sodium chloride, sulphuric acid and purged CO2 gas, the highest corrosion rates were obtained from high carbon content specimen [6]. This paper studies and discusses the erosion- corrosion control problem through field tests on pipeline material of construction under different conditions. 2 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 2. The Problem: Volume 16, Preprint 37 submitted 20 May 2013 The aluminum cell of the Hall-Heroult process produces environment unfriendly secondary products composed of tar, dust, vapors and gases. These cell emissions (duct gases) include O2, N2, CO2, CO, H2O, SO2, HF, and tar [7]. The most important constituents of cell gases are given in Table1. The most aggressive duct gases are: HF, COx, and SOx. The fluoride emissions are gaseous and particulate. Fluoride particulates are solid at a low temperature and are removed with CO2 gases. The gaseous HF is chemisorped on smelter–grade alumina in the dry gas cleaning system. HF adsorption on alumina occurs in preference to adsorption of SO2 and may prevent COS adsorption [7]. The CO present due to the back-reaction of the re-oxidation of dissolved aluminum to alumina can form, presence of moisture and Sulphur compounds, toxic metal carbonyls and can cause stress corrosion cracking in carbon steels at elevated pressures [8]. Thus, we have HF, SO2 and CO in the emitted cell gases which are aggressive enough to attack severely the constructional material of the pipeline. The carbon steel is usually the most economic material used. In such environment, the C-steel can be severely corroded [9]. This is the problem in the transport pipeline of recycled active alumina in Misr Aluminum Co. in Nagaa Hammady, Egypt, and the similar systems. 3. The Experimental work : Field tests are specifically designed to monitor the corrosion behaviour of the Soderberg pipeline, to evaluate alternative materials of construction, to determine the effect of process conditions that cannot be reproduced in laboratory , and to determine the most useful means of reducing corrosive rate. 3 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 Mass loss experiments have been done to determine the effect of carbon content of carbon steel, the effect of orientation ( horizontal- vertical), and the effect of alloying elements (Cr- Mo- NiMn- Nb) on the erosion-corrosion rate. 3.1. Test Materials: The chemical composition of the existing pipeline material in use is shown in Table 2. Four specimens of this material are fixed in the vertical part of the enriched alumina pipeline of Soderberg cell and other four specimens are fixed in the horizontal part, to study the effect of the orientation (horizontal-vertical) on the erosion-corrosion rate. Four specimens of different carbon content steels are fixed in the horizontal pipeline with its chemical composition given in Table 3, to study the effect of carbon content on the erosion-corrosion rate. Five specimens of different steels with compositions shown in Table 4 are selected to study the effect of alloying elements. To increase the reliability of the tests, the specimens were chosen from rolled sheets. 3.2. Equipment and Procedure: Small connections were prepared from the pipeline material each one is 40 cm long, two flanges were welded to install the connection in the pipeline. Fig.1 shows the small connection in the pipeline. Square test specimens with dimensions of 20*20*2mm and a hole of 5mm diameter in the center were utilized in the experimental work. Fig. 2 shows the specimens fixation. There is fiber textolite insulation between the specimens and the wall pipe. The specimens were finished by 120 grit belt. The specimens are de-greased by washing in acetone, dried, and weighed on analytical balance ( 0.1mg). After the experiment, the specimen is cleaned and weighed again and the corrosion rate is calculated from the mass loss. The above 4 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 procedure is according to ASTM G1-81 (preparing, and evaluating corrosion test specimens) [10]. The tests were carried out under the same operating conditions of the pipeline with velocity of 31m/s, average temperature of 35oC, inside gas pressure of 3-4 bar, mass solid to gas mass ratio of 8.37 and alumina mass flow rate of 5 kg/s. The analyses of fresh and eriched alumina are given in Table 5, mass loss per test specimen ,due to the exposure for a specified period of time, is calculated by: W Wo Wi , (1) Where Wo is the original weight of specimen before exposure, and Wi is the weight after exposure. Corrosion rate was calculated using the equation: CR M * 24 * 365 *10 , ρ*A ( 2) where CR = Corrosion rate in mm/yr , M= rate of mass loss in g/hr, = Density of the test specimen in g/cm3, and A = Area in cm2 of the test specimen. The CR is considered as an average value. 4. Results of Test Conditions: All steel specimens were found to corrode. This was evidenced by the decrease in the original mass of the specimens. Tables 6 and 7 show the mass loss of specimens after 45 days for the horizontal and vertical pipelines respectively. From these Tables, it can be seen that the 5 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 average mass loss of specimens of horizontal orientation is greater than that for the vertical orientation. The erosion-corrosion rate of the horizontal orientation is greater than the erosion – corrosion rate of the vertical orientation by a factor of about 2.25. Table 8 shows the mass loss of specimens with different carbon content after 45 day exposure. The results show that the mass loss is affected by the content of carbon. As the carbon content increases the mass loss increases. Kim et al [11] found that the corrosion rate increases with carbon content within the range of about 0.06% to more than 0.15%C. The mass loss and erosion- corrosion rate of different alloy steels are shown in Table 9after 45days. It is clear from Table 9 that the mass loss is dependent on the alloying element. Steel No. 5 has the least mass loss. 5. Discussion: 5.1. Effect of orientation (horizontal-vertical) From Tables 6&7 the erosion-corrosion of horizontal part of the enriched alumina pipeline of Soderberg system is more than the vertical part by a factor of about 2.25.This may be attributed to the gravity effect, since the horizontal part is subjected to the saltation effect which makes the surface subjected to the corrosive agents and the erosive effect of the alumina particles. The saltation effect reduces the cross section of area of the pipeline and thus increasing the gas velocity. The marked increase of the deteriorating erosion-corrosion effect in the horizontal part was verified by the field observation that the replacement of the horizontal part is frequently occurring than the vertical part. Thus, there is compatibility between the field tests and field observation. 6 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 5.2. Volume 16, Preprint 37 Effect of carbon content submitted 20 May 2013 Table 8 indicates that the erosion-corrosion rate increases with increasing the carbon content. In spite of the hardness increase with increasing the carbon content, consequently enhancing erosion resistance; in our case the erosion- corrosion increases, this may be because the corrosion is the dominant. In the work of Kim et al [11] the CR decreases rapidly as the Ccontent increases to about 0.06%, then decreases gradually as C-content increases up to about 0.1%. A further increase in C-content up to about 0.15% increases the CR and then substantially increases with further carbon increases (>0.15%). The proper C-content for low corrosion rates is from 0.05% to less than 0.1%. 5.3. Effect of chemical composition From Table 9 which shows the erosion-corrosion rate of five steels with different alloying elements after 45 days, Steel 1 which did not contain any alloying element is the more deteriorated. Fig 3 shows the erosion –corrosion rate of the five steels after 45days. Steels 2, 3, 4 which contain little amounts of molybdenum and niobium, are more resistant than steel 1. Steel 3 is more resistant than steels 2, 4, which may be attributed to the higher Mn-content. Steel 5, which contains 1% Cr and relatively high percentage of Si and Mn, is the more resistant. The positive effect of low chromium addition is proposed since chromium-enriched surface films are formed and they cause a reduction of the corrosion rate [12]. This information is being used to obtain steels with better corrosion performance than the carbon steel [13]. 7 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Conclusions: Volume 16, Preprint 37 submitted 20 May 2013 1. The orientation of the pipeline affects clearly its deterioration, the horizontal sections are more effected than the vertical ones. 2. The corrosion control is clearly influenced by the C-content of steel and the presence of minor alloying elements. The deterioration increas with C-content,within the investigated range. 3. The pipeline system design and materials selection need to be improved so that the erosioncorrosion problem can be controlled, e.g., the stagnant period, the cleaning of pipeline from the enriched alumina, the versatile change of air velocity, and pipeline orientation. References: [1] J.R. Shadley, S.A. Shirazi, E. Dayalan, M. Ismail, E.F. Rybicki, Erosion–corrosion of a carbon steel elbow in a carbon dioxide environment, Corrosion, 52 (1996) 9, 714-723. [2] A. Neville, T. Hodgkies, J.T. Dallas, A study of the erosion – corrosion behavior of engineering steels for marine pumping applications, Wear, 186- 187(1995) 497-505. [3] S. Zhou, M.M Stack, R.C Newman, Characterization of synergistic effects between erosion and corrosion in an aqueous environment using electrochemical techniques, Corrosion Sci., 12 (1996) 934-946, 1996. [4] M.A. Doheim, S.M. Ahmed, Y.M. Abdelrahman, JES,Assiut Univ.,36(4),july(2008) 463975. [5] Y.M. Abdelrahman, M.Sc. Thesis, Assiut univ.,2009. 8 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 [6] F. Nabhani, A.M. Jasim, S.W. Graham, Electrochemical Behaviour of Low Carbon Steel in Aqueous Solutions, WCE ( world congress on engineering), London, U.K, July 2 - 4, 2007. [7] S.J. Hay, "The formation and fate of carbonyl sulfide (COS) gas in aluminium smelting", PhD Thesis, Univ. of Auckland, Newzealand, 2002. [8] WWW.airproduct.com [9] N. Xu, "Corrosion behaviour of aluminized steel and conventional alloys in simulated aluminium smelting cell environment", Ph.D. Thesis, Univ. of New south Wales, Australia, 2002. [10] M.G. Fontana, Corrosion engineering, Mc Graw Hill, New York, 1987. [11] P.J. Peterson, (ed) Corrosion of electronic and magnetic materials, ASTM intl (1992) STP1148, pp.68-79. [12] S.L. Chawla, R.K. Gupta, Materials Selection for Corrosion Control, ASM International, 1993. [13] P. Greenfield, Stress corrosion failure, Mills and Boon Limited, London,(1971) 1-59. 9 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 Table 1;Analysis showing the effecting species in cell gases constituents Value, mg/m3 HF 250 SO2 400 Tar 100 Dust 2000 Water vapour 10000 CO2 4600 CO 3500 Table 2: Chemical composition of the pipeline material in use Element C Mn P Si Cu Mo Wt.% 0.08 0.55 0.007 0.018 0.019 0.008 10 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 Table 3: Chemical composition of different carbon content samples Sample submitted 20 May 2013 Composition wt. % C Si Mn P 1 0.07 0.15 0.48 0.028 2 0.1 0.18 0.58 0.037 3 0.18 0.34 0.73 0.027 4 0.2 0.24 0.69 0.025 Table 4: Chemical composition of low alloy steel specimens Sample Chemical composition (wt. %) C Mn P S Si Ni Cr Mo Nb 1 0.05 1.18 0.006 0.017 0.08 - - - - 2 0.08 0.8 0.01 0.01 0.15 - - 0.05 0.05 3 0.19 1.8 0.02 0.015 0.26 - - 0.035 0.06 4 0.18 1.1 0.018 0.018 0.26 - - 0.08 0.06 5 0.21 1.3 0.03 0.03 0.3 0.06 1 - - 11 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 Table 5 Analyses of enriched and fresh alumina Specification enriched Fresh F,wt% 1.07 --- S,wt% 0.17 --- C,wt% 0.2 --- SiO2,wt% 0.005 0.008 Fe2O3,wt% 0.018 0.008 Na2O,wt% 0.55 0.4 CaO,wt% 0.05 0.32 Moisture(at 300 C°) 0.69 0.40 L.O.I(at 1000 C°) 2.2 0.87 Bulk density ,g/ m3 0.98 0.95 Angle of repose degree 30 submitted 20 May 2013 33 Sieve Analysis + 150 micron,% 1.61 5 - 45 micron,% 4.23 6 Table 6: mass loss of specimen installed in a horizontal position Specimen (Fig.1) Mass loss, mg 1 2 3 4 Average Loss rate, mm/year 360 330 320 360 342.5 0.89 12 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 Table 7: mass loss of specimens installed in a vertical position. Specimen Mass loss, mg 1 2 3 4 Average Loss rate, mm/year 140 150 170 160 155 0.4 Table 8: mass loss of different carbon content specimens Specimen 1 2 3 4 Carbon content 0.05 0.1 0.18 0.2 Mass loss, mg 150 170 580 1024 Table 9: mass loss and loss rate for different steels after 45 day Steel mass loss, mg loss rate, mm/year 1 1090 2.81 2 641 1.65 3 342 0.88 4 720 1.85 5 88 0.23 13 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 1 1 2 2 3 submitted 20 May 2013 4 3 44 8 cm 40 cm Fig.1: Test section Fixing bolt Specimen 5 mm Pipe wall Insulation 20mm Fig.2: The specimen fixation 14 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 37 submitted 20 May 2013 Erosion-corrosion rate of low alloy steels Erosion-corrosion rate,mm/yr 3 2.5 2 1.5 1 0.5 0 1 2 3 4 5 Alloy Fig.3: Erosion –corrosion rate of different low-alloy steels after 45 days 15 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.