Arini Nikitasari, Sundjono, Gadang Priyotomo, Ahmad Royani
Keywords: Polyphosphate, A192, C1015, Heat Exchanger, Ammonia Plant
Abstract:
The inhibitive performance of polyphosphate on the corrosion of heat exchanger materials i.e carbon steel A192 and C1015 in ammonia plant was explored. Corrosion rate measurement without and with polyphosphate addition were performed to investigate the inhibition of polyphosphate. There were three kinds of polyphosphate concentration and temperature used in this experiment : 75 ppm, 100 ppm, 150 ppm, and 32oC, 37oC, 50oC, respectively. The result revealed the effectiveness of polyphosphate for inhibiting corrosion of heat exchanger materials. The efficiency of polyphosphate boosts with concentration and diminishes with temperature.
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Polyphosphate performance for inhibiting corrosion of heat exchanger materials Arini Nikitasari1, Sundjono1, Gadang Priyotomo1, Ahmad Royani1 Research Center for Metallurgy and Material-LIPI, Puspiptek, 15313, South Tangerang, Indonesia 1 arininikitasari89@gmail.com Abstract The inhibitive performance of polyphosphate on the corrosion of heat exchanger materials i.e carbon steel A192 and C1015 in ammonia plant was explored. Corrosion rate measurement without and with polyphosphate addition were performed to investigate the inhibition of polyphosphate. There were three kinds of polyphosphate concentration and temperature used in this experiment : 75 ppm, 100 ppm, 150 ppm, and 32oC, 37oC, 50oC, respectively. The result revealed the effectiveness of polyphosphate for inhibiting corrosion of heat exchanger materials. The efficiency of polyphosphate boosts with concentration and diminishes with temperature. Keywords: Polyphosphate, A192, C1015, Heat Exchanger, Ammonia Plant. Introduction Heat exchanger is vital equipment for heat transfering and gas cooling in ammonia plant. However, corrosion in heat exchanger equipment is an important issue particularly in ammonia plant. During operation, corrosion products are usually formed on the surfaces of heat exchanger. These deposits reduce the heat transfer efficiency and endanger the lifespan of heat exchanger [1]. Corrosion occurs in the heat exchanger of ammonia plant as a result of an electrochemical reaction between metal and the moisture present in the atmosphere [2]. Moreover, inorganic scaling and fouling deposit on the heat exchanger surface induce under deposit corrosion attack and eventually causes failure of heat exchanger material [3]–[6]. In order to protect heat exchanger material against corrosion, corrosion inhibitor is the best solution due to low cost and ease in injecting. Corrosion inhibitor is organic or inorganic compound that suppresses corrosion, regardless of which electrochemical reaction it affects [7]. Polyphosphate is one of corrosion inhibitor 1 that capable of slowing the rate of cathodic reaction [8]. Polyphosphates consist of phosphorus atom that linked to its neighbors through two oxygen atoms. Thanks to higher phosphate content and also high chelate building potential with multivalentmetal cations, the polyphosphates perform better inhibitive performance compared to other inhibitors. Furthermore, it has been found that polyphosphates have sufficient water solubility to supply corrosion inhibition [9], [10]. Therefore, polyphosphate was chosen as corrosion inhibitor of heat exchanger materials in this experiment. Many research studies have been performed in recent years, in relation with the use of polyphosphate for corrosion inhibition. Nevertheless, deep researches about polyphosphate for inhibiting corrosion of heat exchanger materials have been seldom discussed. The aim of the present work is to study the performance of polyphosphate for inhibiting corrosion of metal A192 and C1015 (heat exchanger materials). Concentration and temperature also varied to observe their effect to corrosion rate. Experiment Details Materials Materials used for test were carbon steel A192 and C1015 whose chemical compositions were shown in Table 1. According to heat exchanger environment in Kujang Ammonia Plant, the shell side medium of heat-exchanger was feed water (corrosion medium) and its contents were displayed in Table 2. Corrosion inhibitor was prepared using polyphosphate (p.a Merck). Concentration of polyphosphate in this experiment were 75 ppm, 100 ppm, and 150 ppm. Polyphosphate was measured using analytical scale and dissolved with feed water in volumetric flask 1000 ml. Table 1. Chemical composition of heat exchanger materials Sample A192 C1015 C Si Mn P Chemical Composition (%) S Ni Cr Mo Al Cu 0.17989 0.17298 0.23616 0.24139 0.51519 0.51664 0.0092 0.0092 0.0203 0.0382 0.04174 0.05280 0.06928 0.03555 0.07178 0.23134 0.07239 0.16836 2 0.20573 0.05453 Table 2. Chemical analysis of feed water No Item Unit Feed Water - 8.27 NTU 0.37 - 0 µmhos 260 ppm 158 1 pH 2 Turbidity 3 Colour (Pt/Co) 4 Conductivity 5 Dissolved solid 6 Calcium Hardness ppm, CaCO3 47.84 7 Total Hardness ppm, CaCO3 64.48 8 Total Alkalinity ppm, CaCO3 77.04 9 Bicarbonate ppm 93.99 10 ppm 0 11 Total Chlorine, Cl2 Chloride, Cl- ppm 13.35 12 Sulphate, SO42- ppm 26.98 13 Sodium, Na ppm 77.84 14 Potassium, K ppm 18.46 15 Total Iron, Fe ppm 0.21 16 Silica, SiO2 ppm 14.10 Exposure test The exposure test were carried out using carbon steel A192 and C1015 coupon (7 cm x 4 cm) in corrosion chamber which installed on heat exchanger of Kujang Ammonia Plant. Position of corrosion chamber showed in Fig.1. Fig.2 displayed the installation of corrosion chamber in Kujang Ammonia Plant. There were 5 duration of exposure test : 28 days, 56 days, 84 days, 112 days, and 140 days. All samples for 28 and 56 days of exposure located at the bottom of corrosion chamber while samples for 84, 112, and 140 days lied on the top of corrosion chamber. Prior to the test, the surface of samples were degreased with acetone and rinsed with absolute ethanol, weighted using a precision of 0.0001 g. Subsequent to the test, specimens were descaled, rinsed with water and absolute alcohol, dried in nature state and weighted again [11]. The corrosion rate (v) was calculated according to Eq. (1) ν = [(weight loss (mg))/(area (cm2) × time (sec))] 3 (1) Figure 1. Position of corrosion chamber Figure 2. Installation of corrosion chamber 4 Electrochemical test Gamry instruments (Serial no. G750) was used to perform the electrochemical test. Carbon steel A192 and C1015 were cut into size (1 cm x 1 cm) as sample of electrochemical test. In this corrosion measurement system, sample were utilized as working electrode, saturated calomel electrode (SCE) as reference electrode, and Pt electrodes as counter electrode. Feed water used as solution in this test. Temperature of the solution was varied at 32oC, 37oC, and 50oC. The electrochemical test permormed twice, in feed water solution without polyphosphate inhibitor and with addition of polyphosphate inhibitor. Result and Discussion Visual and weight loss analysis Visual observation was provided to assist in corrosion monitoring of exposure test. Fig. 3 – Fig. 7 showed visual observation of metal A192 after exposure test during 28, 56, 84, 112, and 140 days, respectively. While, visual observation result of metal C1015 presented in Fig.8 – Fig. 12. Based on the visual observation, corrosion product increase with time of exposure. Corrosion product on the C1015 surface greater than corrosion product on the A192 surface according to visual observation result after exposure test. Table.3 listed result of weight loss measurement. According to Table.3 weight loss increase from 28 days to 56 days of exposure test, but from 84 days to 140 days,the weight loss decrease. The decrease of weight loss after exposure test more than 56 days due to the thickness of corrosion product. Corrosion product covers metal surface and prevents contact between metal and environment as of corrosion rate reduce. Figure 3. Corrosion coupon of A192 after exposure 28 days 5 Figure 4. Corrosion coupon of A192 after exposure 56 days Figure 5. Corrosion coupon of A192 after exposure 84 days Figure 6. Corrosion coupon of A192 after exposure 112 days 6 Figure 7. Corrosion coupon of A192 after exposure 140 days Figure 8. Corrosion coupon of C1015 after exposure 28 days Figure 9. Corrosion coupon of C1015 after exposure 56 days 7 Figure 10. Corrosion coupon of C1015 after exposure 84 days Figure 11. Corrosion coupon of C1015 after exposure 112 days Figure 12. Corrosion coupon of C1015 after exposure 140 days 8 Table 3. Weight loss measurement result Days A192 Weight Loss (mg) C1015 Corrosion Rate (mpy) Weight Loss (mg) Corrosion Rate (mpy) 28 472.5 10.84 610.7 13.97 56 930.9 10.67 1323.7 15.15 84 910.8 6.91 1536.4 11.63 112 812.4 4.62 1908 10.83 140 1002.9 4.56 1800.9 8.59 Influence temperature to corrosion rate of carbon steel A192 and C1015 The influence of temperature to corrosion rate of A192 and C1015 was observed with electrochemical test. Electrochemical test result of A192 at temperature 32 oC, 35oC, and 50oC presented in Fig.13-15, respectively. Fig. 16-18 displayed curve of C1015 electrochemical test at temperature 32oC, 35oC, 50oC, respectively. From the curve of electrochemical test, corrosion rate of A192 and C1015 at various temperature obtained and listed on Table.4. Based on Table. 4, metal C1015 have higher corrosion rate than A192 in all temperature. This result appropriate with visual and weight loss result. Corrosion rate of A192 less than C1015 because chrome content of A192 more than chrome content of C1015 according to Table.1. Corrosion rate of A192 and C1015 increase with temperature. Temperature able to increase the corrosion rate because reaction of corrosion is faster at high temperatures. Therefore, the highest corrosion rate of A192 and C1015 is at temperature 50 oC. 9 Figure 13. Curve of A192 electrochemical test at temperature 32 oC Figure 14. Curve of A192 electrochemical test at temperature 37oC 10 Figure 15. Curve of A192 electrochemical test at temperature 50oC Figure 16. Curve of C1015 electrochemical test at temperature 32oC 11 Figure 17. Curve of C1015 electrochemical test at temperature 37oC Figure 18. Curve of C1015 electrochemical test at temperature 50oC 12 Table 4. Corrosion rate based on electrochemical test Material Corrosion Rate (mpy) o 32 C 37oC 50oC A192 6.777 8.744 11.069 C1015 8.071 11.554 13.949 Polyphosphate inhibitor efficiency Inhibitive performance of polyphosphate was analyzed using the difference of corrosion rate (CR) between without and with polyphosphate addition. Polyphosphate was mixed in various concentration with feed water to investigate the effect of concentration to corrosion rate. Corrosion rate with polyphosphate addition also obtained using electrochemical test as corrosion rate without polyphosphate addition. Fig. 19-20 depicted corrosion rate of carbon steel A192 and C1015, respectively, with polyphosphate addition at various concentration. Based on Fig. 19 and Fig. 20, corrosion rate increase with temperature and decrease with increasing polyphosphate concentration. Table. 5 presented the efficiency of polyphosphate inhibitor. The efficiency inhibitor calculated according to Eq.2. Percentage of polyphosphate efficiency boosts with concentration. This condition indicate that polyphosphate give ideal performance for inhibiting corrosion of heat exchanger materials (carbon steel A192 and C1015). Polyphosphate inhibit corrosion by dissolving into the water and adsorbing on the metal surface, thereby reducing the access of hydrogen ions. The reduction of hydrogen ions leading to metal surface will interfere the reaction of hydrogen evolution. Therefore, polyphosphate is classified as cathodic inhibitors that interfere with the cathodic site of the electrochemical corrosion cell formation. 13 Figure 19. Corrosion rate of A192 at various polyphosphate concentration Figure 20. Corrosion rate of C1015 at various polyphosphate concentration 14 Conclusion Corrosion rate of heat exchanger materials in ammonia plant was assessed through exposure test and electrochemical test. Based on exposure test and electrochemical test, the corrosion rate of carbon steel A192 was lower than carbon steel C1015. Carbon steel A192 was found to be superior in corrosion resistance compared carbon steel C1015 due to higher chromium content. Polyphosphate inhibitor has good performance for inhibiting corrosion of carbon steel A192 and C1015. Polyphosphate able to reduce the corrosion rate up to 40% with concentration 150 ppm at 32 oC. The efficiency of polyphosphate boosts with concentration and diminishes with temperature. Acknowledgement The authors are grateful to Kujang Ammonia Plant for providing essential information and technical guidance made this research possible at Kujang Ammonia Plant. In addition, they would like to thank Research Center for Metallurgy and Material, Indonesian Institute of Sciences for financial support. References [1] ‘Corrosion inhibitors for acid cleaning of desalination heat exchangers : Progress , challenges and future perspectives’, I. B. Obot, A. Meroufel, I. B. Onyeachu, A. Alenazi, and A. A. Sorour, J. Mol. Liq, 296, pp. 111760-111773, 2019. [2] ‘Inhibition of corrosion in amine air cooled heat exchanger : Experimental and numerical study’, P. Valeh-e-sheyda and H. Rashidi, Appl. Therm. Eng, 98, pp. 1241– 1250, 2016. [3] ‘Polyphosphate coated steel sheet for superior corrosion resistance’, T. K. Rout, N. Bandyopadhyay, and T. Venugopalan, Surf. Coat. Technol, 201, pp. 1022–1030, 2006. [4] ‘Fouling corrosion in aluminum heat exchangers’ , S. Jingxin, M. Minyu, W. Tianjing, G. Xiaomei, H. Liguo, and W. Zhiping, Chinese J. Aeronaut, 28, pp. 954–960, 2015. [5] ‘Corrosion inhibition of heat exchanger tubing material ( titanium ) in MSF desalination plants in acid cleaning solution using aromatic nitro compounds’, M. A. Deyab, Desalination, 439, no. pp. 73–79, 2018. 15 [6] ‘Failure analysis of 101-C ammonia plant heat exchanger’, S. A. J. Jahromi, M. M. Alipour, and A. Beirami, Eng. Fail. Anal, 10, pp. 405–421, 2003. [7] ‘Heat and Power Optimization in Ammonia Plant’, M.H Panjeshashi, E. Ghasemian, N. Tahouni, University of Teheran, Iran. [8] ‘Inhibitor Polifosfat Untuk Mengendalikan Korosi Pada Pipa Sistem Pendistribusian Air’, K. Komalasari, Universitas Riau, Indonesia, 2016. [9] ‘The inhibitive performance of polyphosphate-based anticorrosion pigments using electrochemical techniques’, R. Naderi and M. M. Attar, Dye. Pigment, 80, 3, pp. 349– 354, 2009. [10] ‘Polyphosphate derivatives of guanidine and urea copolymer : Inhibiting corrosion effect of armco iron in acid solution and antibacterial activity’, M. Lebrini, F. Bentiss, N. Chihib, C. Jama, J. Pierre, and M. Lagrenée, Corros. Sci, 50, 10, pp. 2914–2918, 2008. [11] ‘Applied Surface Science The influence of temperature on the corrosion resistance of 10 # carbon steel for refinery heat exchanger tubes’, X. Xiu-qing, B. Zhen-quan, F. Yao-rong, M. Qiu-rong, and Z. Wen-zhen, Appl. Surf. Sci, 280, 32, pp. 641–645, 2013. 16