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  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME 202 AN INVESTIGATION OF THE CRACKING PATH OF A HYDROGENATED TIN BRASS HEAT EXCHANGER TUBE Salman A. Al-Duheisat1 and Amjad Saleh El-Amoush2 1 Al-Balqa Applied University, College of Engineering, Materials and Metallurgical Eng, Al-Salt 19117, P. O .Box 7181, Jordan, Tel: 00962-5-3491111, Fax: 00962-5-3530465 2 Faculty of Engineering Technology, Al Balqa Applied University P.O. Box 15008, Amman – Jordan 1. ABSTRACT Tin brass heat exchanger tube was charged with hydrogen and heat treated at various temperatures. It was found that the different heat treatment procedures applied after hydrogen charging affect the cracking path of the tube. The test results revealed that the tin brass tube specimens heat treated for a lower temperatures exhibit completely intergranular path of cracking, while the other specimens heat treated for a higher temperatures shows mixed mode of cracking, i.e. intergranular and transgranular cracking path.. The amount and number of hydrogen cracks were found to increase with increasing the heat treated temperature. Keywords: Tin Brass Heat Exchanger Tube, Hydrogen Charging, Heat Treatment Temperature. 2. INTRODUCTION It is well known that either intergranular or transgranular cracking may occur in brass and that in certain circumstances mixed mode cracking i.e. intergranular and transgranular may occur. Sometimes the cracking changes from being of predominantly one mode to the other. Reason for the mode change have been variously postulated as structural (1), environmental (2) or mechanical (3). It was observed that the alloy X-750 heat treated at 885o C for 24 hours and aging at 704o C for 20 hours showed great susceptibility to intergranular stress corrosion cracking and hydrogen embrittlement (4-6). It was found that the grain refinement improves resistance to hydrogen cracking (4-7), but no quantitative data relating measured hydrogen content to grain size and associated mechanical properties have been obtained. There have been attempts to explain why alloys of small grain size INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2014): 7.9290 (Calculated by GISI) www.jifactor.com IJCIET ©IAEME
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME 203 are less prone to hydrogen damage. Tien (8) calculated the concentration of hydrogen required to saturate grain boundaries with a monolayer of hydrogen at various grain sizes. He found that, by decreasing grain size from 100 to 10 m, the hydrogen coverage on grain boundaries with 10ppm of available hydrogen would decrease from saturation level to only about one site in ten covered. However, Gerberick and Wright (9) found that an increase of grain size from 10 to 160 m raised the threshold stress intensity of an AISI 4340 steel from 20 to 30 MNm(-3/2) and the amount of hydrogen cracking increased. It is well recognized that hydrogen diffusion is affected by defects such as vacancies, dislocations, grain boundaries, interfaces and voids, all of which may be classified as traps. The aim of this study is to investigate the influence of heat treated temperature on the cracking path of a hydrogenated tin brass heat exchanger tube. 3. EXPERIMENTAL PROCEDURE Microscopic examination of a tin brass heat exchanger tube heat treated at 500oC for 20. The material used in this investigation was a commercial tin brass heat exchanger tube provided by the Jordan Petroleum Refinery Company. The material was received in the form of tubing of 20mm outside diameter and 2mm wall thickness. The chemical composition of the material as measured by energy dispersive X-ray (EDX) is shown in figure 1 and listed in Table 1. A number of specimens were cut from this tube with 10mm width. The specimens were annealed for one hour at 300oC, and then slowly cooled to room temperature in a furnace to relieve residual stresses induced from machining. The specimens were heat treated at different temperatures and for various holding times. The heat treatment temperatures and the holding times applied to the tin brass heat exchanger tube are listed in Table 2. Figure 1: EDX analysis of the tin brass heat exchanger tube Table 1: The chemical composition of the tin brass heat exchanger tube, (wt%) Cu Zn Fe Si Sn Pb 71.72 26.88 0.12 0.04 1.18 0.06 Prior to cathodic charging, any thick or substantial oxide or hydroxide layer present on the surface, which might act as a barrier to hydrogen uptake, was removed by slightly polishing the samples on 600-grit paper, then polished and finally pickled in a solution of 5 parts nitric acid, 5 parts orthophosphoric and 1 part acetic acid. These steps are very important in order to promote the hydrogen entrance and for obtaining reliable measurements.
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME 204 The cathodic hydrogen charging technique developed in the laboratory consists of graphite anode. The experimental setup for hydrogen charging into tin brass heat exchanger tube is shown in figure 2. The graphite anodes have high and electrical conductivity. The specimen was made cathode in the electrolytic cell. The electrolytic solution contains 75% (volume) methanol, 22.4% (volume) distilled water, 2.6% (volume) sulphuric acid and 10mg per litter arsenic trioxide to inhibit hydrogen recombination at the surface. Constant current density of 25mA.cm-2 for 24 hours was applied to the specimens. The charging of hydrogen into these specimens was provided from both sides of the specimens. The experiments were performed at room temperature. The study of hydrogen damage was performed by observing the charged surfaces using the SEM microscope. Table 2: Heat treatment temperatures and holding times applied the tin brass heat exchanger tube No. Temperatures o C Holding time Min. 1 500 20 2 600 30 3 700 40 4 750 50 5 800 60 6 850 70 Figure 2: Cathodic hydrogen technique developed in the laboratory 4. RESULTS AND DISCUSSION Microscopic examination of a tin brass heat exchanger tube heat treated at 500oC for 20 min after hydrogen charging showed that cracking occurred mainly along the grain boundaries i.e. intergranular cracking (Fig. 3). The more disordered and high-energy grain boundaries occluded a
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. higher amount of hydrogen. Thus the presence of hydrogen increase regions, either by building up localized pressure or by reducing the cohesion force. Figure 3: Intergranular cracks observed in a tin brass specimen heat treated at 500 The micrograph in figure 4 shows the surface of a heat treated at 700oC for 40 min. It is clearly seen from this figure that the amount of intergranular cracking was increased with increasing heat treated temperatu completely intergranular, as can be seen from this figure, the tin brass specimens heat treated at lower temperature, i.e. at 500 It is believed that the angle grain boundaries angle grain boundaries associated with the tin brass tube specimen heat treated at lower temperature are less prone to cracking than that of temperature. Figure 4: Intergranular and transgranular International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME 205 the presence of hydrogen increased the ease of cracking in these regions, either by building up localized pressure or by reducing the cohesion force. Intergranular cracks observed in a tin brass specimen heat treated at 500 after hydrogen charging The micrograph in figure 4 shows the surface of a hydrogenated tin brass heat exchanger . It is clearly seen from this figure that the amount of intergranular increasing heat treated temperature. Moreover, the crack can be seen from this figure, the initial transgranular cracks observed in heat treated at lower temperature, i.e. at 500oC for 20 min angle grain boundaries plays critical role in the path of cracking. Thus, the low angle grain boundaries associated with the tin brass tube specimen heat treated at lower temperature are less prone to cracking than that of high-angle boundaries resulted from higher heat treating and transgranular cracks observed in a specimen heat treated at min after hydrogen charging International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), d the ease of cracking in these Intergranular cracks observed in a tin brass specimen heat treated at 500oC for 20 min tin brass heat exchanger and . It is clearly seen from this figure that the amount of intergranular the cracking path was the initial transgranular cracks observed in C for 20 min were not present. critical role in the path of cracking. Thus, the low- angle grain boundaries associated with the tin brass tube specimen heat treated at lower temperature resulted from higher heat treating heat treated at 700oC for 40
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. It should be noted here that, the specimens heat treated at a low temperature grain size exhibit a certain amount of texture, with low mismatch between grains, whereas specimens heated to higher temperatures showed a larger extent of grain growth. of the high-angle grain boundaries, the microstructure consisted of grains with a large degree of mismatch separated by such high-angle grain boundaries. These grain boundaries have a high energy and the distortion along them is greater, so more ones as can be seen from Figure 5. It was observed from the test results that the increasing charging time resulted in an increase of a number of hydrogen cracks on the surface of the tin brass specimens. The results showed that the hydrogen cracks formed in the specimens charged for shorte mainly along grains and they are relatively small, however, in the specimens charged for longer time, hydrogen cracks were connected to each other and propagated along the grains and slip lines, therefore they are larger than those in the specimens charged for shorter time. Figure 5: Micrograph of the surface of the specimen The effect of the heat treatment the tin brass heat exchanger tube specimens. The crack density n, which is defined as the number of surface cracks per unit area, are counted on a fixed area of 0. each specimen. The results of this semiquantitative study of the hydrogen cracks are shown in figure 6. It should be noted that in the hydrogen transgranular cracks observed in the charged specimens ha Instead, large hydrogen cracks along the grains were observed. grain boundaries are saturated more quickly and hydrogen cracks formed at grain boundaries of the tin brass specimens and then connected and propagated along the slip lines. This may explain why hydrogen induced cracks have been found to propagate transgranularly when the tin brass specimen heat treated at a higher temperature. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME 206 , the specimens heat treated at a low temperature exhibit a certain amount of texture, with low mismatch between grains, whereas specimens heated to higher temperatures showed a larger extent of grain growth. Because of high migra angle grain boundaries, the microstructure consisted of grains with a large degree of angle grain boundaries. These grain boundaries have a high energy and the distortion along them is greater, so more hydrogen is trapped in them than in the lo It was observed from the test results that the increasing charging time resulted in an increase of a number of hydrogen cracks on the surface of the tin brass specimens. The results showed that the hydrogen cracks formed in the specimens charged for shorter charging time, initiated in groups mainly along grains and they are relatively small, however, in the specimens charged for longer time, hydrogen cracks were connected to each other and propagated along the grains and slip lines, r than those in the specimens charged for shorter time. Micrograph of the surface of the specimen heat treated at 850oC for 7 hydrogen charging heat treatment on the number of hydrogen cracks formed was examined for specimens. The crack density n, which is defined as the number of surface cracks per unit area, are counted on a fixed area of 0.7 mm2, which was randomly marked o each specimen. The results of this semiquantitative study of the hydrogen cracks are shown in figure . It should be noted that in the hydrogen-charged specimens with large grain size, the initial transgranular cracks observed in the charged specimens having small grain size were not presented. Instead, large hydrogen cracks along the grains were observed. With heat treatment temperature, the grain boundaries are saturated more quickly and hydrogen cracks formed at grain boundaries of the ens and then connected and propagated along the slip lines. This may explain why hydrogen induced cracks have been found to propagate transgranularly when the tin brass specimen International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), , the specimens heat treated at a low temperature having smaller exhibit a certain amount of texture, with low mismatch between grains, whereas specimens high migration rate angle grain boundaries, the microstructure consisted of grains with a large degree of angle grain boundaries. These grain boundaries have a high energy hydrogen is trapped in them than in the low-angle It was observed from the test results that the increasing charging time resulted in an increase of a number of hydrogen cracks on the surface of the tin brass specimens. The results showed that r charging time, initiated in groups mainly along grains and they are relatively small, however, in the specimens charged for longer time, hydrogen cracks were connected to each other and propagated along the grains and slip lines, r 70 min after on the number of hydrogen cracks formed was examined for specimens. The crack density n, which is defined as the number of which was randomly marked on each specimen. The results of this semiquantitative study of the hydrogen cracks are shown in figure charged specimens with large grain size, the initial ving small grain size were not presented. With heat treatment temperature, the grain boundaries are saturated more quickly and hydrogen cracks formed at grain boundaries of the ens and then connected and propagated along the slip lines. This may explain why hydrogen induced cracks have been found to propagate transgranularly when the tin brass specimen
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME 207 Figure 6: Effect of charging time on the number of hydrogen cracks formed for the specimens of small grain size From the test results it was observed that the length of the hydrogen cracks increased with increasing the heat treatment temperatures. The above results showed that the hydrogen cracks initiated in groups along grains when the specimens heat treated at lower temperatures. However, these cracks were connected to each other in the specimens heat treated at higher temperatures. 5. CONCLUSIONS 1. The low-angle grain boundaries in tin brass specimens heat treated at lower temperatures are less susceptible to hydrogen cracking than are the high-angle grain boundaries resulted from heat treatment at higher temperatures. Therefore, the high-angle grain boundaries associated with large grains provide an easy path for crack propagation. 2. Intergranular cracking is, therefore more likely to occur with larger grain sizes and its amount and length increase with the heat treatment temperature. 3. The amount and number of hydrogen cracks were found to increase with increasing the heat treatment temperature. 6. REFERENCES 1. P.R. Swan, Corrosion, Vol. 19 (1963), p. 102. 2. E. Mattson, Electrochim. Acta, Vol. 3 (1961), p. 279. 3. Richard W. Hertzberg, Deformation and Fracture Mechanics of Engineering Materials, second edt. 1983, p. 107. 4. M.T. Miglin and H.A. Domian, “Microstructure and Stress Corrosion Resistance of Alloys X-750, 718, and A286 in Light Water Reactor Environments,” Journal of Materials Engineering, 9 (2) (1987), 113-132. 5. C.A. Grove and L.D. Petzold, “Mechanisms of Stress-Corrosion Cracking of Alloy X-750 in High-Purity Water,” Journal of Materials for Energy Systems, 7 (2) (1985), 147-162. 6. P. Skeldon, P.M. Scott, and P. Hurst, “Environmentally Assisted Cracking of Alloy X-750 in Simulated PWR Coolant,” Corrosion, 48 (7) (1992), 553-569. 7. M. Martinez-Madrid, S.L. Chan and J.A. Charles, Mater. Sci. Techn., Vol. 1 (1985), p. 454. 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 0 100 200 300 400 500 600 700 800 900 Numberofcracks Temperature, oC
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 202-208 © IAEME 208 8. A.W. Thompson and I.M. Bernstein, in Advances in Corrosion science and technology, Vol. 7, (ed. M.G. Fontana and R.W. Staehle), 53-175, 1980, New York, Plenum Press. 9. I.M. Bernstein and A.W. Thompson, Int. Met. Rev., Vol. 21 (1976), pp. 269-287. 10. W.M. Cain and A.R. Troiano, Pet. Eng., Vol. 37 (1965), pp. 37, 78. 11. J.K. Tien, in Effect of Hydrogen on Behavior of Materials, (ed. A.W. Thompson and I.M. Bernstein), 1976, pp. 305-321. 12. W.W. Gerberick and A.G. Wright, in Environmental Degradation of Engineering Materials in Hydrogen, (ed. Louthen et al.), 1981, pp. 183-206, Blacksburg, Va, Virginia Polytechnic Institute. 13. Asst. Prof. Samir A. Al-Mashhadi, Asst. Prof. Dr. Ghalib M. Habeeb and Abbas Kadhim Mushchil, “Control of Shrinkage Cracking in End Restrained Reinforced Concrete Walls”, International Journal of Civil Engineering & Technology (IJCIET), Volume 5, Issue 1, 2014, pp. 89 - 110, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. 14. Sanad A.M. and Hassan H.A., “Effect of Corrosion on Concrete Reinforcement Mechanical and Physical Properties”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 3, 2013, pp. 176 - 184, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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