Materials and Corrosion 2012. 63. No. 1 Mechanical degradation failure on leakage of titani ium tubes analyzed the weight loss, hardness deterioration, etc, on pure a)l titanium and its alloys under erosion. However, all these researches were only conducted in laboratories. As for the actual engineering failure cases, El-Dahshan et al. [10] investigate droplet erosion on the titanium tubes in a condenser of one mSF (multi stage flash) distiller, and Ma et al. [11]carried out a failure analysis study of leakage on titanium tubes within condensers of PTA(P-phthalic acid) production lines, and determined the main cause was fatigue fracture. However, such titanium tubes were seashell not related to nuclear power units. Hence, achievement of current study has critical engineering values in equipment design and mechanical failures prevention of titanium heat exchanger tubes that are used in similar seawater environment for not only nuclear power plants, but also equipment in other industries like thermal power, petrochemical, chemical, metallurgical, and b) 2 Experimental As has been illustrated in the Part I, the titanium tubes with specification ofΦ19×14630×0.71 mm in the rcw heat changers are sustained by 23 carbon steel baffle plates .6 mm-thick) with interval distance of 603 mm, and are mm- thick carbon steel plates cladded with titanium. Diameter of the ustaining holes on all the plates was 19.25+0.51 mm, leaving gaps of less than 0.5 mm between the plate and the tubes due to unsealed welding on the inlet of tube sheet For supplementation, the concrete operation parameters of these tubes are listed Table 1 seen from Fig. 1 that a large number of titanium tubes were clogged by different substances in the inlet of one heat exchanger, for example, by seashells( Fig. 1a), sediments(Fig 1b) and even rubber debris(Fig. Ic)that was the originally liner in the inside wall of the seawater chamber. As a result, these clogged tubes were detected to be thinned. and some of them were even Then, by means of scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS), investigation will dom- inantly focus on the microscopic morphologies and micro-area compositions of the ruptures on the leaked tubes clogged by different substances. Meanwhile, features of the clogging substances as sediment, seashell, and rubber debris were also characterized by optical microscopy (OM), SEM, and EDS. Figure 1 External appearances of clogging in one heat exchanger: (a) Particularly, the stress distribution on the wall of the tube when by seashell, (b)by sediment, (c) by rubber debris it is clogged by a seashell, as well as the erosion effect on the thinned part of the tube wall, were both computationally simulated by commercial finite element method(FEM) software ANsYS. The detailed results are as follows Table 1. Operation parameters of the RCW heat exchanger Media Velocity Outlet o(m/s) T(°C) emp.T(°C) Tube side 2.7 35.1 www.matcorr.com o 2012 WILEY-VCH Verlag GmbH& Co KGaA, Weinheimanalyzed the weight loss, hardness deterioration, etc., on pure titanium and its alloys under erosion. However, all these researches were only conducted in laboratories. As for the actual engineering failure cases, El-Dahshan et al. [10] investigated droplet erosion on the titanium tubes in a condenser of one MSF (multi stage flash) distiller, and Ma et al. [11] carried out a failure analysis study of leakage on titanium tubes within condensers of PTA ( p-phthalic acid) production lines, and determined the main cause was fatigue fracture. However, such titanium tubes were not related to nuclear power units. Hence, achievement of current study has critical engineering values in equipment design and mechanical failures prevention of titanium heat exchanger tubes that are used in similar seawater environment for not only nuclear power plants, but also equipment in other industries like thermal power, petrochemical, chemical, metallurgical, and so on. 2 Experimental As has been illustrated in the Part I, the titanium tubes with specification of F19
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0.71 mm in the RCW heat exchangers are sustained by 23 carbon steel baffle plates (16 mm-thick) with interval distance of 603 mm, and are hydraulically expanded at two ends of tube sheet with 78 mm￾thick carbon steel plates cladded with titanium. Diameter of the sustaining holes on all the plates was 19.25 0.51 mm, leaving gaps of less than 0.5 mm between the plate and the tubes due to unsealed welding on the inlet of tube sheet. For supplementation, the concrete operation parameters of these tubes are listed in Table 1. It can be seen from Fig. 1 that a large number of titanium tubes were clogged by different substances in the inlet of one heat exchanger, for example, by seashells (Fig. 1a), sediments (Fig. 1b), and even rubber debris (Fig. 1c) that was the originally liner in the inside wall of the seawater chamber. As a result, these clogged tubes were detected to be thinned, and some of them were even leaked. Then, by means of scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), investigation will dom￾inantly focus on the microscopic morphologies and micro-area compositions of the ruptures on the leaked tubes clogged by different substances. Meanwhile, features of the clogging substances as sediment, seashell, and rubber debris were also characterized by optical microscopy (OM), SEM, and EDS. Particularly, the stress distribution on the wall of the tube when it is clogged by a seashell, as well as the erosion effect on the thinned part of the tube wall, were both computationally simulated by commercial finite element method (FEM) software ANSYS. The detailed results are as follows. Materials and Corrosion 2012, 63, No. 1 Mechanical degradation failure on leakage of titanium tubes 19 Table 1. Operation parameters of the RCW heat exchanger Media Flux Q (m3 /s) Velocity v (m/s) Pressure p (MPa) Inlet temp. T (8C) Outlet temp. T (8C) Shell side Desalinated water 2.21 1.0 0.4 41.5 35.0 Tube side Seawater 3.34 2.7 0.3 30.5 35.1 Figure 1. External appearances of clogging in one heat exchanger: (a) by seashell, (b) by sediment, (c) by rubber debris www.matcorr.com
2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim