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2D PIV study of flow accelerated corrosion downstream a typical industrial gate valve
Progress in Nuclear Energy 121 (2020) 103260
Contents lists available at ScienceDirect
Progress in Nuclear Energy journal homepage: http://www.elsevier.com/locate/pnucene
2D PIV study of flow accelerated corrosion downstream a typical industrial gate valve Abbas Sedghkerdar a, Ali Erfaninia a, b, *, Mohammadreza Nematollahi a, b a b
Shiraz University, School of Mechanical Engineering, Nuclear Engineering Department, Shiraz, Iran Shiraz University, Nuclear Safety Research Center, Nuclear Engineering Department, Shiraz, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Gate valve 2D PIV FAC Wall thinning UT
A critical degradation mechanism of piping systems in either nuclear power plant is Flow Accelerated Corrosion (FAC), which causes wall thinning of pipes and component shells from inside. The valves which are frequently used in power plant piping systems are mostly subjected to FAC. A Gate vale in the feed water piping system of a typical nuclear power plant that it’s downstream had been damaged due to the FAC was considered as a reference. In this study the effect of the mean flow velocity and the opening percentage of gate valve on the flow field downstream the valve was investigated by using 2D PIV. The locus where flow turbulences happen downstream the gate valve was determined by 2D PIV. It is found that there is a very good coincidence between the locus in which the maximum wall thinning measured by Ultrasonic Technique (UT) and that the flow tur bulences happen downstream the gate valve determined by 2D PIV. It is observed that the locus of flow turbulences and intense velocity gradients is in the upper part of the pipe and over the domain of 0.2
1. Introduction Destroying the piping inside protective layer that is caused by fluid flow is called Flow Accelerated Corrosion (FAC). The local turbulence of flow field lead to occurrence of FAC over a limited area in piping system. FAC take place in three phases, first a series of electrochemical reactions take place at the metal–oxide interface, and second, the iron production (Fe2þ) dissolves at the oxide/water interface, finally, the motion of the fluid takes the corrosion species to the bulk flow across the diffusion boundary layer. The transportation of corrosion species into the bulk flow is defined by mass transfer phenomenon. The geometrical config uration of the piping component, fluid flow, fluid temperature and piping composition affect the FAC via their influences on the mass transfer coefficient (Chen et al., 2006; Ahmed, 2010; Muhammadu et al., 2013). Fluid flow as an important factor to FAC occurrence also can affect the corrosion cracking of the piping in nuclear system (Zhang et al., 2019). A lot of intricate failures caused by FAC have been reported at several nuclear power plants around the world Since 1980s (Kanster
et al., 1990; Ahmed, 2010). At Surry Unit 2 power plant in 1986 severe elbow rupture happened in the downstream of T-bend and caused 4 fatalities. At Millstone 3 in 1990 failure occurred in the downstream of control valves, caused the failure of two parallel trains but no injuries. At Louviisa-1 in 1990 failure occurred in the downstream of feeder water systems, without injuries. At Prairie Power Plant in 1995, FAC failure occurred at the downstream of T-bend caused the two fatalities. At Fort Colhoun in 1997 failure occurred at the bend, but no injuries. At Mihama 3 in 2004 failure occurred in the downstream of orifice, caused five fatalities and several injuries. Very recently, at Iatan fossil power plant in 2007 failure occurred at the downstream of the control valve, caused the two fatalities and a huge capital of plant loss (Ahmed et al., 2012). One of the most susceptible areas to FAC is downstream of the valves. The valves in different types are frequently used in power plant piping systems. In this study the effect of the mean flow velocity and the opening percentage of gate valve on the flow field downstream the valve was investigated by using 2D PIV. The gate valve belongs to the feed
* Corresponding author. Shiraz University, School of Mechanical Engineering, Nuclear Engineering Department, Shiraz, Iran. E-mail address: [email protected] (A. Erfaninia). https://doi.org/10.1016/j.pnucene.2020.103260 Received 31 July 2019; Received in revised form 20 December 2019; Accepted 16 January 2020 Available online 23 January 2020 0149-1970/© 2020 Elsevier Ltd. All rights reserved.
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water piping system of a typical nuclear power plant. By developing an experimental test loop and utilizing PIV technique, the flow field downstream the gate valve is visualized and velocity profiles are calculated and the critical zones with high potential of FAC is determined. The results of this paper can be useful for optimizing inspection plans in identifying and predicting the vulnerable FAC locations downstream the gate valves.
Table 1 The characteristic of the reference parallel side gate valve. value Outside Diameter (mm) Wall Thickness (mm) Body Material Disk Material Working Pressure (MPa) Working Temperature (oC)
108 8 Carbon Steel Stainless Steel 5 160
2. Material and methods 2.1. The damaged gate vale due to FAC The valve is paid attention in this study is a parallel side gate valve that is used in the feed water piping system of a typical VVER-1000 nuclear power plant. The characteristic of the gate valve is listed in Table 1. The schematic of the gate valve is shown in Fig. 1. Utilizing Ultrasonic Technique (UT), thickness measurement of the pipe wall downstream the gate valve was performed. The UT inspection data were obtained at grid intersection points marked on the pipe wall downstream the valve. Grid inspection points are illustrated in Fig. 2. The results of wall thickness measurement are shown in Figs. 3 and 4 via contours. It is shown that there is a remarkable thickness reduction in the range of ‘a’-‘e’ in the 1, 11 and 12 clock on the pipe wall downstream the gate valve. It is found that the thinned area due to FAC is located in the upper wall of the pipe in the range of 0.2D-2.4D downstream the gate valve, where D is the internal diameter of the pipe. 2.2. The experimental test loop In order to visualize the flow field downstream a gate valve, a test loop was developed and transparent test section was utilized to do Particle Image Velocimetry (PIV). The schematic of test loop is shown in Fig. 5. Water with temperature of 20 � C is used as a working fluid. The water is pumped from a mixing tank into the main pipe via an electro pump, which is equipped with an inverter to control and adjust the pump frequency and the mass flow rate. The mean velocity of the flow in the pipe is measured by an ultrasonic flow meter. A rectangular acrylic transparent box with dimensions of 200mm � 260mm � 800mm was considered as a jacket that surrounds the test section (gate valve and its downstream pipe). In order to match the refractive index and reduce image distortion resulting from the geometry of the circular pipe, the
Fig. 1. The characteristic of the gate valve.
Fig. 2. Grid inspection points for wall thickness measurement. 2
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Fig. 3. The results of wall thickness measurement using UT.
Fig. 4. The results of wall thickness measurement using UT.
Fig. 5. The schematic of test loop.
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clear box filled with the sodium iodide (NaI) solution. By changing the concentration of NaI solution the laser light path deviation which resulting from the transmission of laser light beam through the acrylic transparent box surrounding a 47 mm-diameter pipe was eliminated and so the optimum NaI solution concentration was determined as 62 wt%. By changing the NaI solution concentration, its refractive index was adjusted as 1.49 that of acrylic transparent box and pipe. A 2D PIV measurement was carried out in this study. A Nd:Yag double pulse laser which has the maximum output of 200W and maximum pulse energy of 200 mJ and visible wavelength of 532 nm was used. The laser generates a pair of laser pulses at a repetition rate of 10 Hz and pulse delay of 5 μs. A CCD camera with resolution of 2048 � 2048 pixels was used. The frame rate of the camera was set at 30. The DaVis 7.2 PIV software was used to calculate flow velocity vectors from obtained images. Glass hollow sphere 110P8 particles with an average diameter of 8 12μm were used as tracers. The density of the tracer particles is in the range of gr 1:05 1:15 cm 3 and their refractive index is 1.5. The configuration of the laser, the CCD camera and the test section is shown in Fig. 6. Laser beam converted into a laser sheet to illuminate the center cross section of the test section. The CCD camera is adjusted perpendicular to the laser sheet. As shown in Fig. 6, the camera was mounted on a tripod equipped with 2-axis sprit level and balanced on a horizontal plane. The camera is also adjusted perpendicular to the laser sheet and clear box face care fully. In Fig. 6, it is the double pulsed laser was installed in a direction looking down from the top with a certain angle due to the test loop configuration. It didn’t make any problem to generate laser sheet along the flow field. The characteristics of experimental test section are listed in Table 2. The length of the pipe upstream the gate valve is more than 26 times of inner diameter and is long enough to establish the fully developed turbulent flow regime at the entrance of the gate valve. By establishing different flow velocities in the pipe and adjusting different opening percentage of the valve the flow field downstream the gate valve is visualized and the mean velocity contours are extracted.
Fig. 6. The (PIV) configuration of the laser, the CCD camera and the test section.
Table 2 The characteristics of experimental test section. value Outside Diameter (mm) Wall Thickness (mm) Inside Diameter (mm) Body Material Disk Material Working Pressure (MPa) Working Temperature (oC) Inlet Mean Velocity (m/s) Opening Percentage of the Gate Valve (%)
53 3 47 PVC PVC 0.1 20 1.3–2.1 25-50-75-100
3. Results and discussion Generally, the oxide layer is formed on the inner surface of pipelines due to the reaction of iron with water. The diffusion of dissolved iron species across the boundary layer of water adjacent to the surface in to the bulk water controls the FAC rate. The mass transport of iron away from the inner surface of a pipe depends directly on the concentration of soluble iron species at the oxide surface and inversely on the boundary layer thickness. An increase in water flow rate or local turbulence result in the boundary layer thickness reduction, which in turn causes an in crease of the FAC rate (Ho Moon et al., 2005; Shoji et al., 2006; IAEA, 2006; Kain et al., 2008; Erfaninia and Nematollahi, 2016). In this study, the flow field downstream the gate valve is visualized by using 2D PIV. The scaling of the pipe downstream the gate valve is shown in Figs. 6 and 7. The velocity contours for different pipe inlet mean velocities and 25% opening of the gate valve are illustrated in Fig. 8. The field of view is confined in the domains of 40mm < x<þ80 mm and 57mm < y < 10mm. The velocity profile across the pipe downstream the gate valve at x ¼ 40, 20, 0, þ20, þ40 and þ 60 mm according to the pipe scaling (Fig. 7), are depicted in Fig. 9 for inlet velocities as 1.3, 1.7, 1.9 and 2.1 m/s and 25% opening of the gate valve. It is found from Fig. 9 that by increasing the inlet velocity the ve locity gradients near the upper wall and in turn the wall shear stress increases downstream the gate valve. After x ¼ þ50 mm (i,e., x ¼ 2.34D) the velocity profile softens and the velocity gradients near the upper wall decreases obviously. The velocity contours for pipe inlet mean velocity as 2.1 m/s and 25%, 50%, 75% and 100% opening of the gate valve are illustrated in Fig. 10. Opening as 25% of gate valve has the highest effect on the eddies
Fig. 7. The scaling of the pipe downstream the gate valve.
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Fig. 8. The velocity contours for different pipe inlet mean velocities and 25% opening of the gate valve.
Fig. 9. The velocity profile for different pipe inlet mean velocities and 25% opening of the gate valve in different cross section of the pipe along downstream the gate valve.
formation and turbulences of the flow downstream the valve. By increasing the opening percentage of the valve, the formation of eddies and the velocity gradient near the upper wall decreases. The velocity profile across the pipe downstream the gate valve at x ¼ 0 mm according to the pipe scaling (Fig. 7), are illustrated in Fig. 11 for inlet velocities as 1.3, 1.7, 1.9 and 2.1 m/s and 25%, 50%, 75% and 100% opening of the gate valve. It is understood from the pictures that the opening percentage as 25% has the strongest effect on the turbu lences and velocity gradient downstream the gate valve. The opening percentage as 50% and 75% have almost similar effects on the turbu lences and velocity gradient downstream the gate valve. The opening percentage as 100% has the minimal effect on the turbulences and ve locity gradient downstream the gate valve. Finally, it is understood that the inlet mean velocity and the opening
percentage of the gate valve have remarkable effects on the velocity gradients and wall shear stress downstream the gate valve which in turn causes FAC and wall thinning of the pipe. It is seen that there is a very good verification on determining the locus where the FAC has high potential to occur by using 2D PIV and the thickness measurement by UT downstream a typical gate valve. As a primary step toward the FAC study, in this paper just the effects of inlet mean flow velocities and the gate valve open percentages on the flow field downstream the valve were investigated experimentally via 2D PIV. Visualizing the flow field and velocity gradients in order to demonstrate the most probable locus of pipe wall thinning which in turn is confirmed by UT thickness measurement, is a significant evidence on the FAC occurrence down steam the gate valve. In order to provide more evidence to support the finding of this study, computational fluid
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Fig. 10. The velocity contours for pipe inlet mean velocity of 2.1 m/s and 25%, 50%, 75% and 100% opening of the gate valve.
Fig. 11. The velocity profile for inlet velocities as 1.3, 1.7, 1.9 and 2.1 m/s and 25%,50%, 75% and 100% opening of the gate valve.
dynamic simulation and mass transfer coefficient (MTC) calculation along the pipe wall down steam the gate valve is suggested and will be considered in next papers.
deviation for both vertical and horizontal components of velocity were calculated. For inlet velocity 2.1 m/s and 25%, 50%, 75% and 100% opening percentage of the gate valve, Figs. 12–15 depict the calculated mean velocity and standard deviation over 200 recorded images, respectively.
3.1. Uncertainty evaluation
4. Conclusion
Different stages of PIV measurement such as test loop apparatus, image acquisition process and data processing method can enter errors in the PIV measurement. By using the proper PIV system set up and calibrations according to the PIV instruction, the systematic error is minimized. In order to calculate the uncertainty evaluation, the velocity fluctuation at a particular location over a specified period of time was calculated for every single image. Over 200 recorded images standard
In this study by developing a test facility and using 2D PIV, the flow filed downstream a typical experimental gate valve is visualized. The effects of inlet flow velocity and the gate valve opening percentage in determining the FAC occurrence locus on the pipe wall downstream the gate valve was studied. Thickness measurement of the pipe wall 6
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Progress in Nuclear Energy 121 (2020) 103260
Fig. 12. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 25% opening of the gate valve.
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Fig. 13. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 50% opening of the gate valve.
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Fig. 14. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 75% opening of the gate valve.
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Fig. 15. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 100% opening of the gate valve.
downstream an industrial gate valve was performed by utilizing Ultra sonic Technique (UT). The valve is a parallel side gate valve that is used in the feed water piping system of a typical VVER-1000 nuclear power plant. The characteristic of the gate valve is listed in Table 1. The results of this study are as follows:
valve. By increasing the opening percentage of the valve, the for mation of eddies and the velocity gradient near the upper wall decreases. � The gate valve opening percentage as 50% and 75% have almost similar effects on the turbulences and velocity gradient downstream the gate valve. The opening percentage as 100% has the minimal effect on the turbulences and velocity gradient downstream the gate valve. � It was seen that there is a very good verification on determining the locus where the FAC has high potential to occur by using 2D PIV and the thickness measurement by UT downstream a typical gate valve.
� It is understood that the inlet mean velocity and the opening per centage of the gate valve have remarkable effects on the velocity gradients and wall shear stress downstream the gate valve which in turn causes FAC and wall thinning of the pipe. � Thickness measurement by using UT showed that there is a remarkable thickness reduction in the 1, 11 and 12 clock on the pipe wall downstream the gate valve. The thinned area due to FAC is located in the upper wall of the pipe in the range of 0.2D-2.4D downstream the gate valve, where D is the internal diameter of the pipe. � It is found from the PIV that by increasing the inlet velocity, the velocity gradients near the upper wall and in turn the wall shear stress increases downstream the gate valve. After x ¼ 2.34D, the velocity profile softens and the velocity gradients near the upper wall decreases obviously. � The gate valve opening percentage as 25% has the highest effect on the eddies formation and turbulences of the flow downstream the
The results of this study can be used to encourage design, safe op erations and increase the reliability and the safety of the piping systems in nuclear and non-nuclear power plants. CRediT authorship contribution statement Abbas Sedghkerdar: Investigation, Data curation. Ali Erfaninia: Conceptualization, Methodology, Software, Investigation, Data cura tion, Writing - original draft. Mohammadreza Nematollahi: Investi gation, Data curation.
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Acknowledgement
Erfaninia, A., Nematollahi, M.R., 2016. Numerical study of mass transfer coefficient in a T-junction. Int. J. Hydrogen Energy 41, 7027–7037. Ho Moon, J., Ho Chung, H., Sung, Ki W., Kim, Uh Ch, Pho, Jae S., 2005. Dependency of single phase FAC of carbon steel and low alloy steels for NPP system piping on pH, orifice distance and material. Nucl. Eng. Technol. 37, 375–384. International Atomic Energy Agency, 2006. Material degradation and related managerial issues at nuclear power plants. In: Proceedings of Technical Meeting Held during February 15–18. 2005 at Vienna by International Atomic Energy Agency. Kain, V., Roychowdhury, S., Mathew, T., Bhandakkar, A., 2008. Flow accelerated corrosion and control strategies in the secondary circuit pipelines in Indian nuclear power plants. J. Nucl. Mater. 383, 86–91. Kanster, W., Erve, M., Henzel, N., Stellwag, B., 1990. Calculation code for erosion corrosion induced wall thinning in piping system. Nucl. Eng. Des. 119, 431–438. Muhammadu, M.M., Sheriff, J., Hamzah, E., 2013. A review of literature for flow accelerated corrosion of mitred bends. Int. J. Emerg. Technol.Adv. Eng. 3, 668–677. Shoji, T., Lu, Z., Takeda, Y., Sato, Y., 2006. Towards proactive materials degradation management in NPP – today and future. In: CD Proceedings of the 14th Asia Pacific Corrosion Control Conference (APCCC), October 21–24. Zhang, J., Yu, H., Wang, M.J., Wu, Y.W., Tian, W.X., Qiu, S.Z., Su, G.H., 2019. Experimental study on the flow and thermal characteristics of two-phase leakage through micro crack. Appl. Therm. Eng. 156, 145–155.
There are special thanks to all individuals who helped the authors to do this study. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.pnucene.2020.103260. References Ahmed, W.H., 2010. Evaluation of the proximity effect on fiow accelerated corrosion. Ann. Nucl. Energy 37, 598–605. Ahmed, W.H., Bello, M.M., Al-Sarkhi, A., El Nakla, M., 2012. Flow and mass transfer downstream of an orifice under flow accelerated corrosion conditions. Nucl. Eng. Des. 252, 52–67. Chen, X., McLaury, B.S., Shirazi, S.A., 2006. A comprehensive procedure to estimate erosion in elbows for gas/liquid/sand multiphase flow. J. Energy Resour. Technol. 128, 70–78.
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Contents lists available at ScienceDirect
Progress in Nuclear Energy journal homepage: http://www.elsevier.com/locate/pnucene
2D PIV study of flow accelerated corrosion downstream a typical industrial gate valve Abbas Sedghkerdar a, Ali Erfaninia a, b, *, Mohammadreza Nematollahi a, b a b
Shiraz University, School of Mechanical Engineering, Nuclear Engineering Department, Shiraz, Iran Shiraz University, Nuclear Safety Research Center, Nuclear Engineering Department, Shiraz, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Gate valve 2D PIV FAC Wall thinning UT
A critical degradation mechanism of piping systems in either nuclear power plant is Flow Accelerated Corrosion (FAC), which causes wall thinning of pipes and component shells from inside. The valves which are frequently used in power plant piping systems are mostly subjected to FAC. A Gate vale in the feed water piping system of a typical nuclear power plant that it’s downstream had been damaged due to the FAC was considered as a reference. In this study the effect of the mean flow velocity and the opening percentage of gate valve on the flow field downstream the valve was investigated by using 2D PIV. The locus where flow turbulences happen downstream the gate valve was determined by 2D PIV. It is found that there is a very good coincidence between the locus in which the maximum wall thinning measured by Ultrasonic Technique (UT) and that the flow tur bulences happen downstream the gate valve determined by 2D PIV. It is observed that the locus of flow turbulences and intense velocity gradients is in the upper part of the pipe and over the domain of 0.2
1. Introduction Destroying the piping inside protective layer that is caused by fluid flow is called Flow Accelerated Corrosion (FAC). The local turbulence of flow field lead to occurrence of FAC over a limited area in piping system. FAC take place in three phases, first a series of electrochemical reactions take place at the metal–oxide interface, and second, the iron production (Fe2þ) dissolves at the oxide/water interface, finally, the motion of the fluid takes the corrosion species to the bulk flow across the diffusion boundary layer. The transportation of corrosion species into the bulk flow is defined by mass transfer phenomenon. The geometrical config uration of the piping component, fluid flow, fluid temperature and piping composition affect the FAC via their influences on the mass transfer coefficient (Chen et al., 2006; Ahmed, 2010; Muhammadu et al., 2013). Fluid flow as an important factor to FAC occurrence also can affect the corrosion cracking of the piping in nuclear system (Zhang et al., 2019). A lot of intricate failures caused by FAC have been reported at several nuclear power plants around the world Since 1980s (Kanster
et al., 1990; Ahmed, 2010). At Surry Unit 2 power plant in 1986 severe elbow rupture happened in the downstream of T-bend and caused 4 fatalities. At Millstone 3 in 1990 failure occurred in the downstream of control valves, caused the failure of two parallel trains but no injuries. At Louviisa-1 in 1990 failure occurred in the downstream of feeder water systems, without injuries. At Prairie Power Plant in 1995, FAC failure occurred at the downstream of T-bend caused the two fatalities. At Fort Colhoun in 1997 failure occurred at the bend, but no injuries. At Mihama 3 in 2004 failure occurred in the downstream of orifice, caused five fatalities and several injuries. Very recently, at Iatan fossil power plant in 2007 failure occurred at the downstream of the control valve, caused the two fatalities and a huge capital of plant loss (Ahmed et al., 2012). One of the most susceptible areas to FAC is downstream of the valves. The valves in different types are frequently used in power plant piping systems. In this study the effect of the mean flow velocity and the opening percentage of gate valve on the flow field downstream the valve was investigated by using 2D PIV. The gate valve belongs to the feed
* Corresponding author. Shiraz University, School of Mechanical Engineering, Nuclear Engineering Department, Shiraz, Iran. E-mail address: [email protected] (A. Erfaninia). https://doi.org/10.1016/j.pnucene.2020.103260 Received 31 July 2019; Received in revised form 20 December 2019; Accepted 16 January 2020 Available online 23 January 2020 0149-1970/© 2020 Elsevier Ltd. All rights reserved.
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water piping system of a typical nuclear power plant. By developing an experimental test loop and utilizing PIV technique, the flow field downstream the gate valve is visualized and velocity profiles are calculated and the critical zones with high potential of FAC is determined. The results of this paper can be useful for optimizing inspection plans in identifying and predicting the vulnerable FAC locations downstream the gate valves.
Table 1 The characteristic of the reference parallel side gate valve. value Outside Diameter (mm) Wall Thickness (mm) Body Material Disk Material Working Pressure (MPa) Working Temperature (oC)
108 8 Carbon Steel Stainless Steel 5 160
2. Material and methods 2.1. The damaged gate vale due to FAC The valve is paid attention in this study is a parallel side gate valve that is used in the feed water piping system of a typical VVER-1000 nuclear power plant. The characteristic of the gate valve is listed in Table 1. The schematic of the gate valve is shown in Fig. 1. Utilizing Ultrasonic Technique (UT), thickness measurement of the pipe wall downstream the gate valve was performed. The UT inspection data were obtained at grid intersection points marked on the pipe wall downstream the valve. Grid inspection points are illustrated in Fig. 2. The results of wall thickness measurement are shown in Figs. 3 and 4 via contours. It is shown that there is a remarkable thickness reduction in the range of ‘a’-‘e’ in the 1, 11 and 12 clock on the pipe wall downstream the gate valve. It is found that the thinned area due to FAC is located in the upper wall of the pipe in the range of 0.2D-2.4D downstream the gate valve, where D is the internal diameter of the pipe. 2.2. The experimental test loop In order to visualize the flow field downstream a gate valve, a test loop was developed and transparent test section was utilized to do Particle Image Velocimetry (PIV). The schematic of test loop is shown in Fig. 5. Water with temperature of 20 � C is used as a working fluid. The water is pumped from a mixing tank into the main pipe via an electro pump, which is equipped with an inverter to control and adjust the pump frequency and the mass flow rate. The mean velocity of the flow in the pipe is measured by an ultrasonic flow meter. A rectangular acrylic transparent box with dimensions of 200mm � 260mm � 800mm was considered as a jacket that surrounds the test section (gate valve and its downstream pipe). In order to match the refractive index and reduce image distortion resulting from the geometry of the circular pipe, the
Fig. 1. The characteristic of the gate valve.
Fig. 2. Grid inspection points for wall thickness measurement. 2
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Fig. 3. The results of wall thickness measurement using UT.
Fig. 4. The results of wall thickness measurement using UT.
Fig. 5. The schematic of test loop.
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clear box filled with the sodium iodide (NaI) solution. By changing the concentration of NaI solution the laser light path deviation which resulting from the transmission of laser light beam through the acrylic transparent box surrounding a 47 mm-diameter pipe was eliminated and so the optimum NaI solution concentration was determined as 62 wt%. By changing the NaI solution concentration, its refractive index was adjusted as 1.49 that of acrylic transparent box and pipe. A 2D PIV measurement was carried out in this study. A Nd:Yag double pulse laser which has the maximum output of 200W and maximum pulse energy of 200 mJ and visible wavelength of 532 nm was used. The laser generates a pair of laser pulses at a repetition rate of 10 Hz and pulse delay of 5 μs. A CCD camera with resolution of 2048 � 2048 pixels was used. The frame rate of the camera was set at 30. The DaVis 7.2 PIV software was used to calculate flow velocity vectors from obtained images. Glass hollow sphere 110P8 particles with an average diameter of 8 12μm were used as tracers. The density of the tracer particles is in the range of gr 1:05 1:15 cm 3 and their refractive index is 1.5. The configuration of the laser, the CCD camera and the test section is shown in Fig. 6. Laser beam converted into a laser sheet to illuminate the center cross section of the test section. The CCD camera is adjusted perpendicular to the laser sheet. As shown in Fig. 6, the camera was mounted on a tripod equipped with 2-axis sprit level and balanced on a horizontal plane. The camera is also adjusted perpendicular to the laser sheet and clear box face care fully. In Fig. 6, it is the double pulsed laser was installed in a direction looking down from the top with a certain angle due to the test loop configuration. It didn’t make any problem to generate laser sheet along the flow field. The characteristics of experimental test section are listed in Table 2. The length of the pipe upstream the gate valve is more than 26 times of inner diameter and is long enough to establish the fully developed turbulent flow regime at the entrance of the gate valve. By establishing different flow velocities in the pipe and adjusting different opening percentage of the valve the flow field downstream the gate valve is visualized and the mean velocity contours are extracted.
Fig. 6. The (PIV) configuration of the laser, the CCD camera and the test section.
Table 2 The characteristics of experimental test section. value Outside Diameter (mm) Wall Thickness (mm) Inside Diameter (mm) Body Material Disk Material Working Pressure (MPa) Working Temperature (oC) Inlet Mean Velocity (m/s) Opening Percentage of the Gate Valve (%)
53 3 47 PVC PVC 0.1 20 1.3–2.1 25-50-75-100
3. Results and discussion Generally, the oxide layer is formed on the inner surface of pipelines due to the reaction of iron with water. The diffusion of dissolved iron species across the boundary layer of water adjacent to the surface in to the bulk water controls the FAC rate. The mass transport of iron away from the inner surface of a pipe depends directly on the concentration of soluble iron species at the oxide surface and inversely on the boundary layer thickness. An increase in water flow rate or local turbulence result in the boundary layer thickness reduction, which in turn causes an in crease of the FAC rate (Ho Moon et al., 2005; Shoji et al., 2006; IAEA, 2006; Kain et al., 2008; Erfaninia and Nematollahi, 2016). In this study, the flow field downstream the gate valve is visualized by using 2D PIV. The scaling of the pipe downstream the gate valve is shown in Figs. 6 and 7. The velocity contours for different pipe inlet mean velocities and 25% opening of the gate valve are illustrated in Fig. 8. The field of view is confined in the domains of 40mm < x<þ80 mm and 57mm < y < 10mm. The velocity profile across the pipe downstream the gate valve at x ¼ 40, 20, 0, þ20, þ40 and þ 60 mm according to the pipe scaling (Fig. 7), are depicted in Fig. 9 for inlet velocities as 1.3, 1.7, 1.9 and 2.1 m/s and 25% opening of the gate valve. It is found from Fig. 9 that by increasing the inlet velocity the ve locity gradients near the upper wall and in turn the wall shear stress increases downstream the gate valve. After x ¼ þ50 mm (i,e., x ¼ 2.34D) the velocity profile softens and the velocity gradients near the upper wall decreases obviously. The velocity contours for pipe inlet mean velocity as 2.1 m/s and 25%, 50%, 75% and 100% opening of the gate valve are illustrated in Fig. 10. Opening as 25% of gate valve has the highest effect on the eddies
Fig. 7. The scaling of the pipe downstream the gate valve.
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Fig. 8. The velocity contours for different pipe inlet mean velocities and 25% opening of the gate valve.
Fig. 9. The velocity profile for different pipe inlet mean velocities and 25% opening of the gate valve in different cross section of the pipe along downstream the gate valve.
formation and turbulences of the flow downstream the valve. By increasing the opening percentage of the valve, the formation of eddies and the velocity gradient near the upper wall decreases. The velocity profile across the pipe downstream the gate valve at x ¼ 0 mm according to the pipe scaling (Fig. 7), are illustrated in Fig. 11 for inlet velocities as 1.3, 1.7, 1.9 and 2.1 m/s and 25%, 50%, 75% and 100% opening of the gate valve. It is understood from the pictures that the opening percentage as 25% has the strongest effect on the turbu lences and velocity gradient downstream the gate valve. The opening percentage as 50% and 75% have almost similar effects on the turbu lences and velocity gradient downstream the gate valve. The opening percentage as 100% has the minimal effect on the turbulences and ve locity gradient downstream the gate valve. Finally, it is understood that the inlet mean velocity and the opening
percentage of the gate valve have remarkable effects on the velocity gradients and wall shear stress downstream the gate valve which in turn causes FAC and wall thinning of the pipe. It is seen that there is a very good verification on determining the locus where the FAC has high potential to occur by using 2D PIV and the thickness measurement by UT downstream a typical gate valve. As a primary step toward the FAC study, in this paper just the effects of inlet mean flow velocities and the gate valve open percentages on the flow field downstream the valve were investigated experimentally via 2D PIV. Visualizing the flow field and velocity gradients in order to demonstrate the most probable locus of pipe wall thinning which in turn is confirmed by UT thickness measurement, is a significant evidence on the FAC occurrence down steam the gate valve. In order to provide more evidence to support the finding of this study, computational fluid
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Fig. 10. The velocity contours for pipe inlet mean velocity of 2.1 m/s and 25%, 50%, 75% and 100% opening of the gate valve.
Fig. 11. The velocity profile for inlet velocities as 1.3, 1.7, 1.9 and 2.1 m/s and 25%,50%, 75% and 100% opening of the gate valve.
dynamic simulation and mass transfer coefficient (MTC) calculation along the pipe wall down steam the gate valve is suggested and will be considered in next papers.
deviation for both vertical and horizontal components of velocity were calculated. For inlet velocity 2.1 m/s and 25%, 50%, 75% and 100% opening percentage of the gate valve, Figs. 12–15 depict the calculated mean velocity and standard deviation over 200 recorded images, respectively.
3.1. Uncertainty evaluation
4. Conclusion
Different stages of PIV measurement such as test loop apparatus, image acquisition process and data processing method can enter errors in the PIV measurement. By using the proper PIV system set up and calibrations according to the PIV instruction, the systematic error is minimized. In order to calculate the uncertainty evaluation, the velocity fluctuation at a particular location over a specified period of time was calculated for every single image. Over 200 recorded images standard
In this study by developing a test facility and using 2D PIV, the flow filed downstream a typical experimental gate valve is visualized. The effects of inlet flow velocity and the gate valve opening percentage in determining the FAC occurrence locus on the pipe wall downstream the gate valve was studied. Thickness measurement of the pipe wall 6
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Fig. 12. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 25% opening of the gate valve.
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Fig. 13. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 50% opening of the gate valve.
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Fig. 14. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 75% opening of the gate valve.
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Fig. 15. The calculated mean velocity and standard deviation over 200 recorded images for inlet velocity 2.1 m/s and 100% opening of the gate valve.
downstream an industrial gate valve was performed by utilizing Ultra sonic Technique (UT). The valve is a parallel side gate valve that is used in the feed water piping system of a typical VVER-1000 nuclear power plant. The characteristic of the gate valve is listed in Table 1. The results of this study are as follows:
valve. By increasing the opening percentage of the valve, the for mation of eddies and the velocity gradient near the upper wall decreases. � The gate valve opening percentage as 50% and 75% have almost similar effects on the turbulences and velocity gradient downstream the gate valve. The opening percentage as 100% has the minimal effect on the turbulences and velocity gradient downstream the gate valve. � It was seen that there is a very good verification on determining the locus where the FAC has high potential to occur by using 2D PIV and the thickness measurement by UT downstream a typical gate valve.
� It is understood that the inlet mean velocity and the opening per centage of the gate valve have remarkable effects on the velocity gradients and wall shear stress downstream the gate valve which in turn causes FAC and wall thinning of the pipe. � Thickness measurement by using UT showed that there is a remarkable thickness reduction in the 1, 11 and 12 clock on the pipe wall downstream the gate valve. The thinned area due to FAC is located in the upper wall of the pipe in the range of 0.2D-2.4D downstream the gate valve, where D is the internal diameter of the pipe. � It is found from the PIV that by increasing the inlet velocity, the velocity gradients near the upper wall and in turn the wall shear stress increases downstream the gate valve. After x ¼ 2.34D, the velocity profile softens and the velocity gradients near the upper wall decreases obviously. � The gate valve opening percentage as 25% has the highest effect on the eddies formation and turbulences of the flow downstream the
The results of this study can be used to encourage design, safe op erations and increase the reliability and the safety of the piping systems in nuclear and non-nuclear power plants. CRediT authorship contribution statement Abbas Sedghkerdar: Investigation, Data curation. Ali Erfaninia: Conceptualization, Methodology, Software, Investigation, Data cura tion, Writing - original draft. Mohammadreza Nematollahi: Investi gation, Data curation.
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Acknowledgement
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There are special thanks to all individuals who helped the authors to do this study. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.pnucene.2020.103260. References Ahmed, W.H., 2010. Evaluation of the proximity effect on fiow accelerated corrosion. Ann. Nucl. Energy 37, 598–605. Ahmed, W.H., Bello, M.M., Al-Sarkhi, A., El Nakla, M., 2012. Flow and mass transfer downstream of an orifice under flow accelerated corrosion conditions. Nucl. Eng. Des. 252, 52–67. Chen, X., McLaury, B.S., Shirazi, S.A., 2006. A comprehensive procedure to estimate erosion in elbows for gas/liquid/sand multiphase flow. J. Energy Resour. Technol. 128, 70–78.
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