The paper presents the results of cavitation erosion tests performed on

two types of samples. The materials of the samples are frequently used

for manufacturing and repairs of the hydro turbines components submitted

to cavitation. The first sample was made by welding of an austenitic

stainless steel on austenito-feritic base material. The second

sample was made similarly with the first but with a martensitic base

material. After the welding processes, on both samples was applied a

hardening treatment by surface peening. The cavitation erosion tests

were performed on vibratory equipment using the indirect method with

stationary specimen. The results show a good cavitation erosion resistance on both samples

Dorian Nedelcu

Marian-Dumitru Nedeloni

Relu Ciubotariu

Vasile Cojocaru

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  215    Marian Dumitru  Nedeloni,  Vasile  Cojocaru,  Relu  Ciubotariu,  Dorian Nedelcu Cavitation  Erosion  Tests  Performed  by  Indirect  Vi-bratory Method on Stainless Steel Welded Samples with Hardened Surface The paper presents the results of cavitation erosion tests performed on two types of samples. The materials of the samples are frequently used for manufacturing and repairs of the hydro turbines components sub mitted to cavitation. The first sample was made by welding of an aus tenitic  stainless  steel  on  austenito feritic  base  material.  The  second sample was made similarly with the first but with a martensitic base material. After the welding processes, on both samples was applied a hardening treatment by surface peening. The cavitation erosion tests were performed on vibratory equipment using the indirect method with stationary specimen. The results show a good cavitation erosion resis tance on both samples.   Keywords:  cavitation  erosion,  peening, vibratory method,  stationary specimen, stainless steel   1. Introduction  In order to study the cavitation erosion resistance of the welded overlays from the blades of the Kaplan hydroturbines submitted to cavitation, samples who simu late the in situ repairs were used [1,2]. The samples were made by welding of an austenitic stainless steel, with good cavitation resistance, on two types of base ma terials: an austenito feritic stainless steel, 1.4571 (X6CrNiMoTi17 12 2, EN 10088 2) and a martensitic stainless steel, 1.4313 (X3CrNiMo13 4, EN 10088 2). The total thickness of the welded overlays was 7 mm for the both samples (table 1). After the welding processes, on both samples was applied a hardening treatment by sur face peening. Table 2 shows the chemical composition of the base materials in ac cordance with test certificates provided by the manufacturer and table 3 shows the chemical composition of the filler material provided by the manufacturer [1,2]. ANALELE UNIVERSITĂłII   “EFTIMIE MURGU” RE IłA ANUL XIX, NR. 1, 2012, ISSN 1453 - 7397    216 Table 1.   Sample  Basic material  Filler material Deposited method Welded layers  thickness Sample 1  austenitic feritic stainless steel 1.4571 austenitic stainless steel welding  overlays 7 mm Sample 2  martensitic stainless steel 1.4313 austenitic stainless steel welding  overlays 7 mm  Table 2.   Chemical composition [%] of austenito feritic stainless steel 1.4571 C  Cr  Mn  Mo  N  Ni  P  S  Si  Ti 0,033  16,78  1,606  2,073  0,015  11,21  0,025  0,001  0,463  0,303 Chemical composition [%] of martensitic stainless steel 1.4313 C  Cr  Mn  Mo  N  Ni  P  S  Si  Ti 0,050  12,93  1,500  0,490  0,510  3,690  0,040  0,015  0,700  0,012  Table 3.   Chemical composition [%] of filler material C  Si  Mn  Cr  Ni  Mo  Co  S  P  Fe 0,246  2,24  10,15  16,24  0,5  0,39  12,37  0,003  0,015  bal  The mechanical properties of the base materials are presented in table 4. For the filler material the producers indicates only the hardness (aprox. 240HB).  Table 4.   The mechanical characteristics of stainless steel 1.4571 austenitic ferritic (X6CrNiMoTi17 12 2) and 1.4313 martensitic stainless steel (X3CrNiMo13 4) Rm  Rp 0.2  Rp 1.0  A50  A5  Hardness Material [N/mm2]  [N/mm2]  [N/mm2]  [%]  [%]   1.4571  559.67  310.71  344.38  53.85  52.85  90 HRB 1.4313  760  630        15  <285 HB 2. Vibratory cavitation method with stationary specimen Cavitation erosion test in the laboratory conditions can be made using three methods: vibratory method (or ultrasonic method), cavitating liquid jet method and Venturi cavitation method. The vibratory method is the most used due the simplic ity  of  the  testing  procedure  and  due  to  the  testing  time,  relatively  short.  This method uses a piezoelectric device or a magnetostrictive device to produce a high   217 frequency vibration. This vibration is transmitted by a booster (mechanical trans former of vibration) and a sonotrode to a test specimen immersed in liquid. The method is standardized by ASTM G 32 norm [3]. The equipment used for the cavitation tests in the Center for Research in Hy draulics, Automation and Thermal Processes of „Eftimie Murgu” University of Re iŃa is an ultrasonic equipment with piezoelectrical converter. The unit consists of the following  components  [4]:  a)  ultrasonic  generator  and  b)  cavitation  stand  with piezelectrical converter, booster, sonostrode and cooling bath. On the materials used in this reaserch were initially made cavitation erosion tests by the direct vibratory method [1,2]. On the direct method, the vibratory de vice  generates  oscillations  on  a  test  specimen  attached  at  the  sonotrode  (by  a thread) and submerged in liquid at a certain depth (figure 1).  Due to the high cavitation resistance of the materials used in the repairs of hidroturbines  components,  the  period  of  testing  for  these  types  of  materials  is large. The thread of sonotode and the thread of sample are submitted to fatigue. Due these aspects the lifetime of sonotrode, at the direct method of testing, is lim ited. In order to increase the lifetime of sonotrode and in order to simplify the samples (test specimens) manufacturing, the indirect vibratory method can be use.      Figure 1. The principle of the direct cavitation method [4]  Figure 2. The principle of the indirect cavitation method [5]  At the indirect method (or stationary specimen method) [figure 2], the speci men is fixed (not attached to the sonotrode) and fully immersed in the liquid. The sonotrode vibrate at a certain distance above the specimen (usually 0.5 0.7 mm) and is also partially immersed in liquid.    218 3. Results of the cavitation erosion research on sample 1  The cavitation erosion tests were performed using the vibratory method with stationary specimen. The frequency of oscillation was f=20 ± 0.5 kHz and the am plitude A=45  m. The water temperature was maintained at 25 ± 2 degrees using a cooling system with water from the Resita water supply system. The distance between the sample and the sonotrode was 0.7mm. Table 5 presents the tests results for the sample 1 (austenitic stainless steel welded on martensitic stainless steel) for 1320 minutes of cavitational attack.   Table 5. Results of cavitation erosion tests on sample 1 Eroded Mass   Total time Phase time  Specimen Mass  phase  cumulative Erosion rate/phase Cumulative erosion rate t   t  m   m   mc  vef  vec [min]  [min]  [mg]  [mg]  [mg]  [mg/min]  [mg/min] 0  0  15126.290  0.0000  0.0000  0.0000  0.0000 7  7  15126.240  0.0500  0.0500  0.0071  0.0071 22  15  15126.170  0.0700  0.1200  0.0047  0.0080 37  15  15126.130  0.0400  0.1600  0.0027  0.0107 52  15  15126.110  0.0200  0.1800  0.0013  0.0120 67  15  15126.090  0.0200  0.2000  0.0013  0.0133 82  15  15126.080  0.0100  0.2100  0.0007  0.0140 97  15  15126.070  0.0100  0.2200  0.0007  0.0147 112  15  15126.060  0.0100  0.2300  0.0007  0.0153 127  15  15126.050  0.0100  0.2400  0.0007  0.0160 142  15  15126.040  0.0100  0.2500  0.0007  0.0167 157  15  15126.030  0.0100  0.2600  0.0007  0.0173 172  15  15126.030  0.0000  0.2600  0.0000  0.0173 187  15  15126.020  0.0100  0.2700  0.0007  0.0180 202  15  15126.010  0.0100  0.2800  0.0007  0.0187 217  15  15126.000  0.0100  0.2900  0.0007  0.0193 232  15  15125.990  0.0100  0.3000  0.0007  0.0200 247  15  15125.980  0.0100  0.3100  0.0007  0.0207 277  30  15125.970  0.0100  0.3200  0.0003  0.0107 307  30  15125.950  0.0200  0.3400  0.0007  0.0113 337  30  15125.930  0.0200  0.3600  0.0007  0.0120 367  30  15125.910  0.0200  0.3800  0.0007  0.0127 397  30  15125.900  0.0100  0.3900  0.0003  0.0130 427  30  15125.890  0.0100  0.4000  0.0003  0.0133 457  30  15125.880  0.0100  0.4100  0.0003  0.0137   219 Table 5 (continued from previous page) 487  30  15125.870  0.0100  0.4200  0.0003  0.0140 517  30  15125.860  0.0100  0.4300  0.0003  0.0143 547  30  15125.850  0.0100  0.4400  0.0003  0.0147 577  30  15125.840  0.0100  0.4500  0.0003  0.0150 607  30  15125.830  0.0100  0.4600  0.0003  0.0153 652  45  15125.780  0.0500  0.5100  0.0011  0.0113 697  45  15125.740  0.0400  0.5500  0.0009  0.0122 742  45  15125.630  0.1100  0.6600  0.0024  0.0147 787  45  15125.600  0.0300  0.6900  0.0007  0.0153 832  45  15125.520  0.0800  0.7700  0.0018  0.0171 877  45  15125.470  0.0500  0.8200  0.0011  0.0182 922  45  15125.430  0.0400  0.8600  0.0009  0.0191 967  45  15125.320  0.1100  0.9700  0.0024  0.0216 1012  45  15125.210  0.1100  1.0800  0.0024  0.0240 1057  45  15125.160  0.0500  1.1300  0.0011  0.0251 1102  45  15125.100  0.0600  1.1900  0.0013  0.0264 1147  45  15125.050  0.0500  1.2400  0.0011  0.0276 1192  45  15124.960  0.0900  1.3300  0.0020  0.0296 1237  45  15124.850  0.1100  1.4400  0.0024  0.0320 1282  45  15124.790  0.0600  1.5000  0.0013  0.0333 1327  45  15124.740  0.0500  1.5500  0.0011  0.0344  Figure 3 shows the graph of cumulative eroded mass variation at sample 1.  0.000.200.400.600.801.001.201.401.601.800 200 400 600 800 1000 1200 1400t [min]∆mc [mg]  Figure 3. Cumulative eroded mass variation. Sample 1   220 The  graphs  of  erosion  rate  (phase  and  cumulative  time)  for  sample  1  are shown in figures 4 and 5. Figure 6 shows pictures of active surface of sample 1 after cavitation erosion tests. Figure 7 shows details of the active surface macro structures obtained with an optical microscope at a magnification scale of 50x.   0.0000.0010.0020.0030.0040.0050.0060.0070.0080 200 400 600 800 1000 1200 1400t [min]Vef [mg/min]  Figure 4. Variation of erosion rate/phase versus time. Sample 1             0.0000.0010.0020.0030.0040.0050.0060.0070.0080 200 400 600 800 1000 1200 1400t [min]Vec [mg/min]           Figure 5. Variation of cumulative erosion rate versus time. Sample 1   221      a) initial  b) 120 minutes  c) 240 minutes      d) 600 minutes  e) 780 minutes  f) 1320 minutes  Figure 6. Surface of sample 1, initial (a) and after cavitation erosion (b f)     a) 120 minutes  b) 360 minutes    c) 780 minutes  d) 1320 minutes  Figure 7. Macrostructure of eroded surface of sample 1   222 4. Results of the cavitation erosion research on sample 2 The sample 2 was tested at the same conditions with the sample 1. The total testing time was only 120 minutes. The results are presented in table 6. Figure 8 shows the graph of cumulative eroded mass variation.  Table 6. Results of cavitation erosion tests on sample 2 Eroded Mass   Total time Phase time  Specimen Mass  phase  cumulative Erosion rate/phase Cumulative erosion rate t   t  m   m   mc  vef  vec [min]  [min]  [mg]  [mg]  [mg]  [mg/min]  [mg/min] 0  0  15212.230  0.00000  0.00000  0.00000  0.00000 5  5  15212.170  0.06000  0.06000  0.01200  0.0120 15  10  15212.020  0.15000  0.21000  0.01500  0.0140 30  15  15211.860  0.16000  0.37000  0.01067  0.012333 45  15  15211.850  0.01000  0.38000  0.00067  0.008444 60  15  15211.830  0.02000  0.40000  0.00133  0.006667 75  15  15211.790  0.04000  0.44000  0.00267  0.005867 90  15  15211.770  0.02000  0.46000  0.00133  0.005111 105  15  15211.760  0.01000  0.47000  0.00067  0.004476 120  15  15211.730  0.03000  0.50000  0.00200  0.004167    0.000.100.200.300.400.500.600 20 40 60 80 100 120 140t [min]∆mc [mg]  Figure 8. Cumulative eroded mass variation. Sample 2    223 The  graphs  of  erosion  rate  (phase  and  cumulative  time)  for  sample  2  are shown in figures 9 and 10. Figure 11 shows pictures of active surface of sample 2 after cavitation erosion tests. Figure 12 shows details of the active surface macro structures obtained with an optical microscope at a magnification scale of 50x.   0.0000.0020.0040.0060.0080.0100.0120.0140.0160 20 40 60 80 100 120 140t [min]Vef [mg/min]  Figure 9. Variation of erosion rate/phase versus time. Sample 2  0.0000.0020.0040.0060.0080.0100.0120.0140.0160 20 40 60 80 100 120 140t [min]Vec [mg/min]  Figure 10. Variation of cumulative erosion rate versus time. Sample 2   224      a) initial  b) 60 minutes  c) 120 minutes  Figure 11. Surface of sample 2, initial (a) and after cavitation erosion (b,c)     a) initial  b) 60 minutes  c) 120 minutes  Figure 12. Macrostructure of eroded surface of sample 2   Comparing the two samples in terms of total mass eroded (Figure 13) can be seen that the total mass loss at 120 minutes is higher for sample 2 (austenitic stainless steel welded on a martensitic base material).  Analyzing the results related to the data of the literature [5], [7], [8], [9] the two types of samples tested have a high resistance at cavitation erosion.   225 00.10.20.30.40.50.60 20 40 60 80 100 120 140t [min]∆mc [mg]Sample 2Sample 1  Figure 13. Comparison of cumulative eroded mass variation 5. Conclusion  The cavitation erosion tests made by indirect vibratory method on two welded samples of austenitic stainless steel with a austenito feritic stainless steel base ma terial  (sample  1)  and  a  martensitic  stainless  steel  (sample  2)  base  materials stainless steel shows that these materials have a high resistance to cavitation ero sion.  The higher erosion resistance is obtained for the sample 1. After 1320 min utes of testing the total eroded mass is about 1.60 mg. The analyses of the surfaces submitted to cavitation don’t show significant transformations of the surface.  According to data from the literature [6] by the loss of material in the vibra tory devices using indirect set up (stationary specimen) is lower than at the direct set up (specimen fixed on sonotrode).  Acknowledgements The work has been funded by the Sectoral Operational Programme Human Resources  Development  2007 2013  of  the  Romanian  Ministry  of  Labour,  Family and  Social  Protection  through  the  Financial  Agreement  (ProDOC) POSDRU/88/1.5/S/61178 and POSDRU/88/1.5/S/50783.   226 References [1]  Cojocaru V., and al., Laboratory tests concerning the influence of sur face hardening on the cavitation erosion resistance, Proceedings of 3rd Wseas  International  Conference  On  Engineering  Mechanics,  Structures, Engineering  Geology  (Emeseg  '10),  Corfu,  2010 07 22,  pag.  210 213, ISSN 1792 4294, 2010; [2]  Frunzăverde D., and al., Influence of welded layers thickness on the cavitation  erosion  resistance,  Proceedings  of  6th  WSEAS  International Conference on Energy, Environment, Ecosystems and Sustainable Devel opment (EEESD '10), Timisoara, 21 23 oct. 2010, pp. 316 320, 2010; [3]  ASTM G32–10, Standard Test Method for Cavitation Erosion Using Vi bratory Apparatus; [4]  TELSONIC,  Operating  Instructions  Cavitations  Test  Equipment  DG 2000, www.telsonic.com; [5]  Chao, C., Hammitt, F. G., et al, ASTM Round Robin Test with Vibratory Cavitation and Liquid Impact Facilities of 6061 T6 Aluminum Alloy, 316 Stainless Steel, Commercially Pure Nickel, The University of Michigan Re port MMPP 344 3 T/01357 4 T, Nov. 1968. [6]  http://www.isaf.tu clausthal.de/en/departments/wear testing/cavitation test astm g32 09/ [7]  Hattori,  S.,  Ishikura  R.,  Revision  of  cavitation  erosion  database  and analysis of stainless steel data, Wear, vol. 268, 2010, pp. 109–116; [8]  Hattori, S., Maeda K., Logistic curve model of cavitation erosion pro gress in metallic materials, Wear, vol. 268, 2010, pp. 855–862; [9]  Ton That,  L., Experimental comparison  of  cavitation  erosion  rates of different steels used in hydraulic turbines”, 25th IAHR Symposium on Hy draulic  Machinery  and  Systems,  2010  published  in  Earth  and  Environ mental Science 12, doi:10.1088/1755 1315/12/1/012052; Addresses: ·  Eng. Marian Dumitru Nedeloni, PhD. stud., University “Eftimie Murgu” of Re iŃa, PiaŃa Traian Vuia, nr. 1 4, 320085, Re iŃa, m.nedeloni@uem.ro ·  Eng. Vasile Cojocaru, PhD. stud., University “Eftimie Murgu” of Re iŃa, PiaŃa Traian Vuia, nr. 1 4, 320085, Re iŃa, v.cojocaru@uem.ro ·  Eng. Relu Ciubotariu, PhD. stud., University “Politehnica” of Timi oara, Bv. Mihai Viteazu, nr. 1, nr. 1 4, 300222, Timi oara, ciubotariu.relu@yahoo.com ·  Prof. PhD. Eng. Dorian Nedelcu, University “Eftimie Murgu” of Re iŃa, PiaŃa Traian Vuia, nr. 1 4, 320085, Re iŃa, d.nedelcu@uem.ro 

Cavitation Erosion Tests Performed by Indirect Vibratory Method on Stainless Steel Welded Samples with Hardened Surface

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