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Failure analysis of propeller shaft used in the propulsion system of a fishing boat
Available online at www.sciencedirect.com
ScienceDirect www.materialstoday.com/proceedings
Materials Today: Proceedings 5 (2018) 9624–9629
The 10th Thailand International Metallurgy Conference (The 10th TIMETC)
Failure analysis of propeller shaft used in the propulsion system of a fishing boat Patchaporn Kettrakul, Piyorose Promdirek * 0F
Department of Materials and Production Technology Engineering, Faculty of Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Pracharat 1, Wongsawang, Bangsue, Bangkok, 10800, Thailand
Abstract This research aims to analyze root cause of the failure of propeller shaft used in the propulsion system of a fishing boat. The shaft was made of austenitic stainless steel type AISI-304 (18Cr-8Ni). The shaft was subjected to sulfur-containing atmosphere because of the biogas, especially hydrogen sulfide from fermentation of the sea fish. The severe fracture of shaft was found in service after two years. The failure analysis methodology such as fracture observation, mechanical and chemical composition testing, were basically investigated. The fracture observation showed apparently the low-stress fatigue fracture. It was found that the initial crack located on the shaft surface, showing possible pitting corrosion. In addition, some compound of sulfur such as iron sulfide was discovered in pitting hole due to the dissolution of H2S in brine. The electrochemical test was carried out by potentiodynamics with the mixture of H2SO4 and brine. The results showed apparently the effect of sulfur contamination on the corrosion behavior. The corrosion rate of sample submerged in 1% of H2SO4 is the highest. The corrosion mechanism and protection were further discussed in this research. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 10th Thailand International Metallurgy Conference. Keywords: Fracture; Fatigue; AISI304; Propeller; Shaft; Pitting; Sulfur; Sea
1. Introduction Due to high corrosion resistance, austenitic stainless steels are mostly used in the several engineering applications, especially in the component of the fishing boat. However, the failure of these components was often concerned with the pitting corrosion [1,2]. The objective of this research is to analyze the root cause of failure of a
* Corresponding author. Tel.: +6-688-688-3058; fax:+6-602-587-4335. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 10th Thailand International Metallurgy Conference.
Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
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propeller shaft in a fishing boat in the gulf of Thailand. The fracture of the propeller shaft in the fishing boat was intensively considered. The shaft was made of austenitic stainless steel type AISI304 (18Cr-8Ni-Fe) without any heat treatment. The diameter and length of the shaft is approximately 0.15 and 3 m respectively. The weight of the shaft is about 1500 kg. The function of this shaft is to transfer the diesel engine’s power to the propeller. The cooling mechanism of propeller shaft was designed by a little leakage of sea water. After 2 years of service, the fracture occurred at the middle of the shaft which was covered by wood bearing. The stinky sea water was also found in the gap between shaft and wood bearing. The propeller shaft was supported by 2 standard bearings, showing bending moment loading by its own weight. The distance between these bearing is about 1.6 m. The schematic diagram of propeller system is shown in Fig.1. Wood Seal
Fracture
Seal
Propeller Shaft
Engine
1.6 m
Bearing
Bearing Fig. 1. The schematic diagram of propeller system.
2. Research methodology After background data collection, the fracture shaft was then examined by macroscopic camera and stereo microscope for visual examination and fractography. The shaft was cut near the fracture surface in the dimension of 3 x 3 x 3 cm3 for microscopic examination and analyzing chemical composition by using emission spectrometer. Moreover, the fractured shaft were investigated by scanning electron microscope (SEM) and X-ray Diffraction (XRD) in order to confirm the causes for the failure of shaft. The fracture shaft was also cut in ASTM E8/E8M standard tensile shape for tensile testing. Finally, the samples of 1 x 1 x 0.5 cm3 were prepared for electrochemical testing by using potentiostat analyzer. The extra experiment was investigated in order to study the effect of Sulphur addition on the corrosion rate of AISI304 in brine solution (3%NaCl). 3. Results and discussion 3.1. Visual examination From the visual examination, uniform corrosion and pitting corrosion were found on the circumferential surface of the shaft as shown in Fig. 2. It was also found that the color of pitting was red-orange-brown like rust color. A lot of holes on the shaft surface were observed by macroscopic camera on the surface and in the cross section. The diameters of the small pitting on the surface were varied from 900 m to 5 mm. The small pitting on the surface was then observed by stereo microscope. The depth of small pitting on the shaft surface were measured. The deepest size is approximately 3.8 mm as shown in Fig.3. By calculation with the depth and service time, the corrosion rate was approximately 1.2 X 10-10 m/s or 1.9 mm/year.
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Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
Fig. 2. The observation of the circumferential surface of the fractured shaft after 2 years of service.
Fig. 3. The depth of small pitting in the cross section of fractured shaft after 2 years of service.
3.2 Fractography According to the load analysis and fractography as shown in Fig.4, It was found that the shaft was subjected to reverse bending fatigue. There were 2 possible zones appeared on the fracture surface, beach marks and final rupture. The beach marks showed the direction of the progression marks on a fatigue fracture. By observing the direction of crack growth by direction of beach mark, initial cracks were found on the circumference surface, showing many holes of the pitting. Furthermore, the small area of the final rupture was also revealed in the Fig.4.
Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
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Final rupture Beach marks
Fig. 4. The fractography of the shaft showed the beach mark and final rupture.
3.3. Chemical analysis Chemical composition of fracture shaft was analyzed by emission spectrometer. The results are shown in Table 1. Comparing to the standard materials of AISI304 [3], the chemical composition of the fracture shaft is available in the range of standard materials. Table 1. Chemical composition of fractured shaft and standard stainless steel type AISI304. %wt
C
Mn
P
S
Si
Cr
Ni
AISI 304 [fractured shaft]
0.05
1.16
0.03
0.02
0.39
18.09
8.67
AISI 304 [standard][3]
0.08 max.
2.00 max.
0.045 max.
0.03 max.
0.75 max.
18.00-20.00
8.00-12.00
3.4. Mechanical testing According to the tensile testing, the results are shown in Table 2. Compare with the standard mechanical properties, all mechanical properties of fracture shaft were lower than that of the standard materials. In order to analysis load and stress which occurred in the shaft. Maximum stress was calculated by analytical method. It was found that the maximum stress (8.882 MPa) occurred in the shaft was much lower than yield strength and ultimate stress of testing materials. It can be concluded that the fracture is not concerned with overload and plastic deformation. Table 2. Mechanical Properties of fractured shaft and standard stainless steel type AISI304. Stainless steel Yield Strength (MPa) Tensile Strength (MPa) Elongation (%) AISI 304 [fractured shaft] AISI 304 [standard] [3]
253
472.5
48.7
290
579.2
55
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Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
3.5. Microscopic examinations Microstructure was observed with an optical microscope. The austenite, ferrite and chromium carbide phase were observed similar to general austenitic stainless steels. There were no significantly difference of phase which may be concerned with the failure. The fractured specimen was further examined by scanning electron microscope (SEM) equipped with EDS. According to the results as shown in Fig.5. The Mn, and S-rich phase were found in the pitting surface (Fig.5 (a)) and in the cross section (Fig.5 (b)). The S-rich precipitate phases were also found in the cross section, being possible iron sulfide. However, Iron sulfide phases, Fe9S10, were confirmed by XRD. In addition, the oxide phase such as chromium oxide and iron oxide were also observed on the circumferential surface of fractured shaft. According to the chemical composition in the Table1, there was little quantity of sulfur in AISI304. It was very interesting that sulfur can possibly diffuse from the environment to the fractured shaft. Due to poor storage of sea fish, the fermentation of sea fish can lead to the production of biogas or fermented fluid with hydrogen sulfide contamination during 2 years of sea fishery. a
c
b
S
100 m
S
10 m
Fig. 5. SEM equipped EDS observation of fractured shaft; (a) surface of pitting; (b) cross section; (c) EDS results
The hydrogen sulfide in biogas can transform to sulfuric acid in brine solution by the reaction as follows: 2H2S+4O2 = 2H2SO4
(1)
Sulfuric acid in brine solution may accelerate the corrosion rate of AISI304, resulting in enormous pitting corrosion on the circumferential surface. 3.6. Electrochamical testing Electrochemical testing was carried out by potentiodynamic measurement in order to study the effect of sulfur addition in brine solution on the corrosion behavior. According to the extra experiment concerned with the several solutions, there were 5 conditions with different H2SO4 quantity in brine solution (0 – 2%H2SO4). The results as shown in Fig.6a, corrosion current density, Icorr, was increased until the condition of 1%H2SO4 and then decreased with increasing of H2SO4 addition. This result was concerned with the increasing of corrosion rate, showing the highest corrosion rate at 1%H2SO4. On the other hand, Electrochemical corrosion potential, Ecorr, is decreased compared with pure brine solution as shown in Fig.6b, there is no significantly effect of H2SO4 addition on the corrosion potential. This result showed thermodynamically possibility of stable reaction. According to the electrochemical results, there was the effect of sulfur in brine solution on the corrosion rate. Therefore, the sulfur from biogas or fermented fluid can dissolve to sea water and transform to the sulfuric acid, leading to the acceleration of pitting corrosion rate.
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Fig. 6. Electrochemical testing with different sulphur contaminations; (a) Current; (b) Potential.
4. Conclusion The propeller shaft used in the fishing boat for 2 years was subjected to reverse bending fatigue, showing low stress fatigue. Due to the use in the aggressively Cl-containing environment of sea water, pitting corrosion occurred on the shaft surface led to the initial crack of fatigue loading. In addition, Sulfur contamination in sea water, causing from fermentation of the sea fish which produced biogas or fermented fluid, can accelerate the corrosion rate of AISI304 in sea water. In order to protect this failure, the propulsion system should be clean and avoid the fermentation of fish in the boat. Furthermore, the shaft should be coated by materials which can construct a strong and continuous film to prevent pitting corrosion. The film should be high strength and stable and also not react with sulfur such as Al2O3, Cr2O3, and NiO. Acknowledgements The authors would like to thank King Mongkut’s University of Technology North Bangkok Department of Materials and Production Technology Engineering for laboratory support and Hummingbird Company for cooperation work and material support. References [1] N. H. N. Yusoff, M. C. Isa, M. M. Muhammad, H. Nain, M. S. D. Yati, S. R. S. Bakar, I. M. Noor, Defence S and T Technical Bulletin 5 (2012) 167-176. [2] R.W.Fullera,* , J.Q.Ehrgott Jr.b, W.F.Heardb, S.D. Robertb, R.D.Stinsonb, K.Solankic, M.F.Horstemeyer, Engineering Failure Analysis 15 (2008) 835-846. [3] http://www.aksteel.com/pdf/markets_products/stainless/austenitic/304_304l_data_sheet.pdf [4] William F. Hosford, Mechanical Behavior of Materials, 2nded., Cambridge University Press, Cambridge, UK, 2010. [5] R.T. Loto*, Materials and Environmental Science. 4(2013) 448-459. [6] William D. Callister, David G. Rethwisch, Materials Science and Engineering, 8thed., Utah, Wiley, 2011. [7] Enos, D. G., & Scribner, The Potentiodynamic Polarization Scan – Technical Report 33, Solatron Instruments, 1997.
ScienceDirect www.materialstoday.com/proceedings
Materials Today: Proceedings 5 (2018) 9624–9629
The 10th Thailand International Metallurgy Conference (The 10th TIMETC)
Failure analysis of propeller shaft used in the propulsion system of a fishing boat Patchaporn Kettrakul, Piyorose Promdirek * 0F
Department of Materials and Production Technology Engineering, Faculty of Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Pracharat 1, Wongsawang, Bangsue, Bangkok, 10800, Thailand
Abstract This research aims to analyze root cause of the failure of propeller shaft used in the propulsion system of a fishing boat. The shaft was made of austenitic stainless steel type AISI-304 (18Cr-8Ni). The shaft was subjected to sulfur-containing atmosphere because of the biogas, especially hydrogen sulfide from fermentation of the sea fish. The severe fracture of shaft was found in service after two years. The failure analysis methodology such as fracture observation, mechanical and chemical composition testing, were basically investigated. The fracture observation showed apparently the low-stress fatigue fracture. It was found that the initial crack located on the shaft surface, showing possible pitting corrosion. In addition, some compound of sulfur such as iron sulfide was discovered in pitting hole due to the dissolution of H2S in brine. The electrochemical test was carried out by potentiodynamics with the mixture of H2SO4 and brine. The results showed apparently the effect of sulfur contamination on the corrosion behavior. The corrosion rate of sample submerged in 1% of H2SO4 is the highest. The corrosion mechanism and protection were further discussed in this research. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 10th Thailand International Metallurgy Conference. Keywords: Fracture; Fatigue; AISI304; Propeller; Shaft; Pitting; Sulfur; Sea
1. Introduction Due to high corrosion resistance, austenitic stainless steels are mostly used in the several engineering applications, especially in the component of the fishing boat. However, the failure of these components was often concerned with the pitting corrosion [1,2]. The objective of this research is to analyze the root cause of failure of a
* Corresponding author. Tel.: +6-688-688-3058; fax:+6-602-587-4335. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 10th Thailand International Metallurgy Conference.
Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
9625
propeller shaft in a fishing boat in the gulf of Thailand. The fracture of the propeller shaft in the fishing boat was intensively considered. The shaft was made of austenitic stainless steel type AISI304 (18Cr-8Ni-Fe) without any heat treatment. The diameter and length of the shaft is approximately 0.15 and 3 m respectively. The weight of the shaft is about 1500 kg. The function of this shaft is to transfer the diesel engine’s power to the propeller. The cooling mechanism of propeller shaft was designed by a little leakage of sea water. After 2 years of service, the fracture occurred at the middle of the shaft which was covered by wood bearing. The stinky sea water was also found in the gap between shaft and wood bearing. The propeller shaft was supported by 2 standard bearings, showing bending moment loading by its own weight. The distance between these bearing is about 1.6 m. The schematic diagram of propeller system is shown in Fig.1. Wood Seal
Fracture
Seal
Propeller Shaft
Engine
1.6 m
Bearing
Bearing Fig. 1. The schematic diagram of propeller system.
2. Research methodology After background data collection, the fracture shaft was then examined by macroscopic camera and stereo microscope for visual examination and fractography. The shaft was cut near the fracture surface in the dimension of 3 x 3 x 3 cm3 for microscopic examination and analyzing chemical composition by using emission spectrometer. Moreover, the fractured shaft were investigated by scanning electron microscope (SEM) and X-ray Diffraction (XRD) in order to confirm the causes for the failure of shaft. The fracture shaft was also cut in ASTM E8/E8M standard tensile shape for tensile testing. Finally, the samples of 1 x 1 x 0.5 cm3 were prepared for electrochemical testing by using potentiostat analyzer. The extra experiment was investigated in order to study the effect of Sulphur addition on the corrosion rate of AISI304 in brine solution (3%NaCl). 3. Results and discussion 3.1. Visual examination From the visual examination, uniform corrosion and pitting corrosion were found on the circumferential surface of the shaft as shown in Fig. 2. It was also found that the color of pitting was red-orange-brown like rust color. A lot of holes on the shaft surface were observed by macroscopic camera on the surface and in the cross section. The diameters of the small pitting on the surface were varied from 900 m to 5 mm. The small pitting on the surface was then observed by stereo microscope. The depth of small pitting on the shaft surface were measured. The deepest size is approximately 3.8 mm as shown in Fig.3. By calculation with the depth and service time, the corrosion rate was approximately 1.2 X 10-10 m/s or 1.9 mm/year.
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Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
Fig. 2. The observation of the circumferential surface of the fractured shaft after 2 years of service.
Fig. 3. The depth of small pitting in the cross section of fractured shaft after 2 years of service.
3.2 Fractography According to the load analysis and fractography as shown in Fig.4, It was found that the shaft was subjected to reverse bending fatigue. There were 2 possible zones appeared on the fracture surface, beach marks and final rupture. The beach marks showed the direction of the progression marks on a fatigue fracture. By observing the direction of crack growth by direction of beach mark, initial cracks were found on the circumference surface, showing many holes of the pitting. Furthermore, the small area of the final rupture was also revealed in the Fig.4.
Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
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Final rupture Beach marks
Fig. 4. The fractography of the shaft showed the beach mark and final rupture.
3.3. Chemical analysis Chemical composition of fracture shaft was analyzed by emission spectrometer. The results are shown in Table 1. Comparing to the standard materials of AISI304 [3], the chemical composition of the fracture shaft is available in the range of standard materials. Table 1. Chemical composition of fractured shaft and standard stainless steel type AISI304. %wt
C
Mn
P
S
Si
Cr
Ni
AISI 304 [fractured shaft]
0.05
1.16
0.03
0.02
0.39
18.09
8.67
AISI 304 [standard][3]
0.08 max.
2.00 max.
0.045 max.
0.03 max.
0.75 max.
18.00-20.00
8.00-12.00
3.4. Mechanical testing According to the tensile testing, the results are shown in Table 2. Compare with the standard mechanical properties, all mechanical properties of fracture shaft were lower than that of the standard materials. In order to analysis load and stress which occurred in the shaft. Maximum stress was calculated by analytical method. It was found that the maximum stress (8.882 MPa) occurred in the shaft was much lower than yield strength and ultimate stress of testing materials. It can be concluded that the fracture is not concerned with overload and plastic deformation. Table 2. Mechanical Properties of fractured shaft and standard stainless steel type AISI304. Stainless steel Yield Strength (MPa) Tensile Strength (MPa) Elongation (%) AISI 304 [fractured shaft] AISI 304 [standard] [3]
253
472.5
48.7
290
579.2
55
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Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
3.5. Microscopic examinations Microstructure was observed with an optical microscope. The austenite, ferrite and chromium carbide phase were observed similar to general austenitic stainless steels. There were no significantly difference of phase which may be concerned with the failure. The fractured specimen was further examined by scanning electron microscope (SEM) equipped with EDS. According to the results as shown in Fig.5. The Mn, and S-rich phase were found in the pitting surface (Fig.5 (a)) and in the cross section (Fig.5 (b)). The S-rich precipitate phases were also found in the cross section, being possible iron sulfide. However, Iron sulfide phases, Fe9S10, were confirmed by XRD. In addition, the oxide phase such as chromium oxide and iron oxide were also observed on the circumferential surface of fractured shaft. According to the chemical composition in the Table1, there was little quantity of sulfur in AISI304. It was very interesting that sulfur can possibly diffuse from the environment to the fractured shaft. Due to poor storage of sea fish, the fermentation of sea fish can lead to the production of biogas or fermented fluid with hydrogen sulfide contamination during 2 years of sea fishery. a
c
b
S
100 m
S
10 m
Fig. 5. SEM equipped EDS observation of fractured shaft; (a) surface of pitting; (b) cross section; (c) EDS results
The hydrogen sulfide in biogas can transform to sulfuric acid in brine solution by the reaction as follows: 2H2S+4O2 = 2H2SO4
(1)
Sulfuric acid in brine solution may accelerate the corrosion rate of AISI304, resulting in enormous pitting corrosion on the circumferential surface. 3.6. Electrochamical testing Electrochemical testing was carried out by potentiodynamic measurement in order to study the effect of sulfur addition in brine solution on the corrosion behavior. According to the extra experiment concerned with the several solutions, there were 5 conditions with different H2SO4 quantity in brine solution (0 – 2%H2SO4). The results as shown in Fig.6a, corrosion current density, Icorr, was increased until the condition of 1%H2SO4 and then decreased with increasing of H2SO4 addition. This result was concerned with the increasing of corrosion rate, showing the highest corrosion rate at 1%H2SO4. On the other hand, Electrochemical corrosion potential, Ecorr, is decreased compared with pure brine solution as shown in Fig.6b, there is no significantly effect of H2SO4 addition on the corrosion potential. This result showed thermodynamically possibility of stable reaction. According to the electrochemical results, there was the effect of sulfur in brine solution on the corrosion rate. Therefore, the sulfur from biogas or fermented fluid can dissolve to sea water and transform to the sulfuric acid, leading to the acceleration of pitting corrosion rate.
Patchaporn Kettrakul and Piyorose Promdirek/ Materials Today: Proceedings 5 (2018) 9624–9629
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Fig. 6. Electrochemical testing with different sulphur contaminations; (a) Current; (b) Potential.
4. Conclusion The propeller shaft used in the fishing boat for 2 years was subjected to reverse bending fatigue, showing low stress fatigue. Due to the use in the aggressively Cl-containing environment of sea water, pitting corrosion occurred on the shaft surface led to the initial crack of fatigue loading. In addition, Sulfur contamination in sea water, causing from fermentation of the sea fish which produced biogas or fermented fluid, can accelerate the corrosion rate of AISI304 in sea water. In order to protect this failure, the propulsion system should be clean and avoid the fermentation of fish in the boat. Furthermore, the shaft should be coated by materials which can construct a strong and continuous film to prevent pitting corrosion. The film should be high strength and stable and also not react with sulfur such as Al2O3, Cr2O3, and NiO. Acknowledgements The authors would like to thank King Mongkut’s University of Technology North Bangkok Department of Materials and Production Technology Engineering for laboratory support and Hummingbird Company for cooperation work and material support. References [1] N. H. N. Yusoff, M. C. Isa, M. M. Muhammad, H. Nain, M. S. D. Yati, S. R. S. Bakar, I. M. Noor, Defence S and T Technical Bulletin 5 (2012) 167-176. [2] R.W.Fullera,* , J.Q.Ehrgott Jr.b, W.F.Heardb, S.D. Robertb, R.D.Stinsonb, K.Solankic, M.F.Horstemeyer, Engineering Failure Analysis 15 (2008) 835-846. [3] http://www.aksteel.com/pdf/markets_products/stainless/austenitic/304_304l_data_sheet.pdf [4] William F. Hosford, Mechanical Behavior of Materials, 2nded., Cambridge University Press, Cambridge, UK, 2010. [5] R.T. Loto*, Materials and Environmental Science. 4(2013) 448-459. [6] William D. Callister, David G. Rethwisch, Materials Science and Engineering, 8thed., Utah, Wiley, 2011. [7] Enos, D. G., & Scribner, The Potentiodynamic Polarization Scan – Technical Report 33, Solatron Instruments, 1997.