- Email: [email protected]
Development of invar joint for hydrogen transfer line in JSNS
Journal of Nuclear Materials 431 (2012) 212–217
Contents lists available at SciVerse ScienceDirect
Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat
Development of invar joint for hydrogen transfer line in JSNS M. Teshigawara ⇑, M. Harada, M. Ooi, T. Kai, F. Maekawa, M. Futakawa J-PARC Center, Japan Atomic Energy Agency, Tokai-mura, Ibaraki-ken 319-1195, Japan
a r t i c l e
i n f o
Article history: Available online 15 November 2011
a b s t r a c t A plan of 2nd moderator fabrication in JSNS is under way. In terms of low thermal expansion, invar joints, such as Invar-Al and Invar-SS316L joints, were developed by friction welding method as a component of hydrogen transfer line. Mechanical tests such as tensile tests, were carried out at room and cold (77 K) temperature conditions. Especially, Invar-SS316L joint gave high tensile strength (yield strength: ca. 20% higher and ultimate strength: ca. 2.5 times higher) and large strain at 77 K, and fractured not at bonding interface but at base metal of invar. In case of Invar-Al joint, it also gave high yield strength, but fracture was occurred at bonding interface. However, these joints will be available for component of hydrogen transfer line. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction 1 MW short pulsed spallation neutron source (JSNS) is one of the main facilities in J-PARC (Japan Proton Accelerator Research Complex) [1]. Fig. 1 shows JSNS target station. In order to provide appropriate neutron pulses to a neutron scattering machine from a moderator, 100% para hydrogen (super-critical, 1.5 MPa, 20 K) is adopted [2–4] as a moderator material. Hydrogen (H2) is supplied to the moderators through H2 transfer line from a H2 circulation system. In the first design, in order to make the moderator vessel and the H2 transfer line, as a material combination, aluminum alloy (A6061-T6) and stainless steel (SS316L) were adopted [5,6] as shown in Fig. 2. It was due to a high neutron transmission of aluminum and an easy multiple pipe fabrication of stainless steel. The moderator vessel should be replaced in every 6 years (30,000 MW h) in the design due to the neutron irradiation damage (20 dpa) of A6061-T6, which is a structural material of the moderator vessel. In the replacement, the H2 transfer line is detached at the coupler connection as also shown in Figs. 1 and 2a. The length of the H2 transfer line is about 5 m between the moderator vessel and the coupler. The H2 transfer line was fixed to the outer pipe with room temperature at near moderator vessel (fixed position as shown in Fig. 2) to minimize a movement of the moderator vessel due to cool down. However, thermal shrinkage of the H2 transfer line (between fixed position and coupler) brings about 20 mm after cooling down. An asymmetrical setting, especially, at an elbow-shaped bend, was adopted [6] to absorb the movement of the H2 transfer line in a vacuum insulation layer due to the thermal shrinkage as shown in Fig. 3. The H2 transfer line is also covered by ⇑ Corresponding author. Tel./fax: +81 292826074. E-mail address: [email protected] (M. Teshigawara). 0022-3115/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2011.11.031
three outer pipes such as vacuum, helium and cooling water pipes. Some troubles such as welding leak, and deformation and contact with other pipes were occurred in the actual fabrication process [7] as shown in Fig. 4. A plan of 2nd moderator fabrication is under way. We have a plan to adopt the invar alloy to make the 2nd moderator fabrication because of very low thermal expansion. The thermal expansion of invar is one order of magnitude lower than that of aluminum alloy or stainless steel. It is also used for many specific applications, especially in cryogenic application, such as LNG (liquefied natural gas) carriers [8,9], and transfer pipes. Recently, it was also utilized to make the H2 transfer line in SNS Ornl [10]. It will give more easily manufacture in the moderator fabrication process. However, the development of the invar joint is required for the conversion of invar alloy to aluminum alloy and stainless steel. We adopted a friction welding method to make the invar joint, such as Invar-aluminum alloy and Invar-stainlesssteel joints. The advantage of the friction welding is that it allows dissimilar materials to be joined. Normally the wide difference in melting points of the two materials, such as aluminum and stainless steel, would make it impossible to weld using traditional techniques, such as gas metal arc welding. We evaluated the mechanical strength of invar-joints, which was also requirement for the Japanese High Pressure Gas Safety Law. In this paper, we report the measured mechanical strength, etc. of invar joints developed by the friction welding method.
2. Experiment Fig. 5 shows a preparation process of an invar joint tensile specimen. We prepared two kinds of friction welding joint, such as Invar-Al (A6061-T6) and Invar-SS316L joints as shown in Fig. 6. Each joint was made in Seimitsu Industrial Co., Ltd. The chemical compositions of invar joints are shown in Table 1. In the
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M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
Coupler
JSNS Moderator 3H2 moderators Super-critical H2 (1.5 MPa, 20 K) Optimized by 100% para H2
Poisond mod.
Decoupled mod.
Coupled mod. 1m Target station Fig. 1. JSNS target station. Three H2 moderators are adopted. These moderators were optimized by 100% para H2 to provide high neutronic performance.
Coupler
H2 in Parallel
SS316L Friction weld joint (A6061-SS316L) Fixed A6061 position (20K-R.T.)
H2 transfer line Coaxial
Moderator head
(a) Coupled moderator
Slide mechanism
(b) Inside structure
Fig. 2. Picture (a) and inside structure (b) of coupled moderator. H2 is circulated to moderator vessel through H2 transfer line. This transfer line is made by aluminum alloy (A6061) and stainless steel (SS316L). Friction weld joint is adopted to convert from coaxial to parallel.
experiment, we used a super-invar as invar material, which contained 5 wt.% cobalt as other composition. The joint shape was a rod (diameter: 50 mm, length: 100 mm), which was including a bonding interface at center. The size of rod was considered to an actual first-installed-moderator-H2-pipe in JSNS. In case of InvarAl joint, pure aluminum (A1070) with thickness of 10 mm is inserted between A6061-T6 and invar to get a good joining. The tensile test specimens were manufactured from this rod by using electric discharge machine (EDM) and lathe machine. The specimen is based on tensile test JIS Z2201, which is corresponded to ISO6892 as shown in Fig. 6. The specimen was cylindrical shape with 4 mm in diameter and 20 mm in gauge length. It was screwed at end position with the size of M10 to set up to tensile testing
machine. Test specimens were sampled along the diameter, such as 22, 29.5 and 38 mm in diameter. These corresponded to the center between outer and inner diameter of actual hydrogen pipes as shown in Fig. 5. The specimens, which were sampled at different radius of the rod, also gave the radius dependence of the friction welding on the strength of the bonding interface. The tensile testing machine is shown in Fig. 7. The loading rate was 0.05 mm/min. Its rate and displacement were measured at crosshead by a laser displacement sensor with the resolution of 3 lm. The load was measured by a load cell (load capacity: 5 tons). The tensile test was carried out at the room and cold (77 K) temperature. Thermo-couple was installed at an upper connecting part of the specimen to monitor the temperature as shown in Fig. 8. Thought,
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M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
actually, the H2 transfer line is cooled down to 20 K in the operation, in this tensile test, the liquid nitrogen temperature (77 K) was adopted, because as for the mechanical strength of invar, aluminum alloy and austenite-stainless-steel, it becomes higher, as getting cold. 3. Experimental results of invar joint 3.1. Invar-SS316L joint
3mm offset
Asymmetrical spacer
10mm
Fig. 3. Measure of thermal shrinkage. Moderator vessel with H2 transfer line is shrunken ca. 20 mm at 20 K. Asymmetrical setting, especially, at elbow-shaped bend, was adopted to absorb the movement of hydrogen pipe in vacuum insulation layer.
Fig. 8 shows typical strain–stress curves of the invar joints. This also includes the result of the Invar-Al joint. The tested specimens are shown in Fig. 9a. The tensile strength of Invar-SS316L joint is shown in Fig. 10a. The tensile test at 77 K gave a high tensile strength (yield: ca. 20% higher and ultimate strength: ca. 2.5 times higher) and large strain to compared with that at room temperature as shown in Fig. 10a. Especially, it is interesting to give a large elongation in cold temperature (77 K). The fracture was always occurred at not bonding interface but base meal of invar as shown in Fig. 9a. It gave no radius dependence on the strength of the friction weld joint as shown in Fig. 10a.
(a) Outside picture Frost
(b) X ray transmission
Contact of welding line
X ray
Fig. 4. Outside picture (a) and X-ray transmission (b) of H2 transfer line at elbow-shaped bend. This is example of unexpected contact at inside part, which was occurred in fabrication process. When H2 transfer line was cooled down, frost was found. This is due to contact of welding line, which was observed in X-ray transmission.
(a) Friction welding
(b) EDM process (Wire cut)
Bonding part
Φ22 Φ29.5 Φ38 (mm)
Invar-Al joint Invar-SS316L joint Size: Φ50 x100L (mm)
(c) Lathe process
Fig. 5. Invar joint tensile specimen preparation. Invar-Al (A6061-T6) and Invar-SS316L joints were prepared by friction welding (a). Tensile specimens were sampled along actual hydrogen pipe diameter by EDM (b). These specimens were finally manufactured by lathe machine (c).
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Invar-Al joint M10
28 20
R15
Unit : mm
4 Invar
A1070
A6061-T6
Invar-SS316L joint
Invar
SS316L
Fig. 6. Tensile specimens of invar joints. Specimen is based on tensile test JIS Z2201, which is corresponded to ISO6892.
Table 1 Chemical compositions of invar-joint materials. wt.%
C
Si
P
Cu
A1070 A6061-T6 SS316L Invar
– – 0.018 –
0.04 0.64 0.48 –
– – 0.033 –
0.01 0.35 – –
Mn
Mg
Cr
Co
Zn
V
Ti
S
Ni
Mo
Fe
Al
0.02 1.39 –
0.02 1 – –
– 0.09 17.04 –
– – – 5.42
– 0.01 – –
0.01 – – –
0.01 0.02 -
– – 0.023 –
– – 12.04 32.5
– – 2.03 –
0.13 0.2 Bal. Bal.
Bal. Bal. – –
Fig. 7. Tensile testing machine (a) loading rate and load capacity were 0.05 mm/min and 5 tons, respectively. The tensile speed and displacement were measured by laser displacement sensor with the resolution of 3 lm. Tensile test was carried out under the room and cold (77 K) temperature. In case of cold temperature, test specimen was filled with liquid nitrogen (b).
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M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
1500
1500
77 K 1000
500
R. T.
Engineering Stress (MPa)
Engineering Stress (MPa)
(a) Invar-SS316L joint
(b) Invar-Al joint
1000
500
77 K R. T.
0
0
10
20
30
40
Engineering Strain (ε, %)
0
0
10
20
30
40
Engineering Strain (ε, %)
Fig. 8. Typical strain–stress curves of invar joint. Two case of invar joint, such as Invar-SS316L (a) and Invar-Al (b) are shown for room temperature (RT) and cold temperature (77 K) testing conditions.
(a) Invar-SS316L joint after tensile test
1 cm SS316L
Invar
(b) Invar-Al joint after tensile test
1 cm Invar
Bonding interface
Fig. 9. Picture of specimens (Invar-SS316L joint (a) and Invar-Al joint (b)) after tensile test for different temperature conditions, such as room and cold (77 K) temperature. Specimens were sampled along the diameter, such as 0, 22, 29.5 and 38 mm in diameter, which correspond to the center between outer and inner diameter of actual hydrogen pipes.
M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
temperature. But in case of Invar-Al joint, fracture were occurred at bonding interface through the experiment. In order to obtain more reliable joint, we want to find the condition that fracture occurs not at bonding but at base metal, because we can focus on the strength of base metal, although we consider not only the strength but also the ductility of bonding interface. There is a possibility that we can get the Invar-Al transition, which does not fracture at bonding interface, by adopting stainless steel (SS316L) between Invar and Al alloy, because SS316L and A6061-T6 joint is already utilized by the friction-welding-method and installed in first installed H2 transfer line in JSNS. We have the plan to make InvarSS316L–Al joint by friction weld. The mechanical strength test of this joint is under way.
1400
Strength (MPa)
1200
(a) Invar-SS316 joint
1000
r
800
217
600 400 200 0
Strength (MPa)
(b) Invar-Al joint 5. Conclusion
150
77K R. T. Ultimate Yield
100
50
0 0
5
10
15
20
25
Radius, r (mm) Fig. 10. Tensile strength of Invar-Al joint as function of radius. The radius is sampled position, which correspond to the center radius between outer and inner diameter of actual hydrogen pipes.
In order to fabricate the H2 transfer line more easily and reliable, we developed invar joints, such as Invar-Al and InvarSS316L joints, by using the friction welding method. We performed mechanical test, such as the tensile test at room and cold (77 K) temperature. Especially, Invar-SS316L joint gave the high strength and large strain at 77 K, and fractured not at bonding interface but at base metal of invar. In case of Invar-Al joint, it also gave high strength, but the fracture was occurred at the bonding interface. However, both joints gave the high yield strength at 77 K to compare with that at room temperature. R&D for more reliable Invar-Al joint is in progress. However, these joints will be available for the H2 transfer line. References
3.2. Invar-Al joint As shown in Fig. 8b, the yield and ultimate strength at 77 K gave higher than that at room temperature, but before achieving ultimate strength, the fracture was occurred at bonding interface between invar and A1070 as shown in Fig. 9b. In case of the room temperature, the fracture was occurred at base metal of A1070 except for the center sampled position as shown in Fig. 9b. This means that the strength of the bonding interface at cold temperature is lower than that of A1070, which has the lowest strength among the friction-welding-joint materials. 4. Discussion Tensile test of invar joints, such as Invar-SS316L and Invar-Al joints at 77 K gave higher yield strength than that at room
[1]. [2] N. Watanabe, M. Harada, T. Kai, M. Teshigawara, Y. Ikeda, J. Neutron Res. 11 (2003) 13–23. [3] T. Kai, M. Harada, M. Teshigawara, N. Watanabe, Y. Ikeda, NIM A 523 (2004) 398–414. [4] M. Harada, N. Watanabe, M. Teshigawara, T. Kai, Y. Ikeda, NIM A 539 (2005) 345–362. [5] M. Teshigawara, M. Harada, T. Kai, H. Kogawa, T. Teraoku, F. Maekawa, N. Watanabe, Y. Ikeda, Development status of moderator–reflector system in JSNS, in: Proc. ICANS-XVI, Dusseldorf-Neuss, Germany, May 12–15, 2003, pp. 601–611. [6] M. Teshigawara, K. Oikawa, M. Harada, F. Maekawa, T. Kato, N. Watanabe, Y. Ikeda, K. Kikuchi, Y. Oda, T. Hirota, JSNS moderator design update, in: Proc. ICANS-XVII, Santa Fe, New Mexico, USA, April 25–29, 2005, pp. 365–373. [7] M. Teshigawara, M. Harada, H. Tatsumoto, T. Aso, F. Maekawa, T. Kato, Fabrication status of moderator–reflector in JSNS, in: Proc. ICANS-XVIII, Guangdong, China, April 25–29, 2007, pp. 469–475. [8] J.J. Wilson, Cryogenics 14 (3) (1974) 115–120. [9] F.S. Harris, Cryogenics 33 (8) (1993) 772–777. [10] T. McManamy, A. Crabtree, D. Lousteau, J. DeVore, L. Jacobs, M. Rennich, JNM 377 (2008) 1–11.
Contents lists available at SciVerse ScienceDirect
Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat
Development of invar joint for hydrogen transfer line in JSNS M. Teshigawara ⇑, M. Harada, M. Ooi, T. Kai, F. Maekawa, M. Futakawa J-PARC Center, Japan Atomic Energy Agency, Tokai-mura, Ibaraki-ken 319-1195, Japan
a r t i c l e
i n f o
Article history: Available online 15 November 2011
a b s t r a c t A plan of 2nd moderator fabrication in JSNS is under way. In terms of low thermal expansion, invar joints, such as Invar-Al and Invar-SS316L joints, were developed by friction welding method as a component of hydrogen transfer line. Mechanical tests such as tensile tests, were carried out at room and cold (77 K) temperature conditions. Especially, Invar-SS316L joint gave high tensile strength (yield strength: ca. 20% higher and ultimate strength: ca. 2.5 times higher) and large strain at 77 K, and fractured not at bonding interface but at base metal of invar. In case of Invar-Al joint, it also gave high yield strength, but fracture was occurred at bonding interface. However, these joints will be available for component of hydrogen transfer line. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction 1 MW short pulsed spallation neutron source (JSNS) is one of the main facilities in J-PARC (Japan Proton Accelerator Research Complex) [1]. Fig. 1 shows JSNS target station. In order to provide appropriate neutron pulses to a neutron scattering machine from a moderator, 100% para hydrogen (super-critical, 1.5 MPa, 20 K) is adopted [2–4] as a moderator material. Hydrogen (H2) is supplied to the moderators through H2 transfer line from a H2 circulation system. In the first design, in order to make the moderator vessel and the H2 transfer line, as a material combination, aluminum alloy (A6061-T6) and stainless steel (SS316L) were adopted [5,6] as shown in Fig. 2. It was due to a high neutron transmission of aluminum and an easy multiple pipe fabrication of stainless steel. The moderator vessel should be replaced in every 6 years (30,000 MW h) in the design due to the neutron irradiation damage (20 dpa) of A6061-T6, which is a structural material of the moderator vessel. In the replacement, the H2 transfer line is detached at the coupler connection as also shown in Figs. 1 and 2a. The length of the H2 transfer line is about 5 m between the moderator vessel and the coupler. The H2 transfer line was fixed to the outer pipe with room temperature at near moderator vessel (fixed position as shown in Fig. 2) to minimize a movement of the moderator vessel due to cool down. However, thermal shrinkage of the H2 transfer line (between fixed position and coupler) brings about 20 mm after cooling down. An asymmetrical setting, especially, at an elbow-shaped bend, was adopted [6] to absorb the movement of the H2 transfer line in a vacuum insulation layer due to the thermal shrinkage as shown in Fig. 3. The H2 transfer line is also covered by ⇑ Corresponding author. Tel./fax: +81 292826074. E-mail address: [email protected] (M. Teshigawara). 0022-3115/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2011.11.031
three outer pipes such as vacuum, helium and cooling water pipes. Some troubles such as welding leak, and deformation and contact with other pipes were occurred in the actual fabrication process [7] as shown in Fig. 4. A plan of 2nd moderator fabrication is under way. We have a plan to adopt the invar alloy to make the 2nd moderator fabrication because of very low thermal expansion. The thermal expansion of invar is one order of magnitude lower than that of aluminum alloy or stainless steel. It is also used for many specific applications, especially in cryogenic application, such as LNG (liquefied natural gas) carriers [8,9], and transfer pipes. Recently, it was also utilized to make the H2 transfer line in SNS Ornl [10]. It will give more easily manufacture in the moderator fabrication process. However, the development of the invar joint is required for the conversion of invar alloy to aluminum alloy and stainless steel. We adopted a friction welding method to make the invar joint, such as Invar-aluminum alloy and Invar-stainlesssteel joints. The advantage of the friction welding is that it allows dissimilar materials to be joined. Normally the wide difference in melting points of the two materials, such as aluminum and stainless steel, would make it impossible to weld using traditional techniques, such as gas metal arc welding. We evaluated the mechanical strength of invar-joints, which was also requirement for the Japanese High Pressure Gas Safety Law. In this paper, we report the measured mechanical strength, etc. of invar joints developed by the friction welding method.
2. Experiment Fig. 5 shows a preparation process of an invar joint tensile specimen. We prepared two kinds of friction welding joint, such as Invar-Al (A6061-T6) and Invar-SS316L joints as shown in Fig. 6. Each joint was made in Seimitsu Industrial Co., Ltd. The chemical compositions of invar joints are shown in Table 1. In the
213
M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
Coupler
JSNS Moderator 3H2 moderators Super-critical H2 (1.5 MPa, 20 K) Optimized by 100% para H2
Poisond mod.
Decoupled mod.
Coupled mod. 1m Target station Fig. 1. JSNS target station. Three H2 moderators are adopted. These moderators were optimized by 100% para H2 to provide high neutronic performance.
Coupler
H2 in Parallel
SS316L Friction weld joint (A6061-SS316L) Fixed A6061 position (20K-R.T.)
H2 transfer line Coaxial
Moderator head
(a) Coupled moderator
Slide mechanism
(b) Inside structure
Fig. 2. Picture (a) and inside structure (b) of coupled moderator. H2 is circulated to moderator vessel through H2 transfer line. This transfer line is made by aluminum alloy (A6061) and stainless steel (SS316L). Friction weld joint is adopted to convert from coaxial to parallel.
experiment, we used a super-invar as invar material, which contained 5 wt.% cobalt as other composition. The joint shape was a rod (diameter: 50 mm, length: 100 mm), which was including a bonding interface at center. The size of rod was considered to an actual first-installed-moderator-H2-pipe in JSNS. In case of InvarAl joint, pure aluminum (A1070) with thickness of 10 mm is inserted between A6061-T6 and invar to get a good joining. The tensile test specimens were manufactured from this rod by using electric discharge machine (EDM) and lathe machine. The specimen is based on tensile test JIS Z2201, which is corresponded to ISO6892 as shown in Fig. 6. The specimen was cylindrical shape with 4 mm in diameter and 20 mm in gauge length. It was screwed at end position with the size of M10 to set up to tensile testing
machine. Test specimens were sampled along the diameter, such as 22, 29.5 and 38 mm in diameter. These corresponded to the center between outer and inner diameter of actual hydrogen pipes as shown in Fig. 5. The specimens, which were sampled at different radius of the rod, also gave the radius dependence of the friction welding on the strength of the bonding interface. The tensile testing machine is shown in Fig. 7. The loading rate was 0.05 mm/min. Its rate and displacement were measured at crosshead by a laser displacement sensor with the resolution of 3 lm. The load was measured by a load cell (load capacity: 5 tons). The tensile test was carried out at the room and cold (77 K) temperature. Thermo-couple was installed at an upper connecting part of the specimen to monitor the temperature as shown in Fig. 8. Thought,
214
M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
actually, the H2 transfer line is cooled down to 20 K in the operation, in this tensile test, the liquid nitrogen temperature (77 K) was adopted, because as for the mechanical strength of invar, aluminum alloy and austenite-stainless-steel, it becomes higher, as getting cold. 3. Experimental results of invar joint 3.1. Invar-SS316L joint
3mm offset
Asymmetrical spacer
10mm
Fig. 3. Measure of thermal shrinkage. Moderator vessel with H2 transfer line is shrunken ca. 20 mm at 20 K. Asymmetrical setting, especially, at elbow-shaped bend, was adopted to absorb the movement of hydrogen pipe in vacuum insulation layer.
Fig. 8 shows typical strain–stress curves of the invar joints. This also includes the result of the Invar-Al joint. The tested specimens are shown in Fig. 9a. The tensile strength of Invar-SS316L joint is shown in Fig. 10a. The tensile test at 77 K gave a high tensile strength (yield: ca. 20% higher and ultimate strength: ca. 2.5 times higher) and large strain to compared with that at room temperature as shown in Fig. 10a. Especially, it is interesting to give a large elongation in cold temperature (77 K). The fracture was always occurred at not bonding interface but base meal of invar as shown in Fig. 9a. It gave no radius dependence on the strength of the friction weld joint as shown in Fig. 10a.
(a) Outside picture Frost
(b) X ray transmission
Contact of welding line
X ray
Fig. 4. Outside picture (a) and X-ray transmission (b) of H2 transfer line at elbow-shaped bend. This is example of unexpected contact at inside part, which was occurred in fabrication process. When H2 transfer line was cooled down, frost was found. This is due to contact of welding line, which was observed in X-ray transmission.
(a) Friction welding
(b) EDM process (Wire cut)
Bonding part
Φ22 Φ29.5 Φ38 (mm)
Invar-Al joint Invar-SS316L joint Size: Φ50 x100L (mm)
(c) Lathe process
Fig. 5. Invar joint tensile specimen preparation. Invar-Al (A6061-T6) and Invar-SS316L joints were prepared by friction welding (a). Tensile specimens were sampled along actual hydrogen pipe diameter by EDM (b). These specimens were finally manufactured by lathe machine (c).
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Invar-Al joint M10
28 20
R15
Unit : mm
4 Invar
A1070
A6061-T6
Invar-SS316L joint
Invar
SS316L
Fig. 6. Tensile specimens of invar joints. Specimen is based on tensile test JIS Z2201, which is corresponded to ISO6892.
Table 1 Chemical compositions of invar-joint materials. wt.%
C
Si
P
Cu
A1070 A6061-T6 SS316L Invar
– – 0.018 –
0.04 0.64 0.48 –
– – 0.033 –
0.01 0.35 – –
Mn
Mg
Cr
Co
Zn
V
Ti
S
Ni
Mo
Fe
Al
0.02 1.39 –
0.02 1 – –
– 0.09 17.04 –
– – – 5.42
– 0.01 – –
0.01 – – –
0.01 0.02 -
– – 0.023 –
– – 12.04 32.5
– – 2.03 –
0.13 0.2 Bal. Bal.
Bal. Bal. – –
Fig. 7. Tensile testing machine (a) loading rate and load capacity were 0.05 mm/min and 5 tons, respectively. The tensile speed and displacement were measured by laser displacement sensor with the resolution of 3 lm. Tensile test was carried out under the room and cold (77 K) temperature. In case of cold temperature, test specimen was filled with liquid nitrogen (b).
216
M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
1500
1500
77 K 1000
500
R. T.
Engineering Stress (MPa)
Engineering Stress (MPa)
(a) Invar-SS316L joint
(b) Invar-Al joint
1000
500
77 K R. T.
0
0
10
20
30
40
Engineering Strain (ε, %)
0
0
10
20
30
40
Engineering Strain (ε, %)
Fig. 8. Typical strain–stress curves of invar joint. Two case of invar joint, such as Invar-SS316L (a) and Invar-Al (b) are shown for room temperature (RT) and cold temperature (77 K) testing conditions.
(a) Invar-SS316L joint after tensile test
1 cm SS316L
Invar
(b) Invar-Al joint after tensile test
1 cm Invar
Bonding interface
Fig. 9. Picture of specimens (Invar-SS316L joint (a) and Invar-Al joint (b)) after tensile test for different temperature conditions, such as room and cold (77 K) temperature. Specimens were sampled along the diameter, such as 0, 22, 29.5 and 38 mm in diameter, which correspond to the center between outer and inner diameter of actual hydrogen pipes.
M. Teshigawara et al. / Journal of Nuclear Materials 431 (2012) 212–217
temperature. But in case of Invar-Al joint, fracture were occurred at bonding interface through the experiment. In order to obtain more reliable joint, we want to find the condition that fracture occurs not at bonding but at base metal, because we can focus on the strength of base metal, although we consider not only the strength but also the ductility of bonding interface. There is a possibility that we can get the Invar-Al transition, which does not fracture at bonding interface, by adopting stainless steel (SS316L) between Invar and Al alloy, because SS316L and A6061-T6 joint is already utilized by the friction-welding-method and installed in first installed H2 transfer line in JSNS. We have the plan to make InvarSS316L–Al joint by friction weld. The mechanical strength test of this joint is under way.
1400
Strength (MPa)
1200
(a) Invar-SS316 joint
1000
r
800
217
600 400 200 0
Strength (MPa)
(b) Invar-Al joint 5. Conclusion
150
77K R. T. Ultimate Yield
100
50
0 0
5
10
15
20
25
Radius, r (mm) Fig. 10. Tensile strength of Invar-Al joint as function of radius. The radius is sampled position, which correspond to the center radius between outer and inner diameter of actual hydrogen pipes.
In order to fabricate the H2 transfer line more easily and reliable, we developed invar joints, such as Invar-Al and InvarSS316L joints, by using the friction welding method. We performed mechanical test, such as the tensile test at room and cold (77 K) temperature. Especially, Invar-SS316L joint gave the high strength and large strain at 77 K, and fractured not at bonding interface but at base metal of invar. In case of Invar-Al joint, it also gave high strength, but the fracture was occurred at the bonding interface. However, both joints gave the high yield strength at 77 K to compare with that at room temperature. R&D for more reliable Invar-Al joint is in progress. However, these joints will be available for the H2 transfer line. References
3.2. Invar-Al joint As shown in Fig. 8b, the yield and ultimate strength at 77 K gave higher than that at room temperature, but before achieving ultimate strength, the fracture was occurred at bonding interface between invar and A1070 as shown in Fig. 9b. In case of the room temperature, the fracture was occurred at base metal of A1070 except for the center sampled position as shown in Fig. 9b. This means that the strength of the bonding interface at cold temperature is lower than that of A1070, which has the lowest strength among the friction-welding-joint materials. 4. Discussion Tensile test of invar joints, such as Invar-SS316L and Invar-Al joints at 77 K gave higher yield strength than that at room
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