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Manufacturing and testing of full scale prototype for ITER blanket shield block
Fusion Engineering and Design 93 (2015) 69–75
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Manufacturing and testing of full scale prototype for ITER blanket shield block Sa-Woong Kim a,∗ , Duck-Hoi Kim a , Hun-Chea Jung a , Sung-Ki Lee b , Sung-Chan Kang c , Fu Zhang d , Byoung-Yoon Kim d , Hee-Jae Ahn a , Hyeon-Gon Lee a , Ki-Jung Jung a a
ITER Korea, National Fusion Research Institute, Daejeon, Republic of Korea WONIL Co., Ltd., Haman, Republic of Korea c POSCO Specialty Steel Co., Ltd., Changwon, Republic of Korea d ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France b
h i g h l i g h t s • • • •
316L(N)-IG forged steel was successfully fabricated and qualified. Related R&D activities were implemented to resolve the fabrication issues. SB #8 FSP was successfully manufactured with conventional fabrication techniques. All of the validation tests were carried out and met the acceptance criteria.
a r t i c l e
i n f o
Article history: Received 2 September 2014 Received in revised form 17 February 2015 Accepted 22 February 2015 Available online 11 March 2015 Keywords: ITER Blanket shield block 316L(N)-IG stainless steel Pre-qualification Manufacturing Testing
a b s t r a c t Based on the preliminary design of the ITER blanket shield block (SB) #8, the full scale prototype (FSP) has been manufactured and tested in accordance with pre-qualification program, and related R&D was performed to resolve the technical issues of fabrication. The objective of the SB pre-qualification program is to demonstrate the acceptable manufacturing quality by successfully passing the formal test program. 316L(N)-IG stainless steel forging blocks with 1.80L × 1.12W × 0.43t (m) were developed by using an electric arc furnace, and as a result, the material properties were satisfied with technical specification. In the course of applying conventional fabrication techniques such as cutting, milling, drilling and welding of the forged stainless steel block for the manufacturing of the SB #8 FSP, several technical problems have been addressed. And also, the hydraulic connector of cross-forged material re-melted by electro slag or vacuum arc requires the application of advanced joining techniques such as automatic bore TIG and friction welding. Many technical issues – drilling, welding, slitting, non-destructive test and so on – have been raised during manufacturing. Associated R&D including the computational simulation and coupon testing has been done in collaboration with relevant industries in order to resolve these engineering issues. This paper provides technical key issues and their possible resolutions addressed during the manufacture and formal test of the SB #8 FSP, and related R&D. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The main function of the SB is to contribute in providing nuclear shielding and support the first wall (FW) panel [1]. It is required to accommodate all the components located on the vacuum vessel (in particular the in-vessel coils, blanket manifolds and the
∗ Corresponding author. Tel.: +82 428795651. E-mail address: [email protected] (S.-W. Kim). http://dx.doi.org/10.1016/j.fusengdes.2015.02.047 0920-3796/© 2015 Elsevier B.V. All rights reserved.
diagnostics). The conceptual, preliminary and final design reviews (FDR) have been completed in the framework of Blanket Integrated Product Team (BIPT) for the signing of Procurement Arrangement (PA). Involving procuring domestic agencies for the blanket SB should be successfully completed the “SB Full Scale Prototype (FSP) pre-qualification program” prior to issuing of the PA. The objective of the SB FSP pre-qualification program is to demonstrate the acceptable quality and the capable of successfully passing the formal test program. The SB #8 FSP has been manufactured and tested in accordance with pre-qualification program based on the
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Fig. 1. Schematics of shield block #8 FSP (front and rear views showing the cut-outs for interfaces as well as the different attachment systems, and cooling configuration).
preliminary design, and related R&D activities were implemented to resolve the fabrication issues. 316L(N)-IG stainless steel forging block with 1.80L × 1.12W × 0.43t (m) was developed by using an electric arc furnace, and as a result, the material properties were satisfied with ITER specification. In the course of applying conventional fabrication techniques such as cutting, milling, drilling and welding of the forged stainless steel block for the manufacturing of SB #8 FSP, several technical problems have been addressed. This paper highlights some of these issues and provides the process of manufacturing and testing results. 2. General description of the shield block The SB #8 located in top modules has very complicated interface configurations. In particular, this module should be tolerated against severe thermal loading from not only nuclear volumetric heating but also plasma heat flux at uncovered regions by EHF (enhance heat flux) FW. The basic configuration of the ITER SB #8 FSP is shown in Fig. 1. Each SB is attached to the vacuum vessel through a mechanical attachment system of flexible supports and a system of keys. Each SB has electrical straps providing electrical connection to the vacuum vessel. Cooling channels are located inside of the SB to remove up to 736 MW of thermal power, and coolant is routed through the FW first and then through the SB. The steel/water ratio has been optimized with respect to neutron shielding to about 85/15. This ratio is achieved by optimizing the number of poloidal cooling channels and their size within the SB. A number of deep slits are introduced into the SB to reduce the impact of the electro-magnetic (EM) loads on the structural loads of the support system and vacuum vessel. Water headers are machined on the side of the module with 10–15 mm welded cover plates. The basic fabrication method for a SB starts from forged steel block and includes drilling of holes, welding of the cover plates of the water headers, cutting of the deep slits, and final machining of the interfaces [2].
from steel, austenitic steel or super-alloys and which are of final thickness less than 5 mm, shall be made from cross-forged material which is electro-slag remelted (ESR) or vacuum arc remelted (VAR). Therefore, ESR structure inserting should be applied because the water connector (inlet and outlet) of SBs has a part of final thickness less than 5 mm. In this work, bore tungsten inert gas (TIG) welding and friction welding was considered as a joint method of the water connector of SBs. The basic configuration of the inlet of the SB #8 FSP is shown in Fig. 2. 316L steel pipes having the thickness of 6 mm for friction welding and 8 mm for automatic bore TIG welding were applied for the R&D activities, respectively, and the test results is shown in Figs. 3 and 4. As shown in those figures, very good visual inspection results have been confirmed by cross-section observation although detail evaluation by non-destructive examination (NDE) and destructive examination (DE) would be needed to ensure the welding performance. Therefore, the friction welding and automatic bore TIG welding could be considered as one of candidate joint methods for ESR structure inserting in the real procurement products even though further effort for technical improvement would be needed to mitigate and optimize the risk, process efficiency and so on.
3. R&D activities 3.1. Electro-slag remelted structure inserting In accordance with the ITER vacuum handbook (VHB) [3], all vacuum quality class (VQC) 1A components which are machined
Fig. 2. The basic configuration of inlet for SB #8 FSP.
S.-W. Kim et al. / Fusion Engineering and Design 93 (2015) 69–75
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Fig. 3. The test result of friction welding using thickness of 6 mm pipes: (a) weld joint and (b) cross-section of weld joint.
Fig. 4. The test result of automatic bore TIG welding using thickness of 8 mm pipes: (a) inside of weld joint and (b) cross-section of weld joint.
3.2. Cover welding and non-destructive examination
bead although almost the whole results can be acceptable as shown in Fig. 5(b) and (c). Narrow gap U-groove shape having welding slot was applied to the cover welding of the SB #8 FSP from these results. Five types of special UT probe which is calibrated and tested with calibration block and reference block base on EN 12668, 0◦ (4 MHz), 25◦ (2 MHz), 45◦ (2 MHz), 60◦ (4 MHz) and 70◦ (2 MHz), were developed to perform 100% volumetric examination of welded regions. Welding deformation also was verified using test block and applied to the SB #8 FSP.
The SB #8 FSP model has many small and complicated shapes of cover plates and difficult part for NDE. The ITER VHB describe that for all VQC 1A water boundaries and vacuum boundary welds which become inaccessible, 100% volumetric examination of production welds shall be performed. Therefore, ultrasonic test (UT) should be most practical method for NDE after cover welding. For such a reason, verification of weld-ability and UT method is essential beforehand to accomplish cover welding and inspection of the SB #8 FSP. Four types of welding design were verified in this R&D activity and the main welding design elements are shown in Table 1. Several trial tests were performed and the results are shown in Fig. 5. Narrow gap U-groove shape having welding slot shows very good welding performance as shown in Fig. 5(a). In the cases of bevel groove and U-groove shape having no welding slot, however, some incomplete penetration parts were found at the edge of back
3.3. Slitting During operation of ITER, large EM load (force and moment) will be produced in SB due to the eddy/halo current interaction with the magnetic field. A number of deep slits are introduced into the SB to reduce the impact of the EM loads on the structural loads of the support system and vacuum vessel as above mentioned. Slitting
Table 1 The main welding design elements for the cover welding of SBs. Groove shape
Slot
Angle (◦ )
Root face (mm)
Root gap (mm)
Plate thickness (mm)
U-groove
O X
12
1
2
15
1
2.5 3.0 3.5 4.0
Bevel groove
X
35
10 15
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S.-W. Kim et al. / Fusion Engineering and Design 93 (2015) 69–75
Fig. 5. Microstructure of cross section for each trial test result of cover welding: (a) U-groove shape having welding slot, (b) U-groove shape having no welding slot, and (c) bevel groove shape having no welding slot.
Table 2 Chemical composition of fabricated 316L(N)-IG steel including required values in the technical specifications. Element
C
Si
Mn
P
S
Ni
Cr
Mo
N
B
Co
316L(N)-IG Min.
–
–
1.60
–
–
12.00
17.00
2.30
0.060
–
–
Cu: max. 0.30 Nb: max. 0.10 Ti: max. 0.10 Ta: max. 0.01
0.030
0.50
2.00
0.025
0.010
12.50
18.00
2.70
0.080
0.002
0.05
Ladle
0.023
0.30
1.78
0.018
0.003
12.25
17.60
2.43
0.074
0.0006
0.026
Cu: 0.09 Nb: 0.006 Ti: 0.004 Ta: 0.001
Product
0.021
0.31
1.76
0.018
0.002
12.10
17.66
2.40
0.077
0.0007
0.025
Cu: 0.09 Nb: 0.006 Ti: 0.004 Ta: 0.001
Max.
was focused on the optimization of slitting conditions to achieve required tolerances. Jig and fixture also important issue due to the complicated shape of the SB #8 FSP. Applicable tolerances, surface roughness less than 4.2 m, slit width in the range of 2.5–3.5 mm and mismatch value in center line between slit width and slit end hole of max. 3 mm, were verified through the results of test block by using band saw machine. Furthermore, appropriate jig and fixture was confirmed with carbon steel mock-up. Optimization of slitting conditions has been completed from this R&D activity and applied to the SB #8 FSP.
4. Manufacturing route 4.1. Fabrication of material 316L(N)-IG steel is grade 316L steel with narrower alloying element ranges and controlled impurities. The closest analogy is X2-17Cr-12Ni-2Mo controlled nitrogen content austenitic stainless steel described in RCC-MR Code, Edition 2007 [4]. Electric arc furnace (EAF), ladle furnace (LF) and vacuum oxygen de-carburization (VOD) for steelmaking process, and heat furnace and oil-hydraulic forging press (9000 t) for forging process was applied to fabricate 316L(N)-IG steel for the SB #8 FSP by POSCO Specialty Steel Co., Ltd., Korea. Chemical composition of fabricated 316L(N)-IG steel including required values in the technical specifications [5] is shown in Table 2. Required inspections, such as ferrite content, magnetic permeability, grain size, non-metallic inclusions and mechanical properties at RT and 250 ◦ C, after fabrication of 316L(N)-IG steel were implemented in accordance with the technical specifications. All of the inspection results met the acceptable criteria in the technical specifications. The results of mechanical properties are shown in Table 3.
4.2. Machining of the SB #8 FSP Based on the developed techniques from R&D activities, conventional machining techniques such as cutting, milling, drilling and welding have been applied for the SB #8 FSP. Overall machining processes are shown in Fig. 6. Appropriate inspections such as visual, dimensional, UT, etc. were performed before start and after complete each process. Especially, visual inspection by endoscope after deep hole drilling was applied to confirm “no blocked or partially blocked water channels” for all of drilled holes on the SB #8 FSP. As examples, visual inspection result by endoscope for drilled deep hole is shown in Fig. 7. Inspection object hole is indicated by dashed circle in Fig. 7(a). The object hole is cross with four other holes, and it can be confirmed that all the holes have no blocked or partially blocked each other as shown in Fig. 7(b). Cover welding is one of key technical issue because the SB #8 FSP has many cover plates with complicated shape. The sequence of cover welding was (1) joining strong back system, (2) connecting purging system (Ar gas), (3) closing all headers, (4) measuring oxygen concentration in the root gap, (5) tack welding of cover plate and visual inspection and (6) welding from root pass. Fig. 8 shows Table 3 Mechanical properties of fabricated 316L(N)-IG steel at RT and 250 ◦ C. Tensile test RT Yield strength (0.2% offset), MPa Tensile strength, MPa Elongation, % 250 ◦ C Yield strength (0.2% offset), MPa Tensile strength, MPa
Spec. min.
Sample 1
Sample 2
220
275
245
525 45
550 58
540 60
135
158
159
415
436
439
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Fig. 6. Overall machining processes for manufacturing of the SB #8 FSP: (a) cutting, (b) milling, (c) semi-finishing, (d) drilling, (e) cleaning, (f) fit-up of cover plate, (g) cover welding, (h) slitting, (i) 1st finishing for front side, (j) 1st finishing for back side, (k) UT inspection, and (l) interface machining and final finishing.
Fig. 7. An example of visual inspection by endoscope for drilled deep hole: (a) inspection object hole and (b) images for the inside of drilled deep hole.
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Fig. 8. The SB #8 FSP during and after cover welding (root pass welding, after third pass welding and after completion): (a) root pass welding, (b) after 3rd pass welding, (c) completion of front side, and (d) completion of back side.
the SB #8 FSP during and after cover welding. Finally, 100% volumetric inspection by UT for all welding region was implemented in accordance with welding procedure specification (WPS) which was verified from welding procedure qualification test (WPQT) based on EN ISO 15614-1. Even if total 4 indications of elongated cavity wormholes were founded, all the indications were acceptable in accordance with acceptance criteria. 4.3. Validation tests In accordance with the ITER VHB, leak test should be carried out on the final component after pressure testing to confirm the soundness of welding processes, and to reduce the risk of incorporating leaks in a system that are subsequently difficult to locate or to repair. Vacuum baking after hydraulic pressure test is needed for the removal of contaminants which can break down to volatile components under the application of temperature, reducing the outgassing rate of the surface by accelerating the thermal desorption of molecular species and opening up incipient leaks, particularly porosity, where the leak path has been blocked by, for example, a carbon inclusion. The hydraulic pressure test and the cold He leak test including baking at 200 ◦ C for 24 h were performed on the final SB #8 FSP in this work. Final cleaning was also performed after completion of validation tests and final machining for attachment parts. Schematic diagram and a picture of cold He leak test system is shown in Fig. 9. The followings are general rules for the hydraulic pressure test. • The test pressure shall be 7.15 ± 0.2 MPa. • The test temperature shall be 22 ± 5 ◦ C. • The test pressure shall be measure and recorded over a period of not less than 30 min. • No pressure drop is acceptable within the 30 min test period. • No permanent deformation of surfaces. And also, the acceptance criteria are: • No visible water leaks.
Fig. 9. Cold He leak test system for SB #8 FSP: (a) a schematic diagram of the test system and (b) a picture of the test system.
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• No visible water leaks and no permanent deformations from the hydraulic pressure test. • Same with background level (0.4 × 10−10 Pa m3 /s) which means no He leak from Cold He leak test. A picture of the SB #8 FSP fabricated under the shield block full scale prototype pre-qualification program is shown in Fig. 10. 5. Summary
Fig. 10. Shield block full scale prototype being fabricated and tested by the SB FSP pre-qualification program.
• No appreciable variation of the test pressure within the tolerance range of ±0.2 MPa. • No permanent deformations as detectable by visual inspection. The acceptance criteria for cold He leak test are: • The vacuum level shall be less than 1.3 × 10−3 Pa. • The sensitivity of the He detector shall be better than 4 × 10−11 Pa m3 /s. • Maximum leak rate shall be 1 × 10−10 Pa m3 /s. • The leak detector reading is monitored until it has stabilized, without any electronic correction. This should take around 10 min, but the time can be longer depending on the size of the system under test. All the validation test results on the final SB #8 FSP were met the acceptance criteria. The main results of the tests are:
Related R&D activities were implemented to resolve the fabrication issues. 316L(N)-IG forged steel was successfully fabricated and qualified in accordance with the technical specifications. The conventional fabrication techniques such as cutting, milling, drilling and welding of the forged stainless steel block were applied for the manufacturing of the SB #8 FSP. All of the tests such as visual & dimensional inspection, NDE, hydraulic pressure test and cold He leak test was carried out and met the acceptance criteria. From those all activities, the acceptable quality and the capable of successfully passing the formal test program in Korea domestic agency have been demonstrated with successful completion of the “SB Full Scale Prototype (FSP) pre-qualification program”, and the Procurement Arrangement was made on November 2013 between Korea domestic agency and ITER organization. Acknowledgments This work is supported by the Ministry of Science, ICT and Future Planning of Republic of Korea under an ITER Project Contract. The view and opinion expressed herein do not necessarily reflect those of the ITER Organization. References [1] A.R. Raffray, M. Merola, Contributors from the Blanket Integrated Product Team, Overview of the design and R&D of the ITER blanket system, Fusion Eng. Des. 87 (5–6) (2012) 769–776. [2] A.R. Raffray, Blanket Design Description Document (FDR), 2013 (Private Communication). [3] L. Worth, ITER Vacuum Handbook, 2009 (Private Communication). [4] RCC-MR Code, Section 2: Materials, AFCEN, 2007. [5] R. Eaton, V. Barabash, Technical Specification – 316L(N)-IG forging for Blanket, 2013 (Private Communication).
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Manufacturing and testing of full scale prototype for ITER blanket shield block Sa-Woong Kim a,∗ , Duck-Hoi Kim a , Hun-Chea Jung a , Sung-Ki Lee b , Sung-Chan Kang c , Fu Zhang d , Byoung-Yoon Kim d , Hee-Jae Ahn a , Hyeon-Gon Lee a , Ki-Jung Jung a a
ITER Korea, National Fusion Research Institute, Daejeon, Republic of Korea WONIL Co., Ltd., Haman, Republic of Korea c POSCO Specialty Steel Co., Ltd., Changwon, Republic of Korea d ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France b
h i g h l i g h t s • • • •
316L(N)-IG forged steel was successfully fabricated and qualified. Related R&D activities were implemented to resolve the fabrication issues. SB #8 FSP was successfully manufactured with conventional fabrication techniques. All of the validation tests were carried out and met the acceptance criteria.
a r t i c l e
i n f o
Article history: Received 2 September 2014 Received in revised form 17 February 2015 Accepted 22 February 2015 Available online 11 March 2015 Keywords: ITER Blanket shield block 316L(N)-IG stainless steel Pre-qualification Manufacturing Testing
a b s t r a c t Based on the preliminary design of the ITER blanket shield block (SB) #8, the full scale prototype (FSP) has been manufactured and tested in accordance with pre-qualification program, and related R&D was performed to resolve the technical issues of fabrication. The objective of the SB pre-qualification program is to demonstrate the acceptable manufacturing quality by successfully passing the formal test program. 316L(N)-IG stainless steel forging blocks with 1.80L × 1.12W × 0.43t (m) were developed by using an electric arc furnace, and as a result, the material properties were satisfied with technical specification. In the course of applying conventional fabrication techniques such as cutting, milling, drilling and welding of the forged stainless steel block for the manufacturing of the SB #8 FSP, several technical problems have been addressed. And also, the hydraulic connector of cross-forged material re-melted by electro slag or vacuum arc requires the application of advanced joining techniques such as automatic bore TIG and friction welding. Many technical issues – drilling, welding, slitting, non-destructive test and so on – have been raised during manufacturing. Associated R&D including the computational simulation and coupon testing has been done in collaboration with relevant industries in order to resolve these engineering issues. This paper provides technical key issues and their possible resolutions addressed during the manufacture and formal test of the SB #8 FSP, and related R&D. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The main function of the SB is to contribute in providing nuclear shielding and support the first wall (FW) panel [1]. It is required to accommodate all the components located on the vacuum vessel (in particular the in-vessel coils, blanket manifolds and the
∗ Corresponding author. Tel.: +82 428795651. E-mail address: [email protected] (S.-W. Kim). http://dx.doi.org/10.1016/j.fusengdes.2015.02.047 0920-3796/© 2015 Elsevier B.V. All rights reserved.
diagnostics). The conceptual, preliminary and final design reviews (FDR) have been completed in the framework of Blanket Integrated Product Team (BIPT) for the signing of Procurement Arrangement (PA). Involving procuring domestic agencies for the blanket SB should be successfully completed the “SB Full Scale Prototype (FSP) pre-qualification program” prior to issuing of the PA. The objective of the SB FSP pre-qualification program is to demonstrate the acceptable quality and the capable of successfully passing the formal test program. The SB #8 FSP has been manufactured and tested in accordance with pre-qualification program based on the
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S.-W. Kim et al. / Fusion Engineering and Design 93 (2015) 69–75
Fig. 1. Schematics of shield block #8 FSP (front and rear views showing the cut-outs for interfaces as well as the different attachment systems, and cooling configuration).
preliminary design, and related R&D activities were implemented to resolve the fabrication issues. 316L(N)-IG stainless steel forging block with 1.80L × 1.12W × 0.43t (m) was developed by using an electric arc furnace, and as a result, the material properties were satisfied with ITER specification. In the course of applying conventional fabrication techniques such as cutting, milling, drilling and welding of the forged stainless steel block for the manufacturing of SB #8 FSP, several technical problems have been addressed. This paper highlights some of these issues and provides the process of manufacturing and testing results. 2. General description of the shield block The SB #8 located in top modules has very complicated interface configurations. In particular, this module should be tolerated against severe thermal loading from not only nuclear volumetric heating but also plasma heat flux at uncovered regions by EHF (enhance heat flux) FW. The basic configuration of the ITER SB #8 FSP is shown in Fig. 1. Each SB is attached to the vacuum vessel through a mechanical attachment system of flexible supports and a system of keys. Each SB has electrical straps providing electrical connection to the vacuum vessel. Cooling channels are located inside of the SB to remove up to 736 MW of thermal power, and coolant is routed through the FW first and then through the SB. The steel/water ratio has been optimized with respect to neutron shielding to about 85/15. This ratio is achieved by optimizing the number of poloidal cooling channels and their size within the SB. A number of deep slits are introduced into the SB to reduce the impact of the electro-magnetic (EM) loads on the structural loads of the support system and vacuum vessel. Water headers are machined on the side of the module with 10–15 mm welded cover plates. The basic fabrication method for a SB starts from forged steel block and includes drilling of holes, welding of the cover plates of the water headers, cutting of the deep slits, and final machining of the interfaces [2].
from steel, austenitic steel or super-alloys and which are of final thickness less than 5 mm, shall be made from cross-forged material which is electro-slag remelted (ESR) or vacuum arc remelted (VAR). Therefore, ESR structure inserting should be applied because the water connector (inlet and outlet) of SBs has a part of final thickness less than 5 mm. In this work, bore tungsten inert gas (TIG) welding and friction welding was considered as a joint method of the water connector of SBs. The basic configuration of the inlet of the SB #8 FSP is shown in Fig. 2. 316L steel pipes having the thickness of 6 mm for friction welding and 8 mm for automatic bore TIG welding were applied for the R&D activities, respectively, and the test results is shown in Figs. 3 and 4. As shown in those figures, very good visual inspection results have been confirmed by cross-section observation although detail evaluation by non-destructive examination (NDE) and destructive examination (DE) would be needed to ensure the welding performance. Therefore, the friction welding and automatic bore TIG welding could be considered as one of candidate joint methods for ESR structure inserting in the real procurement products even though further effort for technical improvement would be needed to mitigate and optimize the risk, process efficiency and so on.
3. R&D activities 3.1. Electro-slag remelted structure inserting In accordance with the ITER vacuum handbook (VHB) [3], all vacuum quality class (VQC) 1A components which are machined
Fig. 2. The basic configuration of inlet for SB #8 FSP.
S.-W. Kim et al. / Fusion Engineering and Design 93 (2015) 69–75
71
Fig. 3. The test result of friction welding using thickness of 6 mm pipes: (a) weld joint and (b) cross-section of weld joint.
Fig. 4. The test result of automatic bore TIG welding using thickness of 8 mm pipes: (a) inside of weld joint and (b) cross-section of weld joint.
3.2. Cover welding and non-destructive examination
bead although almost the whole results can be acceptable as shown in Fig. 5(b) and (c). Narrow gap U-groove shape having welding slot was applied to the cover welding of the SB #8 FSP from these results. Five types of special UT probe which is calibrated and tested with calibration block and reference block base on EN 12668, 0◦ (4 MHz), 25◦ (2 MHz), 45◦ (2 MHz), 60◦ (4 MHz) and 70◦ (2 MHz), were developed to perform 100% volumetric examination of welded regions. Welding deformation also was verified using test block and applied to the SB #8 FSP.
The SB #8 FSP model has many small and complicated shapes of cover plates and difficult part for NDE. The ITER VHB describe that for all VQC 1A water boundaries and vacuum boundary welds which become inaccessible, 100% volumetric examination of production welds shall be performed. Therefore, ultrasonic test (UT) should be most practical method for NDE after cover welding. For such a reason, verification of weld-ability and UT method is essential beforehand to accomplish cover welding and inspection of the SB #8 FSP. Four types of welding design were verified in this R&D activity and the main welding design elements are shown in Table 1. Several trial tests were performed and the results are shown in Fig. 5. Narrow gap U-groove shape having welding slot shows very good welding performance as shown in Fig. 5(a). In the cases of bevel groove and U-groove shape having no welding slot, however, some incomplete penetration parts were found at the edge of back
3.3. Slitting During operation of ITER, large EM load (force and moment) will be produced in SB due to the eddy/halo current interaction with the magnetic field. A number of deep slits are introduced into the SB to reduce the impact of the EM loads on the structural loads of the support system and vacuum vessel as above mentioned. Slitting
Table 1 The main welding design elements for the cover welding of SBs. Groove shape
Slot
Angle (◦ )
Root face (mm)
Root gap (mm)
Plate thickness (mm)
U-groove
O X
12
1
2
15
1
2.5 3.0 3.5 4.0
Bevel groove
X
35
10 15
72
S.-W. Kim et al. / Fusion Engineering and Design 93 (2015) 69–75
Fig. 5. Microstructure of cross section for each trial test result of cover welding: (a) U-groove shape having welding slot, (b) U-groove shape having no welding slot, and (c) bevel groove shape having no welding slot.
Table 2 Chemical composition of fabricated 316L(N)-IG steel including required values in the technical specifications. Element
C
Si
Mn
P
S
Ni
Cr
Mo
N
B
Co
316L(N)-IG Min.
–
–
1.60
–
–
12.00
17.00
2.30
0.060
–
–
Cu: max. 0.30 Nb: max. 0.10 Ti: max. 0.10 Ta: max. 0.01
0.030
0.50
2.00
0.025
0.010
12.50
18.00
2.70
0.080
0.002
0.05
Ladle
0.023
0.30
1.78
0.018
0.003
12.25
17.60
2.43
0.074
0.0006
0.026
Cu: 0.09 Nb: 0.006 Ti: 0.004 Ta: 0.001
Product
0.021
0.31
1.76
0.018
0.002
12.10
17.66
2.40
0.077
0.0007
0.025
Cu: 0.09 Nb: 0.006 Ti: 0.004 Ta: 0.001
Max.
was focused on the optimization of slitting conditions to achieve required tolerances. Jig and fixture also important issue due to the complicated shape of the SB #8 FSP. Applicable tolerances, surface roughness less than 4.2 m, slit width in the range of 2.5–3.5 mm and mismatch value in center line between slit width and slit end hole of max. 3 mm, were verified through the results of test block by using band saw machine. Furthermore, appropriate jig and fixture was confirmed with carbon steel mock-up. Optimization of slitting conditions has been completed from this R&D activity and applied to the SB #8 FSP.
4. Manufacturing route 4.1. Fabrication of material 316L(N)-IG steel is grade 316L steel with narrower alloying element ranges and controlled impurities. The closest analogy is X2-17Cr-12Ni-2Mo controlled nitrogen content austenitic stainless steel described in RCC-MR Code, Edition 2007 [4]. Electric arc furnace (EAF), ladle furnace (LF) and vacuum oxygen de-carburization (VOD) for steelmaking process, and heat furnace and oil-hydraulic forging press (9000 t) for forging process was applied to fabricate 316L(N)-IG steel for the SB #8 FSP by POSCO Specialty Steel Co., Ltd., Korea. Chemical composition of fabricated 316L(N)-IG steel including required values in the technical specifications [5] is shown in Table 2. Required inspections, such as ferrite content, magnetic permeability, grain size, non-metallic inclusions and mechanical properties at RT and 250 ◦ C, after fabrication of 316L(N)-IG steel were implemented in accordance with the technical specifications. All of the inspection results met the acceptable criteria in the technical specifications. The results of mechanical properties are shown in Table 3.
4.2. Machining of the SB #8 FSP Based on the developed techniques from R&D activities, conventional machining techniques such as cutting, milling, drilling and welding have been applied for the SB #8 FSP. Overall machining processes are shown in Fig. 6. Appropriate inspections such as visual, dimensional, UT, etc. were performed before start and after complete each process. Especially, visual inspection by endoscope after deep hole drilling was applied to confirm “no blocked or partially blocked water channels” for all of drilled holes on the SB #8 FSP. As examples, visual inspection result by endoscope for drilled deep hole is shown in Fig. 7. Inspection object hole is indicated by dashed circle in Fig. 7(a). The object hole is cross with four other holes, and it can be confirmed that all the holes have no blocked or partially blocked each other as shown in Fig. 7(b). Cover welding is one of key technical issue because the SB #8 FSP has many cover plates with complicated shape. The sequence of cover welding was (1) joining strong back system, (2) connecting purging system (Ar gas), (3) closing all headers, (4) measuring oxygen concentration in the root gap, (5) tack welding of cover plate and visual inspection and (6) welding from root pass. Fig. 8 shows Table 3 Mechanical properties of fabricated 316L(N)-IG steel at RT and 250 ◦ C. Tensile test RT Yield strength (0.2% offset), MPa Tensile strength, MPa Elongation, % 250 ◦ C Yield strength (0.2% offset), MPa Tensile strength, MPa
Spec. min.
Sample 1
Sample 2
220
275
245
525 45
550 58
540 60
135
158
159
415
436
439
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Fig. 6. Overall machining processes for manufacturing of the SB #8 FSP: (a) cutting, (b) milling, (c) semi-finishing, (d) drilling, (e) cleaning, (f) fit-up of cover plate, (g) cover welding, (h) slitting, (i) 1st finishing for front side, (j) 1st finishing for back side, (k) UT inspection, and (l) interface machining and final finishing.
Fig. 7. An example of visual inspection by endoscope for drilled deep hole: (a) inspection object hole and (b) images for the inside of drilled deep hole.
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Fig. 8. The SB #8 FSP during and after cover welding (root pass welding, after third pass welding and after completion): (a) root pass welding, (b) after 3rd pass welding, (c) completion of front side, and (d) completion of back side.
the SB #8 FSP during and after cover welding. Finally, 100% volumetric inspection by UT for all welding region was implemented in accordance with welding procedure specification (WPS) which was verified from welding procedure qualification test (WPQT) based on EN ISO 15614-1. Even if total 4 indications of elongated cavity wormholes were founded, all the indications were acceptable in accordance with acceptance criteria. 4.3. Validation tests In accordance with the ITER VHB, leak test should be carried out on the final component after pressure testing to confirm the soundness of welding processes, and to reduce the risk of incorporating leaks in a system that are subsequently difficult to locate or to repair. Vacuum baking after hydraulic pressure test is needed for the removal of contaminants which can break down to volatile components under the application of temperature, reducing the outgassing rate of the surface by accelerating the thermal desorption of molecular species and opening up incipient leaks, particularly porosity, where the leak path has been blocked by, for example, a carbon inclusion. The hydraulic pressure test and the cold He leak test including baking at 200 ◦ C for 24 h were performed on the final SB #8 FSP in this work. Final cleaning was also performed after completion of validation tests and final machining for attachment parts. Schematic diagram and a picture of cold He leak test system is shown in Fig. 9. The followings are general rules for the hydraulic pressure test. • The test pressure shall be 7.15 ± 0.2 MPa. • The test temperature shall be 22 ± 5 ◦ C. • The test pressure shall be measure and recorded over a period of not less than 30 min. • No pressure drop is acceptable within the 30 min test period. • No permanent deformation of surfaces. And also, the acceptance criteria are: • No visible water leaks.
Fig. 9. Cold He leak test system for SB #8 FSP: (a) a schematic diagram of the test system and (b) a picture of the test system.
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• No visible water leaks and no permanent deformations from the hydraulic pressure test. • Same with background level (0.4 × 10−10 Pa m3 /s) which means no He leak from Cold He leak test. A picture of the SB #8 FSP fabricated under the shield block full scale prototype pre-qualification program is shown in Fig. 10. 5. Summary
Fig. 10. Shield block full scale prototype being fabricated and tested by the SB FSP pre-qualification program.
• No appreciable variation of the test pressure within the tolerance range of ±0.2 MPa. • No permanent deformations as detectable by visual inspection. The acceptance criteria for cold He leak test are: • The vacuum level shall be less than 1.3 × 10−3 Pa. • The sensitivity of the He detector shall be better than 4 × 10−11 Pa m3 /s. • Maximum leak rate shall be 1 × 10−10 Pa m3 /s. • The leak detector reading is monitored until it has stabilized, without any electronic correction. This should take around 10 min, but the time can be longer depending on the size of the system under test. All the validation test results on the final SB #8 FSP were met the acceptance criteria. The main results of the tests are:
Related R&D activities were implemented to resolve the fabrication issues. 316L(N)-IG forged steel was successfully fabricated and qualified in accordance with the technical specifications. The conventional fabrication techniques such as cutting, milling, drilling and welding of the forged stainless steel block were applied for the manufacturing of the SB #8 FSP. All of the tests such as visual & dimensional inspection, NDE, hydraulic pressure test and cold He leak test was carried out and met the acceptance criteria. From those all activities, the acceptable quality and the capable of successfully passing the formal test program in Korea domestic agency have been demonstrated with successful completion of the “SB Full Scale Prototype (FSP) pre-qualification program”, and the Procurement Arrangement was made on November 2013 between Korea domestic agency and ITER organization. Acknowledgments This work is supported by the Ministry of Science, ICT and Future Planning of Republic of Korea under an ITER Project Contract. The view and opinion expressed herein do not necessarily reflect those of the ITER Organization. References [1] A.R. Raffray, M. Merola, Contributors from the Blanket Integrated Product Team, Overview of the design and R&D of the ITER blanket system, Fusion Eng. Des. 87 (5–6) (2012) 769–776. [2] A.R. Raffray, Blanket Design Description Document (FDR), 2013 (Private Communication). [3] L. Worth, ITER Vacuum Handbook, 2009 (Private Communication). [4] RCC-MR Code, Section 2: Materials, AFCEN, 2007. [5] R. Eaton, V. Barabash, Technical Specification – 316L(N)-IG forging for Blanket, 2013 (Private Communication).