CORROSION BEHAVIORS OF INCONEL 690TT AND INCOLOY 800MA STEAM GENERATOR TUBES IN HIGH TEMPERATURE HIGH PRESSURE WATER
Jianqiu WANG,Fa HUANG,Wei KE()
Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
Jianqiu WANG, Fa HUANG, Wei KE. CORROSION BEHAVIORS OF INCONEL 690TT AND INCOLOY 800MA STEAM GENERATOR TUBES IN HIGH TEMPERATURE HIGH PRESSURE WATER. Acta Metall Sin, 2016, 52(10): 1333-1344.
Inconel 690TT and Incoloy 800MA have been widely used as steam generator heat transfer tubes in nuclear power plants (NPPs). The corrosion behaviors of these two alloys in high temperature high pressure water have to be fully addressed. This work systematically studied the microstructures of the as-received Inconel 690TT and Incoloy 800MA steam generator tubes (SGTs) and compared the oxide films formed on the tubing materials in high temperature water using several analytical methods including SEM, EBSD, GIXRD, SAED and STEM. The results show that from outer surface to inner surface of Inconel 690TT SGTs, the deviation degrees from the ideal Σ3 misorientation and the average value of Kernel average misorientation (KAM) gradually increase. The outer surface of Inconel 690TT SGTs are weakest. For Incoloy 800MA SGTs, the deviation degrees from the ideal Σ3 misorientation are within 0~1°, and the change of KAM average value is small. Exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h, oxide films of both Inconel 690TT SGTs and Incoloy 800MA SGTs have duplex structure. On Inconel 690TT SGTs, the outer layer is Fe-rich spinel and small NiO particles; the inner layer mainly is NiO, porous and less protective with the thickness of 716 nm. On Incoloy 800MA SGTs, the outer layer is big polyhedral spinel; the inner layer is small polyhedral spinel and protective with the average thickness of 150 nm; Cr is enriched at the interface between inner oxide layer and matrix. In high temperature water with dissolved oxygen, due to the preferential dissolution of Cr, Incoloy 800MA is more corrosion resistant than Inconel 690TT.
Table 1 Chemical compositions of Inconel 690TT and Incoloy 800MA steam generator tubes (SGTs) (mass fraction / %)
Fig.1 Cross sectional SEM images of Inconel 690TT tube (a) outer part (b) middle part (c) inner part
Fig.2 Cross sectional SEM images of Incoloy 800MA tube (a) outer part (b) middle part (c) inner part
Fig.3 Cross sectional EBSD grain boundary images of Inconel 690TT tube (The blue lines denote the random grain boundary (RGB), the red lines denote the coincidence site lattice (CSL) boundary, and the white lines denote the low angle boundary (LAB)) (a) outer part (b) middle part (c) inner part
Fig.4 Cross sectional EBSD grain boundary images of Incoloy 800MA tube (The blue lines denote the random boundary, the red lines denote the CSL boundary, and the white lines denote the low angle boundary) (a) outer part (b) middle part (c) inner part
Fig.5 Grain boundary character distributions of Inconel 690TT and Incoloy 800MA tubes
Fig.6 Deviation degrees from the ideal Σ3 misorientation of Inconel 690TT and Incoloy 800MA tubes
Fig.7 Kernel average misorientation (KAM) average value of Inconel 690TT and Incoloy 800MA tubes
Fig.8 Cross sectional STEM image (a) and corresponding SAED patterns (b) of the outer part of Inconel 690TT tube
Fig.9 STEM image and corresponding SAED patterns (insets) of the outer part of Incoloy 800MA tube
Fig.10 Low (a) and high (b) magnified SEM images of the oxide film formed on Inconel 690TT exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h
Fig.11 EDS analyses of positions 1 (a), 2 (b) and 3 (c) in Fig.10b
Fig.12 GIXRD spectra of the oxide film formed on Inconel 690TT exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h under different grazing incident angles ω
Fig.13 Cross sectional STEM image (a), and corresponding SAED patterns of positions 1 (b), 3 (c) and 4 (d) of the oxide film formed on Inconel 690TT exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h
Position
Ni
Cr
Fe
O
1
56.16
1.05
0.97
41.80
2
49.63
0.78
1.25
48.32
3
31.05
9.42
3.84
55.66
4
48.83
0.58
1.16
49.41
5
48.46
1.55
1.96
48.01
Table 2 EDS analyses of positions 1~5 in Fig.13a (atomic fraction / %)
Fig.14 FIB secondary electron (SE) images of Inconel 690TT tube(a) selected oxide film is protected by Pt and the material on one side is removed(b) sample is tilted for observation
Fig.15 Low (a) and high (b) magnified SEM images of the oxide film formed on Incoloy 800MA exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h, and the EDS analysis of oxide particles (c)
Fig.16 GIXRD spectra of the oxide film formed on Incoloy 800MA exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h under different ω
Fig.17 Cross sectional STEM image (a) and corresponding SAED patterns of positions 1 (b), 3 (c) and 4 (d) of the oxide film formed on Incoloy 800MA exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h
Position
Ni
Fe
Cr
O
1
12.06
24.47
3.23
60.21
2
12.72
22.78
3.61
60.87
3
11.15
20.18
5.56
63.08
4
13.73
21.05
4.33
60.87
5
11.34
22.32
4.44
61.88
6
15.35
20.92
4.74
58.97
7
15.41
23.63
4.61
56.33
Table 3 EDS analyses of positions 1~7 in Fig.17a (atomic fraction / %)
Fig.18 SEM image (a) and EDS analysis (b) across the oxide film of Incoloy 800MA exposed to 325 ℃ pure water containing 0.75×10-6 O2 for 720 h (Position 1 corresponding to interface between inner and outer oxide layers; position 2 corresponding to interface between inner oxide layer and matrix)
Fig.19 Oxidation mechanism of Inconel 690TT and Incoloy 800MA in high temperature high pressure water with dissolved oxygen
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