技術解説 Quantification of Rust and Prediction of Cracking PWR Metal corrosion was classified into two types general ( or uniform ) corrosion ( rust ) and passive or localized corrosion ( cracking ) based on the characteristics of corrosion damage morphology and of corrosion mechanisms in order to summarize the concepts regarding the evaluation of both corrosion types. In addition, this article presents scenarios for the guaranteeing through tests of the long-term soundness of materials used for plant components and the evaluation of stress corrosion cracking in the primary water environment of Pressurized Water Reactor ( PWR ). Such evaluations are being carried out intensively in recent years. 1. 緒言 ( Corrosion ) ( 1 ) ( 2 ) ( 3 ) 第 1 図 - ( a ) - ( b ) ( a ) ( b ) a ( SCC ) a da/dt e a da/dt t t t 第 1 図 Fig. 1 Concepts behind classification of corrosion based on characteristics of corrosion damage morphology and corrosion mechanisms, and life prediction 48 IHI Vol.51 No.4 ( 2011 )
PWSCC ( Primary Water Stress Corrosion Cracking ) 2. さび と ひび 第 2 図 ( CUI Corrosion Under Insulation ) ( SCC Stress Corrosion Cracking ) SCC ( APC Active Pass Corrosion ) ( TR Tarnish Rupture ) Fe Fe 2+ + 2e Stress Corrosion Cracking SCC ( O 2 + 2H 2 O + 4e 4OH - ) FAC ( SCC ) ( CF ) ( HE ) SCC SCC SCC SCC ( APC ) ( TR ) FAC Flow Assisted Corrosion 第 2 図 Fig. 2 Classification of corrosion based on characteristics of corrosion mechanisms and morphology of corrosion damage IHI Vol.51 No.4 ( 2011 ) 49
m cm 1 mm/y ( Passivity ) ( 4 ) Cr 2 O 3 ( Crevice ) Cl - ( Hydrogen Embrittlement ) 3. さび の定量 第 3 Cr ( mm/y ) 10 2 10 1 10 0 10 1 10 2 10 3 10 4 0 2 4 6 8 10 ph 12 14 第 3 図 ph Fig. 3 ph dependence of corrosion ( rust and cracking ) rate of carbon steel and stainless steel 図 ph 0.2 mm/y 1/2 0.1 mm/y ( Cl - ) ( DO ) ph ( 1 mm/y ) 0.1 mm/y 1 mm/10 y 10 1 mm/y 4. ひび の予測 第 4 図 ( SCC ) SCC 第 5 図 50 IHI Vol.51 No.4 ( 2011 )
( a ) ( b ) 25 µm 第 4 図 Fig. 4 Example of cracking in stainless steel T 200 150 100 50 0.001 0.01 0.1 1 10 111 121 010 010 000 NaCl 121 SCC 111 121 221 010 222 110 332 110 0 10 0 10 1 10 2 10 3 10 4 10 5 Cl ( ppm ) Type304 SCC 第 1 表 第 5 図 ( SCC ) Fig. 5 Areas of stainless steel with pitting corrosion, crevice corrosion and SCC ( cracking ) ( temperature chloride concentration diagram ) 第 1 表 Table1 Standards for degradation level, risk of damage, longevity and sensitivity to damage 3 > 0.01 2d 2 > 0.001 0.01 > 2d 4d 1 > 0.000 1 0.001 > 4d 10d 0 0.000 1 > 10d d ( 5 ) 50 10 第 1 表 70 500 ppm [ Cl - ] 1 2 SCC 1 1 0.001 0.000 1 Type304 18Cr-8Ni Cr ( Cr 23 C 6 ) Cr Cr Cr Cr Type304 18 12 Cr C - 800 450 - - Cr TTS ( Time-Temperature-Sensitization ) ( 6 ) ( R a Reactivation Ratio ) JIS ( 7 ) DOS ( 8 ) C Type304L Nb Ti C 第 6 図 IHI Vol.51 No.4 ( 2011 ) 51
1.0 0.8 SCC SCC 0.6 V SCC ( mm /y ) 5 4 3 2 1 Type304 R a =35 Type304L R a =0 H(t) 0.6 0.4 0.2 0.6 6.2 0.0 0.0 0 5 10 15 20 t ( y ) 0.5 0.4 0.3 0.2 0.1 F(t) 0 R a = 35 0.1 g/m 2 ( Type304L ) 第 6 図 ( 9 ) 10 2 10 1 10 0 10 1 Cl ( g/m 2 ) 第 6 図 Fig. 6 Dependence on amount of adhering sea salt of average rate of cracking in sensitized stainless steel in wet oceanic environments, and cracking rate comparison between sensitized and non-sensitized stainless steel ( 10 ) 第 7 図 SSC C SCC 1 100 0.6 6.2 10 ( 11 ) SCC a ( 12 ) a = a 0 f f f f f f = a 0 [ f C (E - E R,SCC )] -1 (S T /S y - 0.5) -2 ([Cl - ]) -0.5 R a -4.1 exp (6.8 10 2 /T ) ( 1 ) f C E S T S y [Cl - ] R a T 第 7 図 SCC SCC Fig. 7 Difference in time to detect cracks between sensitized materials ( for which SCC countermeasures have yet to be taken ) and materials for which SCC countermeasures have been taken 5. PWR 環境における SCC 感受性評価の例 ( BWR ) SCC 52 IHI Vol.51 No.4 ( 2011 )
BWR SCC ( PWR ) PWR SCC BWR 288 0.2 ppmdo 7 MPa DO DO SCC PWR 315 360 22 MPa PWSCC SCC PWSCC SSRT Slow Strain Rate Tensile SCC RUB Reverse U-bend SCC UCL Uniaxtual Constant Load SCC 400 RUB 第 8 図 PWSCC SSRT L SSRT 360 PWR ( 500 ppm B 2.0 ppm Li DO < 5 ppb DH ( Dissolved Hydrogen ) 30 cckg / H 2 O ) 0.1 mm/min Alloy600 ( 16Cr - 75Ni - 9Fe ) Ni Alloy82 ( IDSCC ( Inter Dendritic Stress Corrosion Cracking ) ) PWSCC Alloy690 ( 30Cr-60Ni-10Fe ) Alloy52 PWSCC PWSCC 6. さび と ひび のセンシング ( Fe ) ( Ag ) Fe-Ag ( 13 ) ( a ) SSRT ( b ) SSRT ( c ) Alloy82 IDSCC ( d ) Alloy52 SCC 500 µm 第 8 図 PWR SSRT SCC Fig. 8 Evaluation using SSRT tests of SCC susceptibility in flow accelerated corrosion of PWR IHI Vol.51 No.4 ( 2011 ) 53
( Electrochemical Signal ) ( 14 ) 100 mm mm ( 15 ) ( 11 ) ( 16 ) ( 17 ) ( 18 ) AE ( Acoustic Emission ) ( 19 ) 参考文献 ( 1 ) 1993 p. i ( 2 ) ISO/TC156/WG1 ISO 8044 39 3 1990 3 pp. 148 154 ( 3 ) Q&A 110 1988 p. iv ( 4 ) ( III ) 12 10 1977 10 pp. 718 725 ( 5 ) 2007 3 ( 6 ) 39 11 1990 11 pp. 641 652 ( 7 ) JIS G0580-2003 2003 3 ( 8 ) IHI DOS A-94 < http://www. iic-hq.co.jp/services/j/06.html > 2011-07-04 ( 9 ) ( 1 ) 4 4 2006 1 pp. 29 34 ( 10 ) G. Nakayama, M. Akashi and A. Ohtomo : A probabilistic assessment for the stress corrosion cracking lifetime of sensitized 304 stainless steel in sodium chloride solutions ISIJ International vol. 31 No. 2 ( 1991. 2 ) pp. 223 228 ( 11 ) M. Akashi and G. Nakayama Stress-corrosion crack initiation process model for BWR plant materials Proceeding of international symposium on plant aging and life predictions of corrodible structures Sapporo Japan ( 1995. 5 ) pp. 99 106 ( 12 ) 48 3 1999 3 pp. 162 168 ( 13 ) ACM 43 10 1994 10 pp. 550 556 ( 14 ) 42 479 1993 8 pp. 930 933 ( 15 ) 59 12 2010 12 pp. 890 899 ( 16 ) 41 12 1992 12 pp. 809 815 ( 17 ) 2007 A-310 2007 5 ( 18 ) K. Tohgo and N. Ogi : Monte carlo simulation of stress corrosion cracking in structural metal materials Key Engineering Materials Vols. 306 308 ( 2006 ) pp. 447 452 ( 19 ) AE AE 53 11 2004 11 pp. 709 714 54 IHI Vol.51 No.4 ( 2011 )