Study of Corrosion Life Prediction and its Testing Methods of Screws

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1 Study of Corrosion Life Prediction and its Testing Methods of Screws T.Kitai, O.Minomura, Y.Sato, The Fasteners Cooperative Association of Kansai, Japan e mail info@kansaineji.com 1

2 FCK founded 2002 (merged 5 fastener associations in Kansai) Members : Over 200 fastener related companies Makers Bolt, Nut, Screw, Washer SuppliersWire, Heat treatment, Plating Issues from housing industries (1) Life prediction of screws (2) Cr 6+ in Zn plating FCK R&D group started to investigate in 2003 (1) Salt spray test (ISO 9227, ASTM B117, JIS Z 2371) (2) Cyclic corrosion test (SAE J2334 etc.) (3) Outdoor exposure environment 2

3 Object Correlation between test time and outdoor exposure time Selection of better plating for screws Outdoor exposure months Fig.1 Prediction curve of screws life (occurrence of corrosion) 3

4 Acid Deposition Monitoring Network in East Asia(EANET) Kansai Area 4

5 Table 1 Round Robin test results The Fasteners Cooperative Association of Kansai, Japan coefficient (C) + coefficient of determination (R 2 ) (perfect value = 2) 5

6 Table Round 2 Round Robin Robin test test results results The Fasteners Cooperative Association of Kansai, Japan coefficient (C) + coefficient of determination (R 2 ) (perfect value = 2) 6

7 ph Fig.2 ph value of Rainfall in East Asia Reference;EANET

8 Maximum corrosion The Fasteners Cooperative Association of Kansai, Japan NaCl Fig.3 Salts Corrosion of alternate immersion and drying Ref:Y.Sato,Reports of Industrial Research Institute, Osaka Pref Japan(1969) Concentration of salts (mol) 8

9 Indoor Accelerated Corrosion Tests 1) JIS Z 2371 (Salt spray test,b117) Electrolyte Solution : 5wt% NaCl Ambient Condition: 35 1 Spray : 24Hr continuous 2) SAE J2334 / ISO A(2005) Electrolyte Solution : 5wt% NaCl, ph 3.5 (nitric acid, sulfuric acid solution mixed) 1Cycle: Spray (35 1,2hours) Dry(60 1,4hours) Wet(50 1,2hours) 3) FCK Method (The Fasteners Cooperative Association of Kansai Method) Electrolyte Solution : 0.5wt% NaCl +0.1wt% CaCl N (H 2 SO 4 ), (ph 4) 1cycle :Spray (50 1,16 hours) Dry(50 1,RH20 ~ 30%, 8 hours) Cyclic test apparatus: Model: ISO 3 CYR (Manufactured by Suga Test Instruments Co., ) 9

10 Table 3 Materials and Plating of Specimens 10

11 China Chongqing Feb.2005 Feb.2006 Feb.2004 Nagoya Feb.2004 Omaezaki Osaka Feb.2004 Japan Miyako island July 2007 July 2009 Fig.4 Exposure Sites 11

12 Chongqing, China Osaka, Japan Fig. 5 Outdoor Exposure 2years 12

13 Fig. 6 Concentration of Ions in Rainfall 13

14 Occurrence Time rust (months) Sample Name Fig. 7 Results of outdoor Exposure 14

15 Occurrence time of rust (months) Rust does not occur Carbon Steel Fig. 8 Results of FCK indoor accelerated test (After 72days) 15

16 Conclusions The correlation between the test time(x:days) of FCK Method and outdoor exposure time (Y:months) until red rust is noticed in Omaezaki, Japan Y (months) = 0.51X (days) Correlation between outdoor and indoor testing Methods C+R 2 SAE J2334 / ISO A FCK Outdoor exposure time (months) Indoor accelerated test time (days) 16

17 (A) Y S Y S ( = 0.77 X FCK ( ) (B) Y L Y L ( = 4.36 X FCK ( ) FCK FCK20 17