,, Case Analysis of Stainless Steel Corrosion in Hot Spring Waters and Using Titanium as a Measure against Corrosion Toshihiro Yamate Tec

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,, 491 496 2011 Case Analysis of Stainless Steel Corrosion in Hot Spring Waters and Using Titanium as a Measure against Corrosion Toshihiro Yamate Technical Research Laboratory Takenaka Co., Ltd.

sulfide. Corroded samples were analyzed, remaining handrails were observed closely, an immersion test was conducted at the sources of springs, and corrosion potentials were measured.

1 ,, Case Analysis of Stainless Steel Corrosion in Hot Spring Waters and Using Titanium as a Measure against Corrosion Toshihiro Yamate Technical Research Laboratory Takenaka Co., Ltd. In hot spring facilities in Kusatsu, Gunma Prefecture, in about two months, SUS304 stainless steel handrails corroded and dissolved uniformly in acid sulfate-chloride spring water containing hydrogen sulfide. Corroded samples were analyzed, remaining handrails were observed closely, an immersion test was conducted at the sources of springs, and corrosion potentials were measured. The result showed that the causes of the corrosion were low ph (ph 2 or less) and the corrosion action of free hydrogen sulfide. Because the handrails corroded in only the type of spring water containing hydrogen sulfide at the two sources of springs with a ph of 2 or less, hydrogen sulfide had a particularly significant impact on the corrosion and accelerated the active dissolution of SUS304 stainless steel. As a measure against corrosion, titanium instead of SUS304 stainless steel was used for handrails. Rusting or local corrosion was not observed about 18 months after use. Key words : stainless steel, corrosion, hot spring water, ph, H 2 S, corrosion products, corrosion potential Table 1 Source name and location of each bathtub. 1) 3) (SUS304) 4 1 SUS304 ( ) 2 (No. 1 ) 8 (No. 2 ) 12 No. 1 No. 3 ( A) No. 4 ( B) Table 1 18 ( A) No. 1 No. 3 No. 1, No No. 1, No. 2 Fig. 1, Fig. 2 () SUS304 A No Fig. 3 Fig. 4 ( B) No ( 2011 ) (1 5 1, Ohtsuka, Inzai, Japan) No. 1 EDX ( JSM 6300) Fig.5 S Fig. 6 EPMA ( JXA 8100) S, O, Cr, Fe, Ni ( ) Fe, Cr, Ni No. 1 No. 3

492 材料と環境 Fig. 1 State of corrosion of handrail in bathtub No.1, about 2 months use. Fig. 2 State of corrosion of handrail in bathtub No.

浴槽の手摺から採取したさびについて XRD (マックスサイエンス MXP18 およびリガク RU 2000) により分析した結果硫酸ニッケルのみが同定されたいずれもピークがブロードであり

bathtub No.1 が示された非晶質のさびについても結合エネルギーから化合物の形態を推定するため XPS (島津製作所 ESCA 3200) による状態分析を行った No.

7 によればそれぞれ硫化物 FeS, FeS 2, NiS 硫酸塩 FeSO 4, NiSO4 酸化物 Fe2O3, Cr2O3, CrO3 水酸化物 Cr(OH)3 などの生成が示唆されるまた Fig.

2 492 材料と環境 Fig. 1 State of corrosion of handrail in bathtub No.1, about 2 months use. Fig. 2 State of corrosion of handrail in bathtub No.2, about 8 months use. Fig. 3 State of active dissolution of handrail in bathtub No.3, about 12 months use. 浴槽の手摺から採取したさびについて XRD (マックスサイエンス MXP18 およびリガク RU 2000) により分析した結果硫酸ニッケルのみが同定されたいずれもピークがブロードであり結晶性の低い化合物であること Fig. 4 State of corrosion of handrail in bathtub No.3, about 12 months use. Fig. 5 Analysis result by EDX of corrosion products of SUS304 handrail in water line part. bathtub No.1 が示された非晶質のさびについても結合エネルギーから化合物の形態を推定するため XPS (島津製作所 ESCA 3200) による状態分析を行った No. 3 浴槽のさびについて XPS による分析結果を Fig. 7 に示す Fig. 7 によればそれぞれ硫化物 FeS, FeS 2, NiS 硫酸塩 FeSO 4, NiSO4 酸化物 Fe2O3, Cr2O3, CrO3 水酸化物 Cr(OH)3 などの生成が示唆されるまた Fig. 5, Fig. 7 において銅およびその化合物 (Cu2S, CuSO4) が少なからず検出されている Table 2 に示す 2 つの源泉の水質分析結果によれば泉質 A の銅濃度は 0.01 mg/l 未満であり手摺材の SUS304 に含まれる銅が 0.3 (mass 蛍光 X 線分析法島津製作所 MFX2400) であることから銅は手摺素材に由来するもの (不純物) と考えられる SUS304 中の銅は微量であるがさび中での濃化により検出された可能性がある 2.3 水質分析 ph は現地で測定しほかの水質項目は冷蔵して分析室に搬入し速やかに分析した分析は工業用水試験法

9 A H 2 S 7.3 mg/l B 0.0 mg/l A SO 4, Cl SO 4 /Cl (mg/l) A 2.93 B 2.03 SO 4 SUS304 (SCE) ( EM 02) (665 425 75 mm) ( A 46.

3 Fig. 6 Analysis result by EPMA of corrosion products of SUS304 handrail in water line part (bathtub No.1). Fig. 7 Analysis result of corrosion products of SUS304 handrail by XPS in bathtub No.3. (JIS K 0101) ( JIS K 0102) ph 1.9 A H 2 S 7.3 mg/l B 0.0 mg/l A SO 4, Cl SO 4 /Cl (mg/l) A 2.93 B 2.03 SO 4 SUS304 (SCE) ( EM 02) ( mm) ( A 46.2 B 47.8 ) 41.5 (SCE) SUS304, SUS mm (SUS304 ) No. 3, No. 4 Table 3 A No. 3 SUS V(vs. SCE) B No V(vs. SCE) Fig. 8 A SUS304

Table 2 Water quality of the hot spring sources. Fig.

different sources (V vs. SCE, No.3 and 4). SUS316 SUS304 0 V 41.5 0.

4 Table 2 Water quality of the hot spring sources. Fig. 8 Time variation of corrosion potentials of SUS304 and SUS316 test pieces in the hot spring sources. Fig. 9 Appearances of stainless steel test pieces in the hot spring water after 41.5 hours dipping. Table 3 Corrosion potential of SUS304 stainless steel in the two bathtubs with different sources (V vs. SCE, No.3 and 4). SUS316 SUS304 0 V V B SUS304, SUS316 0 V SUS316 SUS304 mv SUS304, SUS316 A Fig. 9 SUS316 B SUS304, SUS316 SUS304, SUS316 ph (ph d ) ph 2 ph SO 4 /Cl (mg/l) A A SUS V(vs. SCE) SUS304 ( V vs. SCE) A SUS304 ph 2 ph Fig. 3 ph 2 A S S A (No. 1 No. 2 No. 3) (No. 2 ) H 2 S H HS HS H S (II) Fe S FeS H 2 S

10 Appearances of titanium handrail after about 18 months use. SUS304 SUS316 SUS329J4L 2) A SUS316 SUS329J4L 18 No. 1 ( A) No.

5 (H 2 S 0 15 ppm by mole, ph 3, 60 ) SUS304L (R p ) (i cr. ) 4) H 2 S SUS304L FeS 2 (II) FeS 4) FeS 2 multi-pourbxi diagram ph 2 4) B ph 1.7 ph(ph d ) B ph d ph 2 SUS304 ph d Fig. 10 Appearances of titanium handrail after about 18 months use. SUS304 SUS316 SUS329J4L 2) A SUS316 SUS329J4L 18 No. 1 ( A) No. 4 ( B) Fig. 10 Fig A B 3 Fig V B A A SUS304 Fig. 11 Time variation of corrosion potentials of titanium handrail. 1) SUS304 ( A ph 1.9) 2 2) ( B ph 1.7) SUS ) 2 18 SUS304

6 ( ) ( ) 1) M. Nakata, T. Komano and S. Tsujikawa, Proceedings of JSCE Materials and Enviroments 99, Japan Society of Corrosion Engineering, p.17 (1999). 2) K. Iino, M. Akanuma, N. Katayama, T. Saito and T. Suzuki, Hokkaido Industrial Examination Room Report, p.113 (2008). 3) A. Maekita, K. Oda, N. Oyama and M. Nishikawa, Proceedings of JSCE Corrosion and Protection 81, Japan Society of Corrosion Engineering, p.86 (1981). 4) A. Davoodi, M. Pakshir, M. Babaiee and G. R. Ebrahimi, A comparative H 2 S corrosion study of 304 L and 316 L stainless steel in acidic media, Corrosion Science,, 399 (2011). Manuscript received July 14, 2011; in final form September 7, 2011 (SUS304) 2 ph (ph 2 ) ph 2 SUS ph

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