51313-02618-Alloy Composition and Temp. Effect on Corr. Behavior of Stainless Steels in Hot Alkaline Solutions

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Product Number: 51313-02618-SG

ISBN: 02618 2013 CP

Author: Pekka Pohjanne

Publication Date: 2013

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Corrosion behavior of austenitic stainless steel EN1.4301 (UNS S30403) duplex stainless steels EN1.4162 (UNS S32101) EN1.4362 (UNS S32304) EN1.4462 (UNS S32205) and EN1.4410 (UNS S32507) as well as ferritic stainless steels EN1.4509 (UNS S43932 ) and EN1.4521 (ASTM 444) was evaluated with U-bend specimens in the alkaline solutions containing 500 g/l NaOH 100 g/l NaOH + 55 g/l Na2S (HWL hot white liquor) and 15 g/l NaOH + 150 g/l Na2S (HBL hot black liquor) at temperatures of 140 and 190°C. Corrosion rates were determined from weight losses of the samples. The propensity to stress corrosion cracking (SCC) was characterized with optical microscopy and FESEM. In addition the corrosion products were analyzed with EDS and XRD.

Based on the results the highest corrosion rates were obtained in the 500 g/l NaOH whereas in HBL and HWL the corrosion rates were significantly lower. Increase in solution temperature resulted in higher corrosion rates especially in pure NaOH. Molybdenum alloying enhanced corrosion particularly at 190°C and at the presence of Na2S whereas chromium seems to improve corrosion resistance. Severe SCC was observed in the austenitic and ferritic stainless steels. The XRD analyses showed that different corrosion products are formed in sulfides containing solutions than in the pure NaOH. In contrast in pure NaOH various oxides were formed whereas at the presence of Na2S also sulfide containing corrosion products such as iron-nickel-sulfides were formed.