[ Duplex ]
Figure 7 . SCC failure of S32550 super duplex agitator shaft in a mineral processing plant at 220 ° C with 31 bar oxygen and < 50 mg / L chloride . Photo courtesy of Steve Clarke and Maria Kincer .
Figure 8 . A S32304 digester and impregnation vessel digester for a Canadian Kraft pulp mill awaiting assembly . [ Photo courtesy of Steve Clarke ] advisable to test it in the actual service environment or a close laboratory simulation of it . In reducing environments containing large quantities of H 2 S at elevated temperatures and low pH values , alloys 825 and 625 ( UNS N08825 and N06625 ) have no limits of use in the solution annealed condition in ISO 15156 / NACE MR0175 . In more strongly reducing environments , such as hydrochloric acid , the nickel molybdenum alloys ( UNS N10665 , N10675 and N10629 ) are recommended .
Conclusions
••
Duplex stainless steels have good resistance to SCC , and there are numerous examples in service where they have performed well .
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Under strongly oxidising or reducing conditions duplex stainless steels may suffer SCC .
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The limits of use in reducing sour brines are well established , but the limits of use under strongly oxidising conditions are less well known .
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Only small concentrations of chloride may lead to SCC in strongly oxidising solutions .
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Where duplex alloys are susceptible to SCC it is necessary to consider more expensive titanium or nickel alloys .
References
1 . D R McIntyre and R Francis ( eds ), Environmental Cracking : Guidelines for Preventing Stress-Corrosion Cracking , Hydrogen Assisted Cracking and Liquid Metal Embrittlement in the Chemical Process Industries , MTI , St . Louis , MO , USA , 2016
2 . ASTM G36 , Standard Practice for Evaluating stress Corrosion Cracking Resistance of Metals and Alloys in a Boiling Magnesium Chloride Solution , ASTM , West Conshohocken , PA , USA .
3 . ASTM G123 , Standard Test Method for Evaluating Stress Corrosion Cracking of Stainless Alloys with Different Nickel Content in Boiling Acidified Sodium Chloride Solution , ASTM , West Conshohocken , PA , USA .
4 . R F A Pettersson and E Johansson , Stress Corrosion Resistance of Duplex Grades , Duplex Stainless Steels 2010 conference , Beaune , France , October 2010 , KCI . 5 . J Sedriks , Corrosion of Stainless Steels , J Wiley and Sons , 2nd Edition , 1996 . 6 . B Ozturk , J J Dunn , J F Grubb , Corrosion Properties of Duplex Stainless UNS S32003 Alloy , Paper 186 , corrosion 2008 ,
NACE International , Houston , TX , USA , March 2008 . 7 . R Francis , The Corrosion of Duplex Stainless Steels ; A Practical Guide for Engineers , NACE International , Houston , TX ,
USA , 2018 . 8 . J D Atkinson , J R Saithala and H S Ubhi , Stress Corrosion Cracking Potentials of Stainless Steels in Dilute Chloride Solutions at 130 ° C , Eurocorr 2008 , Edinburgh , Scotland , September , 2008 , European Federation of Corrosion . 9 . R Francis , Galvanic Corrosion : A Practical Guide for Engineers , 2nd edition , NACE International , Houston , TX , USA ,
2017 . 10 . R Cottis and R Newman , Stress Corrosion Cracking Resistance of Duplex Stainless Steels , Offshore Technology Report
OTH 94 440 , UK Health and Safety Executive , 1994 . 11 . ISO 15156 / NACE MR0175 , Petroleum and Natural Gas Industries , Materials for use in H2S – Containing Environments in
Oil and Gas Production , Part 3 Corrosion Resistant Alloys , Published by ISO and NACE International . 12 . V Linton , N Laycock , D Keen and P Boon , SCC Failure of a Super Duplex Separator Vessel in an Ammonium Nitrate Plant ,
Mat . Perf . 47 , 9 ( 2008 ) 64
13 . P Woollin and M Maligas , Testing of Super Duplex Stainless Steel for Sour Service , Paper 132 , Corrosion 2003 , March 2003 , NACE International , Houston , TX , USA .
24 Stainless Steel World April 2023 www . stainless-steel-world . net