51316-7456-Development of an Improved Version of UNS N08825 with Higher Corrosion Resistance

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Product Number: 51316-7456-SG

ISBN: 7456 2016 CP

Author: Julia Rosenberg

Publication Date: 2016

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Corrosion resistant Alloy UNS N08825 has been primarily used in the chemical process industry. In oil and gas exploration it is used because of its high resistance to stress corrosion cracking and sulphide stress cracking. However due to its low molybdenum concentration of 3% this alloy has a limited resistance to pitting and crevice corrosion in chloride containing environments.The main target of a new alloy development was to increase the critical pitting and crevice corrosion resistance while maintaining mechanical strength.In this paper the development of the new alloy will be presented. To improve the corrosion resistance the molybdenum content was increased from about 3% to 5.5-6%. This improvement results in a higher critical pitting temperature in chloride containing media. While the current Alloy UNS N08825 withstands a temperature of 35°C in a ferric chloride test solution the improved Alloy UNS N08852 endured up to a temperature of 50°C. Corrosion rates according to ASTM G 28 critical pitting temperatures according to ASTM G48-Method C and electrochemical investigations of unwelded and welded samples will be presented as well as the mechanical properties in cold-worked and soft annealed condition.The first upscaling of the alloy was successful and cold worked strip material was produced for the production of down hole control line tubing.