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51313-02621-TSA Coatings for the Mitigation of Corrosion and EAC of Welded Duplex SS at Elevated Temperature

Product Number: 51313-02621-SG
ISBN: 02621 2013 CP
Author: Dave Harvey
Publication Date: 2013
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Duplex stainless steels are susceptible to localised corrosion and environmentally assisted cracking when subjected to loads and temperatures approaching their material design limits. Conventional organic coatings provide limited mitigation due to their rapid degradation at elevated temperature. Whilst the use of thermally sprayed aluminum (TSA) to mitigate the corrosion of C-steels and austenitic stainless steels is well-documented there are little or no published data relating to its behaviour on duplex stainless steels (DSS) or other high strength alloys.

This paper summarises the results of a TWI Joint Industry Programme which comprised a detailed evaluation of the performance of TSA-coated 22Cr DSS welds subjected to pitting corrosion external chloride stress corrosion cracking and hydrogen cracking. The effect of plastic strain (at values simulating pipe reeling) on TSA coating integrity and behaviour was investigated. TSA corrosion rate data were produced at ambient and elevated temperature using two electrochemical techniques. The effects of sealant selection on TSA coating behaviour were characterised. Recommendations for the application of TSA coatings on 22Cr DSS are provided.

Keywords: coatings; thermal spray; stress corrosion; duplex stainless steels; pipeline steels; cracking; welded joints; hydrogen embrittlement.

Duplex stainless steels are susceptible to localised corrosion and environmentally assisted cracking when subjected to loads and temperatures approaching their material design limits. Conventional organic coatings provide limited mitigation due to their rapid degradation at elevated temperature. Whilst the use of thermally sprayed aluminum (TSA) to mitigate the corrosion of C-steels and austenitic stainless steels is well-documented there are little or no published data relating to its behaviour on duplex stainless steels (DSS) or other high strength alloys.

This paper summarises the results of a TWI Joint Industry Programme which comprised a detailed evaluation of the performance of TSA-coated 22Cr DSS welds subjected to pitting corrosion external chloride stress corrosion cracking and hydrogen cracking. The effect of plastic strain (at values simulating pipe reeling) on TSA coating integrity and behaviour was investigated. TSA corrosion rate data were produced at ambient and elevated temperature using two electrochemical techniques. The effects of sealant selection on TSA coating behaviour were characterised. Recommendations for the application of TSA coatings on 22Cr DSS are provided.

Keywords: coatings; thermal spray; stress corrosion; duplex stainless steels; pipeline steels; cracking; welded joints; hydrogen embrittlement.

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