Available data on embrittlement of duplex stainless steels (DSS) under cathodic protection (CP) in seawater, including some data previously unpublished, was reviewed. Results show hydrogen enters duplex alloys at typical protection potentials (-1 VSCE), but that the risk of failure is very low. The austenite phase tends to block cracks in the ferrite, and very high stresses are needed to produce fracture of the austenite or austenite-ferrite phase boundaries for crack propagation to occur. The smaller the grain size, the more resistant DSS is to embrittlement. Current design stresses for duplex alloys are well below stresses needed to produce failure. Service experiences with cathodically protected DSS were reviewed, and the few failures explained. At normal protection potential, the risk of failure of DSS from hydrogen embrittlement (HE) is extremly low. Hydrogen enters DSS under CP in seawater. HE is reduced by a fine grain size and a phase balance with 50 % or more austenite. Thermal aging of DSS greatly increases susceptibility to HE. Cold working up to about 35 Rockwell hardness (HRC) does not increase susceptibility to HE significantly. Crack propagation is blocked by austenite. High stresses sufficient to plastically deform the austenite are needed to initiate and propagate cracks. There is evidence of up to 7 years of successful service with cathodically protected duplex alloys subsea. The known service failures have resulted either from excessive cold work or thermal aging and a high ferrite content, all of which reduce the resistance to embrittlement. In view of severe loads necessary to cause cracking and the relatively low design stresses used for DSS.
Effects of cathodic protection on duplex stainless steels in seawater
Einfluß des kathodischen Schutzes auf nichtrostende Duplexstähle in Meerwasser
Corrosion, Houston ; 53 , 3 ; 234-240
1997
7 Seiten, 13 Bilder, 2 Tabellen, 13 Quellen
Article (Journal)
English
Duplex-Stahl , nichtrostender Stahl , Wasserstoffversprödung , kathodischer Korrosionsschutz , Meerwasser , Meerestechnik , Unterwasserbereich , Korrosionsstrom , Materialbruch , Erprobung , mechanische Spannung , Ferrit (Alpha-Mischkristall) , Austenit , Rissausbreitung , Rissbildung , Kaltumformen , Wärmebehandlung (Materialbearbeitung) , Spannungsdehnungsdiagramm , Versprödung , Chrom-Nickel-Stahl , Korrosionsschaden
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