Impact of graphite gasket/duplex stainless steel couples on crevice chemistry and the likelihood of crevice attack in seawater
- National Physical Lab., Middlesex (United Kingdom). Centre for Materials Measurement and Technology
Crevice corrosion in seawater usually is assumed to be induced by attainment of a critical solution chemistry. Electrochemical polarization measurements were made on a graphite laminate gasket and a super-duplex stainless steel (DSS) in deaerated 1M sodium chloride (NaCl) solution over a range of pH. The open-circuit potential of the graphite was significantly more noble than that of the DSS, and the kinetics of the hydrogen ion reduction were greater at potentials more positive than {approximately} 0.0 V{sub SCE}. Data were used as input to a model of crevice chemistry, and predictions were made for potentials up to 0.4 V{sub SCE}. For crevices of parallel plates of DSS-DSS and DSS-plastic, the usual acidic conditions were predicted. However, for a DSS-graphite combination, there was no significant decrease in pH. The latter was a consequence of the enhanced kinetics for cathodic reduction of hydrogen ions and water on the graphite which, when confined within the crevice, opposed the fall in pH associated with the metal-ion hydrolysis process. The predictions suggested that coupling to graphite, contained within the crevice, may act to prevent crevice corrosion initiation in contrast to the usual perception of behavior when coupling to more noble materials. In practice, there have been significant crevice corrosion failures of DSS associated with graphite gaskets. However, in all cases, the failures were in chlorinated systems for which corrosion potentials are particularly high and beyond the range for which a benefit from graphite could be anticipated.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 315930
- Journal Information:
- Corrosion, Journal Name: Corrosion Journal Issue: 2 Vol. 55; ISSN 0010-9312; ISSN CORRAK
- Country of Publication:
- United States
- Language:
- English
Similar Records
Modeling of Crevice Corrosion Stability of a NiCrMo Alloy and Stainless Steel
Effects of cathodic protection on duplex stainless steels in seawater