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Temperature as a pitting and crevice corrosion criterion in the FeCl 3 test
Author(s) -
Renner M.,
Heubner U.,
Rockel M. B.,
Wallis E.
Publication year - 1986
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19860370405
Subject(s) - crevice corrosion , corrosion , alloy , materials science , metallurgy , pitting corrosion
The FeCl 3 test is applied to an increasing extent for examining the resistance to pitting and crevice corrosion. Two methods having proved their value are described, the chemical properties of the FeCl 3 solution with regard to hydrolysis, pH and redox potential behaviour at various test temperatures are set forth and finally numerous results of the application of this test to high‐alloy stainless steels and nickel alloys are presented. These results have been used to establish, be means of multiple regression, two empirical equations that allow to estimate rather accurately the critical pitting and crevice corrosion temperatures (CPT, CCT) from the contents of the decisive alloying constituents. These temperatures vary by about 2.5°C in the CPT test and by approx. 10°C in the CCT test, which can be reduced, however, by extending the test period beyond 24 hours. This is due to the fact that corrosion potentials in a 10% FeCl 3 · 6H 2 O solution take a long time to stabilize. The variation of the critical crevice temperature can be further reduced by pressing the crevice blocks at a higher torque to the specimen. Another section particularly deals with the application of the CPT test for determining the influence of the matrix on the resistance to local corrosion. Consequently, the CPT test lends itself excellently to the examination of welds and as a quality control. Finally, CPT test results are compared with pitting data determined electro‐chemically in artificial seawater. This shows that the ranking order with regard to corrosion resistance is identical, although media and processes differ considerably from each other.