8th Spring Meeting of the International Society of Electrochemistry

8 th Spring Meeting of the International Society of Electrochemistry
35
The “Wedging Action” of Compounds as a Damage
Process Important to Professor Fontana
Roger W. Staehle
Staehle Consulting
22 Red Fox Road
North Oaks, Minnesota 55127
651 482 9493, 651 484 5735 (f)
rwstaehle@gmail.com
Keynote Lectures
“Font” was always interested in expanding corrosion products as important in various
damage processes. Such damage occurs in the expansion of corrosion products on
reinforcing bars in concrete and welded joints. He also felt that such damage was
important to the initiation and propagation of stress corrosion cracking. This expansion
of compounds, oxides, was first calculated and summarized for various metals by
Pilling and Bedworth (J. Inst. Met. 29, 534, 1923) in 1923. However, the forces exerted
by growing crystals was first identified in a reference by Becker and Day (Proc. Wash
Acad Sciences, VII, 283, 1905) in 1905 who referred also to studies by Jean Lavalle in
1853 and by Lehmann in 1888 on the same subject. Forces exerted in concrete by the
expansion of corrosion products from corroding reinforcing bars were studied and
forces measured in detail by Rosa et al. (#18 Bu. Standards 1919 GPO) and reported in
1919. Similar work was undertaken in his MS thesis and reported by Rosengarth (MS,
1981 Penn State Univ) in 1981. In 1962 Pickering et al. (Corr. Jnl. 18, 1962) showed
that the force of corrosion products grown in a crevice could be measured for
specimens of stainless steel exposed to 200°C chloride electrolytes. In this same paper,
they showed that the forces in a crevice would produce sufficient stresses at the bottom
of a crevice to initiate SCC; thereupon they removed the crevice element and the SCC
continued to grow due only to the forces of expanding corrosion products inside the
SCC. This is illustrated in Figure 1. Of substantial economic concern has been the
growth of corrosion products inside the superheated crevices of tube supports in the
steam generators of pressurized water reactors as summarized by Staehle. Such
expansion causes the tubes to deform and sustain SCC at locations of high plastic
strains as shown in Figure 2. Other recent results associated with the presence of lead
impurities in these superheated crevices have shown that the lead greatly accelerates
oxidation of Alloy 690 tubing (Proc. 5 th CNS SG meet). Professor Fontana’s instincts
again demonstrated that his intuitions in corrosion were right.
Fig. 1 Fig. 2