CORROSION ANALYSIS: LOW-CAPACITY PUMP. Large Sodium Pump Study, Phase II. Page: 12 of 30
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The Effect of Temperature
The variation of corrosion rate with temperature was consistent with
Arrhenius-type rate behavior. The UKAEA data shown in Figure 2 were
best described by the equation:
S = 2.3 X 10-6 exp 17,500 cm sec . (2)
where S = corrosion rate.
Analysis of the G.E. Data indicated that an increase of 100*F produced
approximately a three-fold increase in the rate of corrosion, consistent
with the temperature term in Equation 1.
The Effect of Velocity
A velocity dependence was observed only up to about 10 to 15 ft/sec
(Figure 1). Above this range, the corrosion rate is essentially
independent of velocity. The initial velocity dependence agrees with
the theoretical model for a diffusion controlled process given by:
R = 0.023 (D/d) (N - N ) Re8 Sc0.33 (3)
D = the diffusion coefficient of iron in sodium
d = the pipe diameter
Re = Reynolds number (=dVp/y)
Sc = the Schmidt number (=u/pD)
p = the density of sodium
i = the viscosity of sodium
N x = the mole fraction of iron dissolved in the sodium at saturation
for a given oxygen content.
Since Re is a function of V, RV0.8. Above 10 to 15 ft/sec however,
it was shown experimentally that R was independent of velocity, and
therefore that some other limiting process was involved. Thorley
and Tyzak~l] suggested that the slow deposition of iron in the cooler
parts of the circuit and/or some chemical process involving iron
removal from the sodium via a double oxide, was responsible.
Hopenfeld and Darley4] pointed out that a transition from a mass
transfer controlled process to a surface reaction controlled process
would give this result.
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Thomas, K.C. & Shiels, S. CORROSION ANALYSIS: LOW-CAPACITY PUMP. Large Sodium Pump Study, Phase II., report, October 31, 1970; Madison, Pennsylvania. (https://digital.library.unt.edu/ark:/67531/metadc1034653/m1/12/: accessed March 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.