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An analysis of corrosion of steels by liquid sodium
JOURNAL OF NUCLEAR MATERIALS 47 (1973) 129-131.0
AN ANALYSIS OF CORROSION
NORTH-HOLLAND PUBLISHING CO., AMSTERDAM
OF STEELS BY LIQUID SODIUM *
P. ROY and M.K. SCHAD General Electric Company, Breeder Reactor Department,
Sunnyvale, California, USA
Received 8 December 1972
The use of liquid sodium as a heat transfer fluid in Liquid Metal Fast Breeder Reactors (LMFBR) has resulted in a great deal of research effort to understand the fundamental aspects of corrosion of steels in flowing sodium. The effects of parameters, like oxygen concentration in sodium, sodium velocity and temperature on corrosion of steels, has received a great deal of attention. The purpose of this communication is to analyze the effect of velocity of sodium on corrosion of steels. It has been observed [I -41 that at temperatures above 1200’F (650°C), corrosion of steels increases with increase of sodium velocity up to a critical velocity, after which it becomes independent of sodium velocity. For example, Thorley and Tyzack’s [33 data show that corrosion rates of steel become indepeni dent of sodium velocity above - 14-15 fps, [3], whereas data from Roy et al. [I 1, Schrock et al. [2], and Furukawa [4] show that the corrosion rates increase with increase of sodium velocity up to - 20-25 fps, fig. 1. Based on this observation, it was proposed [I, 51 that, in the velocity dependent range, diffusion of reactants (e.g., corrosion products or oxygen) across the laminar sub-layer ia the rate controlling step. At higher velocities, the laminar sub-layer diminishes sufficiently so that the surface reaction rates become the rate controlling step, and are independent of velocity. It is obvious that if the hypothesis is correct, the corrosion data from various investigations should be analyzed
V 0
I
5
I
10 Sodium
I
I
15 20 velocity (fps)
I
I
25
30
I
35
Fig. 1. Corrosion of stainless steels as a function of sodium velocity: l 1200”F, 25 ppm oxygen, 131; v1325’F, < 10 ppm oxygen, [2] n 1300”F, < 5 ppm oxygen, [l].
on the basis of the thickness of the laminar sub-layer and not the velocity of sodium, although the two parameters can be related for simple specimen gee metries. Thorley [6] made an attempt to correlate the corrosion data in terms of Reynold’s number, which could be translated into the thickness of the laminar sub-layer provided the pipe diameter remained con-
* Work performed under Contract No. AT(04-3)
- 189, Project Agreement No. 15 between the Atomic Energy Commission and General Electric Company. 129
P. Roy, M.K. &had, Corrosion of steels by liquid sodium
130
IL--0
5
10 Sodium
15 20 25 velocity (fps)
30
J
Thickness
Fig. 2. Variation of laminar sub-layer thickness at constant Reynold number: Reynolds’s number = 100 000, pipe diame ter = 0.1 - 0.65 in (2.5 mm - 16.25 mm).
stant. However, the thickness of the laminar sub-layer can be different for an identical Reynold’s number if the pipe diameter is not constant. According to Schlichting [7], the laminar sub-layer thickness can be calculated by, 6-sv/v*,
(1)
where the friction velocity, v* =x$C
(2)
and the shearing stress at the wall, r. = 0.04 /&
,f d-f
)
10-4
10-5
35
(3)
where p = sodium density, ii = mean velocity (in pipe), v = kinematic viscosity = p/p, d = diameter of the pipe, P = absolute viscosity. Using eq. (l), the calculated thickness of the laminar sub-layer at a constant Reynold’s number and various pipe diameters is shown in fig. 2. This analysis shows that comparison of corrosion data from various laboratories, in terms of sodium velocity or Reynold’s number is not adequate. For the purpose of comparison, an attempt was made to correlate the limited corrosion data in the
of laminar
1o-2
1 o-3
sub - layer
(in.)
Fig. 3. Corrosion of austenitic steel in sodium as a function of laminar sub-layer thickness: l constant bore and o variable bore, 1200”F, 25 ppm oxygen (3); q variable bore, 1300”F, < 5 ppm oxygen [l]; v variable bore, 1325”F, < 10 ppm oxygen.
literature (where the geometry and sodium flow are known). A plot of corrosion rates of steels normalized against the thickness of the laminar sub-layer is shown in fig. 3. Due to the complicated geometry of the Furukawa and Nehei [4] corrosion specimens, similar calculations are not applicable, and consequently, were not included in the analysis. The data from Thorley and Tyzack [3], Roy et ai: 111, and Schrock et al. [23 seem to indicate that corrosion rates of steels become independent of fluid turbulance below a boundary layer thickness of 0.0002 inch (5 pm). Furthermore, this analysis appears to resolve the apparent anomaly among various data on effects of sodium velocity on corrosion rates of steels in liquid sodium. It is recommended that in future corrosion tests, the specimen geometry should be designed such that calculations of this type could be made, in order to evaluate and compare the corrosion data from various laboratories. Finally, it should be pointed out that at present the sodium velocity is used as one of the parameters
P. Roy, M.K. &had,
Corrosion of steels by liquid sodium
in all the design allowances for corrosion in LMFBk systems. The present analysis indicates that the boundary layer thickness should be determined from the velocity and geometry and then used in establishing the corrosion design allowances rather than the sodium velocity itself.
[l] P. Roy, G.P. Wozadlo and F.A. Comprelh, Proc. Internat. Conf. on Sodium Technology, Argonne (USA), ANL 7520, Part 1 (1968) p. 131.
131
[2] S.L. Schrock, J.N. Baysden, R.L. Miller and D.E. Lohr, Corrosion by Liquid Metals, (Plenum Press, New York, 1970) p. 41. [3] A.W. Thorley and G. Tyzack, Alkali Metal Coolants (IAEA, Vienna, 1967) p. 97. [4] K. Furukawa and I. Nehei, Proc. Internat. Conf. on Sodiurn Technology, Argonne (USA), ANL 7520, Part 1 (1968) p. 143. [5] L.F. Epstein, Chem. Eng. Prog. Sym. Ser., No. 20, Vol. 53 (1967). [6] A. Thorley, IAEA Specialists Meeting on: Fission and Corrosion Product Behavior in Primary System of LMFBR’s, Bensberg/FRG, CONF-710959 (1971). [7] H. Schlichting, Boundary Layer Theory, (McGraw Hill, New York, 1955) p. 407.
AN ANALYSIS OF CORROSION
NORTH-HOLLAND PUBLISHING CO., AMSTERDAM
OF STEELS BY LIQUID SODIUM *
P. ROY and M.K. SCHAD General Electric Company, Breeder Reactor Department,
Sunnyvale, California, USA
Received 8 December 1972
The use of liquid sodium as a heat transfer fluid in Liquid Metal Fast Breeder Reactors (LMFBR) has resulted in a great deal of research effort to understand the fundamental aspects of corrosion of steels in flowing sodium. The effects of parameters, like oxygen concentration in sodium, sodium velocity and temperature on corrosion of steels, has received a great deal of attention. The purpose of this communication is to analyze the effect of velocity of sodium on corrosion of steels. It has been observed [I -41 that at temperatures above 1200’F (650°C), corrosion of steels increases with increase of sodium velocity up to a critical velocity, after which it becomes independent of sodium velocity. For example, Thorley and Tyzack’s [33 data show that corrosion rates of steel become indepeni dent of sodium velocity above - 14-15 fps, [3], whereas data from Roy et al. [I 1, Schrock et al. [2], and Furukawa [4] show that the corrosion rates increase with increase of sodium velocity up to - 20-25 fps, fig. 1. Based on this observation, it was proposed [I, 51 that, in the velocity dependent range, diffusion of reactants (e.g., corrosion products or oxygen) across the laminar sub-layer ia the rate controlling step. At higher velocities, the laminar sub-layer diminishes sufficiently so that the surface reaction rates become the rate controlling step, and are independent of velocity. It is obvious that if the hypothesis is correct, the corrosion data from various investigations should be analyzed
V 0
I
5
I
10 Sodium
I
I
15 20 velocity (fps)
I
I
25
30
I
35
Fig. 1. Corrosion of stainless steels as a function of sodium velocity: l 1200”F, 25 ppm oxygen, 131; v1325’F, < 10 ppm oxygen, [2] n 1300”F, < 5 ppm oxygen, [l].
on the basis of the thickness of the laminar sub-layer and not the velocity of sodium, although the two parameters can be related for simple specimen gee metries. Thorley [6] made an attempt to correlate the corrosion data in terms of Reynold’s number, which could be translated into the thickness of the laminar sub-layer provided the pipe diameter remained con-
* Work performed under Contract No. AT(04-3)
- 189, Project Agreement No. 15 between the Atomic Energy Commission and General Electric Company. 129
P. Roy, M.K. &had, Corrosion of steels by liquid sodium
130
IL--0
5
10 Sodium
15 20 25 velocity (fps)
30
J
Thickness
Fig. 2. Variation of laminar sub-layer thickness at constant Reynold number: Reynolds’s number = 100 000, pipe diame ter = 0.1 - 0.65 in (2.5 mm - 16.25 mm).
stant. However, the thickness of the laminar sub-layer can be different for an identical Reynold’s number if the pipe diameter is not constant. According to Schlichting [7], the laminar sub-layer thickness can be calculated by, 6-sv/v*,
(1)
where the friction velocity, v* =x$C
(2)
and the shearing stress at the wall, r. = 0.04 /&
,f d-f
)
10-4
10-5
35
(3)
where p = sodium density, ii = mean velocity (in pipe), v = kinematic viscosity = p/p, d = diameter of the pipe, P = absolute viscosity. Using eq. (l), the calculated thickness of the laminar sub-layer at a constant Reynold’s number and various pipe diameters is shown in fig. 2. This analysis shows that comparison of corrosion data from various laboratories, in terms of sodium velocity or Reynold’s number is not adequate. For the purpose of comparison, an attempt was made to correlate the limited corrosion data in the
of laminar
1o-2
1 o-3
sub - layer
(in.)
Fig. 3. Corrosion of austenitic steel in sodium as a function of laminar sub-layer thickness: l constant bore and o variable bore, 1200”F, 25 ppm oxygen (3); q variable bore, 1300”F, < 5 ppm oxygen [l]; v variable bore, 1325”F, < 10 ppm oxygen.
literature (where the geometry and sodium flow are known). A plot of corrosion rates of steels normalized against the thickness of the laminar sub-layer is shown in fig. 3. Due to the complicated geometry of the Furukawa and Nehei [4] corrosion specimens, similar calculations are not applicable, and consequently, were not included in the analysis. The data from Thorley and Tyzack [3], Roy et ai: 111, and Schrock et al. [23 seem to indicate that corrosion rates of steels become independent of fluid turbulance below a boundary layer thickness of 0.0002 inch (5 pm). Furthermore, this analysis appears to resolve the apparent anomaly among various data on effects of sodium velocity on corrosion rates of steels in liquid sodium. It is recommended that in future corrosion tests, the specimen geometry should be designed such that calculations of this type could be made, in order to evaluate and compare the corrosion data from various laboratories. Finally, it should be pointed out that at present the sodium velocity is used as one of the parameters
P. Roy, M.K. &had,
Corrosion of steels by liquid sodium
in all the design allowances for corrosion in LMFBk systems. The present analysis indicates that the boundary layer thickness should be determined from the velocity and geometry and then used in establishing the corrosion design allowances rather than the sodium velocity itself.
[l] P. Roy, G.P. Wozadlo and F.A. Comprelh, Proc. Internat. Conf. on Sodium Technology, Argonne (USA), ANL 7520, Part 1 (1968) p. 131.
131
[2] S.L. Schrock, J.N. Baysden, R.L. Miller and D.E. Lohr, Corrosion by Liquid Metals, (Plenum Press, New York, 1970) p. 41. [3] A.W. Thorley and G. Tyzack, Alkali Metal Coolants (IAEA, Vienna, 1967) p. 97. [4] K. Furukawa and I. Nehei, Proc. Internat. Conf. on Sodiurn Technology, Argonne (USA), ANL 7520, Part 1 (1968) p. 143. [5] L.F. Epstein, Chem. Eng. Prog. Sym. Ser., No. 20, Vol. 53 (1967). [6] A. Thorley, IAEA Specialists Meeting on: Fission and Corrosion Product Behavior in Primary System of LMFBR’s, Bensberg/FRG, CONF-710959 (1971). [7] H. Schlichting, Boundary Layer Theory, (McGraw Hill, New York, 1955) p. 407.