|
TABLE 2: CORROSION RATE OF ZIRCONIUM IN HNO3 WITH
IMPURITES (TEMPERATURES HELD AT BOILING POINT FOR 8 DAYS)
| |
|
Corrosion
Rate (m m/year)
|
| |
|
Liquid
Phase |
Vapor
Phase |
| Nitric
Acid, % |
Impurity
|
Nonwelded
|
Welded
|
Nonwelded
|
Welded
|
| 30/50/70
|
0.1
or 1% FeCl3 |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 30/50/70
|
0.1
or 1% seawater |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 30/50/70
|
0.1%
NaCl |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 30
|
1%
NaCl |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 50
|
1%
NaCl |
<2.5
|
<2.5
|
12.7
|
35.6
|
| 70
|
1%
NaCl |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 0
|
Saturated
Cl2 |
<2.5
|
102
|
<2.5
|
91.4
|
| 30
|
Saturated
Cl2 |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 50
|
Saturated
Cl2 |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 70
|
Saturated
Cl2 |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 30/50/70
|
1%
Fe |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
| 30/50/70
|
1.45%
304 S.S. |
<2.5
|
<2.5
|
<2.5
|
<2.5
|
Although stress corrosion cracking
has been a concern for using zirconium in nitric acid, results
of U-bend tests indicate that zirconium has excellent resistance
to stress corrosion cracking in relatively high HNO3 concentrations
and elevated temperatures (Table 3). Tests have also shown
that impurities have little effect on the susceptibility of
zirconium to stress corrosion cracking at nitric acid concentrations
up to 70% and room temperature. Proper equipment design and
stress relieving at elevated temperatures can help to mitigate
this problem at higher concentrations.
TABLE 3: RESULTS OF U-BEND TESTS FOR ZR IN NITRIC
ACID (TOTAL TEST EXPOSURE OF 7 DAYS)
| Condition
|
Nitric
Acid (%) |
Temperature
(° C)
|
Time
to Failure (Days) |
| As-welded
|
65
|
149
|
Did
not fail |
| As-welded
|
65
|
204
|
Did
not fail |
| Longitudinal
|
65
|
204
|
Did
not fail |
| Transverse
|
65
|
204
|
Did
not fail |
| As-welded
|
70
|
149
|
4
|
| As-welded
|
70
|
204
|
1
|
| Longitudinal
|
70
|
204
|
Did
not fail |
| Transverse
|
70
|
204
|
Did
not fail |
Three of Seven 1
2 3 4
5 6
7
|
