|
TABLE 5: CORROSION OF ZIRCADYNE 702 VS. COMPETITOR
ALLOYS IN 65% NITRIC ACID AT ELEVATED TEMPERATURES
| |
Corrosion
Rate (mpy)
|
| Alloy
|
121°
C (250° F)
|
149°
C (300° F)
|
204°
C (400° F)
|
| Carpenter
7-Mo |
9.5
|
480
|
2482
|
| Carpenter
7-Mo Plus |
7.9
|
---
|
---
|
| Carpenter
7-Mo Plus (welded) |
9.1
|
---
|
---
|
| Sandvik
2RE10 |
4.9
|
86
|
1064
|
| Uddeholm
44 LN |
5.4
|
315
|
---
|
| Uddeholm
44 LN (welded) |
10.3
|
336
|
---
|
| Uddeholm
25 L |
5.3
|
166
|
---
|
| Uddeholm
25 L (welded) |
8.1
|
116
|
---
|
| VDM
2521 LC |
35
|
410
|
7600
|
| VDM
2522 LCN |
36
|
580
|
12500
|
| Zircadyne
702 |
0.0
|
0.0
|
0.0
|
| Zircadyne
702 (welded) |
0.0
|
0.0
|
0.0
|
Titanium can sometimes be used to solve
the problems of stainless steel in nitric acid, however its
corrosion behavior is complicated. In contrast to stainless
steel, titaniumÕs corrosion resistance actually improves as
the level of some impurities increases in nitric acid. Unlike
zirconium, however, titanium cannot naturally form a stable,
protective oxide film on its surface in pure nitric acid,
which restricts its use in hot, pure solutions or vapor condensates
of nitric acid. Titanium is also very sensitive to the presence
of titanium ions resulting from corrosion (Table 6).
TABLE 6: EFFECT OF TITANIUM ION ON CORROSION IN
BOILING NITRIC ACID (24 HOUR TEST)
| Ti+4
Ion Concentration |
Corrosion
Rate (mpy) |
| (ppm)
|
40%
HNO3 |
68%
HNO3 |
| 0
|
30
|
32
|
| 20
|
8.7
|
2.4
|
| 40
|
2.0
|
0.4
|
| 80
|
0.8
|
0.4
|
Based on these limitations, zirconium
becomes the clear choice as the material of construction for
critical nitric acid processing equipment. The superiority
of its corrosion resistance under different operating conditions,
and the elimination of the resulting corrosion by-products
give zirconium the edge over stainless steel and titanium
in HNO3. Zirconium can also be the most cost-effective solution
for solving nitric acid corrosion problems; longer equipment
life, higher purity product streams, reduced maintenance and
downtime can all be achieved with the proper use of zirconium.
Six of Seven 1
2 3
4 5
6 7
|
