Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

dilution markedly decreases the attack in a solution containing cupric acetate. This is probably attributable to the formation of a protective film on the surface, such as a basic cupric acetate. Note that the addition of ferric ion as the chloride produced significantly higher corrosion rates than when ferric acetate was used as an additive in glacial acetic acid. A comparison of the effect of the same additives in the 50 per cent acid suggests that the chloride was not mainly responsible for the greater attack in the 100 per cent acid, but that the small amount of water added as the ferric chloride hydrate produced the greater corrosion. Further evidence that chloride ion does not greatly affect the corrosion of copper-nickel alloys in organic acids is shown in Table XXVI. Adding 0.05 to 2.0 per cent sodium chloride to a synthetic mixture of various organic acids produced a ten-fold change in the corrosion rate on copper and the cupro-nickel alloys. However, the rates remained low enough that copper and copper-nickel alloys

could still be used as materials of construction without a practical limitation. Increasing nickel content in the alloy provided no change in the corrosion resistance. Data for Type 316 stainless steel are provided in this table for comparison. The excellent corrosion resistance of the cupro-nickel alloys in hot acetic acid and the retention of that resistance in chloride-contaminated acid has significant commercial implications. The chemical industry around the world has constructed seashore installations predominantly during the past 20 years. For such plants, the least costly cooling water system is the direct use of filtered seawater. The cupro- nickel alloys are essentially a standard for handling clean saline cooling water in condensers and other heat exchange surfaces if compatible with the process stream. Consequently, in organic acid plants using unpolluted salt- water cooling of condensers, the C70600 alloy (90-10 cupro-nickel) is widely used, and C71500 alloy (70-30 cupro-nickel) and Alloy 400 are used for certain special

TABLE XXV

Corrosion of Copper-Nickel Alloys in Acetic Acid Solutions

Conditions: Quadruplicate specimens exposed in pure aqueous acid solutions for 120 hours at the boiling temperature except tests without air sparging were extended to 336 hours. Additives added as shown.

Corrosion Rate

3200 ppm Cu++ Added as Cu(OAc) 2

2900 ppm Fe+++ Added as Fe(OH)(OAc) 2

2100 ppm Fe+++ Added as FeCl •6H 0 3 2

Per Cent

Per Cent

No Air Sparge

Air Sparged

Acetic Acid

Nickel in Alloy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

100

0 10 20 30 67 100 0 10 20 30 67 100 0 10 20 30 67 100 0 10 20 30 67 100

.01 .02

0.4 0.7

.08 .08

3 3

51

20 52

.25 .30

10 12

.76 .76

30 30

1.32

.01

0.3

.08

3

2.87

113

.28

11

.74

29

.01

0.2

.08

3

6.15

242

.25

10

.74

29

Nil

0.1

.05

2

2.97

117

.18

7

1.30

51

.04

1.4

.03

1

81

32

.13

5

5.21

205

75

.03

1

.03

1

.03

1

.03

1

.05

2

.01

0.4

50

.03

1

7.87

310

.48

19

3.28

129

3.00

118

.03

1

5.41

213

.79

31

2.64

104

2.59

102

.03

1

4.95

195

.86

34

2.69

106

2.06

81

.03

1

4.78

188

.84

33

2.36

93

2.46

97

.03

1

2.13

84

.91

36

1.83

72

2.82

111

.08

3

1.60

63

.71

28

1.98

78

4.39

173

25

.05

2

.03

1

.03

1

.03

1

.03

1

.15

6

Portion of Data from Reference 48

Page 22