Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

Combinations of sulfuric acid and the organic acids are often found in the process industry. The mineral acid is added to catalyze certain reactions with the organic acid or to react with unwanted impurities in the acid. The effect of adding one or two per cent of strong sulfuric acid to an eight-carbon organic acid is shown in Table L. Under these conditions, Type 304 stainless steel was as resistant as the Type 316 alloy in the temperature regions explored. The anamolous data of test 4 suggest that the stability of the stainless steels may be borderline under these conditions, although even higher temperatures failed to destroy the passivity of the alloys. The strong oxidizing capacity of the concentrated sulfuric acid probably aids in maintaining

passivity of the stainless steels in this medium. As discussed in the section on acetic acid, the use of a heating coil in such an environment would pose a different problem. Under heat-flux conditions, it is unlikely that the 300 series stainless steels would show adequate resistance to such a mixture. Also, if a water wash of the organic acid is to be made to remove the sulfuric acid, the aqueous phase containing a dilute mineral acid could be extremely aggressive to the 300 series alloys. Higher alloys of the “20” type for wrought materials or the CN-7M castings would be minimal for resistance to the diluted mineral acid in the presence of the organic acid.

TABLE XLIV

Corrosion of Stainless Steels in Propionic Acid Below the Boiling Temperature

Conditions: Duplicate tests in various concentrations of propionic acid at 75 and 50 ºC (167 and 122 ºF) without aeration or deaeration.

Corrosion Rate

% Propionic Acid

Type 420 Stainless Steel

Type 304 Stainless Steel

Type 316 Stainless Steel

75 ºC (167 ºF)

50 ºC (122 ºF)

75 ºC (167 ºF)

50 ºC (122 ºF)

75 ºC (167 ºF)

50 ºC (122 ºF)

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

2.54

100

.03

1

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

99 80 67 50 33 20

52.32

2060

6.09

240

.05

2

.05

2

<.03

<1

.03

1

90.93

3580

9.27

365

.03

1

.05

2

Nil

Nil

Nil

Nil

79.76

3140

1.65

65

<.03

<1

<.03

< 1

Nil

Nil

<.03

<1

39.88

1570

4.83

190

<.03

<1

Nil

Nil

<.03

< 1

<.03

<1

42.67

1680

1.57

62

<.03

<1

Nil

Nil

<.03

< 1

Nil

Nil

Corrosion Rate

% Proponic Acid

Type 318 Stainless Steel

HASTELLOY alloy C

HASTELLOY alloy B

75 ºC (167 ºF)

50 ºC (122 ºF)

75 ºC (167 ºF)

50 ºC (122 ºF)

75 ºC (167 ºF)

50 ºC (122 ºF)

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

<.03 <.03

<1 <1

Nil

Nil

Nil Nil

Nil Nil

Nil Nil

Nil Nil

.64 .30

25 12

.15 .61

6

99 80 67 50 33 20

.03

1

24

Nil

Nil

Nil

Nil

.03

1

Nil

Nil

.28

11

.30

12

Nil

Nil

Nil

Nil

<.03

<1

Nil

Nil

.10

4

.38

15

<.03

<1

Nil

Nil

Nil

Nil

Nil

Nil

.08

3

.20

8

<.03

<1

Nil

Nil

Nil

Nil

Nil

Nil

.05

2

<.03

< 1

Corrosion Rate

% Propionic Acid

INCONEL alloy 600

MONEL alloy 400

Copper

75 ºC (167 ºF)

50 ºC (122 ºF)

75 ºC (167 ºF)

50 ºC (122 ºF)

75 ºC (167 ºF)

50 ºC (122 ºF)

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

.38 .48

1 5

<.03

<1

1.19

47

.48 .41

19 16

>1.27

>50

1.02 1.09

40 43

99 80 67 50 33 20

19

.41

16

.15

6

.23

9

.18

7

.36

14

.13

5

.23

9

.28

11

.41

16

.10

4

.20

8

.13

5

.28

11

.25

10

.38

15

.10

4

.18

7

.10

4

.05

2

.28

11

<.03

<1

.13

5

.13

5

.13

5

.18

7

.05

2

.13

5

Page 41