Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

TABLE IV Comparison of Nickel and Manganese Austenitic Steels in Organic Acid Exposures Conditions: Duplicate specimens tested in the boiling solution (temperatures shown) for 48 hours or longer. Air not excluded or added.

Corrosion Rate

Type 304

CRUCIBLE*

Type 316

Temperature

Stainless Steel

alloy 223

Stainless Steel

Test Medium

ºC

ºF

mm/y

mpy

mm/y

mpy

mm/y

mpy

117 104

242 219

.46

.18

.18 .05

7 2

.01 .01

0.4 0.3

Acetic acid, 100% Acetic acid, 75% Acetic acid, 50% Acetic acid, 25% Acetic acid 99%;

4.06

160

102

216

6.98

275

Nil

<0.1

.08

3

100

212

7.11

280

<.008

0.3

Nil

Nil

117

242

.33

13

2.26

89

.22

8.5

Acetic anhydride 1%

Acetic acid 90%;

Formic acid 10%

109

228

.23

9

.08

3.1

.17

6.5

Formic acid, 20% 2-Ethyl butyric acid, 100% Esterification mixture 1

102

216

1.75

69

4.75

187

.56

22

185

365

.53

21

.04

1.5

.04

1.4

86

187

.41

16

2.79

110

.02

0.7

(1) Synthetic mixture of 75% butyl acetate, 11% butanol,10% acetic acid, 4% water, 0.3% sulfuric acid.

*Trademark of Colt Industries, Inc.

TABLE V

When molybdenum is added to produce such alloys as Types 316 and 317 stainless steels, and other alloys, a remarkable increase in resistance to hot organic acids occurs. The startling efficacy of molybdenum is best shown by curves from Uhlig (Figure 2). Note that in the two ex- posures defined for these curves, the effect of molybdenum is fully realized at approximately 2.2 per cent. In the vast majority of organic acid environments, this approximate amount of molybdenum provides satisfactory corrosion resistance. For this reason, Types 316 and 316L stainless steels are utilized for the overwhelming majority of hot organic acid applications. Relative values of corrosion resistance for three common alloys in hot process acid are shown in Table IV to supplement the data for the Type 316 stainless steel shown in Table II. Data generated by all major acetic acid producers confirm that for a pure, uncontaminated acetic acid of any concentration, Type 316 stainless steel or its low carbon counterpart Type 316L is usable as a material of construction to temperatures beyond the boiling point. (See Effect of Temperature.) These alloys are used extensively in the fabrication of distillation columns, heat exchangers, decanters, piping and other apparatus employed in the production or processing of acetic acid. Under certain conditions of exposure, it has been found that additional amounts of molybdenum in the alloy are beneficial. Types 317 and 317L stainless steels are available for such applications when required. Tables V through VIII show process corrosion data where the superiority of the Type 317 stainless steel can be observed.

Corrosion of Alloys in Acetic-Hydroxy Acid Solution

Conditions: Exposure of approximately 50 days in strip- ping of acetic acid at temperatures shown from a 70% acetic acid containing ca. 8%  -hydroxy acids, 20% manganese salts and residues. Nitrogen blanket on system.

Corrosion Rate

124 ºC (255 ºF) 140 ºC (284 ºF)

Alloy

mm/y

mpy mm/y mpy

Type 304 Stainless Steel Type 316 Stainless Steel (annealed) Type 316 Stainless Steel (sensitized) Type 216 Stainless Steel Type 317 Stainless Steel Type 326 Stainless Steel (IN-744) CARPENTER alloy 20Cb-3 INCOLOY alloy 825 JESSOP alloy JS-700

.01

0.4

1.12

44

Nil

<0.1

.09

3.7

.01 Nil Nil Nil .00 .01 Nil

0.3 <0.1 <0.1 <0.1 0.1 0.2 <0.1 <0.1

.11 .05 .08

4.2 2.0 3.2

2.84 .05 .03 .01

112 1.8 1.2 0.3

HASTELLOY alloy G

Nil

.01

0.4

The effect of further alloying on the corrosion resistance of commercial alloys is indicated in succeeding sections.

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