Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

Previous comments regarding temperature were in reference to the bulk temperature of a liquid or vapor in contact with a metal surface at essentially the same temperature. These conditions do not exist in heat ex- changers, calandrias and interchangers of an acetic acid process. When a metal surface at a higher temperature is used to evaporate the acid, higher corrosion rates occur than obtained isothermally. One explanation is that the constant heating and cooling of a heat exchanger surface cracks the protective oxide film on a stainless steel to expose active metal. Also, ebulition of the liquid at the surface supplies a mechanical force to dislodge the film.

Decomposition products of organic compounds can form on the hot surface. Lastly, any corrosive heavy ends in the liquid can concentrate at the surface to attack the metal, or tars can form over the metal to produce crevice corrosion in a random configuration. For these reasons, an actual heat exchange test should be conducted in any questionable mixture. Groves, et al. 10 have described a simple apparatus for conducting heat exchange “hot wall” tests. Their data are reproduced in Table XV and illustrate the significant increase in attack which occurs on an alloy when using the surface as a heat exchange medium. Further use of this

TABLE XV

Corrosion by Acetic Acid Under Heat Transfer Conditions

Temperature

Corrosion Rate

Type 304 Stainless Steel

Type 316 Stainless Steel

Without Heat Transfer

With Heat* Transfer

CARPENTER alloy 20 Cb-3

HASTELLOY alloy B

INCONEL alloy 600

MONEL alloy 400

ºC

ºF

ºC

ºF

mm/y mpy

mm/y mpy

mm/y mpy

mm/y mpy

mm/y mpy

mm/y mpy

Test Medium Ace 1 ti 0 c % Acid

101

214

–

–

<.03 <.03 <.03 <.03 3.30 5.33 5.59 6.35 1.75 6.60 8.64

<1 <1 <1 <1

<.03 <.03 <.03 <.03 <.03 <.03 <.03 <.03 <.03 <.03

<1 <1 <1 <1 <1 <1 <1 <1 <1 <1 13 10

<.03 <.03 <.03 <.03 <.03

<1 <1 <1 <1 <1

.08 .18 .15 .10 .13 .13 .05 .05 .18 .18 .08

3 7 6 4 5 5 2 2 7 7 3

.51 .71 .69 .20

20 28 27 49 44 31 14 22 36 45 14 8

1.30

51

– – – – – – – – –

– – – – – – – – –

110 125 140 110 125 140 110 125 140 – –

230 257 284 230 257 284 230 257 284 – –

14.73 580 >25.40 >1000 >25.40 >1000 1.93 76 3.05 120 3.68 145 3.30 130 .03 1 3.05 120 1.73 68 5.59 220

50%

102

216

130 210 220 250

1.24 1.12

.05 .08

2 3

.79

<.03

<1

36

99.6%

118

244

69

.18 .13 .05

7 5 2

<.03

<1

.56 .91

260 340

33

1.14

51

20

.25

2.54

100

.36

*Metal temperature Reference 10. See that publication for apparatus and technique used.

TABLE XVI

Corrosion with Heat Exchange in Aqueous Acetic Acid Containing Additives

Test Conditions: Apparatus and procedure same as de- scribed in Reference 10. Metal tempera- ture 110 ºC (230 ºF) with bulk liquid tem- perature of 100 ºC (212 ºF). Test periods of 4 to 96 hours used. All results represent duplicate specimens.

Corrosion Rate

Type 304 Stainless Steel

Type 310 Stainless Steel

Type 316 Stainless Steel

Type 329 Stainless Steel

CARPENTER alloy 20 Cb-3

HASTELLOY alloy C-276

AMBRALOY* 901

MONEL alloy 400

Test Medium

Acetic

Acid Additive 56% 1% H SO 2

mm/y mpy

mm/y mpy mm/y mpy mm/y mpy

mm/y mpy mm/y mpy mm/y

mpy

mm/y

mpy

36.07 1420

Nil

Nil

5.84- 230- 15.24 600 76.63 3017

Nil-

Nil-

64

25

–

–

–

–

.23

9

4

80 30 5.72 225

56% 5% H SO 2

22.35 880

Nil- Nil- 61.57 24 24 50.8 200

17.93 706

–

–

36.58 1440

.91

36

4

25% 4% Formic Acid

28.83 1135

.71

28

Nil

Nil

Nil

Nil

Nil

Nil

–

–

1.17

46

*Trademark of Anaconda American Brass Co. Reference 43

Page 13