Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

TABLE XVIII

Corrosion of Alloys in Acetic Acid

Corrosion Rate

Per Cent

Temperature

Type 410 Stainless Steel

Type 430 Stainless Steel

Ni-Resist Type 2

Acetic Acid

ºC

ºF

Cast Iron

Carbon Steel

mm/y mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y mpy

5 5

25 99 25 25

77

– – 254 10,000 – – – – – – – – – – – – – – – – – – – – – – 27.69 1,090 – – – – – – – – – – – – – – – – – – 2.03 80 – – – – 20.07 790

.25*

10*

– – – – – – – – – – – – – – – – – – – –

– – – – – – – – – – – – – – – – – – –

<.03

< 1

.91

36

210

57.15

2250

–

–

–

–

10 20 20 20 25 25 25 30 40 50 50 60 75 75 75 95 95

77 77

–

–

<.03 <.03 3.05 4.27

< 1 < 1 120 168

.53

21

.20*

8*

– – – – – – –

– – – – – – –

100 116

212 241

– – – – –

– – – – –

25

77

–

–

.58

23

104 116 116 116

219 241 241 241

.38 .25

15 10

127

5000

<.03 <.03 <.03

< 1 < 1 < 1

–

–

.20*

25

77

8*

1.96

77

116 110

241 230

– – –

– – –

1.02–7.62

40–300

– –

– –

– –

– –

25 65

77

1.68

66

149 241

7.62

300

1.02 1.27

40 50

– – – – – – – – – – –

– – – – – – – – – – –

116

–

–

25

77

1.02

40

– – –

– – –

116

241

16.51

650

99.9 99.9 99.9

25

77

.76

30

– 1.27–4.86 50–585 – – – – – – .01 0.3 – – – –

.53

21

116

241 194

12.7 6.86 1.65 1.70

500 270

6.86

270

90 25 35 50

–

–

100 100 100 100 100

77 95

65

Nil

Nil

67 1.78–11.18 70–440 – – – –

– –

– –

122 212 241

100 116

1.27

50

.64–5.08

25–200

Data combined from various published articles and private communications. *Rates obtained under quiescent conditions. Removal of the corrosion film will greatly increase the rate of attack.

are some rare cases where the corrosion resistance of these alloys is no better than Type 316 stainless steel, but usually they provide a higher plateau of corrosion resistance to hot organic acids. The higher cost of these materials requires that their area of use in a process be pinpointed and justified by longer service life. The cast and wrought alloys of this category are essen- tially the same in chemical resistance although some small difference may be noticed in a specific environment. The cast alloys are exemplified by ACI CN-7M. There are many proprietary alloys of this general type which bear trade names. Quite often the designation ends with the number “20,” and indeed this group of alloys is known to many as the “type 20” alloys. Alloys included in this category are: wrought CARPENTER* alloy 20Cb-3 and cast DURIMET** 20, ALLOYCO*** 20, WORTH- ITE**** and others.

alloy is particularly critical and must be thoroughly under- stood when appraising the alloy for acid services. Duplex stainless steels can also exhibit good corrosion resistance in acetic and other organic acid environments. Type 329 stainless steel and cast ACI CD-4MCu are examples. Tables II, III, VIII, XVI and XXVIII show the excellent corrosion resistance evidenced by these alloys in certain specific exposures. These alloys are also more sensitive to changes in environment than are the aus- tenitic stainless steels. However, in the proper application, the alloy can exhibit good stability while providing resis- tance to stress-corrosion cracking. It is for this latter reason that the duplex alloys are sometimes appraised for organic acid use. E. Iron-Base Nickel-Chromium-Copper- Molybdenum Alloys When an acetic acid environment is too corrosive for utilization of Types 316 or Type 317 stainless steels, the next group of materials usually considered are the iron- based alloys containing higher percentages of nickel and chromium with molybdenum and copper added. There

* Trademark of Carpenter Technology Corporation ** Trademark of The Duriron Company, Inc. *** Trademark of Aloyco Inc. **** Trademark of Worthington Corporation

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