Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

Pitting and crevice corrosion can occur on essentially all alloys in these environments and must be appraised before a material is selected. Extensive comments on the processing of the fatty acids and the selection of materials of construction are contained in references 28-34. One of the most important sources of fatty acids today is the pulp and paper industry where tall oil fractions are recovered and refined. These are composed of the straight- chain fatty acids and mixed rosin acids. Table LI shows results compiled from various sources. Whenever possible, the stream compositions have been defined.

Note that Types 316 and 316L stainless steels are useful for many tall oil processing requirements but, in some instances, either an excess of light ends or an excep- tionally high temperature causes high rates with this alloy. In these cases, the use of Types 317 or 317L stainless steels or alloys with a higher molybdenum content should be investigated in the search for an economical material of construction. If these alloys are inadequate, the use of more highly alloyed materials can be considered. The nickel-base molybdenum-chromium-iron alloys show es- sentially a nil corrosion rate in all such exposures. Alloy 600 is a contender for use in a number of applica- tions and should not be overlooked. The use of nickel- copper alloys or copper-nickel alloys varies depending on the oxidizing capacity of the solution, as would be expected. In the absence of oxidants, the rate of attack on these alloys is acceptably low. It has been stated that streams containing a higher proportion of the straight chain fatty acid produced more corrosion than those containing a higher ratio of rosin (cyclic) acids. This does not appear to be invariably true. The presence or absence of steam has a significant effect on the corrosion to be expected, particularly as observed for the stainless steels. The oxidizing capacity of the water reduces corrosion rates on the stainless steels appreciably while accentuating attack on the nickel-copper and/or copper-base alloys. As with any other corrosive environment, the effect of temperature must be carefully defined. Table LII shows data for five alloys exposed to the same refined tall oil

TABLE LII

Effect of Temperature on Corrosion in Refined Tall Oil

Conditions: Laboratory tests conducted in liquid of same oil at various temperatures.

Corrosion Rate

285 ºC (545 ºF) 300 ºC (572 ºF) 315 ºC (599 ºF) 330 ºC (626 ºF)

Material

mm/y mpy

mm/y mpy

mm/y mpy

mm/y mpy

Type 302

4.57

180

12.7

500

20.32 800

–

–

Stainless Steel Type 316 Stainless Steel Type 317

.10

4

1.35

53

12.7

500

.10

4

.03

1

.53

21

–

–

.03

1

Stainless Steel HASTELLOY alloy C

.13

5

.10

4

–

–

.10

4

INCONEL alloy 600

.25

10

.25

1 0

.33

13

.28

11

TABLE Llll

Corrosion of Metals in Vegetable Fatty Acids

Conditions a Temp. ºC (ºF) Time, days Exposure

1 370 (698) 45 Liq-vap.

2 370 (698) 3 Vapor

3 190 (374) 30 Liquid

4 190 (374) 23 Liq-vap.

5 277 (530) 50 Vapor

6 116(240) 32 Vapor

7 255(491) 42 Vapor

Corrosion Rate

Alloy

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

– –

– –

– –

– – –

38 48

1 5

1.04

41

3.05

120 430

25

10

– – 12.45 49

Carbon Steel Cast Iron Ni-Resist Type 2

19

–

–

10.92

–

–

–

–

03

1

20

8

43

17

01

05

86 34 25 10 05 2 Nil Nil – – Nil 0.1 20 8 .20 8 – – Nil Nil _

01

0.2

–

–

Nil

Nil

Nil

0.1

97

38

Nil

0.1

Type 304 Stainless Steel Type 309 Stainless Steel Type 316 Stainless Steel Type 317 Stainless Steel INCONEL alloy 600 Nickel 200 MONEL alloy 400 C71500 (70-30 Cupro-nickel) HASTELLOY alloy C

–

–

–

–

Nil

Nil

–

–

–

–

–

–

Nil

0.1

–

–

Nil

Nil

Nil

0.1

Nil

0.1

Nil

0.1

–

–

–

–

Nil

Nil

–

–

–

–

–

–

Nil

0.1

Nil

0.1

Nil

Nil

Nil

0.1

0.3

1

Nil

0.1

08

3

25

10

10

4

10

4

30

12

03

1

.08

3

.18

7

.05

2

.13

5

.25

10

.02

0.9

–

–

–

–

01

0.4

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

a Conditions:

1–Field test in closed autoclave converting castor oil to drying oil. 2– Field test in top of kettle while refining high purity linseed oil. 3–Field test in receiving tank for dirty palm used in tin-plate line. 4–Field test in distillation column handling crude vegetable oils plus palmitic and stearic acid (acid value of 85-95). 5–Field test in distillation column for cottonseed oil acids. 6–Field test in top of distillation column handling palmitic and stearic acids. 7–Field test in top of distillation column deodorizing crude cottonseed fatty acids by steam distillation.

Page 45