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High Nickel alloy’s corrosion behavior in Organic acid

With nominal exceptions, organic acids are weak and non-oxidizing in nature. The usually encountered acids are monocarboxylic acids such as formic acid, acetic acid, propionic acid and butyric acids. Commonly the corrosivity of these acids becomes weaker with increasing the length of carbon chain. Therefore, formic acid is the most powerful corrosive acid; aeration and temperature considerably increase the corrosion rate.

Nickel alloy 200

Nickel alloy 200 has outstanding resistance to organic acids of whole contents, if nominally dissolved oxygen is available. Although, corrosion rates in aerated media can be large. For instance, in 85% acetic acid saturated with air at ambient temperatures, a corrosion rate of 400 mpy or 10.2 mm/a has been noticed. In the equivalent tests, Nickel alloy 200 in acetic acid of 0.1 % content corroded at 10 mpy or 0.25 mm/a and in 5% acid at 40 mpy or 1.02 mm/a. The following table shows the resistance of Nickel alloy 200 to corrosion by acetic acid and other organic acids in the different conditions.

Acid Conditions Temp, of or oc Test time, days Corrosion rate, mpy or mm/a
Acetic anhydride 99% and acetic acid 1% In stable 310 or 154 638 0.2 or 0.01
Acetic anhydride 60% and acetic acid 40% In stable 284 or 140 0.6 or 0.02
Butyric acid Distillation, liquid

Distillation, vapor

230 to 265 or 110 to 130

212 to 250 or 100 to 121

32

 

7

36 or 0.91

 

9 or 0.23

2% butyric acid Liquid

liquid

Room

160 or 71

7

10

2.3 or 0.06

5.4 or 0.14

2% citric acid Lab. Submerged

Lab. Submerged

Lab. Aerated

Room

160 or 71

180 or 82

5

10

3

0.8 or 0.02

5.5 or 0.14

34 or 0.86

5% citric acid Lab. Submerged

Lab. Aerated

Lab submerged

86 or 30

86 or 30

140 or 60

7

7

7

5 or 0.13

15 or 0.38

20 or 0.51

58% citric acid Lab immersed Boiling 7 17 or 0.43
90% formic acid Storage tank, liquid

Storage tank, vapor

Stable, liquid

Stable, vapor

Atmosphere

Atmosphere

212 or 100

212 or 100

 

14

7

8

27

4 or 0.10

7 or 0.18

18 or0.46

7 or 0.18

50% hydroxyacetic acid Lab, submerged

Lab. submerged

86 or 30

Boiling

 

7

7

0.3 or 0.01

7.6 or 0.19

2% lactic acid Lab. Submerged

Lab. Submerged

Room

160 or 71

7

7

2.1 or 0.05

3.4 or 0.09

10 to 22% lactic acid Vac. Evaporator 130 or 54 15 51 or 1.30
85% lactic acid Lab. Submerged Room 7 2.7 or 0.07
About 85% lactic acid Vac. Evaporator, liquid

Vac. Evaporator, vapor

 

120 to 180 or 49 to 82

120 to 180 or 49 or 82

120

 

120

10 or 0.25

 

11 or 0.28

66% propionic, 17% iso-butyric, 17% n-butyric acids Reboiler liquid 300 or 149 21 24 or 0.61
57% tartaric acid Vac. Evaporating pan 130 or 54 10 7.5 or 0.19

Monel alloy 400

Monel alloy 400 is normally not resistant comparable to other nickel based alloys to several organic acids. In unaerated acetic acid at room temperature, the corrosion rates are less than 4 mpy or 0.10 mm/a for whole concentrations. Aeration and temperature increase the corrosion rates, although, and the progressive accretion of cupric ions as corrosion products aggravates corrosion in an autocatalytic manner. In acetic acid above 50%, the corrosion rate decreases and in an analysis of glacial acid at 230oF or 110oC, the rate was merely 13 mpy or 0.33 mm/a. Monel alloy 400 is utilized for distillation of fatty acids at temperatures about 500oF or 260oC.

Incoloy alloys 800, 825, 020 and 25-6MO

Incoloy alloy 800 behaves almost similarly to austenitic stainless steels when subjected to organic acids. However the lab data may refer a suitable corrosion resistance, practically a molybdenum bearing alloy is used.The availability of molybdenum in Incoloy alloy 825, 020 and 25-6MO improves the resistance of these alloys to corrosion in organic acids. They are extremely resistant to boiling highly concentrated acetic acid, acetic-formic acid combinations, and maleic and phthalic acids. The data from lab corrosion tests for Incoloy alloy 825 are described in the following table:

Acid Corrosion rate, mpy or mm/a
Acetic acid <0.1 or <0.003
Formic acid 2.5 or 0.06
Lactic acid 0.3 or 0.008
Maleic acid 0.1 or 0.003
Phthalic acid <0.1 or <0.003
Oxalic acid 20 or 0.51

Inconel alloy 600

Inconel alloy 600 offers adequate resistance to hot and highly concentrated organic acids for instance, formic or acetic acid. It offers excellent resistance to ambient temperature acetic acid but not to hot fatty acids like stearic, oleic, linoleic and abietic.

Inconel alloy G-3, 625, C-276 and 686

Inconel alloy 625 offers adequate resistance to organic acids. The outcomes from 48 hours lab tests in boiling acid solutions are glacial acetic less than 1 mpy or <0.03 mm/a, 1:1 acetic-acetic anhydride-4 mpy or 0.10 mm/a, 10% acetic + 2% formic -1 mpy or 0.03 mm/a and 5% formic -3 mpy or 0.08 mm/a. Inconel alloys G3 and C276 also offer good resistance to organic acids.