Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

exposures. For a complete description of the excellent properties of these alloys in seawater, see “Guidelines for Selection of Marine Materials.” 15 In addition, if mechan- ical problems arise which allow seawater contamination of the process stream, such as a leaking condenser tube, the cupro-nickels and Alloy 400 are not excessively corroded by the contaminated acid. K. Nickel-Chromium Alloys The nickel-chromium alloys represented by Alloy 600 and ACI CY-40 are little used in the production and handling of acetic acid. In general, the iron-base alloys with chromium, nickel and molybdenum exhibit superior corrosion resistance in the acid streams and economic considerations dictate no better choice. For certain specific appurtenances on the major equipment, INCONEL alloy 600 has been used when required because of availability or to take advantage of certain mechanical properties of the alloy. However, these uses have been minimal. The more corrosion-resistant iron-base nickel-chromium-molyb- denum-copper alloys are used to combat stress-corrosion cracking when the stainless steels are not useful and forestall any consideration of the nickel-chromium alloys for the new construction of major items of equipment. When existing equipment of the versatile nickel-chromium alloy is available, the processing of various acetic acid mixtures is permissible if the corrosion characteristics of the medium have been properly defined. In general, the lower concentrations of acetic acid (< 60%) in aqueous solution can be handled without excessive corrosion. If oxygen is present in the solution, the nickel-chromium alloy is superior to the nickel-copper or cupro-nickel alloys in corrosion resistance. Data showing the resistance of the basic nickel-chro- mium alloys to corrosion by acetic acid are presented in Tables VII, VIII, XV XVII, XXII, XXVII, XXVIII and XXX.

This 15,000 pound capacity reactor kettle of INCONEL alloy 600 was used for over 27 years for the dehydration or polymerization of castor, linseed and soybean oils. Alloy 600 was chosen to withstand the corrosive effects of vegetable oil acids and C 18 fatty acids at a temperature of 600 ºF.

L. Iron-Nickel-Chromium Alloys Alloy 800 has fair resistance to hot acetic acid solutions. The iron and chromium of the alloy dictate that conditions should be slightly oxidizing to realize the best resistance from the alloy. However, the alloy cannot compete with Alloy 825 or other metals containing molybdenum as a prime candidate for process use. The good chloride stress-corrosion cracking resistance of the alloy makes use of the material attractive for small, specialty applications, but the corrosion rate must be determined closely to assure that adequate life will be obtained. As a general statement, the better solution to a problem involving acetic acid corrosion and chloride stress- corrosion cracking is the use of the “type 20” alloys, or the nickel-base iron-chromium-molybdenum-copper alloys.

TABLE XXVI

Effect of Sodium Chloride in a Mixed Acid Medium on the Corrosion of Copper-Nickel Alloys

Conditions: Duplicate specimens immersed in a boiling 116 ºC (241 ºF) solution of 60% acetic acid, 10% formic acid, 10% heavy organic acids and 20% water for 100 hours.

Corrosion Rate

C70600 (90-10 Cupro-Nickel)

C71500 (70-30 Cupro-Nickel)

Type 316 Stainless Steel

Per Cent NaCI Added to Acid

Copper

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

0.05

.01

0.4

.01

0.3

.01

0.3

.38

15

0.10 1.0 2.0

.01

0.3

.01

0.3

.01

0.5

.56

22

.08

3

.05

2

.08

3

12.27

483

.10

4

.08

3

.10

4

22.66

892

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