Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

TABLE XXXI

Corrosion of Stainless Steels in Vinegar Production

Corrosion Rate

Test 1

Test 2

Test 3

Test 4

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

Alloy

Nil*

Nil Nil

Nil Nil

Nil Nil

Nil Nil

Nil Nil

Nil Nil

Nil Nil

Type 304 Stainless Steel Type 316 Stainless Steel Type 304 Stainless Steel sensitized for 1 hour at 677 ºC (1250 ºF)

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

*No detectable attack in the form of general corrosion, pitting or crevice corrosion.

Test 1 Storage Tank

Test 2

Test 3

Test 4 Storage Tank

Location

Accumulator

Freezer

40-66

80-122

50-300

80-320

Vinegar Concentration (Grain) Temperature Range ºC ºF Test Duration

21-35 70-95

27-34 80-93

–17 to –2 2-28

0-16 32-60

all tests 150 days

TABLE XXXII

the acetic acid is fully vaporized, the stream is essentially innocuous from a corrosion standpoint. However, proper- ties of the cracking tube alloy are significant. The catalytic properties of nickel can cause breakdown of hydrocarbons at high temperatures. For this reason, various nickel-free alloys have been developed (Fe-Cr, Fe-Cr-Al, Fe-Cr-Al-Si) for use in such services. However, the operating temperatures of 700-750 ºC (1292-1382 ºF) can develop sigma and other adverse metallurgical conditions in the iron-chromium alloys. To make furnace operations less critical and to obtain improved fabricability, the use of cast austenitic alloys was explored. It was found that the inner surface of the tubing was rapidly coated with a deposit of carbon which sealed the process stream from catalytic effects conferred by the metal surface. Thus, advantage can be taken of the better ductility and fabricability of the austenitic alloys for such service. Rates of degradation of the various alloys caused by the oxidation reactions that occur in the environment are shown in Table XXXII. Handling of the acetic anhydride and its dilution with acetic acid presents no problem other than that described under the processing of acetic acid. Type 304 stainless steel is eminently satisfactory for the distillation, storage, or shipment of the anhydride. Nickel plating showed a nil rate of attack in acetic anhydride at ambient temperature during a 121-day test.

Deterioration of Alloys in Glacial Acetic Acid Vapors at 750 C (1382 F)

Average Penetration

Initial Exposure 200 hours

Second Exposure 100 hours

Metal

mm/y

mpy

mm/y

mpy

.48

19

1.22

48

Type 430 Stainless Steel Type 446 Stainless Steel ACI HK Alloy

–

–

.91

36

.18

7

.41

16

Type 304L stainless steel equipment and piping and ACI CF-8M valves for metering acetic anhydride to process kettles. Courtesy Walworth Company- Aloyco Valves.

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