Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

facility can be constructed of Type 316L stainless steel. There are certain precautions, however: •The high temperature of the reactor requires that the Type 316L stainless steel be fully qualified and in its most corrosion-resistant condition. (See Effect of Microstruc- ture.) Type 316L stainless steel clad construction over a steel substrate offers the most economy for the high pressure reactor but the fabrication techniques must assure that the maximum corrosion resistance of the stainless steel is retained. • Proper operation of the plant is essential. Although Type 316L stainless steel is resistant to the normal conditions of operation existing in the reactor, if the temperature reaches much more than the nominal 185 ºC (365 ºF), the corrosion rate for the alloy increases rapidly. • There have been instances in which weld deposits have been less corrosion resistant than the base metal, perhaps because of compositional differences. For this reason, many welds are made using a more highly alloyed weld rod or filter wire. • Circulating pumps for the hot process liquid are usually of a solution treated CN-7M alloy casting. If temperatures are maintained at lower levels for the reaction, the CF-8M or CF-3M alloy castings will exhibit a satisfactory service life. The acids longer than acetic (propionic, butyric, etc.) produced in the reaction add little if any to the corrosivity of the stream, because temperatures of the process following the reaction are lower than those required to promote corrosion of the stainless steels by these acids. (See section on Higher Organic Acids.)

TABLE XXX

Corrosion of Alloys in Synthetic Reactor Product from Methanol-Carbon Monoxide Process for Acetic Acid Conditions: Aqueous 70% acetic acid at the boiling tem- perature 107 ºC (243 ºF) without and with catalyst (ca. 6% cobalt acetate hydrate and 6% potassium iodide). Purged with CO.

Corrosion Rate

Without Catalyst

With Catalyst

mpy

Alloy

mm/y

mpy mm/y

,

41

16 20

15*

6*

Type 304 Stainless Steel Type 321 Stainless Steel Type 347 Stainless Steel Type 316 Stainless Steel

.51

.25*

10*

1.91

75

.33*

13*

.15

6

.08*

3*

<.03

<1

.03*

1*

24Cr-20Ni-Mo-Cu** CARPENTER alloy 20 INCOLOY alloy 825 INCOLOY alloy 800 HASTELLOY alloy C HASTELLOY alloy B INCONEL alloy 600 Nickel 200 MONEL alloy 400

–

–

.23*

9*

–

–

.05

2

–

–

.13*

5*

–

–

.10*

4*

–

–

.20

8

–

–

.38

15

15

6

.33

13

<.03

<1

.41

16

C71500 (70-30 Cupro-Nickel) C70600 (90-10 Cupro-Nickel) Aluminum Bronze

.48

19

.94

37

.53

21

1.14

45

.18

7

2.34

92

Titanium DURIRON

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

* Pitting occurred. Authors correctly reported only observations and weight loss of coupons. For comparison, the weight loss was convert- ed to corrosion rate on basis of data given. ** Contained 2.3% Mo and 2.0%Cu Reference 18

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