Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

The superiority of this class of alloy may be noted by reference to Tables II, V, XXVII and XXIX. Particularly when the acid is contaminated with agents inimical to the use of Type 316 stainless steel, these alloys usually provide significant improvement in resistance. For hot acid pumps, the CN-7M composition shows greater resistance to erosion-corrosion than CF-8M castings and is often used in installations that are otherwise entirely of Type 316L stainless steel construction. The higher nickel content of the “type 20” alloys provides a fully austenitic structure, imparts good strength with ductility, is in optimum ratio with the chromium for maximum corrosion resistance in the iron-base alloys and increases the resistance of the alloy to chloride stress- corrosion cracking considerably. The wrought or cast “type 20” alloys will not crack in many environments which produce stress-corrosion cracking in Type 316 stainless steel. The “type 20” alloys are susceptible to sensitization as described for the 300 series stainless steels unless stabilized or solution annealed. Low carbon con- tents or the addition of columbium is used to combat the problem. “Knife-line attack” may sometimes occur along beads of multiple-pass welds in the metal-stabilized alloys. Castings should be used in the solution annealed condition.

Black, Sivalls and Bryson Inc. utilize a number of different alloys to resist various corrosives in its extensive line of rupture disks. Included are Alloys 400, 600, and HASTELLOY alloy C-276 as well as Type 316 stainless steel and other high nickel alloys to insure reliability.

environments and far superior to Type 316L stainless steel in the hotter, more aggressive organic acid environments. This is shown in Tables V, VII, XII1, XXVII, XXVII and XXX. Their superiority is also indicated in later sections of this bulletin. (See Tables LI, LVIII, LXVII, LXXIV and LXXVIII.)

F. Nickel-Base Chromium-Iron- Molybdenum-Copper Alloys

The nickel-base Cr-Fe-Mo-Cu alloys such as HASTEL- LOY* alloy G and INCOLOY** alloy 825 are generally equivalent to 316L stainless steel in “mild” acetic acid

*Trademark of Cabot Corporation ** Trademark of the Inco family of companies

TABLE XIX

Average a Corrosion Rates of Precipitation Hardening Stainless Steels in Acetic Acid

Acetic Acid Concentration

100%

75%

50%

25%

Corrosion Rate

Alloy

mm/y

mpy

mm/y

mpy

mm/y

mpy

mm/y

mpy

4.90

193

1.32 2.21

52 87

7.67 <.03

302 < 1

4.27 <.03 <.03 <.03

168

Type 430 Type 304 PH15-7Mo (as received) b PH15-7Mo (Al 750) PH15-7Mo (TH1050) PH15-7Mo (RH950) 17-7PH* (as received) 17-7PH (A1750) 17-7PH (TH1050) 17-7PH (RH950) 17-4PH* (as received)

.43

17

<1 <1 <1 30 20 <1 <1 <1 <1 <1 <1 <1 2

<.03

< 1

.05

2

03

1

08 08 08 30 38 28 25 25 28 33 23

3 3 3

<.03

< 1 1 2

<.03

< 1

30 18 46 10 03 05 15 03 25 05

71 56 28 28

28 22 11 11 <1 <1 <1 <1 <1 3

76 51

7

12 15 11 10 10 11 13

18

<.03 <.03 <.03 <.03 <.03 <.03 <.03 .05

4 1 2 6 1

<.03

08

<.03 <.03 <.03 <.03

17-4PH (H900) 17-4PH (H1025) 17-4PH (H1150)

10

9

2

a. Average of duplicate specimens for three 48-hour exposure periods in boiling acid. b. Heat Treatment– A = Annealed T = Transformation near 760 ºC (1400 ºF) H = Hardening between 482-593 ºC (900-1100 ºF) of T or R material R = Refrigerate treated to –73 ºC (–100 ºF) *Trademark of Armco Steel Corporation

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