Alloy	Number of Attacked Crevices*	Maximum Depth of Penetration, mils**

HASTELLOY^® C-276 alloy	0	0
HASTELLOY C-22^® alloy	0	0
HAYNES^® 625 alloy	11	3
Type 317LM Stainless Steel	20	12
Alloy No. 904L	23	19
20Cb-3^® alloy	24	76
Alloy 825	24	125

Maximum possible number of crevices was 24. *To convert mils per year (mpy) to mm per year, divide by 40. 20Cb-3 is a trademark of Carpenter Technology Corporation.

Comparative Crevice-Corrosion Tests Data in 10% Ferric Chloride

	Average Corrosion Rate Per year, Mils*
Alloy	77°F (25°C)	122°F (50°C)	167°F (75°C)

HASTELLOY^® C-276 alloy	0.2	0.2	1.4
HASTELLOY^® C-22^® alloy	0.1	0.1	0.5
HASTELLOY^® C-4 alloy	0.3	0.5	20
FERRALIUM^® 255 alloy	0.4	811	663
HAYNES^® 625 alloy	1.5	124	510
20Cb-3 alloy	205	380	700
Type 316 Stainless Steel	312	460	780
Alloy 825	730	707	680

* Average corrosion rate on duplicate samples even though most corrosion occurred under crevice. Tests were for 100 hours with grooved block. To convert to mils per year (mpy) to mm per year, divide by 40.

Comparative Stress-Corrosion Cracking Data

Alloy	Time, hrs. to crack in 45% Magnesium Chloride at 309°F (154°C)

Type 304 Stainless Steel	1-2
Type 316L Stainless Steel	1-2
20Cb-3 alloy	22
Alloy 825	46
HAYNES^® 625 alloy	No cracks - 1000
HASTELLOY^® G-30^® alloy	No cracks - 1000
HASTELLOY^® C-276 alloy	No cracks - 1000
HASTELLOY^® C-22^® alloy	No cracks - 1000

Comparative Immersion Critical Pitting and Critical Crevice-Corrosion Temperatures in Oxidizing NaCl-HCl Solution

The chemical composition of the solution used in this test is as follows; 4% NaCl + 0.1% Fe₂(SO₄)₃ + 0.021 M HCl. This solution contains 24,300 ppm chlorides and is acidic (pH2). In both pitting and crevice-corrosion testing the solution temperature was varied in 5°C increments to determine the lowest temperature at which pitting-corrosion initiated (observed by examination at a magnification of 40x of duplicate samples) after a 24-hour exposure period (Pitting Temperature), and the lowest temperature at which crevice-corrosion initiated in a 100-hour exposure period (Crevice-Corrosion Temperature).

	Critical Pitting Temperature		Critical Crevice-Corrosion Temperature
Alloy	°C	°F	°C	°F

HASTELLOY^® C-22^® alloy	>150	>302	102	212
HASTELLOY^® C-276 alloy	150	302	80	176
HASTELLOY^® C-4 alloy	140	284	50	122
HAYNES^® 625 alloy	90	194	50	122
HASTELLOY^® G-30^® alloy	70	158	40	104
FERRALIUM^® 255 alloy	50	122	35	95
Alloy 904L	45	113	20	68
Type 317LM Stainless Steel	35	95	15	59
Type 317L Stainless Steel	25	77	10	50
Alloy 825	25	77	≤-5	≤23
20Cb-3 alloy	20	68	≤-5	≤23
Type 316 Stainless Steel	20	68	≤-5	≤23

20Cb-3 is a trademark of Carpenter Technology Corporation.

Comparative Immersion Crevice-Corrosion Temperatures in 6% Ferric Chloride Solution (ASTM G48; MTI Project)

The chemical composition of the solution used in this test is as follows: 6% Fe₂Cl₃. In the crevice-corrosion test, the solution temperature was varied in 2.5°C increments to determine the lowest temperature at which crevice corrosion initiated in a 24-hour exposure period (Crevice-Corrosion Temperature).

	Critical-Corrosion Temperature
Alloy	°C	°F

HASTELLOY^® C-22^® alloy	>100	>212
HASTELLOY^® C-276 alloy	95	203
HASTELLOY^® C-4 alloy	42.5	109
HAYNES^® 625 alloy	40	104
HASTELLOY^® G-30^® alloy	30	86
Nickel 200	30	86
FERRALIUM^® 255 alloy	45	113
Alloy 904L	5	41
Type 317 Stainless Steel	2.5	37

Comparative Critical Pitting Temperatures in Oxidizing H₂SO₄-HCl Solution

The chemical composition of the solution used in this test is as follows: 11.5% H₂SO₄ + 1.2% HCl + 1% FeCl₃ + 1% CuCl₂. This test environment is a severely oxidizing acid solution which is used to evaluate the resistance of alloys to localized corrosion. It is considerably more agressive than the oxidizing NaCl-HCl test. Experiments were performed in increments of solution temperature of 5°C for a 24-hour exposure period to determine the critical pitting temperature, i.e. the lowest temperature at which pitting corrosion initiated (observed at a magnification of 40x of duplicate samples.)

	Critical Pitting Temperature
Alloy	°C	°F

HASTELLOY^® C-22^® alloy	120	248
HASTELLOY^® C-276 alloy	110	230
HASTELLOY^® C-4 alloy	90	194
HAYNES^® 625 alloy	75	167

HASTELLOY Alloys Excel in Pitting Resistance

As a class, C-type alloys excel in pitting corrosion resistance. However, comparison tests in a severe pitting environment show HASTELLOY^® C-22^® alloy to be in a class by itself.

Samples were subjected to a solution of 11.5% H₂SO₄ + 1.2% HCl + 1%FeCl₃ +1% CuCl₂.
Solutions for cupons 625 and C-4 were at 102°C, while C-276 and C-22 were at 125°C.

Haynes International, Inc. 800-354-0806 765-456-6012

HASTELLOY® C-276 alloy Information*

Excellent corrosion-resistance to both oxidizing and reducing media and excellent resistance to localized corrosion attack.

HASTELLOY^® C-276 alloy Information*

Excellent corrosion-resistance to both oxidizing and reducing media
and excellent resistance to localized corrosion attack.