To assess the resistance of alloys to pitting and crevice attack, it is customary to measure their Critial Crevice Temperatures and Critical Pitting Temperatures in acidified 6 wt.% ferric chloride, in accordance with the procedures defined in ASTM Standard G 48. These values represent the lowest temperatures at which crevice attack and pitting attack are encountered in acidified ferric chloride, within 72 hours.

	Critical Crevice Temperatures		Critical Pitting Temperatures
ALLOY	°C	°F	°C	°F
316L	0	32	15	59
254SMO^®	30	86	60	140
625	40	104	100	212
C-22	80	176	>120	>248
C-276	55	131	>120	>248
C-2000	80	176	>120	>248

Critical Pitting Temperatures in Green Death Solution

Another solution commonly used for assessing the pitting resistance of nickel alloys is 11.5% sulfuric acid + 1.2% hydrochloric acid + 1% ferric chloride + 1% cupric chloride, otherwise known as Green Death. Listed are Critical Pitting Temperatures of C-2000 and other alloys in Green Death, based on tests of 24 hours.

	Critical Crevice Temperatures
ALLOY	°C	°F
316L	25	77
625	75	167
C-4	90	194
C-22	120	248
C-276	105	221
C-2000	110	230

Seawater Crevice Corrosion Results

Seawater is probably the most common aqueous salt solution. Not only is it encountered in marine transportation and offshore oil rigs, but it is also used as a coolant in coastal industries. Listed are some recent data, generated as part of a U.S. Navy study at the LaQue Laboratories in Wrightsville Beach, North Carolina.* Crevice tests were performed in both still (quiescent) and flowing seawater, at 29°C, plus or minus 3°C. Two samples of each alloy were tested in still water for 180 days, and two samples of each alloy were tested in flowing water for 180 days. Each sample contained two possible crevice sites.

	Quiescent	Quiescent	Flowing	Flowing
ALLOY	No. of Sites	Depth, mm	No. of Sites	Depth, mm
316L	2	1.80	2	0.32
254SMO	2	1.25	2	0.01
625	2	0.11	2	<0.01
C-22	0	0	0	0
C-276	1	0.12	0	0
C-2000	0	0	0	0

*Ref. D. M. Aylor et al, Paper No. 329, CORROSION 99, NACE International, 1999.

Uniform Corrosion Data (C-2000, C-4, C-22, C-276, 625)

Chemical	Conc.	Temperature		Corrosion Rate
	wt.%	°C	°F	C-2000		C-4		C-22		C-276		C-625
	wt.%	°C	°F	mm/y	mpy	mm/y	mpy	mm/y	mpy	mm/y	mpy	mm/y	mpy
Hydrochloric Acid	1	Boiling		0.01	0.2	0.48	18.8	0.06	2.2	0.33	13.0	0.23	8.9
	5	79	175	<0.01	0.1	0.98	38.6	1.44	56.6	0.75	29.4	4.65	183.0
	10	38	100	<0.01	<0.1	0.19	7.3	0.01	0.4	0.17	6.8	0.30	11.9
	20	38	100	0.16	6.3	0.14	5.4	0.20	7.7	0.14	5.4	0.36	14.1
Hydrobromic Acid	2.5	Boiling		0.01	0.2	0.08	3.3	0.02	0.6	0.13	5.0	<0.01	0.1
	5	93	200	0.01	0.2	0.76	29.9	0.01	0.3	0.15	5.8	0.60	23.7
	7.5	93	200	<0.01	0.1	0.76	29.9	0.45	17.8	0.73	28.7	0.93	36.5
	10	79	175	<0.01	<0.1	0.53	20.9	0.01	0.3	0.51	20.0	0.82	32.3
	20	66	150	<0.01	<0.1	0.35	13.7	0.46	18.2	0.37	14.5	0.65	25.7
Hydrofluoric Acid	1	79	175	0.18	7.0	N/T	N/T	0.21	8.2	0.40	15.9	0.31	12.2
	5	52	125	0.09	3.7	N/T	N/T	0.15	6.0	0.34	13.4	0.70	27.4
	10	52	125	0.22	8.7	N/T	N/T	0.33	13.1	0.41	16.0	2.23	87.8
	20	52	125	0.48	18.8	N/T	N/T	0.53	21.0	0.48	18.8	4.33	170.5
Sulfuric Acid	10	93	200	0.02	0.8	0.19	7.3	0.04	1.6	0.14	5.5	0.24	9.5
	20	93	200	0.03	1.0	0.38	15.1	0.28	11.0	0.40	15.6	0.58	23.0
	30	93	200	0.04	1.5	0.54	21.3	0.68	26.8	0.42	16.4	0.68	26.9
	40	79	175	0.01	0.5	0.38	15.0	0.31	12.3	0.19	7.5	0.58	22.8
	50	79	175	0.02	0.7	0.63	24.7	0.40	15.9	0.26	10.3	0.89	35.2
	60	79	175	0.02	0.9	0.67	26.4	0.67	26.4	0.30	11.8	0.92	36.2
	70	66	150	0.01	0.2	0.14	5.7	0.28	11.0	0.05	1.8	0.63	24.7
	80	66	150	0.06	2.2	0.13	5.1	N/T	N/T	0.04	1.6	0.91	35.8
	90	79	175	0.07	2.9	0.71	27.9	N/T	N/T	0.05	1.9	6.97	274.5
Nitric Acid	20	Boiling		0.02	0.7	0.38	15.0	0.06	2.3	0.66	25.9	0.01	0.3
	40	Boiling		0.24	9.5	1.27	50.0	0.26	10.4	4.42	174.0	0.14	5.5
	60	93	200	0.19	7.4	0.73	28.7	0.19	7.6	2.03	80.0	0.06	2.4
	70	93	200	0.29	11.4	0.95	37.4	0.33	13.0	2.62	103.0	0.08	3.2
Phosphoric Acid	50	Boiling		0.03	1.1	0.27	10.7	0.03	1.3	0.18	6.9	0.02	0.9
	60	Boiling		0.08	3.2	0.11	4.3	0.56	21.9	0.28	11.1	0.16	6.2
	70	Boiling		0.15	6.0	0.13	5.1	1.04	41.0	0.13	5.2	0.89	35.2
	80	Boiling		0.40	15.6	0.26	10.3	3.02	119.0	0.31	12.3	4.90	193.0
Chromic Acid	10	66	150	0.10	3.9	N/T	N/T	0.13	5.0	0.13	5.0	0.13	5.2
Chromic Acid	20	66	150	0.61	24.1	N/T	N/T	0.68	26.7	0.53	21.0	1.00	39.3
Acetic Acid	99	Boiling		<0.01	<0.1	<0.01	0.1	<0.01	0.1	<0.01	0.1	<0.01	0.1
Formic Acid	88	Boiling		0.01	0.4	0.05	2.0	0.02	0.9	0.04	1.4	0.24	9.3
ASTM G 28A**		Boiling		0.67	26.3	3.52	138.6	1.02	40.0	5.97	235.0	0.48	18.8
ASTM G 28B***		Boiling		0.11	4.2	N/T	N/T	0.20	8.0	1.23	48.3	N/T	N/T

*N/T = not tested
**G 28A = 50% H₂SO₄ + 42 g/l Fe₂(SO₄)₃
***G 28B = 23% H₂SO₄ + 1.2% HCl + 1% FeCl₃ + 1% CuCl₂

Stress Corrosion Cracking

A common solution for assessing the resistance to chloride-induced stress corrosion cracking of a material is boiling 45% magnesium chloride. This table indicates the times required to induce cracking in U-bend samples of several materials. The tests were stopped after six weeks (1008 hours).

Alloy	Time to Cracking
316L	2 h
254SMO	24 h
625	No cracking in 1008 h
C-22	No cracking in 1008 h
C-276	No cracking in 1008 h
C-2000	No cracking in 1008 h

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HASTELLOY® C-2000® alloy Information*

An extremely versatile nickel alloy resistant to corrosion in all acids and choride solutions, over wide temperature ranges.

HASTELLOY^® C-2000^® alloy Information*