This document discusses the corrosion resistance of various nickel alloys in different environments. It states that nickel alloys offer much higher corrosion resistance than other alloys, especially in intense conditions. They can withstand corrosion from seawater, acids like hydrochloric acid and hydrofluoric acid, and salt solutions better than stainless steels. Alloys with higher chromium, molybdenum, and copper content have the best resistance to pitting, crevice corrosion, and stress corrosion cracking. Hastelloy alloys generally perform very well across many corrosive environments.

1. Corrosion resistant Nickel alloys behavior
Nickel alloys offer wide levels of corrosion resistance that are impossible to attain with other alloys.
The corrosion resistant nickel based alloys are widely useful industrial materials. In the intensely
vigorous conditions, they show more considerable enhancement than stainless steels. Moreover the
higher installation cost of nickel alloys is easily overcome by their prolonged life, thus decreased
apparatus downtime. These are very easily formable and weldable into complicated commercial
parts.
In this article, nickel alloys corrosion conduct in sea water and different salt solutions and
hydrochloric, hydrobromic and hydrofluoric acid conditions is shown. When adequate data is
present, 0.1mm per annum harts offer evaluations with the stainless steels. To state the resistance
of specific nickel alloys to chloride based pitting and crevice corrosion, their critical pitting
temperature limits and crevice temperature limits referred as CPT and CCT respectively, in acidic
ferric chlorides are provided, alongside those for more common stainless steels. To state the relative
resistance of nickel alloys and stainless steels to stress corrosion cracking, test outcomes for U bend
specimens in boiling magnesium chloride are stated.
Marine
Marine water attack the marine tubes, oil rigs, and coastal structures and facilities that utilize a sea
water as a coolant. As a chloride, it can cause pitting, crevice corrosion and stress corrosion cracking
of metallic materials and uniform corrosion. Additionally, marine devices can be covered to produce
crevice corrosion called as under deposit attack. Biofouling is also a kind of attack in marine water.
Definitely, nickel alloys have high marine water corrosion resistance. Specifically those containing
copper like Monel alloy 400 offer resistance to biofouling. For static or slowly moving water
conditions, chromium and molybdenum based nickel alloys offer higher resistance to pitting and
crevice corrosion.
Few latest crevice corrosion information for marine water produced as a component of a U S navy
analysis at the North Carolina labs are described in the following figure:
Nickel Alloy Quiescent marine water Running seawater
Count of
corrosive sites
Depth,
mm
Count of
corrosive sites
Depth, mm
Steel 316L 2 1.80 2 0.32
254SMO 2 1.25 2 0.01
Inconel 625 2 0.11 2 Less then
0.01
Hastelloy C22 0 0 0 0
Hastelloy C276 1 0.12 0 0
Hastelloy C2000 0 0 0 0
Crevice analysis wee performed out in both static and running seawater at 29oC more or less 3oC.
Double specimens of every alloy were performed in static water for 180 days and double specimens
of every alloy were analyzed in running seawater for 180 days. Every specimen consisted of two

2. feasible crevice places. in static seawater the outcomes show those produced in acidic ferric chloride
with Hastelloy C-22 and Hastelloy C-2000 alloys as the highly resistant materials. In the running
marine water, crevice corrosion of stainless steels was shallower and not any of the nickel -
chromium-molybdenum alloys attained crevice corrosion.
Salt solutions
However several salts result in many issues for nickel alloys, some can cause insidious and
unpredictable corrosion forms. For instance, water solutions containing chloride salts are found to
cause pitting and crevice corrosion and stress corrosion cracking of stainless steels in specifically.
Many halide salts such as bromides and fluorides result in identical effects.
In addition of anions, cations can also be significant when dealing with salts in aqueous systems. For
instance, ferric and cupric ions can significantly change the electrochemistry of acid systems, causing
cathodic reactions of higher potential and potential corrosion of materials that were otherwise
stable. The nickel-copper and nickel-molybdenum alloys are specifically inclined to these effects.
The Nickel alloys normally are highly resistant to chloride ion stress corrosion cracking and some
such as nickel-chromium-molybdenum alloys attain high resistance to pitting and crevice corrosion.
Actually, most of their success in chemical applications is resulted by these properties.
To analyze the alloys resistance to crevice and pitting corrosion, it is essential to determine their CCT
and CPT in acidic 6% ferric chloride as per with processes stated in ASTM standard G48. This data
shows the minimum temperatures at which crevice and pitting corrosions occur in acidic ferric
chloride in a 72 hours time frame. The CCT and CPT values for many nickel alloys and stainless steels
are provided in following table:
Alloys Critical crevice temperature Critical pitting temperature
oC oF oC oF
316L 0 32 15 59
254SMO 30 86 60 140
28 17.5 64 45 113
31 42.5 109 72.5 163
G-30 37.5 100 67.5 154
G-35 45 113 95 203
625 40 104 100 212
725 (age-hardened) 25 77 85 185
C-22 80 176 More than 120 More than 248
C-22HS (Annealed) 100 212 More than 120 More than 248
C-22 HS (age-hardened) 75 167 110 230
C-276 55 131 More than 120 More than 248
C-2000 80 176 More than 120 More than 248
This information clearly states the advantage of the chromium bearing nickel alloys above
the stainless steels. A widespread solution for describing the resistance to chloride ion stress
corrosion cracking of metallic materials is boiling 45% magnesium chloride. Normally U
shaped samples are analyzed in this condition for tests times about 1008 hours, with
disturbances to investigate for cracking. The information for many nickel alloys and stainless

3. steels are represented in the following table:
Alloy Cracking period, hours
Steel 316L 2
254SMO 24
28 36
31 36
G-30 168
G-35 No signs of cracking in 1008 hours
Inconel 625 No signs of cracking in 1008 hours
Hastelloy C-22 No signs of cracking in 1008 hours
Hastelloy C-276 No signs of cracking in 1008 hours
Hastelloy C-2000 No signs of cracking in 1008 hours
This table describes that nickel alloys containing lower iron levels like nickel -chromium-molybdenum
alloys provide the maximum resistance to stress corrosion cracking.
Hydrobromic Acid
Hydrobromic acid is a very strong mineral acid, in fact a more suitable solvent for solvent for
some ore minerals as compare to hydrochloric acid due to its higher boiling point and more
powerful reducing performance. The basic action of hydrobromic acid is the generation of
inorganic bromides for operations like medicines, adhesives and photosensitive emulsions.
In nickel alloys, the materials containing high magnitude of molybdenum offer the maximum
resistance to hydrobromic acid and other halogen acids.
It is found that Hastelloy B3 alloy can perform up to its boiling point in hydrobromic acid
conditions, however the corrosion rates by 0.1 mm per year are assumed at temperatures over 40oC
or 100oF. Hastelloy C2000 alloy is very unlike. The corrosion rates lesser than 0.1mm per annum are
assumed over a large limit. The contaminants and residuals always exist in the industrial processes, if
these are oxidizing agents, then these are harmful to nickel-molybdenum alloys. The nickel-chromium-
molybdenum alloys withstand oxidizing conditions and even remain advantageous from
them. These alloys include ferric ions, cupric ions, oxygen, chlorine and hydrogen peroxide.
Hydrochloric Acid
Hydrochloric acid is a very essential chemical for nickel based alloys in the chemical plants. It is
widely occurred as well as very vigorous chemical to the stainless steels. Moreover hydrochloric acid
is indirectly accountable for the industrial effects of chloride salts on metallic materials. Hastelloy
alloys can withstand 0 to 20% HCL concentrations to their boiling point without getting corrosion
above 0.5 m per annum. Essentially the rate of 0.3 mm per year or lower is standard above 40oC.
The nickel-chromium-molybdenum alloys come in the second level service in HCl conditions after
Hastelloy alloys and are recommended at small acid contents and high temperatures. The nichrome
alloys containing higher magnitude of molybdenum for example Inconel 625 also provide significant
resistance to HCl.
For outlook, an evaluation of functionality of nickel-chrome-molybdenum alloys and three kinds of
austenitic stainless steel is done.
Hydrofluoric Acid
It is a water solution of HF. It is essential in several chemical processes, significantly those included
with the generation of coolants, adhesives and fluropolymers. It also pickles different metals and to
etch glass.
Hydrofluoric acid is one of the detrimental acids due to its wide corrosion to skin. A process

4. including HF at the high temperatures and moderate content is very complicated condition. The
reactive metals such as are readily corroded by HF, and stainless steel normally attain high corrosion
rates.
Nickel alloys offer small to moderate corrosion rates in hydrofluoric acid at the broad concentration
and temperature limits and hence fit for several kinds of devices included in the production and
operation of acid. it is supposed that nickel alloys offer resistance to hydrofluoric acid due to
generation of security layers that is nickel fluoride.
The lab attribution of nickel alloys in hydrofluoric acid have not been as broad as it has with other
popular inorganic acids primarily due to its detrimental behavior. Following possible alloys perform
with HF:
1. Monel 400 and Hastelloy C2000 are one of the highly resistant alloy. Monel is fit when fully
submerged, Hastelloy excels in vapor regions over the hot acid solutions.
2. In hydrofluoric acid lab tests, the time of testing is essential. It may relate to the period it
takes for security fluoride layers to produce on the various alloys.
3. The nickel alloys are sensitive to stress corrosion cracking in hydrofluoric acid and in the
related vapor regions. Hence care should be taken to prevent applied or residual stresses in
nickel alloy parts subjected the chemical.
The following table describes the outcomes of a latest analysis including an acid content about 20%,
a temperature of 79oC and test time of 240 hours:
Alloy Corrosion rates, mm/y Highest depth of cracking, mm
Immersed suspended Immersed suspended
Inconel
625
18.76 2.93 0 0
Hastelloy
C22
0.34 0.80 0.32 0.13
Hastelloy
C276
0.51 0.78 0.43 0.20
Hastelloy
C2000
0.40 0.69 0.17 0.06
G35 18.76 1.54 0 0
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