The corrosion rate of nickel based alloys increases by the chlorates and some sulfur based compounds in caustic soda that should be discarded in case it is feasible.

1. Corrosion resistance of Nickel finish
Replacement or maintenance of corrosion hurt equipment is the major need of modern industry.
Even in US, the investment of corrosion is around billions of dollars per annum. Almost 15% of loss
could be cut down by using improved materials, processes or designs through implementation of the
latest technologies. Other industrial countries also make the similar investment to recover corrosion
damaged alloys.
The corrosion rate of metals can be decreased by coating them with thin layers of mild reactive
metals or alloys. Different techniques such as electroplating, vapor accumulation, metal spraying and
electroless accumulation, are highly successful. But many metallic finishes have been found
potentially porous and have small barriers to corrosion. Now, with the production of electroless
nickel, these issues have been concurred. In the present time due to its outstanding corrosion
resistance and enhanced significance becoming the reliable, the finishing is widely considered for
several applications.
Corrosion Resistance Is Tremendous
Electroless Nickel is a security finish. It secures the beneath metal by shielding it from surrounding,
instead through galvanization. Due to it amorphous properties and passivity, although the corrosion
resistance of electroless nickel is tremendous and in several conditions more than that of pure nickel
or chromium based alloys. When suitably executed, the finishing is fully resistant to alkalies, salt
solutions and brines to chemical an petroleum conditions and to different kinds of hydrocarbons and
solvents. The Finishing also provide excellent resistance to ammonia solutions to organic and
reducing acids. It is just corroded by powerful oxidizing conditions like nitric acid.
Natural Corrosion:
An electroless nickel is fully resistant to corrosion in rural, industrial and seawater conditions. When
tested in three different locations, in fact extremely thin coatings were observed to offer full security
to well made substrates for six to fifteen months. These analyses also described 0.5 mill or 12 micro-m
thick electroless nickel layer to offer enhanced security as compare to that of 1 mill or 25 micro-m
thick finishing of electrolytic nickel.
An exclusive feature of electroless nickel is its inertness from beneath accumulated or interface
corrosion. In contrast to electrolytic deposits, if corrosion starts by pin holes or damaged regions,
there is no possibility for it to travel in natural or submerged water conditions. Usually as the
influenced region enriches with corrosion, further corrosion of the material decrease and may
impede.
Marine Water
Finishes can offer highly suitable security from corrosion in marine equipments. The ship hardware,
fittings and valves as well as land based systems are usually secured with 3 mil or 75 micro-m thick
deposits. In an Arabian sea water analysis, finished ball valves have provided good performance in
the marine water injection apparatus for about five years without getting any attack. Removal and
evaluation of single valve was done after four years of service and it was observed to be in its new
condition.

2. Lab tests in presence of air, artificial seawater at temperatures about 200oF has states the largest
loss of electroless nickel to be about only 0.04 mpy or 1 micro-m per year. Due to its intense
hardness, the accumulation has provided outstanding resistance to impingement and erosion or
corrosion in marine water and is widely utilized for pumps, valves and identical devices. The
vibratory cavitation analyses have described finishes to attain resistance similar to that of stainless
steel and high chromium based alloys in the marine and natural water kinds.
Natural Waters
Rust of electroless nickel in fresh and very pure water is nominal. Analyses in tap water have
described the nominal attack rate of 0.01 to 0.03 mpy at ambient temperature. The attack in air
saturated, deionized water is compared with finishing to plain steel. Infact at temperatures up to
200oF or 95oC, the largest reduction in finish is only about 0.04 mpy or 0.1 micro-m per annum.
Identical resistance of finish to attack in quenching water, boiler feed water, condensate and the
similar is outstanding. Infact at temperature limits of 650oF or 350oC, the reduction in deaerated,
double distilled water is lower than 0.08 mpy.
The electroless nickel also provides high resistance to condensation steam. The autoclave analyses
at which 360oF or 180oC steam, saturated with oxygena dn carbon dioxide was condensed on eat
movement units described the coating to be intact even after 4.5 days. While this time, commercial
glas linings generally are intensely etched.
The solution pH scale has noticeable effect on the variety of metals corrosion, such as electroless
nickel. A solution of 0.1% HCl in deionized water was deionized water was neurtralized using sodium
hydroxide to create solutions having pH scale of 1.4 -12. Immersion analyses at ambient
temperature limits described that three pH corrosion of the accumulation was equally lesser than
0.08 mpy and mean only 0.04 mpy. At smaller pH corrosion was accelerated however it was not
more than 0.8 mpy.
Water was neutralized using sodium hydroxide to create solutions having pH scale of 1.4 -12.
Immersion analyses at ambient temperature limits described that three pH corrosion of the
accumulation was equally lesser than 0.08 mpy and mean only 0.04 mpy. At smaller pH corrosion
was accelerated however it was not more than 0.8 mpy.
Inorganic Acids
Electroless nickel offers significant resistance to reduction acids. The standard finish reduction rate
lies beteen 0.3 to 1 mpy. It is not usually employed for longer applications, however it is safe for use
for intermittent or short range applications like acid cleaning or back washing. The electroless nickel
finishes normally offer lower resistance to oxidizing acids. In these conditions, reductions can be
very large and electrless nickel is not preferred for application.
Sulfuric Acid (H2SO4)
The sulfuric acid is used on the largest scale in the industrial applications. Its nature, although is
strange. At ambient temperature limits, with magnitudes smaller than 85%, it acts as reducing agent.
However when used in larger magnitudes, it treats as oxidizing agent. The nature of electroless

3. nickel follows this acid. lower than 85% magnitudes, the finishes offer high resistance at ambient
temperatures, and are corroded by 0.3 to 1.1 mpy . With concentration more than 85%, the
corrosion rate of finish accelerates quickly and in oleum may increase to 10 mpy. The resistance of
electroless nickel to sulfuric acid is evaluated.
Hydrochloric Acid (HCl)
The finishes offer significant resistance to HCl at ambient temperature about 10% magnitude. In
such dilute solutions corrosion rates are normally up to 1 mpy or 25 micro-m per year. At larger
magnitudes, the corrosion is accelerated and becomes 2 to 3 mpy. The corrosion rate further
increases by increasing temperature or due to availability of oxidizing salts.
Hydroflouric Acid
However hydrofluoric acid is weaker than HCl or H2SO4, it is more corrosive than both and very
tough to occupy. Only gold, platinum and Teflon are extremely resistant to corrosion. However the
resistance of industrial nickel based alloys can be suitable for many applications. These alloys
produce thing security fluoride layers on their surfaces that prevent the regular corrosion.
The resistance of electroless finishing to hydrofluoric acid solutions is suitable for dilute solutions.
Lower than 25% magnitude, corrosion rates are normally up to 1 mpy or 25 micro-m per year. The
nature of electroless nickel in hydrofluoric acid solutions is stated in the following table:
Attack rate off electroless nickel in HF acidic solutions at ambient temperatures
Magnitude, % Corrosion rate, micro-m per
year
Corrosion rate, mpy
2 27 1.1
10 30 1.2
25 30 1.2
40 53 2.1
52 46 1.8
Phosphoric Acid
Electroless nickel provides adequate resistance to phosphoric acid at ambient temperatures in all
magnitudes. For acid concentration about 85%, the corrosion rate is hardly 0.1 mpy. Using the
commercial acid that consists of ferric salts, the corrosion rate may increase and the finish is not
usually made. The attack also increases in fortified acids or due to increased temperature limits.
Nitric Acid
This acid is a very powerful oxidizing material in all weight percentages. The resistance provided by
nickel alloys is very controlled. An electroless nickel can solely be utilized for magnitudes about 10%
at ambient temperatures. The attacks are normally 0.5 to 1 mpy. With increase in acid magnitudes,
corrosion rate increases terribly and becomes 1 inch per annum.
Caustic Alkalies

4. The finishing has excellent resistance to caustic soda, caustic potash and various other alkalis at
large magnitudes and high temperatures. For weight lower than 50%, attack is nominal due to the
creation of security oxide layers. In fact for acid weights up to 72% with temperatures about 230ooF
or 110oC, electroless nickel finishes provide suitable resistance, in one filed test the attack rate of
the finish was about 0.7 mpy or 18 micro-m per year as compare to 0.5 mpy or 13 micro-m per year
for wrought nickel and 41 mpy or 1000 micro-m for plain steel.
The corrosion rate of nickel based alloys increases by the chlorates and some sulfur based
compounds in caustic soda that should be discarded in case it is feasible. For instance, the inclusion
of 0.4 percent sodium chlorate increases the corrosion rate of electroless nickel ten times. It also
increases by the inclusion of sulfur materials like sodium sulfite. The availability of hydrogen sulfite,
although is not damaging and may enhance the resistance power of finish.
Ammonia Solutions
The electroless nickel may offer outstanding resistance to ammonia and crucial resistance to
ammonia hydroxide solutions. In the presence of pure ammonia, the corrosion rate is normally
lower than 0.2 mpy. The presence of water hydrolizes ammonia to produce nickel complex
compounds due to which corrosion rate increases. It is shown in the following table:
Solution Corrosion rate
Micro-m per year Mpy
2% ammonia 28 1.1
10% ammonia 23 0.9
28 % ammonia 16 0.6
27%ammonium chloride 8 0.3
66%ammonium nitrate 10 0.4
25% ammonium hypophospate 5 0.2
43% ammonia sulfate 3 0.1
In the salt solutions of ammonia, electroless nickel also show significant resistance. In the
ammonium chloride and nitrate, the attack is almost 0.4 mpy or 10 micro—m per annum, whereas
in phosphate and sulphate solutions the corrosion rates are generally 0.2 mpy or 5 micro-m per
annum. It is also shown in the above table.
Petroleum : The petroleum manufacturing conditions cause complex types of corrosion that contain
various corrosion agents, with additional influence of temperature, pressure, velocity and abrasives.
The popular types of attacking agents in oil field are salt water, carbon dioxide and hydrogen sulfide,
however the presence of nitrogen, sulfur and oxygen and organic as well as inorganic acids are also
available.
The finishing of electroless nickel have been employed in the petroleum production plants from the
several years to prevent corrosion and erosion. The outcomes of the latest analysis to evaluate the
featured functionality of electroless nickel in oil field conditions are stated.
It is found that in the presence of carbon dioxide at temperature of 200oF or 95oC, the attack rate of
electroless nickel is 0.2 mpy. It shows an enhancement by 98% over the corrosion rate of plain steel.

5. In hydrogen sulfide saturated and combined carbon dioxide plus hydrogen sulfide is available, a
tenacious sulfide layer produces, improving the passivity of the finished layer and avoiding further
corrosion. Other tests have stated that sulfide layers will produce with magnitude of hydrogen
sulfide lower up to 4ppm and at high temperature limits up to 180oC or 350oF.
As several production conditions comprise of minimum a trace of hydrogen sulfide, finishing offers a
full security from oil field attack. In one sour gas system situated in Middle East, coated chokes and
valves have been utilized for 8 to 10 years at 200oF or 95oC and velocities about 50 fps without any
significant attack. Earlier utilized steel parts attained attacks about 80 to 120 mpy.
Organic Acids
The standard organic acids are weak and non-oxidizing in nature. They generally show lower activity
with increase in their molecular weight and length of carbon atoms. For example ammonia, several
organic acids offer high complex property with nickel ions and water, hence the decrease in
electroless nickel is enhanced by increasing magnitude of water.
The electroless nickel finishing offers outstanding resistance to the different kinds of concentrated
organic acids. In dilute solutions, although, corrosion is high. Attack also increases by aeration and
high temperature. The outcomes of analysis wit deposits in aerated organic acids are described in
the following table:
Acid Corrosion rate
Micro-m per annum Mpy
Glacial acetic 0.8 0.03
10% acetic 25 1
0.25% Benzoic 10 0.4
90% carbolic 0.2 0.01
5% carbolic 5 0.2
5% citric 2 0.07
Cresol 0.2 0.01
88% formic acid 13 0.5
85% lactic acid 1 0.05
Oleic Nominal nominal
10% Oxalic 3 0.1
Elevated temperature conditions
The melting point of electroless nickel is 1630oF or 890oC. Following, its significance at the high
temperatures is controlled. Similar to other nickel alloys, the finishes are highly resistant to nitriding
and are utilized as a maskant for industrial surface hardening processing. In oxidizing flue gases, air
or steam, electroless nickel filming get small corrosion at temperatures about their melting point. In
the presence of sulfur, for example reducing flue gases and some refinery process streams,
sulfidation of the coating may take place at temperatures about 525oF or 275oC.
Salts

6. The finished layers offer superior resistance to neutral and alkaline salts and acid salts. The solutions
of these compounds like sodium and potassium chlorides, sulfates, phosphates and carbonates have
minor influence on coatings. The accumulations have been broadly utilized in chemical conditions
and for food, pharmaceutical and medical applications. The attack rate of electroless nickel in some
salt solutions is described in the following table:
Salt Corrosion rate
Micro-m per year Mpy
27% Al2(SO4)3 5 0.2
26% BaCl2 0.2 0.01
42% CaCl2 0.2 0.01
5% CuCl2 25 1
5% CuSO4 18 0.7
1% FeCl3 200 8
25% KCl Nominal Nominal
28% K2CO3 0.2 0.01
35% MgCl2 2 0.1
26% NaCl 0.2 0.01
18% Na2Co3 1 0.05
47% NaNO3 Nominal Nominal
46% NaH2PO4 3 0.1
14% Na2S Nominal Nominal
31% Na2SO4 0.8 0.03
36% Pb(NO3)2 0.2 0.01
80% ZnCl2 7 0.3
The acid salts like magnesium chloride, zinc chloride and aluminum sulfate result in accelerated
corrosion of electroless nickel. The finish, although, provides significant resistance to these agents
and often offers adequate service.
The oxidizing halide salts like cupric, mercuric and specifically ferric chloride, result in rigorous
corrosion of electroless nickel finishes and should be prevented for use. The oxidizing solutions
comprising of chlorine like sodium hypochlorite also result in quick damage of finishing.
Fluorescence
Stress Corrosion Cracking
A fascinating feature of electroless nickel coating is their property to prevent corrosion cracking of
the beneath metal. They can avoid metal cracking in conditions that usually result in quick metal
failure. For example, in a single array of analyses in boiling 42% magnesium chloride, the samples of
Cr-Ni stainless steel finished with 0.4 mil of heat processed, Electroless nickel were discovered to be
intact after 80 days, while unfinished samples were damaged in six to eight hours.
The finishes have also been noticed to be very effective in avoiding cracking of plain and low alloy
steel due to caustic materials, specifically in steam and condensate conditions. Few latest analyses
state that these finishes may also be advantageous in decreasing sulfide cracking of high strength

7. steels in petroleum conditions. The influence of electroless nickel coatings on stress corrosion
cracking seems to be resulted by two individual aspects:
1. Finishing treats as an obstruction among the base metal and cracking conditions.
2. More significant, the accumulation apparently results in a shift in the corrosion strength of
the alloy from the stress corrosion area into a strength range where cracking is impossible.
Effect of Heat Processing
One of the crucial factors influencing the corrosion of electrolesss nickel is heat processing. As
deposits are heated to temperatures upto 500oF or 260oC, structural variations start to take place
within the alloy. Initially coherent and then different particles of nickel phosphide (Ni3P) produce
across the finish then at temperatures more than 650oF or 340oC. Electroless nickel starts to
crystallize and to lose its amorphous nature. At the elevated temperatures, the particles
conglomerate, producing a matrix of Ni3P. Not just do these variations have an impulsive effect on
the coating hardness, but these also result into intense loss of corrosion resistance.
As the nickel phosphide particles produce inside the coating, they can decrease the phosphorous
magnitude of the remaining material. It decreases its passivity and improves its corrosion. The
particles also produce nominal active corrosion cells, further adding to the finish damage. A
secondary effect of heat processing is that accumulation contracts as it hardens, usually causing
cracks in finish that can disclose the base metal to corrosion.
The influence of heat processing on the corrosion of electroless nickel in 10% HCl :
Heat Processing Deposit hardness,
VHN
Corrosion rate
Micro-m per year Mpy
None 480 15 0.6
375oF or 190oC for 1.5 hours 500 20 0.8
550oF or 290oC for 6 hours 900 1900 74
550oF or 290oC for 10 hours 970 1400 56
650oF or 340oC for 4 hours 970 900 34
750oF or 400oC for 1 hours 1050 1200 49
For these analyses, samples of the deposit were heat processed to show various commercial
treatments and then shown to 10% HCl at ambient temperature. Baking at 375oF or 190oC, similar
to that utilized for hydrogen embrittlement relief, resulted in no considerable increase in corrosion.
The hardening, although resulted in increased corrosion of nickel finish from 0.6 mpy to 30 mpy or
by 50 times. The analyses in other conditions described an identical loss in corrosion resistance after
hardening. Corrosion resistance is essential, it is important to not use in hardened coatings.
Conclusion
Electroless nickel is widely utilized for various different but usually complimentary causes. In the
various applications, this finish can decrease the corrosion rate and erosion, decrease friction and
wear and prevent stress corrosion cracking. It can decrease repair and maintenance costs and
enhance apparatus life and consistency. Due to its exclusive combination features, Electroless Nickel

8. has been proven to be significant for industry and has been rapidly utilized to replace several costly
alloys.