Continuing developments in metallurgical techniques and production methodologies have urged the development of Nickel alloys and their wider applications in the chemical industry.

1. Corrosion and heat resistant Nickel alloys
Continuing developments in metallurgical techniques and production methodologies have urged the
development of Nickel alloys and their wider applications in the chemical industry.
The Nickel alloys provide a combination of outstanding corrosion resistance, strength, toughness,
metallurgical stability, fabricability and weldability. Several nickel alloys further attribute excellent
heat resistance, making them the superior choices for applications that need chemical resistance
and strength at high temperatures.
This article of wrought nickel based alloys include a broad range of wrought corrosion resistant
alloys that are widely employed in chemical plants. The chemical composition and UNS serial nos of
these alloys are stated in the following table:
Alloy UNS
no.
Nickel Chromium Molybdenum Iron Tungsten Copper Other
elements
Nickel
200
N02200 99.6
Monel
400
N04400 66.5 1 31.5 1
Inconel
600
N06600 75 15.5 8
Inconel
625
N06625 62 21.5 9 2.5 3.8
(niobium
+
tantalum
Inconel
690
N06690 61 29 9
Incoloy
825
N08825 42 21.5 3 29.5 2.3 1
(Titanium)
Hastelloy
G3
N06985 44 22 7 19.5 1.5 2 2.1
(Niobium)
Hastelloy
G30
N06030 43 29.8 5 15 2.8 1.7 1
(Niobium
+
Tantalum)
Hastelloy
C276
N10276 57 15.5 16 5.5 3.8
Hastelloy
C22
N06022 56 33 13 3 3
Hastelloy
C2000
N10200 59 23 16 1.5 1.6
Inconel
622
N06022 58 20.5 14.2 2.3 3.2
Inconel
686
N06686 60 21 16 5 3.7
59 N06059 60 23 15.8 1.5
Hastelloy
N10665 69 1 28 2
B2
Hastelloy N10675 68.5 1.5 28.5 1.5 3

2. B3
Hastelloy
B4
N10629 66 1 28 3.5
Alloy Properties
Nickel alloys are costlier than stainless steels. Although, economic evaluations on an initial cost,
instead depending on life-cycle, can be misleading. For example, Nickel-chromium-molybdenum
alloys cost hardly five times costlier than nickel -chrome stainless steels and about double of super
austenitic stainless steels.
Attaining the outstanding corrosion resistance of nickel alloys, the basi c cost premium can usually
be regained through long term service as the nickel alloys equipments provide prolong life, nominal
maintenance and mild collapses.
The physical characteristics of Nickel alloys are widely similar to as that of austenitic stainless steel
300 series. Nickel based alloys offer thermal expansion rates equivalent to carbon steel, but
considerably smaller than stainless steel 300 series. However the thermal conductivity of pure nickel
metal is more than the carbon steel, several nickel alloys have considerably smaller conductivities, in
some cases, even smaller than austenitic stainless steels.
Excluding the pure nickel, the nickel alloys utilized in chemical processing are significantly stronger
than steel 300 series. The Nickel alloys also attain better ductility as described in the following table:
Alloy Ultimate tensile strength, ksi Yield strength, ksi Elongation, %
Nickel 200 55 15 40
Monel 400 70 28 35
Inconel 600 80 35 30
Inconel 625 110 55 30
Inconel 690 85 35 30
Incoloy 825 85 35 30
Hastelloy G3 90 35 45
Hastelloy G30 85 35 30
Hastelloy C-276 100 41 40
Hastelloy C22 100 45 45
Hastelloy C2000 100 41 45
Inconel 622 100 45 45
59 100 45 45
Hastelloy B2 110 51 40
Hastelloy B3 110 51 40
Hastelloy B4 110 51 40
The highest permissible design stresses for several alloys utilized in chemical plant devices are stated
in section 8 of the ASME boiler and pressure vessel code.
The Nickel alloys attain fully austenitic microstructures. Almost all grades used in the chemical
industry are solid solution strengthened. They attain their high strength features due to the inclusion
of suitable harness like molybdenum and tungsten, instead carbide production. Similar to austenitic

3. stainless steels, solid solution nickel alloys cannot be reinforced through heat processing, only
through cold processing.
Another wide category of nickel based alloys are reinforced through a precipitation hardening heat
processing. These are reserved significantly for ultra high strength applications like those occurred in
deep oil and gas production and wide high pressure processes.
Excluding those chosen parts in valves and rotating machinery, precipitation hardened nickel alloys
find controlled application in chemical units. Taken in this alloy category are heat resistant
superalloys used in gas turbines, combustion chambers and aerospace engineering.
Corrosion Resistance
Nickel alloys offer a step up from traditional stainless steels and super austenitic iron based alloys in
resisting corrosion through a broad range of acids, alkalis and salts. An excellent property of nickel
alloys is outstanding resistance to aqueous solutions containing halide ions. In this relation, nickel
alloys are quite better than austenitic stainless steels that are nominally susceptible to corrosion by
wet chlorides and fluorides.
This excellent corrosion nature of nickel alloys manifests itself not just for lower metal loss but in the
ability to better withstand localized corrosion, significant pitting and crevice corrosion, intergranular
corrosion, stress corrosion cracking etc. Such types of local attacks, more than normal thing, counted
for several of the corrosion based failures in the chemical plants.
The Nickel alloys offer corrosion resistance partly to the inherent smaller reactivity of nickel in
context to iron as determined by its nobler oxidation potential in the EMF series. Identical to
stainless steel, chromium based nickel alloys offer the potential to passivate that treats as a suitable
corrosion preventer.
Another benefit of nickel over iron is the ability to take major fractions of alloying constituents
without producing brittle phases. The common alloying inclusions for improved corrosion resistance
are chromium, molybdenum and copper. Their contributions are specified as following:
Relative resistance ratings of nickel alloys in common chemical units are described in the following
table:
Alloy Sulfuric
acid
Phosph
oric
acid
Hydrochl
oric acid
Hydroflu
oric acid
Nitric
acid
Organ
ic
acids
Strong
alkalis
Reduc
ing
acids
Oxidizin
g salts
Nickel
200
Satisfac
tory
Satisfac
tory
Satisfact
ory
Excellen
t
Not
preferre
d
Excell
ent
Excellen
t
Excell
ent
Not
preferre
d
Monel
400
Excellen
t
Satisfac
tory
Satisfact
ory
Excellen
t
Not
preferre
d
Excell
ent
Excellen
t
Excell
ent
Not
preferre
d
Incon
el 600
Satisfac
tory
Satisfac
tory
Not
preferre
d
Satisfact
ory
Satisfac
tory
Excell
ent
Excellen
t
Excell
ent
Satisfac
tory
Incon Excellen Excellen Excellent Excellen Excellen Excell Excellen Excell Excellen

4. el 625 t t t t ent t ent t
Incon
Satisfac
Excellen
Satisfact
Excellen
Excellen
Excell
Excellen
Excell
el 690
tory
t
ory
t
t
ent
t
ent
Excellen
t
Incolo
y 825
Excellen
t
Excellen
t
Satisfact
ory
Not
preferre
d
Excellen
t
Excell
ent
Satisfac
tory
Excell
ent
Satisfac
tory
Hastel
loy G3
Excellen
t
Excellen
t
Satisfact
ory
Excellen
t
Excellen
t
Excell
ent
Excellen
t
Excell
ent
Excellen
t
Hastel
loy
C276
Excellen
t
Excellen
t
Satisfact
ory
Excellen
t
Satisfac
tory
Excell
ent
Excellen
t
Excell
ent
Excellen
t
Hastel
loy B2
Excellen
t
Excellen
t
Excellent Excellen
t
Not
preferre
d
Excell
ent
Excellen
t
Excell
ent
Not
preferre
d
These general instructions are not made for particular purposes but just as a beginning in the
materials selection procedure.
Welding Guidelines
Most of nickel alloy welds are done through shielded metal arc welding and gas metal arc welding.
The nickel alloy weldments are highly ductile, and their small thermal expansion properties decrease
residual stresses and warpage. The post weld heat processing is normally needed for precipitation
hardenable grades. The specifications made by AWS for welding electrodes of nickel alloy and filler
metals are described in the following table:
Alloy Welding electrode Filler metal
Nickel 200 ENI-1 ERNi-1
Monel 400 ENiCu-7 ERNiCu-7
Inconel 600 ENiCrFe-3 ERNiCrFe-3
Inconel 625 ENiCrMo-3 ERNiCrMO-3
Hastelloy G3 ENiCrMo-9 ERNiCrMo-9
Hastelloy G30 ENiCrMo-11 ERNiCrMo-11
Hastelloy C276 ENiCrMo-4 ERNiCrMo-4
Hastelloy C22 ENiCrMo-10 ERNiCrMo-10
Inconel 622 ENiCrMo-10 ERNiCrMo-10
Inconel 686 ENiCrMo-14 ERNiCrMo-14
59 ENiCrMo-13 ERNiCrMo-13
The welding methods for nickel alloys are almost similar to those utilized for austenitic stainless
steel. Although, because of higher strength of Nickel rich weld puddles and smaller penetration
properties of nickel alloys, the manufacturing of complete penetration welds may need
improvement of joint configurations and welding methods. The Nickel alloys are less tolerant as
compare to ferrous materials to contamination that results into weld embrittlement.
Pairing of high ductility, low thermal expansion and capacity to bear dilution through various
metallic elements has constructed nickel enriched welding consumables universally approved for
welding unlike metals. It not only involves welds of nickel alloys to iron alloys, even also stainless

5. steel welds to carbon alloy steels. Identically, nickel alloys can be weld accumulated on carbon steel
without the chance of failure.
Kinds of nickel alloys
The Nickel alloys are industrially available materials in the wide ranges of product forms such as
plate, sheet, wire, wiremesh, strip, pipe, tubing, rod, bar etc. Chosen ASTM specifications for few of
these are specified in the following table:
Alloy Plate/
sheet
Seamless
pipe
Welded
pipe
Seamless tubes Welded tubes
Nickel 200 B162 B161 B725 B161 B730
Monel 400 B127 B165 B725 B165 B730
Inconel
B168 B167 B517 B167 B516
600
Inconel
625
B443 B444 B705 B444 B704
Inconel
690
B168 B167 B167
Incoloy
825
B409 B407 B407 B515
Hastelloy
G-3
B582 B622 B619 B622 B616
Hastelloy
G-30
B582 B622 B619 B622 B616
Hastelloy
C276
B575 B622 B619 B622 B626
Hastelloy
C22
B575 B622 B619 B622 B626
Hastelloy
C2000
B575 B622 B619 B622 B626
Inconel
622
B575 B622 B619 B622 B626
Inconel
686
B575 B622 B619 B622 B626
59 B575 B622 B619 B622 B626
Hastelloy
B333 B622 B366 B622 B626
B2
Hastelloy
B3
B333 B622 B366 B622 B626
Hastelloy
B4
B333 B622 B366 B622 B626
The Nickel alloys are also made as castings. These normally have various properties derived from
their wrought counterparts. The nickel alloys are normally categorized as per their basic alloying
elements. The elements of nickel alloys widely utilized in the chemical treatment devices are stated
following:

6. Pure Nickel: Pure Nickel or alloy 200 offers high resistance to the several reducing acids and salts,
however it is not a suitable option for operating in strong oxidizing conditions like nitric acid. The
crucial attribute of pure nickel is its outstanding resistance to caustic alkalis even in the molten state.
However excellent resistance to dry hydrogen conditions, nickel is not sufficiently resistant lower the
water dewpoint. For applications above 600oF, a low carbon grade called as Nickel 201 is
recommended for use.
Nickel-Copper alloy 400: The corrosion nature of nickel-copper alloy 400 or Monel metal is similar to
nickel. It performs excellent in the reducing conditions and can suitably perform in the aeration and
oxidizing conditions. Monel alloy 400 offers outstanding resistance to halogen acids and compounds,
specifically in the hydrofluoric acid and hot gas containing fluorine or hydrogen fluoride. Monel 400
is commonly utilized in dealing with sulfuric acid solutions, marine water and brines. It is used in the
applications that need high strength like for valve and pump components. Monel alloy K500 is a
precipitation hardenable alloy, another grade of Monel.
Nickel-Chromium-Iron alloy 600: The inclusion of chromium to nickel alloy increases the
appropriateness of Inconel alloy 600 in the oxidizing conditions. However only moderate for mineral
acids. Inconel alloy 600 offers outstanding resistance to organic acids and is utilized broadly in the
fatty acid treatment. It is also used broadly in manufacturing and handling caustic and alkali
chemicals.
Inconel alloy 600 is also an outstanding material for elevated temperature applications needing heat
and corrosion resistance. The excellent functionality of this alloy in hot halogen conditions makes it a
suitable option for organic chlorination methods. Other high temperature disintegration processes
against that alloy 600 has shown outstanding resistance are oxidation, carburization and nitridation.
Nickel-Chromium-Molybdenum alloy 625:The inclusion of molybdenum to Nickel-chromium systems
enhances resistance to mineral acids and salts. Molybdenum provides resistance to pitting and
crevice corrosion by wet chloride. It is very powerful with high resistance to fatigue, alloy 625LCF, a
lower grade of Inconel alloy 625,it offers good resistance to low cycle and thermal fatigue.
Similar to Inconel alloy 600, alloy 625 also provides corrosion resistant and heat resistant behavior. It
is a high strength alloy and it provides resistance to halogen corrosion, oxidation and carburization
that has made alloy 625 a preferred choice for chemical and petrochemical industries that include
elevated temperature and rigorous conditions.
Ni-Cr alloy 690: Alloy 690 contains the maximum magnitude of nickel among all nickel based alloys
ready for fabrication of pressure device that confers outstanding resistance to oxidizing conditions. It
is widely used for hot concentrated sulfuric acid, nitric acid and nitric-hydroflouric acid mixtures and
oxidizing salts, the high concentration of chromium also enhances resistance to hot sulfidizing
conditions.
Nickel-Chromium-Iron Alloy 825: Due to its almost 30% magnitude of iron, Incoloy 825 is a part of
family of super austenitic stainless steels. It performs good in sulfuric and phosphoric acid
operations. However providing sufficient resistance to HCl, Incoloy 825 is attacked by chloride pitting
and crevice corrosion, specifically in static and unaerated solutions. The presence of high content of
iron makes alloy 825 highly resistant to nickel based alloys to alkali and halogens.

7. Nickel-Chromium-Ferrous-Molybdenum G alloys: Hastelloy alloy G3 provides enhanced corrosion
resistance than Monel 400, Inconel 600 and Incoloy 825 in the variety of applications. It is
particularly resistant to sulfuric acid and mixed phosphoric acid and can adhere into reducing and
oxidizing media. The recently produced alloy G-30 has good weldability and it provides enhanced
corrosion resistance in all conditions, considerable in weld heat influenced regions.
Ni-Cr-Mo C alloys: The Hastelloy C-276 is a preeminent alloy used in the chemical plants for
outstanding corrosive conditions that exceed the capability of stainless steel series. The alloy
provides excellent resistance to acids, acid salts and broad spectrum of other vigorous materials that
occur in the chemical treatment operations.
Alloy C276 is specifically effective in these rigorous conditions such as wet chlorine and
hypochlorites, due to presence of molybdenum element, Hastelloy C276 is widely resistant to
chloride based pitting and crevice corrosion. The hunt for alloys offering improved metallurgical
characteristics and corrosion resistance as compare to Hastelloy C276 has encouraged to alloy
manufacturers to develop and commercialize the various proprietary C grade alloys such as C22,
C2000, 622, 59 etc.
These alloys contain almost similar content of molybdenum but considerably higher magnitude of
chromium as compare to that present in alloy C276. Few grades also consist of tungsten and copper.
The influence of these nominal alloying agents on metallurgical characteristics and corrosion
resistance is complex.
Nickel-Molybdenum B alloys: Hastelloy B2 alloy has outstanding resistance to sulfuric, phosphoric
and hydrochloric acids in the reducing conditions. It is specifically suitable for apparatus that are
used to deal with hydrochloric acid at the magnitudes and temperatures about their boiling points.
The oxidizing chemicals have rigorous influence on the corrosion resistance property of this alloy,
such as powerful oxidizing agents like ferric and cupric salts that may exist as pollutants.
The newly produced Hastelloy B3 and Hastelloy B4 alloys provide enhanced characteristics than alloy
B2. The practical benefit of these grades is reduced production of unwanted microstructures while
fabrication that results into embrittlement.