World Pipelines Article

®
Volume 14 Number 2 - February 2014
Vacuworx manufactures, sells, rents, and
services vacuum lifting equipment for
heavy-duty material handling industries.
Figure 1. Complex carbide wires
provide excellent corrosion and
erosion resistance, as well as exhibit
excellent weldability when cladding
plate, pipe ID or elbow ID.
Finding
the right
formula
Ravi Menon and Jack Wallin, Stoody Company,
Victor Technologies, USA discuss the
development of corrosion-abrasion resistance
overlays for oilsands pipelines.
T
he Canadian oilsands are the world’s best test grounds for wear resistant
overlay alloys. Stoody has been working with owner operators and
contractors in the region for many years to develop wear resistant alloys
for the numerous wear conditions encountered in this harsh environment.
One application is in the transportation of the oilsands to the processing facilities
(Figure 2). The internal diameter (ID) of many miles of oilsands pipeline are overlaid
with various hardfacing wires. During transportation of oilsand slurry, significant wear
occurs in the pipe, with the most being in the extrados (inner diameter) of elbows
Table 1. Chromium wire compositions typically fall into two categories: hypoeutectic (1.5/2C - 20/23Cr) and hypereutectic (5/6C - 23/28Cr)
Designation/nomical composition
Stoody product
Typical
hardness
(HRC)
Microstructure
Maximum
thickness in. (mm)
2 C-23 Cr hypoeutectic
Stoody 133
38
Austenite-eutectic carbide
2 (50)
5 C-25 Cr hypereutectic
Stoody PC2009
47
Austenite-primary chromium carbide
2 (50)
Micro-alloyed, 5 C-25 Cr-M (B)
hypereutectic
Stoody CP2000
62
Austenite-primary chromium carbide
2 (50)
Complex, 5 C-25 Cr-CLX (Nb, V, B)
hypereutectic
Stoody CP2001
65
Austenite-primary chromium, V carbides
0.5 (12)
metal sheath. Accordingly, cored wires
offer versatility due to the wide variety
of alloys that can be included within the
powdered metal core, as well as the alloy
content provided by the sheath. Cored
wires continue to provide a unique route
in the development of specialty alloys for
hardfacing. Most hardfacing alloys have
relatively low ductility and cannot be
produced as monolithic (continuous) wires
without incurring significant processing cost.
Hardfacing with iron based
wires
The largest share of hardfacing welding
consumables are iron-based alloys, which are
the most economical to produce. The wire
Figure 2. Transportation of sand slurry creates some of the harshest wear and
sheath material is typically a low carbon
corrosive conditions for piping.
steel. The core materials constitute either
simple metal powders or fairly complex
mixtures of matrix-carbide components. Within the ironbased family, the most common group of hardfacing wires
is comprised of the chromium carbide type. These include
wire compositions that range from the hypoeutectic to the
hypereutectic side of the Fe-Cr-C alloy system. In general,
the hypereutectic alloys (typical composition 5C-25Cr)
have significantly better low stress wear resistance as
measured using the ASTM G65 Procedure A test (G65
test) when compared to hypoeutectic alloys (typical
composition 2C-25Cr).
The G65 test is the most commonly used test to
compare the low stress abrasion resistance of hardfacing
alloys. In general, comparisons of most iron-based alloys
can be made using weight loss as the test criterion.
Figure 3. Micro-alloyed (5C-25Cr-M) wires show better wear
performance on the as-cladded surface as well as at a depth
However, when comparing alloys from different alloy
75% below the surface.
systems (such as iron, nickel and cobalt based alloys),
volume loss should be used as a criterion as the materials
have significantly different densities.
where the flow direction changes, and along the bottom
ID in straight pipe. The selection of the hardfacing wire
alloy type is dependent on the location of the piping in
Conventional chromium carbides for
the process string, nature of the corrosive media, as well as
hardfacing
many other factors.
There are three main types of conventional chromium
carbides used in the oilsands for hardfacing slurry pipe:
The versatility of cored wires
)) Simple: carbon 5% and chromium 25% (Stoody PC2009).
Metal-cored wire is comprised of a metal sheath filled
)) Micro-alloyed: carbon content 5% and chromium 25%
with powdered metal alloys. Flux-cored wire is a mixture
(5C-25Cr-M) (Stoody CP2000).
of powdered metal and fluxing ingredients inside a
february 2014 / Reprinted from World pipelines
)) Complex: carbide 5C-25Cr-CLX (alloyed with Mo, V and
Traditionally, the complex carbides containing Mo, W, Nb
and V (6C-19Cr-5Mo-5Nb-2W-2V) can provide better wear
resistance; however, these deposits tend to be extremely
brittle. Moreover, wire costs escalate significantly with the
The most common iron based chromium carbide wires
addition of the alloying elements such as Mo, V and W. A
are of the 5C-25Cr type (Table 1). Specially formulated
micro-alloyed version, 5C-25Cr-M, has been successfully
chromium carbide wires are designed for applying abrasion
used in critical applications where a combination of wear
resistant deposits inside pipe. The formulation has been
and toughness are required. This type of wire also finds
optimised to result in superior weldability for overlaying
significant use in the cladding of pipe used for slurry
pipe ID in the flat position and elbows in the horizontal
transport in the oilsands.
position. The deposits have an excellent tie in and a flat
Many of these applications require a minimum degree
bead profile. They are relatively low cost and are typically
of wear resistance as measured with the G65 test on
available in diameters ranging from 1/8 - 0.035 in. (3.2 the as-cladded surface, as well as at a depth 75% below
0.9 mm).
the surface. In addition to this requirement, under bead
However, for applications that require a greater degree
cracking is not permitted. Wires of the 5C-25Cr-M type
of wear resistance, these compositions are modified.
have been used successfully in
this application. A comparison
of the G65 wear resistance
of the conventional 5C-25Cr
against the micro-alloyed
version is shown in Figure 3.
For more severe abrasion
applications, a modified
complex version – 5C-25CrCLX (5C-25Cr-Nb-V) – has been
developed. These deposits
provide an enhanced degree
of wear resistance due to the
presence of secondary carbides
of Nb and V. In contrast to
the complex carbides of the
6C-19Cr-5Mo-5Nb-2W-2V type,
this alloy is leaner in secondary
carbide formers. As a result,
multiple passes can be applied
for thicker build-up, and the
deposits having better ductility.
The leaner composition also
results in a more economical
wire.
The complex carbide
deposits also perform well
in pin-on-disc tests that are
designed to simulate high stress
abrasion. In slurry-jet testing
specific to the application
Figure 4. This slurry pipe example shows ID wear and the beginning application of a chromium
required for slurry pipe, the
carbide alloy.
complex carbide
deposit performs
Table 2. Nickel based hardfacing alloys have gained popularity for applications that encounter severe wear
better than the
and/or corrosion
micro-alloyed version.
The microstructure
Designation
Stoody Product
Bulk hardness (HRC) Microstructures
of the 5C-25Cr-CLX
45 - 65% cast tungsten carbides in a Ni-Si-B matrix
deposit consists
Ni-WC1
Stoody 160
55
of precipitates of
45 - 65% cast and macrocrystalline tungsten carbides
Nb and V carbides
Ni-WC2
Stoody 160FC
55
in a Ni-Si-B matrix
located in the matrix
Nb) (Stoody CP2001).
Reprinted from World pipelines / February 2014
between the primary chromium carbides. In summary,
modified complex carbide wires of the 5C-25Cr-CLX type
possess optimal properties for a wide variety of wear
environments that include low stress and high stress
abrasion as well as slurry jet erosion.
Modified chromium carbide iron based
wires
Vol. Loss (cu.mm)
Pipe repair wires (Stoody PR2009) are specially
formulated chromium carbide metal cored wires designed
for the repair of worn ID claddings in pipe elbows. The
formulation has been optimised to result in superior
weldability for overlaying pipe ID in the horizontal
position. Special deoxidisers in the formulation enable
pipe repair wire to achieve sound pipe ID claddings when
repairing worn chromium carbide overlays containing
hydrocarbon contamination embedded in the their relief
check cracks. The weld deposits have an excellent tie
in and a flat bead profile. The spatter and overspray
levels are the lowest in the industry, resulting in high
deposition efficiency. The weld deposits contain a high
concentration of uniformly distributed primary chromium
carbides throughout the thickness resulting in excellent
G-65 wear results.
Stoody corrosion and wear resistance wire
(Stoody 136) deposit is an erosion and corrosion resistant
8
7
6
5
4
3
2
1
0
alloy deposit. Stoody corrosion and wear resistance
wire a specially designed complex carbide alloy suited
for hardfacing/cladding applications where erosion and
corrosion are of equal concern. The ability of this alloy
to resist high abrasion in a corrosive environment makes
it optimal for hardfacing/cladding pipe, plate and vessels
subjected to erosion and corrosion (Figure 1).
Nickel based tungsten carbide wires
Nickel based wires of the Ni-Cr-B-Si type have been
used for many years. Several versions of these wires that
have had tungsten carbide (WC) incorporated into them
have gained popularity for applications that encounter
severe wear and/or corrosion. These wires (Table 2) have
evolved into those that contain mixtures of cast carbides
of various particle sizes (Ni-WC1) and those that contain
a mixture of cast and macrocrystalline carbide (Ni-WC2).
Larger wire diameters such as 1/8 in. (3.2 mm) and
7/64 in. (2.8mm) can encapsulate up to 65 percent carbide
by weight; the smaller wires, typically 1/16 in. (1.6 mm),
can hold up to 45%.
Note in Figure 5 that the wear data is measured in the
units of volume loss, as the comparison is being made
between materials of differing densities. Specifically,
for application in the oilsands piping, slurry-jet erosion
tests also show the superior performance of the blended
cast-macrocrystalline deposits (Ni-WC2). In Figure
5b, the Ni-WC2 deposit out performs the Ni-WC1,
as well as chromium carbides deposits of the
5C-25Cr-M and the 5C-25Cr-CLX types.
The superior performance of the Ni-WC2
deposits is related to the greater stability of the
macrocrystalline carbide to withstand degradation
during arc welding, as well as matrix hardening
that occurs due to the decomposition of the cast
carbide. This has led to the specification of such
wires for applications in the oilsands where the
performance of conventional chromium carbides
deposits is not adequate.
Nickel based tungsten carbide wires can be
specified for applications where conventional
chromium carbides do not meet necessary wear
resistance requirements.
90
Conclusion
45
Conventional hardfacing wires may not provide
the solutions that are required by slurry pipes
in the oilsands. The cored wire route offers a
powerful technique to design unique wires for
such applications. In the iron-based alloy family,
special complex carbide wires can significantly
improve life for these applications (Figure 4).
Nickel based tungsten carbide wires provide wear
resistance for extreme wear conditions.
20
5C-25Cr-M
5C-25Cr-CLX
Ni-WC1
Ni-WC2
Figure 5a and 5b. In G65 tests (a) and slurry-jet tests (b), the Ni-WC2
deposits performed the best when compared to Ni-WC1 as well the
5C-25Cr-M and 5C-25Cr-CLX chromium carbide deposits.
february 2014 / Reprinted from World pipelines

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