Note: Descriptions are shown in the official language in which they were submitted.
1
USE OF ELECTROCHEMICAL INTERFERENCE MATERIAL TO MITIGATE STRESS
CORROSION CRACKING OF FERRITIC STEEL UNDER INSULATION
TECHNICAL FIELD
[001] The technical field generally relates to mitigating intergranular
stress corrosion
cracking (IGSCC) in insulated ferritic steel pipelines, pipes, fittings and
vessels under
insulation.
BACKGROUND
[002] In certain industries, such as oil sands extraction and thermal in
situ
hydrocarbon recovery operations among others, ferritic steel pipes, fittings
and vessels
having mineral wool insulation on the outside can undergo IGSCC. This can
occur when
the mineral wool comes in contact with water, for example. There are various
corrosion
issues related to insulated pipes and an improved technology is needed to help
mitigate
such corrosion issues, notably IGSCC challenges.
SUMMARY
The technology includes the use of an interference material that is provided
to interfere
with electrochemical potential of a ferritic steel substrate to inhibit IGSCC
when insulation
in contact with the ferritic steel is exposed to water.
In some implementations, there is provided an intergranular stress corrosion
cracking
(IGSCC)-protected assembly, comprising: a ferritic steel substrate; insulation
provided
about the ferritic steel substrate for thermal insulation thereof; and an
interference material
located in between the ferritic steel substrate and the insulation, the
interference material
being selected to interfere with electrochemical potential of the ferritic
steel substrate to
inhibit IGSCC when the insulation is exposed to water.
In some implementations, the ferritic steel substrate is a pipe. In some
implementations,
the ferritic steel substrate is a vessel, optionally a pressure vessel. In
some
implementations, the insulation is mineral wool. In some implementations, the
assembly
includes an outer cladding. In some implementations, the interference material
comprises
aluminum. In some implementations, the interference material is aluminum. In
some
Date Recue/Date Received 2024-02-23
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implementations, the interference material is provided as a foil. In some
implementations,
the interference material is provided as a mesh. In some implementations, the
interference
material is provided as a particulate, such as a powder or particles. In some
implementations, the interference material is provided as a coating that is
sprayed or
coated onto the substrate and/or the insulation. In some implementations, the
substrate
has an uncoated ferritic steel outer surface, the interference material is
selected to
interfere with the electrochemical potential at temperatures between 70 C and
200 C, the
assembly is configured to be located in an exterior environment exposed to
water, and the
substrate comprises residual stresses in the ferritic steel. In some
implementations, the
ferritic steel of the substrate is pipeline grade, piping grade, fitting grade
and pressure
vessel plate grade ferritic steel.
In some implementations, there is provided a method for mitigating
intergranular stress
corrosion cracking (IGSCC) of a ferritic steel substrate surrounded with
insulation,
comprising providing an interference material in between the ferritic steel
substrate and
the insulation, the interference material being composed of a material and
configured to
interfere with electrochemical potential of the ferritic steel substrate to
inhibit IGSCC when
the insulation is exposed to water.
In some implementations, the ferritic steel substrate is operated in a thermal
in situ
hydrocarbon recovery operation at temperatures between 70 C and 200 C. In some
implementations, the thermal in situ hydrocarbon recovery operation comprises
a Steam-
Assisted Gravity Drainage (SAGD) process, a solvent-assisted recovery process,
a
solvent-dominated recovery process, or an in situ combustion process. In some
implementations, providing the interference material comprises wrapping a
distinct layer
of the interference material around the ferritic steel substrate. In some
implementations,
providing the interference material comprises spraying or coating onto the
substrate or the
insulation. In some implementations, providing the interference layer
comprises retrofitting
an existing assembly, comprising: removing the insulation from the ferritic
steel substrate,
applying the interference material onto an outer surface of the ferritic steel
substrate and/or
onto the insulation, and then reinstalling insulation over the substrate. In
some
implementations, the method includes surveying a plurality of substrates to
identify
substrates that are at-risk for IGSCC, the surveying optionally comprising
visual
inspection, neutron backscatter, real-time radiography, real-time imaging, or
infrared
Date Recue/Date Received 2024-02-23
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camera techniques and identifying wet insulation; optionally sampling
identified wet
insulation to further assess risk of IGSCC, optionally by assessing leachates
from the wet
insulation; optionally assessing residual stresses in the substrates to
identify elevated
residual stress locations that are at-risk for IGSCC; and for at-risk
substrates, applying the
interference material, optionally at the at-risk locations exposed to wet
insulation and/or
the elevated residual stress locations.
BRIEF DESCRIPTION OF DRAWINGS
[003] Fig 1 is a cross-sectional cut view of an example IGSCC-protected
assembly
including a tubular steel substrate, an interference layer, insulation, and an
outer cladding.
[004] Fig 2 is a longitudinal cut view of an example IGSCC-protected
assembly
showing insertion of an interference layer between a tubular steel substrate
and insulation.
[005] Fig 3 is a cross-sectional cut view of an example insulated substrate
and
various forms of interference materials that can be used for application
between the
carbon steel and the insulation.
[006] Fig 4 is an example potentiodynamic polarization curve for steel.
DETAILED DESCRIPTION
[007] The present disclosure relates to mitigating intergranular stress
corrosion
cracking (IGSCC) in ferritic steel pipes and vessels that have mineral wool
insulation on
the outside, by providing an electrochemical interference material, such as
aluminum, in
between the ferritic steel surface and the mineral wool insulation. The
interference material
can be composed of a metal, such as zinc, aluminum or magnesium and their
alloys, and
can take the form of foil or mesh wrapped around the ferritic steel or of
powder, particles
spray coating or paint applied so as to be present in between the ferritic
steel and mineral
wool insulation. The interference material can be provided during initial
installation or can
be applied by retrofitting an installed pipe or vessel between the ferritic
steel surface and
the mineral wool insulation by opening up the insulation to expose the
ferritic steel,
applying the interference material, and enclosing the insulation back around
the ferritic
steel. In the context of the present disclosure, ferritic steel can be defined
as steel that is
composed of iron and carbon as the base, including additional elements that
can also be
Date Recue/Date Received 2024-02-23
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added, and includes low-carbon steels, medium-carbon steels, high-carbon
steels and
low-alloy steels, that are commonly used in piping, vessels, tanks, pipeline,
drums, heat
exchangers, structural steels and equipment.
[008] The interference material can reduce IGSCC risks for the insulated
pipes or
vessels. It has been observed that, when contacted with water, mineral wool
can cause
IGSCC in the pipe or vessel. The intermediate interference material, such as
aluminum,
zinc, magnesium or their alloys, placed between the mineral wool and surface
of the pipe
or vessel can help disturb the electrochemical potential causing the stress
corrosion
cracking of the ferritic steel. It is noted that any material capable of
interfering with the
electrochemical potential of the steel structure can be used for the
interference material at
the operating conditions in question, and aluminum is a prime example. The
interference
material can also be selected for certain factors including cost, properties
at the
temperatures and humidity levels encountered for exterior pipe and vessel
applications
and/or applications (e.g., in certain oil sands processing facilities).
Materials that have
corrosive properties at the target operating conditions or that convert to
compounds (e.g.,
salts) that could cause issues can be avoided.
[009] Referring to Fig 1, an IGSCC-protected assembly 10 is shown and
includes a
ferritic steel substrate 12, such as a pipe, a pipeline, a vessel or an
equipment, which is
surrounded by insulation 14 and an outer cladding 16. The IGSCC-protected
assembly 10
also has an interference material 18 provided in between the ferritic steel
substrate 12 and
the insulation 14. In this embodiment, the interference material 18 is in the
form of a
distinct layer, such as a mesh or foil. The ferritic steel substrate 12 can
have a generally
tubular structure having a passage 20, inner surfaces 22 and outer surfaces
24. Note that
the ferritic steel structure can take a different shape that is not tubular or
vessel shaped.
[0010] The interference material 18 can have various forms and can be
composed of
various materials. For example, the interference layer can be provided as a
mesh, a foil,
a continuous sheet, or other forms in contact with the outer surface 24 of the
ferritic steel
substrate 12. The interference material can be a relatively pure metal (e.g.,
Aluminum) or
an alloy that can include two or more metal elements. The interference
material 18 can
provide a complete barrier between the insulation and the outer surface of the
ferritic steel
substrate, or it can have small apertures if it has a mesh or grid structure.
The interference
material can also have various thicknesses depending on the design of the
assembly.
Date Recue/Date Received 2024-02-23
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When aluminum foil is used, it can be ultra-thin foil, standard foil, heavy-
duty foil or extra-
heavy-duty foil, thus having a thickness ranging from less than 10 microns to
30 microns
or above. The interference material can be provided as a distinct pre-formed
sheet that is
then installed about the ferritic steel surface. When aluminum foil or mesh is
used, it can
be applied in a single layer or in multiple layers around the pipe, pipeline
or vessel. When
a mesh is used, the apertures can be small or large.
[0011] Referring to Fig 3, the interference material 18 can take many
forms and can
be applied in various ways: as paste 26, powder 28, paint 30, particles 31,
distinct layer 32
such as foil or mesh, spray 34 and so on. When the interference material is
applied as a
fluid or slurry, it can be coated or sprayed, dispersed, injected or diffused
onto some or all
of the ferritic steel surface that is in contact with the mineral wool and/or
on the mineral
wool area that will be in contact with the ferritic steel. When the
interference material is in
solid particular form, it can be mixed and distributed into the mineral wool
that will be in
contact with the ferritic steel. When the interference material is applied as
a distinct layer,
it can be wrapped around the ferritic steel before the insulation envelops the
pipe, pipeline
or vessel. In some scenarios, the interference material can be a metal solid
which is
vaporized for deposition on the insulation and/or the ferritic steel surface.
In addition, the
interference material can be applied evenly about the wool or ferritic steel
surface, or it
could be applied mainly in certain areas, such as areas that tend to be wetter
(e.g., bottom
of pipelines).
[0012] The interference material, when applied as a distinct layer, can be
configured
to be malleable to facilitate wrapping around the ferritic steel surface to
provide a fitted
wrap about the pipe or vessel. The interference material can be in direct
contact over the
entire outer surface of the pipe or vessel, or there can be regions of direct
contact and
regions of being spaced apart. The interference material can include a single
layer of the
material or multiple layers of the same material or different materials. The
interference
layer can be provided such that it is in direct contact with both the ferritic
steel substrate
and the surrounding insulation, although it is also possible to have coatings
or layers of
other materials in between.
[0013] Implementations of the technology can help mitigate Corrosion Under
Insulation
(CUI) issues in thermal in situ hydrocarbon recovery operations and oil sands
extraction
Date Recue/Date Received 2024-02-23
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operations. Since CUI is another damage mechanism for ferritic steel piping
and pipelines,
the techniques described herein can further help mitigate such issue. The
technology can
also increase the safety and efficiency of steel pipes and pipelines as well
as pressure
vessels; and can also prevent costly repairs and maintenance. The technology
can also
prolong the lifespan of facilities and equipment.
[0014] The technology that uses an interference material can present
advantages over
alternative methods, such as the use of expensive spray coatings or providing
a polymeric
coating over pipes to provide a physical barrier. For example, the
interference material
can be implemented more economically and efficiently and does not require
updating the
insulation system as a whole.
[0015] The mineral wool insulation can have various compositions and be
from various
different suppliers. Mineral wools designed for hot pipe insulation have been
found in
recent years to cause IGSCC and problems related to the use of such mineral
wools could
be mitigated using methods described herein.
[0016] The insulated substrate can be part of any application in the oil
and gas field or
other industries, e.g., refining, upgrading, distribution, chemical plants,
food processing
plants, and other light and heavy industries, where mineral wool is being used
on ferritic
materials. Various applications where the insulated substrate is exposed to
water, which
can leak into the insulation, and/or contains fluid that is under pressure or
has elevated
temperatures could notably benefit from the electrochemical interference
technology
described herein. The substrate can be a pipe, fittings, vessels that are
exterior and
exposed to the elements and could be buried (e.g., buried pipelines). The
substrate can
be bare and uncoated ferritic steel where the mineral wool has moisture in it
from
infiltration leading to leachate formation, operating between 70 C and 200 C,
and residual
stresses in the carbons steel (e.g., from manufacturing, fabrication and/or in
service and
including induction bends, filter welds on pipe shoes, longitudinal seam
welds, girth welds,
groove welds of nozzles, etc.). Water ingress through cladding of the
substrate forming
mineral wool insulation leachates in contact with 70 C to 200 C bare ferritic
steel can lead
to IGSCC and the interference material can help mitigate such issues.
[0017] Existing substrates can be inspected to assess for the desirability
of applying
the interference material. For example, substrates can be surveyed for the
presence of
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wet insulation, which may be performed using visual inspection, neutron
backscatter, real-
time radiography, real-time imaging, or infrared camera techniques. For
example, wet
insulation can be darker than dry insulation which can be used for
identification. If wet
insulation is detected, the insulation can be sampled and tested in
laboratory, e.g., using
CPP, U-bend SCC or other lab screening tests, if desired. Higher risk areas of
substrate
can receive the application of interference material to mitigate future issues
related to
IGSCC.
[0018]
Regarding the technology, it is noted that IGSCC initiation in carbon steel
under
mineral wool is potential dependent and electrochemical interference to
prevent crack
initiations. Potentiodynamic polarization curves for steel and the zones 1 and
2 where the
SCC frequently appears, can be determined (see e.g., Fig 4). As the applied
potential of
ferritic steels is modified, the ferritic steel corrosion current density
changes. There can be
typical transition points (see zones 1 and 2 in Fig 4) in the potentiodynamic
polarization
curve, from where the steel undergoes active corrosion, forms a passive film
on the
surface, and then the film becomes damaged by dissolution as the potential
changes. This
cycle of active corrosion, formation of a passive film, and passive film
dissolution in these
zones is what initiates and grows the crack. Grain boundaries have chemical
inhomogeneities and are more active to corrosion than the grains, and
therefore are more
prone to cracking along the grain boundaries called intergranular Stress
Corrosion
Cracking. The role of stress is to enhance the breakdown of the passive film
at the crack
tip. An effect of aluminum or other interference material in the present
technology can be
to act as a sacrificial anode that corrodes itself in lieu of the steel in an
aqueous
environment. Steel therefore will not undergo full cycle active corrosion,
passive film
formation, or film dissolution, so crack initiation and growth is prevented
for as long as the
interference material in this electrical circuit is not fully consumed.
[0019] Several alternative implementations and examples have been described
and
illustrated herein. The implementations of the technology described above are
intended to
be exemplary only. A person of ordinary skill in the art would appreciate the
features of
the individual implementations, and the possible combinations and variations
of the
components. A person of ordinary skill in the art would further appreciate
that any of the
implementations could be provided in any combination with the other
implementations
disclosed herein. It is understood that the technology may be embodied in
other specific
Date Recue/Date Received 2024-02-23
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forms without departing from the central characteristics thereof. The present
implementations and examples, therefore, are to be considered in all respects
as
illustrative and not restrictive, and the technology is not to be limited to
the details given
herein. Accordingly, while the specific implementations have been illustrated
and
described, numerous modifications come to mind.
Date Recue/Date Received 2024-02-23
