POLYETHYLENE | Pipeline Coatings
Summary
TLDRIn this episode of 'Bite-Sized Corrosion,' Vanessa and Neil delve into the complexities of pipeline coatings, focusing on polyethylene coatings. They discuss the benefits and challenges of these coatings, including their toughness, chemical resistance, and the difficulty of adhesion. The conversation explores various types of polyethylene coatings, such as single-layer, two-layer, and 3-layer polyethylene (3LPE) systems, and touches on issues like cathodic shielding and AC interference. The episode aims to guide new engineers on selecting appropriate coatings for pipeline projects, considering factors like environment, service life, and cost.
Takeaways
- 🌟 The session is part of a series discussing pipeline coatings, starting with polyethylene coatings.
- 🎨 Vanessa Silly Fisher and Neil Webb are the hosts of the series, aiming to shed light on the complexities of pipeline coatings.
- 🔍 Vanessa shares a personal anecdote about the challenges of identifying coatings in the field, highlighting the importance of understanding different types of coatings.
- 🛠️ Polyethylene coatings are prevalent due to their toughness, high electrical resistance, and good chemical resistance, making them suitable for pipelines.
- 📦 The black color of polyethylene coatings is due to carbon black pigment, which is a significant component of the material.
- 🧲 One of the main challenges with polyethylene is its poor adhesion to pipes, as it doesn't stick to other materials easily.
- 🔄 The industry has developed solutions like 'Yellow Jacket' coatings, which use a bitumen-based adhesive to improve adhesion between the polyethylene and the steel pipe.
- 📚 The 3-layer polyethylene (3LPE) system combines the corrosion resistance of epoxy with the electrical and mechanical properties of polyethylene, offering a robust coating solution.
- 🛡️ Proper surface preparation is critical for the application of coatings like fusion-bonded epoxy (FBE), which includes cleaning and a phosphoric acid-based wash as a pre-treatment.
- 🔩 Field joints, where pipes are joined together, require special attention with coatings to ensure they are protected to the same standard as the rest of the pipeline.
- 🌐 AC interference is a concern for polyethylene coatings due to their high electrical resistance, which can lead to inductive and capacitive interference issues.
- 🔄 The balance between the electrical insulation properties of the coating and the environmental conditions it will encounter is crucial for effective pipeline protection.
Q & A
What is the main topic of the 'bite-sized corrosion' series for 2022?
-The main topic of the 'bite-sized corrosion' series for 2022 is pipeline coatings, specifically focusing on polyethylene coatings in the first session.
Why is knowledge of the specific coating applied to a pipeline important?
-Knowledge of the specific coating applied to a pipeline is important because it affects pipe laying logistics, backfilling, long-term performance, cathodic protection, and AC mitigation.
What is Vanessa Silly Fisher's initial experience with pipeline coatings?
-Vanessa Silly Fisher's initial experience with pipeline coatings was overwhelming. She was on-site to investigate a corrosion problem that turned out to be a coating issue and found the experience challenging due to her lack of knowledge at the time.
What is the typical color of polyethylene coatings and why?
-Polyethylene coatings are typically black due to the significant pigment content of carbon black in the material.
Why are polyethylene coatings widely used for pipelines?
-Polyethylene coatings are widely used for pipelines because they are tough, have high electrical resistance, excellent chemical resistance, and are not easily damaged.
What is one of the main challenges with applying polyethylene coatings to pipes?
-One of the main challenges with applying polyethylene coatings to pipes is adhesion. Polyethylene is very inert and does not stick to anything else easily, making it difficult to get the coating to adhere to the pipe.
What is the purpose of the 'Yellow Jacket' coating in pipeline applications?
-The 'Yellow Jacket' coating is a polyethylene external extrusion or shrink sleeve that is applied over a layer of bitumen-based adhesive. It provides chemical adhesion between the steel and the polyethylene and offers good chemical and corrosion resistance.
What does 3LPE stand for and what does it combine in terms of pipeline coating properties?
-3LPE stands for 3-Layer Polyethylene. It combines the corrosion-resistant characteristics of epoxy with the electrical resistance, chemical resistance, water impermeability, and mechanical toughness of polyethylene.
What is the significance of the epoxy layer in a 3LPE system?
-The epoxy layer in a 3LPE system is significant because it provides a corrosion-resistant interface between the steel and the polyethylene. It is essential for the system's effectiveness and must be equivalent to a standalone epoxy system.
How does AC interference impact polyethylene coatings?
-AC interference impacts polyethylene coatings because of the high electrical resistance of polyethylene, which provides insulation between the pipe and its environment. This insulation can lead to inductive and capacitive interference, causing high voltages on the pipe due to its insulation from the earth.
What are some alternative polyethylene coating systems mentioned in the script?
-Some alternative polyethylene coating systems mentioned in the script include cold-applied and hot-applied tapes, and heat shrink sleeves, which are based on polyethylene and are used for field joints and mainline wrapping.
Outlines
🌟 Introduction to Pipeline Coatings Series
The script introduces a six-session series on pipeline coatings, starting with a focus on polyethylene coatings. Vanessa Silly Fisher and Neil Webb are the hosts. Vanessa shares a personal anecdote about her early days in the industry, highlighting the complexity of understanding pipeline coatings. The importance of knowing the type of coating applied to a pipe is emphasized, as it affects various aspects of pipeline logistics and performance. The series aims to address questions engineers should ask when selecting a coating for a pipeline project.
🔍 Understanding Polyethylene Coatings
This paragraph delves into the specifics of polyethylene coatings, their benefits such as toughness, electrical resistance, and chemical resistance, and their widespread use in the industry. Challenges with polyethylene, such as its inability to adhere to surfaces, are discussed. The paragraph explains how sintered polyethylene coatings are applied using a mechanical interlocking method but lack inherent corrosion inhibition. It also touches on the development of 'Yellow Jacket' coatings, which combine polyethylene with a bitumen-based adhesive to improve adhesion and corrosion resistance.
🛠️ The Evolution of 3-Layer Polyethylene (3LPE) Coating
The paragraph discusses the development of 3LPE coatings, which combine the corrosion-resistant properties of epoxy with the electrical resistance and mechanical toughness of polyethylene. It explains the process of applying 3LPE, involving a hot melt adhesive layer and extrusion over a pipe. Early issues with the bonding of the epoxy layer to the steel are mentioned, along with improvements over time. The importance of proper surface preparation for coating application is emphasized, including the use of phosphoric acid-based washes and the phasing out of chromate treatments due to environmental concerns.
💰 Cost Implications and Field Joint Protection
This section examines the financial considerations of using 3LPE coatings, noting that while the coating itself is more expensive, it can lead to cost savings in pipe laying operations due to reduced backfilling material requirements. The importance of protecting field joints with additional coatings is highlighted, ensuring they meet the same standards as factory-coated pipes. The paragraph also introduces the topic of AC interference and its impact on polyethylene coatings, setting the stage for further discussion in future sessions.
⚠️ Addressing AC Interference and Coating Selection
The final paragraph addresses the challenge of AC interference, which can cause high voltages on pipes due to the high electrical resistance of polyethylene coatings. The need for a temporary earth connection during pipeline construction to prevent shock is mentioned. The paragraph concludes with a metallurgical perspective on balancing the electrical insulation properties of the pipeline against the environmental factors it will encounter, suggesting that the choice of coating may depend on the presence of AC interference and the need for electrical insulation.
🔄 Other Polyethylene Coating Systems
The script concludes with a brief overview of other polyethylene-based coating systems, such as tapes and heat shrink sleeves, which are used for field joints and mainline wrapping. These systems are highlighted for their ease of application and versatility in providing additional protection to bare pipes. The discussion sets the stage for more detailed exploration of tapes in upcoming sessions.
Mindmap
Keywords
💡Polyethylene coatings
💡Pipeline corrosion
💡Coating adhesion
💡Fusion bonded epoxy (FBE)
💡3-layer polyethylene (3LPE)
💡Cathodic protection
💡AC interference
💡Surface preparation
💡Field joint coating
💡Bitumen-based adhesive
💡Environmental impact
Highlights
Introduction to a six-session series on pipeline coatings with Vanessa Silly Fisher and Neil Webb.
Discussion on the importance of understanding different pipeline coatings and their impact on logistics, performance, and protection.
Vanessa shares her initial experience with pipeline coatings and the challenges faced in identifying the type of coating.
Overview of polyethylene coatings, their benefits, and common use in the industry due to their durability and chemical resistance.
Challenges with polyethylene coatings, particularly the difficulty in achieving adhesion to the pipe surface.
Explanation of the process of applying sintered polyethylene coatings using a fluidized bed for mechanical adhesion.
The limitations of polyethylene in terms of under film creep resistance and corrosion inhibition when damaged.
Introduction of 'Yellow Jacket' coatings, a two-layer system combining polyethylene with a bitumen-based adhesive for improved adhesion and corrosion resistance.
Description of 3LP or 3-layer polyethylene (3LPE) system, integrating epoxy for corrosion resistance with polyethylene's mechanical and electrical properties.
Historical issues with 3LPE and the evolution of the epoxy layer to ensure effective bonding and corrosion protection.
The necessity of proper surface preparation for effective coating application, including the use of phosphoric acid-based washes.
Economic considerations of coating selection, including the cost savings associated with polyethylene coatings during pipe laying.
Addressing field joint coatings and the importance of protecting bare steel during pipeline construction.
The impact of AC interference on polyethylene coatings and the need for balancing electrical insulation with susceptibility to interference.
Discussion on alternative polyethylene systems, such as tapes and heat shrink sleeves, for field applications and mainline wrapping.
The importance of considering the environment and specific project requirements when selecting pipeline coatings.
Conclusion and anticipation of further discussions on pipeline coating selection criteria in the final session of the series.
Transcripts
well good afternoon everyone and
welcome to bite-sized corrosion
in fact i say welcome back it's really
wonderful that you've joined us again
today
and we're really really excited to kick
off 2022
with a six session series where neil and
i will be discussing pipeline coatings
for those of you who don't know me my
name is vanessa silly fisher
and as i've already indicated i'm joined
today by neil webb
today we'll start the series by
discussing polyethylene coatings and
we'll try and answer the question
how many layers
just remembering and looking at that
picture of the truckload of pipes
it reminds me just how challenging it
can be to try and figure out what a
pipeline coating is
in fact i'm quite ashamed actually
embarrassed when i remember when i
really started out in the industry many
years ago now
i went to site to investigate a
corrosion problem
which
turned out to be a coating problem and i
was very green
and in some ways actually i found the
whole experience quite overwhelming i
was trying to take in as much
information as i could
what could have caused this problem what
were the conditions
frantically scribbling notes everywhere
and on my return to the office neil i
don't know if you remember you asked me
this clanger question
so vanessa what was the coating
my word
silence
i realized that i had no idea
so i sheepishly think i said
black
and i wondered then like many do how on
earth
can you tell the difference between
these pipeline coatings
that is a challenging
question what
is the coating
and
there are many different coatings
available for pipelines
and
having knowledge of which coating is
actually applied to the pipe is really
important
because it affects the
pipe laying
logistics it affects the
back filling it affects the long term
performance it affects the cathodic
protection it affects the ac mitigation
and so
the
selection of a coating for a particular
pipeline
in terms of its environment and its
service life and so on
is very very important and actually the
last session of this series is going to
be devoted to
some of the
questions that we should be asking
ourselves as engineers when you're faced
with a pipeline project and that is
which coating should i be using which
ones are suitable because not all
coatings are suitable for all conditions
so let's change this up a little bit and
let's start thinking as a new engineer
where do we even start
it's a good place to start is black
the
pipeline that you see in this photograph
is in fact a polyethylene coated pipe
the pipe sections themselves were coated
in the factory with polyethylene and
generally polyethylene is black
due to the fact that it has a
significant pigment content of carbon
black
in the
makeup of the material
and polyethylene coatings in general are
excellent
for
pipeline service because they're tough
they have high electrical resistance
they have very very good chemical
resistance
and they don't get damaged very easily
and so
for that reason polyethylene coatings
form a large percentage of the coatings
that are applied to pipelines you make
them sound as though they're almost
perfect and
we know that's not the case let's have a
look at some of the challenges
associated with the polyethylene
coatings neil if you think about
polyethylene polyethylene is the
material that is generally used for
plastic bags you'll see on the recycling
labels either
number two or number three i remember
correctly which is low density and high
density polyethylene
and
have you ever tried to fix something
made out of polyethylene when i mean fix
it have you tried to glue it back
together yeah nothing sticks to it but
like absolutely plastic wrap in the
kitchen
yeah so if nothing sticks to
polyethylene conversely polyethylene
doesn't stick to anything else
and so
when you put polyethylene onto a pipe
you are immediately faced with a
challenge
that how on earth do you get the
polyethylene to stick to the pipe
and adhesion is one of the paramount
characteristics
that is important for a pipeline coating
and that is good adhesion
because we don't want corrosion to occur
underneath the coating and that brings
us to the the second
limitation of polyethylene because
polyethylene is so inert it doesn't have
particularly good under film creep
resistance or inhibition of corrosion if
and when the pipeline coating is damaged
in this photograph we see a very good
example
of a large diameter pipeline that is
coated with sintered polyethylene in
this situation
the
pipe is blast cleaned to provide a rough
surface which gives you mechanical
adhesion
and then the heated the pipe is heated
and the pipe is dipped into a fluidized
bed of polyethylene powder
the powder then sticks to the pipe
surface it fuses and forms a coating
which is a couple of millimeters thick
and you land up with this centered
polyethylene coating which is then
secured to the pipe purely by mechanical
interlocking
between the polyethylene and the rough
surface of the pipe
one of the challenges that i see with
that is that
although it's holding onto the pipe
it doesn't have any corrosion inhibition
in and of itself
that is correct because as i said the
polyethylene itself is very inert and it
doesn't interact
with the the moisture and oxygen there's
no
what i like to call glue factor
there's no glue factor nothing that
makes it stick
to the underlying steel it's just this
mechanical interlocking and i'm not
saying
that it doesn't work it does work
but it does have its own shortcomings
and in order to address
those shortcomings the industry
has had a number of developments
and one of the first ones that came
along was well if we've got
polyethylene which has got good
electrical and mechanical properties
uh
how can we get it to stick to the pipe
and
one of the first
options
then was
this material
which a lot of our international viewers
will recognize
and they've probably heard of the term
yellow jacket
coatings and
it is a trade name i granted but it is a
polyethylene external either extrusion
or shrink sleeve that is put over a
layer of
bitumen
based adhesive a mixture of bitumen and
polymers very much like we use in many
other products for the pipeline industry
and it is used between the steel and the
polyethylene
because it is one of the few things that
does provide you a with some adhesion
some chemical adhesion and also it
provides you with
good chemical resistance or corrosion
resistance on the layer underneath the
polyethylene up against the steel itself
so effectively you've described
something now that is two layers and i
suppose we could term a two-layer
polyethylene well you're absolutely spot
on the money there because you will find
two layer polyethylene
described in the literature and in the
standards
as one of the material systems that is
available for pipeline coatings
now the product that i and probably many
of our listeners i'm really familiar
with
is 3lp or 3-layer polyethylene and i
don't recall that having any bitumen
anything in it so let's have a look and
see what's in 3lpe
well the 3lpe system is the next step if
you want to call it that we know that
epoxy
is
one of the real workhorses of the
corrosion engineer and the corrosion
protection fraternity
and
epoxy coated pipelines have been used
extensively
overseas in particular we had them in
south africa for a while
but epoxy coatings also have some
shortcomings we're going to talk about
epoxies on their own tomorrow taking the
good corrosion resistant
characteristics of the epoxy
and combining that with the electrical
resistance and the chemical resistance
and
water impermeability and mechanical
toughness
of polyethylene
has brought about the development of the
three layer polyethylene or three lpe as
it's known or trilaminate is another
phrase that is often used and in this
photograph you can see
that we have an fbe coded pipe and
this pipe is rotating in a an
application plant
and the white layer that you see over
there is only a hot melt adhesive a bit
like the glue gun that you use
around the the diy fraternity
and then the
polyethylene the black layer at the back
is also then extruded over the top as
the pipe spirals and you get this
thick polyethylene layer with an
intermediate layer of adhesive and the
underlying epoxy and that then gives you
your three layer polyethylene system
which has both the corrosion protection
and the mechanical properties and the
electrical properties that are desirable
for a pipeline so in other words we now
have the perfect coating
maybe not
well i wish
so the three layer polyethylene
comprises this layer of epoxy
in between the steel
and the polyethylene on the outside but
it had some issues when it first was
produced because initially the
industries thought that it was only
necessary to put a smidgen of epoxy
onto the steel in order to provide an
interface between the steel and the
polyethylene
and over the years it was discovered
that this led to this bonding
between the the system and the steel
and
the systems over the years have
gradually been improved and it is now
pretty much accepted that
[Music]
the
epoxy
inner layer has to be the equivalent
of a standalone epoxy system if it's
going to work
underneath the polyethylene because even
though polyethylene has a very low
water vapor transmission rate it does
still allow water vapor through and if
the epoxy layer underneath is not
man enough for the job
we land up with with this bondment of
polyethylene of the 3lp system
and effectively a loose bonded sleeve
now it's still
pretty tight around the pipe but there
may well be water underneath it it's not
a problem
unless
there is a defect in the coating
mechanical damage in other words or a
failed field joint or something like
that that allows electrolyte to be
transferred between the space underneath
the coating
and the external environment
and when that happens then you get under
film corrosion underneath the
polyethylene cathodic protection can't
do anything about it because of the
electrical
shielding properties of the polyethylene
and in fact we have this situation that
is known as cathodic shielding in that
situation but cathodic shielding and
cathodic disbondement really i think are
a subject or on their own that will have
to talk about it
on another day
in terms of getting your pipe ready for
your fbe you're gonna have to have
really critical
surface preparation cleaning
pre-treatment
has that been improved over the years or
are we still using kind of
the old original standards
i think there's not really a lot wrong
with the old the old standards except
perhaps that they were not
stringent enough
so
you have to have a typically a
sa3
surface preparation grade you have to
have
a good mechanical profile
in other words angular not rounded it
has to be clean and it has to be
particularly free of dust
and that is possibly one of the most
critical aspects and in order to achieve
that a lot of the pipelines now use a
phosphoric acid-based wash
as a pre-treatment for the application
of
fusion bonded epoxy
and there has also been other chemical
treatment
notably chromate treatment
which has been given the black flag
by the environmental
lobby
and
it's unfortunate because a chromate
treated pipe or chromate pre-treated
pipe actually has absolutely
outstanding
corrosion resistance properties
with with a fusion bonded epoxy coating
on it
and
the industry really has to jump through
hoops
in order to compensate for the lack of
that chromate sadly that's often the
case but all of those
improvements surely have pushed up the
price
of 3lpe comparatively to the other
coatings
for sure but we need to remember that
the
cost of the coating itself standalone
has applied in the factory is not the
only consideration when looking at the
overall financial system of costing of a
project if you have a polyethylene
coated pipe
you
have significant advantages
in terms of the
cost of pipe laying
and in this particular project
the selection of the polyethylene
coating which you can see on the pipe
that is strung on the left hand side of
the trench allow the trenching and back
filling operations to be substantially
less expensive
than if you had a different coating
which required a higher grade
of backfilling materials like for
example sand padding
and bedding and so on don't get me wrong
this pile of rocks in the front is not
suitable and that represents an area
where there would have to be some due
care taken but the bulk of that trench
was cut out of the soil
and pipe was just laid in the native
soil put back in without any
restrictions and that is a huge cost
saving and that in fact
was what drove the selection of this
particular project
because the pipe laying was that much
less expensive
given the material that was applied
through the pipeline in the factory
the other concern that engineers we
shouldn't
lose sight of is
the bare bits of steel that still need
to be joined together when we get our
field joint coating yeah well we saw
that
end of a pipe a few slides back and
here's one of those pipes that's now
being welded together
and you can see the epoxy toe sticking
out from underneath polyethylene
and this particular joint has now been
coated with a fusion bonded epoxy it
could have been a liquid epoxy and then
this in turn will get over wrapped
with a further either polyethylene or
perhaps a bbc or a shrink sleeve or
in the form of either an extrusion or a
tape to provide the additional
mechanical and electrical protection so
that the field joints are protected to
the same standard
as majority of the line pipe
that is factory coated
and here's an example of the interface
between the
line pipe of the the factory coated pipe
coming in from outside
through the wall of a valve chamber and
then the pipe in the chamber epoxy
coated and the interface in this case
has been protected with an adhesive tape
and we're going to be talking about
tapes in some detail
in one of the later programs
neil another consideration that we are
now needing to take into account with
our coatings is
what i always talk about as the new pink
on the block which is ac interference
let's just chat quickly about
what impact ac interference has
on the polyethylene coatings
well the advantage of the polyethylene
coatings is their extremely high
electrical resistance
and
this then provides the
insulation
between
the pipe and its environment the soil
the challenge of course is that
electrical interference or ac
interference
is not
necessarily conductive in other words it
doesn't have to travel through the
coating you get what we call inductive
interference
as well as capacitive interference
which
actually cause very high voltages on the
pipe
irrespective
of the presence or in fact in many cases
because of the presence of this
insulating layer because it means that
the pipe is insulated from earth and the
induced voltage is then able to be
present in the pipeline
instead of discharging through the
coating because of the coatings high
electrical resistance
and in this picture we can actually this
is taken during pipeline construction
phase when the pipes are above ground
you can see the proximity of those
overhead power lines and in order to
prevent the operators from being shocked
whilst working with the pipes above
ground because they've obviously got to
weld them into a long string pick them
up put them in the trench and so on
these pipes are being erst with a
temporary earth connection
in order to discharge in this case any
capacitive
interference
and so being a metallurgist i'm allowed
to say it
all metallogists
have
two hands
on the one hand you have a pipeline with
a good electrical characteristic and
insulation which reduces
the cost of cathodic protection
on the other hand you have a highly
insulated pipeline which is susceptible
to ac interference
so the challenge then is to balance
the
pipeline
and its coaching and the characteristics
of the coaching
against
the environment that the coating is
going to see
so you may well
find that
a coating of
lower resistance may be preferable
in an area where you have got a lot of
ac interference in an area with highest
dc straight currents you may want to
have a pipeline with good electrical
insulation characteristics and that is
going to be one of the subjects that we
address in some detail
in the last session of the series when
there's no ways that we will be able to
cover the full suite of
pipeline coating selection in a 20
minute presentation
but we can certainly
give you all some pointers
on what to consider and what questions
to ask
in terms of selecting coatings for a
particular
project neil are there other
polyethylene systems other than the the
fusion bonded
polyethylene the scented polyethylene
and the two and three lps
most of the other systems are based on
tapes
and so there's a range of polyethylene
based tapes that are available cold
applied and hot applied significantly
used for field joints but also for
mainline wrapping if you have a
situation where you get bare pipe
delivered to a site and you need to give
it some additional protection it's quite
easy
to apply a tape you don't need fancy
equipment
in order to
achieve that and we'll we'll be talking
about tapes in some detail later on and
then for fuel joints in particular which
is another coarser on its own
there are heat shrink sleeves available
which are wrap around
all based on polyethylene because you
can get polyethylene to shrink
when you heat it
those would be the two primary
systems
that that are available
great neil thank you and i hope that
that everybody who's been joining us
today has
found some of your own questions have
been clarified
when we've discussed the polyethylene
coatings
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