2. O
il and gas transmission pipelines should be considered as
critical elements of infrastructure in the transportation of
fuel, supplying energy and power and providing sustained
growth and development.
Today, pipelines operate in some of the most severe weather
conditions on earth and pipeline owners and design engineers require
pipe coatings to perform with excellence in extreme environments. From
coating new pipe, to coating bends and fittings, valves and girth welds,
to repair work, they constantly seek products that can provide effective
corrosion protection to ensure operational pipeline effectiveness over
the medium‑ to long‑term.
Understanding coatings:
a many layered thing
Craig J R Thomas, Jotun Powder Coatings A/S, Dubai, UAE, gives an
overview of fusion‑bonded epoxy pipe coatings, and the ways in which
they serve, and are evolved for, the pipeline industry.
3. External pipe coating systems have been designed to
form a barrier between the metal surface of the pipe and
the surrounding environment. Since its introduction in the
1960s, stand alone fusion‑bonded epoxy (FBE) has proven
its capability as an external pipe coating and is now the
most commonly used anti‑corrosion pipeline coating in
North America and the Kingdom of Saudi Arabia.
Over the last four to five decades, international oil and
gas companies have grown to recognise the many benefits
of externally coating oil and gas pipelines. It has become
standard industry practice.
In today’s world, pipe coating manufacturers have to
be able to offer total corrosion engineering solutions,
where FBE coatings and systems can be tailored to suit the
uniqueness of each and every pipeline project at any time,
under any condition.
Jotun offers an extensive range of stand alone coatings,
primers for three‑layer polyolefin systems, high operating
temperature FBE coatings, dual‑layer FBE, low application
temperature FBE as well as three‑layer FBE coatings to meet
ever increasing and demanding pipeline coating requirements
around the world. Its products carry a proven track record of
over 40 years protecting more than 130 000 km of pipelines.
Corrosion and modern methods of protection
Corrosion engineering can be defined as “the specialist
discipline of applying scientific knowledge, natural laws and
physical resources in order to design and implement materials,
structures, devices, systems and procedures to manage the
natural phenomenon known as corrosion.”1
Management of corrosion through the use of FBE coatings
is a specialist area and involves a combined effort between
pipeline owners, design engineers, construction contractors,
applicators and most importantly pipe coating manufacturers.
There are two main ways to protect pipelines from
corrosion – external coatings and cathodic protection.
External pipe coatings are “intended to form a continuous film
of electrical insulating material over the metallic surface to
be protected. The function of such a coating is to isolate the
metal from direct contact with the electrolyte, interposing
a high electrical resistance so that electrochemical reactions
cannot occur.”2
FBE coatings are very effective in the prevention of steel
corrosion, as they provide both superior barrier properties
and excellent adhesion to the surface of the steel. The oxygen
permeability of FBE is less than 20% than that of polyethylene
(PE), however, FBE is subject to a higher rate of moisture
permeability.2
When FBE and PE are used together in a coating
system, their permeability properties complement each other
and produce an effective barrier to substances that feed
corrosion.
Stand alone FBE and three‑layer polyolefin (3LPO) systems
are the most commonly used external pipe coatings in the
world. Use of dual‑layer FBE has increased in recent years
on account of the specific topcoat performance that can
be offered. As the material to be transported in pipelines
becomes hotter, high operating temperature FBE coatings
systems are featuring more and more in specifications.
Three‑layer FBE also has its place in the pipe coating industry
portfolio, as it can fulfil a number of key operational and
performance requirements, not previously possible.
The main focus of this article will be the niche areas
of high operating temperature FBE coatings, dual‑layer and
three‑layer FBE, to demonstrate how the boundaries of science
and technology are being pushed to the limits and beyond.
Handling high operating temperature
Over recent years, changes in oil and gas industry drilling
and transmission operations mean there is a growing need
for FBE coatings that can adapt to different and varying
service conditions whilst maintaining corrosion protection
performance. Pipeline systems are increasingly transporting
materials at higher temperatures, as pipeline owners cater for
deeper drilling operations and more remote reserves, seek
to prevent hydrate formation, minimise wax deposition and
maintain low material viscosity.
The specific performance characteristics of high operating
temperature FBE coatings, which nowadays can reach the
performance levels of standard FBEs, help the industry to
transport material at higher temperatures. This increases
pumping efficiency, can eliminate compressor aftercoolers,
improves flow efficiency and promotes flow assurance.
Figure 1. Pipe stack showing FBE‑coated steel pipe.
JUNE 2013 | Reprinted from World Pipelines
4. There are many factors that contribute to successful
FBE coating performance and one of the most important
attributes of FBE is glass transition temperature (Tg). When
pipe wall temperature exceeds the Tg of the FBE coating,
the binding polymer transforms from a hard and relatively
brittle to a softer, rubber‑like state. This involves a change
in mechanical properties and increased permeability of the
coating to moisture and oxygen. When FBE is used as primer
in 3LPO coating systems, the residual stress in the polyolefin
topcoat may cause loss of adhesion between the FBE and
topcoat or at the steel‑FBE interface, if the FBE coating is in its
rubber‑like state.
FBE manufacturers are striving to push the Tg boundaries
higher than ever before whilst maintaining product properties,
application characteristics, mechanical and anti‑corrosion
performance at a level suitable for the pipeline industry
and comparable to standard FBE coatings. Historically, high
Tg FBE materials have suffered from a compromised level
of flexibility, which becomes particularly important when
laying pipelines in cold regions or offshore via reel‑lay barge.
Extended cure times of some high Tg FBEs can actually
complicate the pipe coating process.
High operating temperature FBE coatings exhibit cure times
comparable to standard FBE coatings, which ensures suitability
for conventional electrostatic spray application using existing
pipe coating lines. There is a demand for comprehensive
product choice suitable for pipelines operating at different
temperatures. The coating products should be tried, tested
and they should have succeeded; track record is pivotal. In
addition, the FBE should be suitable for use as a girth weld
coating to ensure corrosion protection of field joints as well.
There are a small number of global powder coating
manufacturers that can provide the solution with niche ranges
of high operating temperature FBE coatings, designed to meet
the exacting demands of corrosion protection of pipelines
operating at elevated temperatures. As an anti‑corrosion
coating, standard FBE typically takes on temperatures up to
100 ˚C (212 ˚F), but Jotapipe HT, developed and manufactured
by Jotun, raises the level of protection offered to 150 ˚C
(302 ˚F). This coating series incorporates advanced technology
that has allowed Jotun to push the glass transition
temperature boundary whilst meeting all requirements of
the major international pipe coating specifications and
offering levels of coating flexibility suitable for reel‑lay barge
application.
High operating temperature FBE coatings have the
following benefits:
FF High glass transition temperature.
FF Proven track record.
FF Standard FBE coating cure times.
FF Tolerant to reel‑lay barge methods.
FF Suitable for a range of operating temperatures.
FF Suitable for use as a girth weld coating.
Dual‑layer systems
With increasingly aggressive and varying environments, there
is a continuous demand for pipeline coatings to provide
enhanced performance. As a result, the traditional stand alone
Figure 3. Steel pipe externally coated with J‑Trac – a three‑layer
FBE coating system from Jotun.
Figure 2. Insulated offshore pipe coating system using Jotapipe HT
2004. (Photo courtesy of Bredero Shaw.)
Reprinted from World Pipelines | JUNE 2013
5. FBE coating is evolving into a dual‑layer and multi‑functional
coating system.
Since their introduction in 1991, dual‑layer powder coatings
have grown in popularity and are now even considered for
use on pipelines operating at higher temperatures. Dual‑layer
FBE systems provide a relatively low cost solution that is not
only resistant to mechanical damage, but is also non‑shielding
to cathodic protection. Dual‑layer FBE coatings are formulated
to deliver specific topcoat performance.
Dual‑layer FBE systems comprise an anti‑corrosion primary
coating, over which a topcoat is immediately applied. It is
the topcoat that delivers the additional features that pipeline
owners now require resulting in overall enhanced system
performance.
At times, pipeline owners may require extra grip, especially
when constructing subsea pipelines, so a rough coat has been
designed to provide a textured surface. The anti‑slip nature
of the rough coat considerably improves the adhesion of the
concrete weight coat to the anti‑corrosion primary coating.
In 1998, the ‘basic’ system was further enhanced through
use of an abrasion‑resistant overcoat (ARO) coating to provide
a tough outer layer to protect the anti‑corrosion FBE base
layer from mechanical damage during handling, backfilling,
directional drilling and general operation.
When a pipeline trench is backfilled, the FBE coating
can be exposed to countless impacts from falling stones
and rocks that can damage the anti‑corrosion coating.
Testing to the latest industry standards has shown that using
dual‑layer FBE significantly reduces impact damage to the
anti‑corrosion coating. The abrasion and gouge resistance of
dual‑layer FBE provides an exterior shield that protects the
FBE anti‑corrosion base layer from damage also caused by
directional drilling and dragging of pipes in the field or on the
right-of-way.
Pipeline project delays and overstocking can lead to
FBE‑coated pipes being left in coating yards or near pipelaying
sites for extended periods of time. Weathering can impact
the effectiveness of FBE coatings. In particular, solar radiation
causes degradation of the epoxy binder surface, causing
the FBE to ‘chalk’. This process can result in a reduction
of FBE coating thickness by up to 40 μm/yr3
. A UV‑stable
dual‑layer coating provides exceptional weathering resistance.
This protection maintains and extends the life of the primary
anti‑corrosion FBE layer, allowing pipes to be used after
prolonged periods of storage. When compared to standard
FBE coatings after weathering, the performance of this type of
dual‑layer coating is substantially better.
Dual‑layer FBE has the following benefits:
FF Reduced pipe damage.
FF Proven success.
FF Industry compliance – meets key FBE specifications.
FF Operating temperature performance up to 100 ˚C (212 ˚F).
FF Minimal plant modification.
FF Ease‑of‑application.
FF Verifiable quality assurance/quality control.
Tripling the system
No matter how good stand alone FBE coatings and extruded
coating systems are, there are still some disadvantages, which
are well documented. FBE coating systems have now been
developed that combine all the advantages and none of the
weaknesses of either stand alone FBE or multi‑layer extruded
coatings. One such system is J‑Trac from Jotun, which is a
three‑layer FBE system. The synergistic coating system removes
the possibility of internal stresses normally associated
with a 3LPO system and eliminates issues of compatibility
between coating layers of different chemical nature, creating
a protective system that is stable and does not suffer from
general disbondment as seen in alternative polyolefin and
other non‑polar coating systems.
The three layers of FBE result in a coating system that
is unstressed and able to provide greater protection over
longer periods of time. Working together, the three layers are
extremely tough and resilient, creating outstanding corrosion
protection for pipeline systems. Very little modification is
required to apply a three‑layer FBE system minimising costs
and expensive time delays. The system therefore offers
ease‑of‑application with no intercoat time concerns typical
for side‑extruded PO systems; there is no requirement for PO
extruders. A three‑layer FBE system provides the optimum
balance of performance and value, especially when compared
to 3LPO systems. In addition, three‑layer FBE offers raised weld
coverage and compatibility with traditional girth weld coating
solutions.
Three‑layer FBE has the following benefits:
FF Reduced system stress.
FF Cost‑competitive.
FF Minimal plant modification.
FF Raised weld coverage.
FF Outstanding resilience.
FF Traditional girth weld coating compatibility.
Low application temperature FBE coatings
There is increasing pressure to adopt energy efficient practices
to save time, money and to minimise the impact on the
environment.
Pipe coating manufacturers have developed a range of
pipe coatings that can be applied at lower temperatures. Less
energy and time is required during the curing process, making
this an efficient, ‘green’ and economic solution. Having a
coating material that can be applied at lower temperatures
enables pipeline engineers to specify high strength steels such
as those used in high pressure, strain‑based design pipelines
fore for example. This may also allow thinner walled pipe to
be used reducing pipe, shipment and therefore overall pipeline
project costs.
Applied at temperatures lower than conventional
FBE coatings, low application temperature FBEs still need
JUNE 2013 | Reprinted from World Pipelines
6. to meet the main pipe coating specifications and standards
whilst providing additional energy and operational efficiencies;
anti‑corrosion performance shall not be compromised. An
example of such a material type is Jotapipe LT, a range of
FBE coatings from Jotun designed with a speciality low‑melt
viscosity and higher reactivity binder system. Application and
curing takes place at temperatures significantly lower than that
of conventional FBE coatings.
Conclusion
Over the last five decades, FBE coatings have clearly
demonstrated performance excellence in corrosion protection
and have replaced older technologies, especially in the area of
corrosion protection of steel pipelines.
FBE coating manufacturers are ready for the future
challenges laid down by the pipeline industry and can help the
industry with ‘greener’ coating solutions.
Pipeline engineers now have a comprehensive range of
corrosion engineering solutions at their disposal for very
demanding conditions and stringent requirements, whether
that be the heat of the material flowing inside the pipeline,
the potentially aggressive and challenging construction/
pipe laying environment or temperature extremes of the
outside world.
Innovation‑minded companies such as Jotun serve the
pipeline industry by providing high performance coating
solutions as well as engaging in active research and
development programmes targeted at meeting and exceeding
future pipe coating needs.
References
1. Corrosion engineering, Wikipedia (en.wikipedia.org/wiki/corrosion_engineering)
(04/2013).
2. KEHR, J. A., RAU M. and SIDDIQUI E., ‘Fusion‑Bonded Epoxy (FBE) and Dual‑Layer
FBE Materials Provide Enhanced Performance For Pipeline Installation’,
ASME India Oil Gas Pipeline Conference, New Delhi, India, (16 ‑ 18 March 2009).
3. KEHR, J. A., ‘Fusion‑Bonded Epoxy (FBE): A Foundation for Pipeline Corrosion
Protection’ (2003).
Bibliography
1. KEHR, J. A., ‘Fusion‑Bonded Epoxy (FBE): A Foundation for Pipeline Corrosion
Protection’ (2003).
2. KEHR, J. A., MALLOZZI, M., ‘Fast, Worry Free Pipeline Installation with
Dual‑Layer FBE Coatings’, ACA Corrosion Control 007, Sydney, Australia,
(25 ‑ 28 November 2007).
3. PRATT, J. A., MALAZZI, M. and D’Souza, A., ‘Advances in Damage Resistant
Coating Technology’, NACE Corrosion 2011, Houston Texas, (13 ‑ 17 March 2011).
4. THOMAS, C., ‘Covering the World’s Pipelines – Inside and Out’, World Pipelines
(10/2010).
Reprinted from World Pipelines | JUNE 2013
