a high performance, damage tolerant fusion bonded epoxy coating

7/29/2019 A High Performance, Damage Tolerant Fusion Bonded Epoxy Coating

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The Shop-Coated Pipeline That Cracked

FromJPCL,September 2011 | Free Product Information

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The Shop-Coated Pipeline That Cracked

Valerie D. Sherbondy

Senior Chemist, KTA-Tator, Inc.

Valerie Sherbondy is a senior chemist for KTA-Tator,Inc., a consulting and engineering firm specializing

in industrial protective coatings. Ms. Sherbondy has

been employed by KTA since 1990 and has provided laboratory support for the investigation of

hundreds of coating failures and coating testing programs. In addition, Ms. Sherbondy serves asthe Laboratory Quality Assurance Officer, overseeing the A2LA and NELEC accreditations of

the laboratory. She holds a BS in chemistry and a BS in business from the University ofPittsburgh and is an SSPC Certified Protective Coating Specialist (no. 467-921-0326), a

member of the American Chemical Society (ACS), and a committee chair for NACE

International.

Richard A. Burgess

Series Editor, KTA-Tator, Inc.

Gas transmission pipelines are often coated in a shop using fusion bonded

epoxy (FBE) coating systems. These coatings are chosen for their resistance tochemicals in soil and excellent impact resistance, which means less damageduring the transportation and installation of the pipe sections and less

mechanical damage during backfilling. Shop operations for abrasive blast

cleaning and coating application are automated, and the resulting applied filmsare generally uniform. One drawback is that the weld areas and joints that

connect pipe sections must be prepared and coated in the field are generally not

as uniform and consistent from joint to joint as are the stick to stick shop-applied coatings. A second drawback with the same FBE coating materials

applied in the shop is that they are more difficult to apply in the field due to

widely variable environmental conditions.

Additional resources must be devoted to inspection of the field-applied coating. In this case from

the F-Files, the added field inspection resources paid off when unexpected defects in the shop-

applied coatings were discovered. Inspection of the joint areas indirectly extended to theneighboring FBE coated pipe, which revealed occasional cracking and blistering. A failure

investigation was initiated, and several pipe sections were removed for examination and

laboratory analysis of the coating.

In This Article

Background

Laboratory Investigation

Conclusions

Recommendations

Valerie D.

Sherbondy,

Senior Chemist,

KTA-Tator, Inc
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Background

The specification provided for coating the pipe sections required that the steel surfaces be

prepared in accordance with SSPC-SP 10, Near-White Blast Cleaning, and that the resultant

profile be angular with a depth of 1.5 to 3.5 mils. Once prepared for coating, the pipe sectionswere to be heated to between 460 F and 500 F, not exceed 500 F. A two-coat FBE coating

system was specified. The primer was specified to be applied to achieve a dry film thickness

(DFT) of 1620 mils, with an average of 18 mils. The topcoat, or outer jacket, was to be applied

immediately after the first coat. The topcoat was to be applied to achieve a DFT of 3036 mils.The total system DFT was specified to be in the range of 4656 mils. The primer was green, and

the topcoat was brown. The pipes were prepared and coated in a shop and then shipped to a

single location for installation.

The field observations included isolated blisters in the coating on the exterior of the pipe and

cracks in the FBE coating film at the field bend locations. It was reported that only four or fiveinitial blisters were observed in the field before the pipe sections were installed and welded.

Additional blisters were observed on the pipe sections after field installation. The blisters wererepaired in the field, with the exception of those on a blistered pipe section sent to the laboratory

for examination. In addition, cracks at field bend locations were holiday tested and repaired inthe field shortly after the bending procedure. It had been noted that in some instances cracks

were not apparent after bending and had appeared the following day.

The total FBE thickness around defective areas was measured using a nondestructive electronic

coating thickness gage. The thickness readings were obtained in a minimum of six areas on each

pipe sample. The average coating system thickness measurements revealed a range of 54.860.6mils. The nondestructive measurements were consistent with the overall thickness determined by

microscopy and confirmed that the total system thickness exceeded the specified range of 4656

mils.

Laboratory Investigation

Coated samples were cut from larger pipe sections at the field site by the contractor andsubmitted to the laboratory. The samples were to be representative of the typical FBE coating

defects observed in the field and included a section of the cracking that was reportedly occurring

at the installation site and a pipe section containing blisters observed during installation. Properly

heated and cured control samples of the specified primer and topcoat materials were provided bythe coating manufacturer.

High voltage holiday testing was performed on the pipe sections received by the laboratory priorto sectioning for laboratory testing. This testing was performed to determine if the cracks in the

coating sample extended through the FBE coating film to the substrate. It was confirmed that the

cracks did extend through the coating, or at least sufficiently deep enough to result in detectionof the discontinuity.

The laboratory used a plasma cutter to section the pipe samples and isolate the areas exhibiting

defects for examination. During the plasma cutting process, additional blisters formed in the FBEcoating in the heat-affected zone. The blistering occurred when the coating surface temperature

adjacent to the cut line was in the range of 210 F to 220 F. As the surface cooled, most of the

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A High Performance, Damage Tolerant Fusion Bonded Epoxy Coating

D.G. Enos, J.A. Kehr, C.R. Guilbert

3M CompanyCorrosion Protection Products Dept.

3M Austin Technical Center

6801 River Place Blvd.

Austin, TX 78726USA

ABSTRACT

A novel technique has been developed which significantly improves the damage tolerance of epoxy coated

components in a variety of corrosive environments. Characterization of these coatings via an array of AC and DC

electrochemical techniques has revealed considerable improvements in the overall corrosion performance as a result

of this technology. The quality of the protective coating is thereby maintained, despite minor damage, which may

occur on the job site. Furthermore, this improved corrosion performance enhances cathodic disbondment (CD)performance while the impact resistance and flexibility of the fusion-bonded epoxy (FBE) coating are unaffected.

INTRODUCTION

Corrosion is a global problem, consuming three to four percent of gross national product in the developed

countries of the world.[1] Selecting economical and effective techniques for minimizing the effects of corrosion is a

critical design decision for pipeline systems. Corrosion protection is essential to prevent leaks, environmental

disasters, fire and explosion, personal injury, service disruption and costly maintenance. Thus, in addition to

effectively dictating the lifetime of the pipeline, the corrosion prevention system also significantly influences thepipelines operational costs such as general maintenance, pumping energy, and capacity upgrades. Although these

protective measures are critical, they represent only a small fraction of the overall long-term cost of a pipeline

system.

Today, higher operating temperatures and a host of hostile environmental conditions that pipeline materials

encounter during installation and use require a new generation of coatings [2] to protect both the interior and

exterior of the pipe. Hydrogen sulfide (H2S), increased levels of carbon dioxide (CO2) and other factors contribute to

a pipeline environment that increases levels of internal corrosion. There are many possible solutions to theseproblems including use of corrosion resistant alloys, inhibitors, and corrosion protective linings and coatings. FBE

coatings have offered an effective solution to these problems for nearly 40 years.

As the times and exposure conditions have changed, FBE coatings have evolved as well. More demanding

transportation, storage, installation, and pipeline operating conditions require the use of advanced FBE-based world-

class coatings to protect the pipe exterior. In addition, improved field application technology provides comparable-

quality same-system coatings for the girth weld. FBEs have been formulated to operate in these very harsh service

environments.

Background, History, and Advantages of FBE Linings and Coatings

An FBE is a one part, heat curable, thermosetting epoxy resin powder. It is a material that utilizes heat to

melt and adhere to a metal substrate. It provides a coating with no trapped solvents, excellent adhesion, and a tough,

smooth finish resistant to abrasion and chemicals. FBE coatings have been in use since 1960 to protect pipelines

from corrosion. It is estimated that over sixty thousand miles (ninety-five thousand kilometers) of FBE coated

pipelines are installed around the world.

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FBE is currently specified in the oil, gas, and water pipeline industries. It has been used as an internal

lining in desalination plants in Australia and the Middle East and on gas [5] and oil transmission lines It has been in

use protecting downhole tubing for over twenty years. More recently, it has been used in sour crude pipelines [4]. In

addition to its use as a stand-alone exterior coating, FBE is the favored primary coating for three-layer polyolefin

corrosion coatings, where it has been in use since 1979.

In the water industry, FBE provides a thinner lining than competing materials such as concrete, enablingsmaller pipe sizes and reduced bulk and weight during handling and installation of pipe. The smooth, hard FBE

coating provides reduced friction compared to uncoated or concrete-lined pipe. This results in more efficient flow,

reduced energy costs, and lower-installed pump or compressor investment. It has been used on valves, pumps, and

fittings in water districts for both water and sewer systems in California for nearly thirty years. It is in use protecting

brine-pit piping systems, solving both erosion-corrosion problems as well as general corrosion [5]. FBE has been

used in high-sand-content seawater cooling pipework for ten years and is still in excellent condition. It has beenapplied to valves and pipework handling seawater for the US Trident Submarine program and has a twenty-year

history in the pump manufacturing industry effectively protecting against cavitation and slurry damage. In the UK, it

has protected drinking water pipework since 1978, with coating on over two hundred thousand square meters [6].

Specific formulations meet the drinking-water requirements in many countries.

There are reports of six to eighteen percent flow efficiency improvements in gas transportation when using

FBE internally lined pipe as opposed to bare steel pipe [ ]. Using the six percent figure on an eight-hundred mile

(thirteen-hundred kilometer), DN 750 (NPS 30) pipeline with a discharge pressure of 140 kPa (960 psig) and acompressor station every eighty miles (one-hundred-thirty kilometers), the potential savings are over four million

dollars in compressor equipment cost and an annual energy savings of about a million dollars.

Damage Tolerant FBE Coatings

Although FBE coatings are extremely effective corrosion protection materials in a wide variety of

environments, their overall effectiveness is still closely tied to the quality of the applied coating. As with nearly all

barrier coatings, defects caused by mishandling or misuse of the coated pipe significantly reduce its ability to

provide the superior corrosion protection required for many applications. Coating damage frequently occurs during

the handling and installation of a pipeline, or is the result of rock damage occurring during backfill [7]. The solutionto this problem is seemingly quite simple: if the FBE coated pipe is treated properly, and the coating remains

structurally sound, the pipeline should readily meet or exceed its design life. Unfortunately, the type of damage

which is causing the problems discussed above is nearly impossible to avoid. Policing jobsites and preventing theuse of questionable construction practices is problematic at best. Similarly, preventing rock damage during backfill

is nearly impossible, and even more difficult to verify. Nevertheless, irrespective of the pipe coating condition, or

the abuse level, it still needs to get the job donepreventing the onset of corrosion and subsequent structural

problems. It is better to assume that damage to the coating is inevitable, and, instead of trying to prevent it, design

the coating to survive it with much of its corrosion-preventive properties intact. In this study, such a coating ispursued.

Through the addition of microencapsulated materials, a self-healing FBE coating has been designed. As

illustrated below, this coating is considerably more damage tolerant than traditional FBE coatings. The mechanical

damage which weakens conventional coatings instead ruptures the microcapsules which in turn heal the FBE

coating, preserving its barrier properties. What follows is a brief description of the coating technology under

evaluation, along with promising preliminary results.

Microencapsulation is a technique through which liquid materials, such as oils, are encapsulated within a

seamless, solid shell. An example of microencapsulated oil is presented in Figure 1. A wide variety of shell wallmaterials are available the appropriate choice is determined by a combination of the application, the material to be

encapsulated, and the desired stimulus to rupture the capsule (e.g., impact, pH, or solution chemistry). In general,

microcapsules are between 5 m to 200 m (0.2 mils to 8 mils) in size with wall thicknesses on the order of 1 m to

2 m (0.04 mils to 0.08 mils). Fill materials may be either aqueous or non-aqueous in nature. What is important to

note is that, once encapsulated, liquid-based fill materials behave as a solid. As a result, considerably larger

quantities of the fill material may be added to a coating without adversely affecting its properties.

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As an example, suppose a liquid inhibitor has been demonstrated to effectively halt corrosion of the metal

to be coated. The coating formulator then makes the decision that the inhibitor should be added to the current

coating formulation. However, in the case of a powder coating such as an FBE, only very limited concentrations of

a liquid additive may be added before the powder begins to clump and hinder application. If that same liquid isencapsulated prior to addition to the powder, large concentrations of the inhibitor may be added with little or no

detrimental effect on the handling or application of the coating material. A similar scenario holds for liquid-basedcoatings, where large additions of an inhibitor may hinder cure of the coating or degrade physical properties.

In this study, a series of modified coatings were formulated and produced, as illustrated in Figure 2. As can

be seen in the figure, the coating consists of two layers. The first layer is a primer layer containing the

microcapsules. The microcapsules contain approximately 80% active fill, and are approximately 50 m (2 mils) in

size. The epoxy matrix of the primer layer is an unmodified, flexible FBE. The second layer of the coating, or the

topcoat, is composed entirely of an unmodified FBE. More details on the actual formulation may be found below inthe Experimental Methods section.

Also illustrated in Figure 2 is the manner in which the coating is designed to function. The coating will

behave the same as a traditional FBE until it has been subjected to mechanical damage. This damage may be the

result of an impact to the coating, microcracking of the coating during bending on the job site, etc. Once damaged,

the microcapsules release their protective fill. By placing the microcapsules close to the steel surface in the primer

layer, they are able to deliver their protective fill directly to the regions near the metal surface where they are

needed. A variety of fill materials have been investigated, consisting essentially of combinations of corrosioninhibiting materials and sealants. Once released, the fill material reseals the coating and prevents the onset of

corrosion, preserving the protective benefits of the FBE.

Although placing the microcapsules in the primer layer is the simplest embodiment of this coating concept,

it is not the only one. Figure 3 illustrates a coating that has microencapsulated additions in both the topcoat and the

primer layer. In this example, a series of different microcapsules could be envisioned, each serving a different

purpose. Microcapsules containing corrosion inhibiting materials could be placed in the primer layer, ensuring their

delivery directly to the metal surface. In the topcoat, capsules containing sealants could be used, their purpose being

to reseal the damage site and hold in place the inhibitive materials released from the primer layer. In addition,

microcapsules containing a dye could also be incorporated into the topcoat. Upon damage, the dye capsules wouldrupture, releasing their fill and locally discoloring the coating (e.g., turn a green coating red), easing the

identification of damage sites along the pipe for later repair with appropriate patch materials.

EXPERIMENTAL METHODS

Coating Composition and Preparation

Prior to coating, mild steel bars were degreased in 2-butanone (MEK) and isopropanol, then grit blasted toa near-white metal finish in accordance with NACE No.2/SSPC-SP 10. Each bar was preheated for 45 minutes to a

temperature of 400F (205C), after which they were coated via a fluidized bed system. A two-step coating was

accomplished by first dipping the sample into the primer bed, after which the sample was immediately transferred

to, and coated in the topcoat bed. Samples were left in each fluidized bed for sufficient time to allow the coating to

build to the desired thickness. Coating thickness was verified using a magnetic thickness gauge.

The FBE coatings investigated in this study were based on a flexible fusion bonded epoxy resin. Controlsamples were coated with 400 m (16 mils) in a single coating operation. Microcapsule containing coatings were

produced by first depositing a primer layer 150 m (6 mils) in thickness which consisted of 85% unmodified FBE +

15% microcapsules, followed by a 250 m (10 mils) top coat of unmodified FBE. The two layers were applied

sequentially (i.e., no additional preheating).

Electrochemical Testing

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Solution Preparation. All solutions were prepared using distilled water and reagent grade chemicals. The cathodic

delamination testing solution was made in accordance with ASTM G8 [8] and contained 1% each of sodium

chloride, sodium carbonate, and sodium sulfate.

Corrosion initiation tests were conducted in mildly acidic, 3.5 wt% sodium chloride solutions. The sodiumchloride solutions were first made to the desired concentration after which the pH was adjusted (via HCl) to 5.

Cathodic Delamination (CD). Samples were prepared by machining a 6 mm (0.25 inch) defect in the center of a

11.4 cm x 11.4 cm (4.5 inch x 4.5 inch) coated panel. The samples were then placed in the cell pictured in Figure 4.

Next, the solution was added and the samples polarized for 30 days at 1.44 V vs. a saturated calomel reference

electrode. Periodic electrochemical impedance spectroscopy (EIS) spectra were taken from each sample throughout

the 30 days. Upon completion of the test, the coating around the intentional holiday was removed with a knife and

the delamination radius measured in accordance with ASTM G8. Four replicates of both the control and the capsulecontaining samples were investigated.

Impact Corrosion Testing. Following coating, samples were subjected to an impact of 80 in-lbs (9 Nm) with a

0.625-inch (15.9-mm) diameter tup. A holiday detector was utilized to verify that the coating had been disrupted

and that bare metal was exposed. Next, the samples were placed into a pH 5, 3.5% NaCl solution for 30 days.

Throughout the testing, periodic electrochemical impedance spectra were taken from each sample. Four replicates

of both the control and microcapsule containing coatings were investigated.

Electrochemical Impedance Spectroscopy. EIS testing was performed utilizing a PAR Model 273A Potentiostat in

combination with a Solartron 1255 FRA and two PAR Model 314 Multiplexers. All experiments were conductedunder software control via ZPlot (Scribner Associates, Inc.). Experiments were performed about a DC bias of 1.44

VSCE for the CD experiments, and about the open circuit potential for the impact-damaged samples. The

perturbation frequency was scanned between 106 Hz and 1 mHz. A waveform of 25 mVRMS was used in all cases.

RESULTS

Cathodic Delamination Testing

Cathodic delamination testing was performed for traditional FBE coated samples as well as for the

microcapsule loaded coating. Four replicates of each coating were evaluated. Figure 5 illustrates the typical results

for the two coatings. As can be seen in the figure, the delamination radius was reduced by 60% from 9.8mm (0.38inches) for the traditional FBE to 4.2mm (0.17 inches) for the capsule loaded coating. There was very little

variation among the four replicates of each coating. On an area basis, the delaminated area was reduced by 68%.

Neither coating was discolored, blistered, or observably swelled after the 30-day experiment.

Corrosion Initiation from a Damage Site

To determine if the microencapsulated additions actually prevent the onset of corrosion, coated samples

were damaged as discussed above and placed into a mildly acidic, high chloride solution. While in the bath,

electrochemical impedance spectroscopy was used to qualitatively evaluate changes occurring at the damage site.

Figures 6 and 7 present a comparison of impedance data for the conventional and modified FBE coatings. As is

clearly evident in the figures, a second time constant is present in the case of the modified coating. This second time

constant represents the newly sealed layer resulting from the ruptured microcapsules. Throughout the time of the

test it can be seen that the polarization resistance of the modified FBE coating remained significantly higher thanthat of the conventional FBE coating. Based on this information, it may be inferred that the modified coating is

providing increased protection compared to the standard FBE coating.

To further demonstrate the ability of the modified coating to provide increased protection, samples were

prepared as described above, then placed into a pH 5, aerated, 3.5 wt% NaCl solution at 60C (140F). Within a

matter of hours, rust blooms were observed within the damage site for all conventional FBE coated samples. In the

case of the modified FBE coated samples, no corrosion initiation was observed within the defect for two weeks.

This is illustrated in Figures 8a and 8b. Note the minor attack visible on the modified FBE coating as compared to

the severe attack visible on the conventional coating. After 6 weeks, more significant corrosion was visible on the

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modified FBE coated sample. However, the corrosion of the conventionally coated sample was again more severe

then the microcapsule containing, modified FBE coating.

DISCUSSION/SUMMARY

To summarize, a modified FBE coating has been presented which possesses an extraordinary self-healing

ability. This self-healing characteristic is achieved through the use of microencapsulated additions that arepositioned close to the metal/coating interface. In the particular example presented in this paper, the microcapsules

are designed to rupture and release their protective fill when the FBE coating is subjected to mechanical damage.

These protective fill materials may include corrosion inhibiting materials as well as sealants for the coating. As a

result, a protective material is delivered to and held in place at the steel surface within a damage site. In addition,

the damaged coating is sealed, and the protective nature of the coating is preserved.

Experiments were conducted on coatings containing a wide variety of microcapsule types and fill materials.

Preliminary results for one of the more promising combinations were presented above. As was discussed

previously, electrochemical testing to determine if the microcapsules increase the corrosion resistance of a damaged

coating revealed that the onset of corrosion was delayed considerably. In addition, in an industry standard cathodic

disbondment test, a significant improvement in performance was observed.

Other advantages of this technology revolve about the self-healing capability of these coatings in

combination with other features that may be attained through the use of microencapsulated additions. For example,through the use of dye capsules, a coating could be produced that, in addition to possessing the self-healing

capabilities described above, would positively indicate where damage occurred. This indicator would enable moreefficient repair of damage areas via an appropriate patch material. In addition to aiding the patch process, the newly

sealed layer formed by the ruptured microcapsules further enhances the performance of the patch, providing a more

effective barrier to the external environment. Perhaps most important, though, is that the modified FBE coating will

be able to effectively handle the abuse which current FBE experiences en route to and at the job site.

The microcapsule containing coating also provides additional benefits when used in conjunction with a

cathodic protection system. When such a system is utilized, one of the primary factors dictating operational cost and

overall effectiveness is the total defect area present in the coating. As the total defect area increases, the amount ofcathodic protection current required to protect those areas increases thus increasing the cost of operation. In

addition, as the overall cathodic protection current increases, the effective throwing power of the CP system

decreases, due to IR drop. In other words, a larger portion of the applied potential will be comprised of IR drop unless compensated, insufficient cathodic protection will be applied. Since the overall effect of the coating

described above is to minimize the amount of damage experienced by the pipe, such a coating will also reduce the

cost and help maintain the effectiveness of a cathodic protection system as well.

In addition to the benefits described above, the modified FBE coating offers a number of advantages oversimilar corrosion prevention technologies. Although this approach appears to be simply the addition of corrosion

inhibitors to a coating, it is much more than that. Corrosion inhibitors are added in such a way that very large

concentrations (considerably more than could be added to a coating via conventional means) are delivered to the

damage site, while very little of the material is wasted. This is in contrast to the typical procedures followed when

using inhibitors. When protecting the internals of a pipe system, the use of chemical corrosion inhibitors requires

that large quantities of inhibitor be added to the process stream to protect a relatively small amount of material (i.e.,

the entire stream must be treated, even though only that portion which is in contact with the steel needs to have

inhibitor present the remainder is waste). In the case of external protection of the pipe, the use of inhibitors istypically not possible due to environmental concerns. The system above alleviates many of the problems of using

inhibitors so, protection of the external surface of a pipe is possible, since the inhibitor is confined to the coating.By sealing the inhibitive materials in place at the damage site, there is no need to continuously augment the system

with additional inhibitor.

Another advantage of a modified FBE coating as presented above is its similarity in performance and

handling to traditional FBE coatings. By maintaining a form that is handled in the same manner as conventional

FBE coatings, no new technologies must be invested in and learned by applicators. The modified FBE coating may

be applied via electrostatic spray or through a fluidized bed. The only change required is the addition of another

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series of spray guns in the existing equipment (this assumes, of course, that a multi-layer coating is applied). Since

the coating behaves identically to a conventional FBE coating, no new pipeline construction practices or procedures

need be adopted.

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CONCLUSIONS

In conclusion, in this study a robust FBE coating has been designed through the application of

microencapsulated additions. Upon being damaged in a manner that would compromise a conventional FBE, the

microcapsules are ruptured, releasing their protective chemistry. As a result, the damaged FBE coating is healed,retaining much of the protective properties that it possessed prior to damage. The list below summarizes the benefits

of this technology and its advantages:

The modified FBE coating presented in this study possesses superior resistance to corrosion initiation in the

damaged state compared to conventional FBE coatings.

The modified FBE coating presented in this study possesses superior resistance to cathodic delamination

compared to conventional FBE coatings.

Unlike cathodic protection, increased maintenance requirements or expensive equipment that is subject to

failure in the field does not accompany this increased resistance to corrosion.

The overall effect of this coating is the reduction of defect area on a coated pipe. Since the cost to operate a CP

system is a direct function of the defect area, this coating reduces operation costs associated with the use of a

CP system.

Implementation of this technology will be facilitated by the fact that the same technologies are used in itsapplication. No new technologies must be mastered by coating applicators the modified FBE can be readily

applied with existing equipment and methods.

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ACKNOWLEDGEMENTS

The authors gratefully acknowledge the technical support provided by Susan Weiland and Stephen Daniell

in the 3M Corrosion Protection Products Department.

REFERENCES

1. Islam, Moavin, Condition Evaluation of Reinforced Concrete Structures: A Case Study, Paper No. 521,

NACE National Corrosion Conference, Corrosion 95.

2. Strobel, Rupert F., Fusion-Bonded Epoxy Coatings for Pipeline Corrosion Protection, 1981, 3M Company

publication.

3. Corrosion Control Report: Internal Pipe Coatings are a Wise Investment, Pipeline and Gas Journal, March

1993, pp. 67-69.

4. Read, Thomas, Yates Field Crude Line Coated Internally, Externally, Pipeline and Gas Journal, February

1982.

5. Carlson, Ron E., Jr., Internal Pipeline Corrosion Coatings Case Studies and Solutions Implemented, Paper

No. 27, NACE 1992 Annual Corrosion Conference.

6. Langford, Paul, Dr., New Developments in Coatings for the Internal Protection of Water Industry Line Pipe,unpublished, 1993.

7. Norman, D., Gray, D., Fusion-Bonded Epoxy Pipe Coatings 10 Years Experience, Materials Performance,

Vol. 32, No. 3 (1993), p.36.

8. Standard test Methods for Cathodic Disbonding of Pipeline Coatings, ASTM Standard G8-96.

10


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Figure 1: Micrograph of typical microcapsules containing a protective fill.

Figure 2: Schematic illustrating the function of a single primer layer containing corrosion-preventative

microencapsulated additions.

11

Damage

Self Healing

Newly SealedLayer

Steel

FBE


12/15

Figure 3: Schematic illustrating the function of a coating in which both the primer and top layer contain

microencapsulated additions. By careful selection of the fill materials, the function of the top and bottom layers

may be tailored (e.g., primer provides corrosion inhibiting materials, while the top layer provides materials which

seal the damage site and possibly provide a visual indication of the damaged area.Figure 4: Schematic of electrochemical cell used for the testing and evaluation of the FBE coated plates (i.e., CD

testing, impact testing, etc.).

12

Damage

Self Healing, Indicating

Newly Sealed

Layers

Steel

Damage Indicator

Acrylic Cell Body

O-Ring

SealDefect

Coated Sample

Clamping System

WE

CE RE


13/15

Figure 5: Typical cathodic disbondment results after 30 days in 1% sodium chloride + 1% sodium sulfate +1%

sodium carbonate at room temperature with an applied potential of 1.44 VSCE for (a) unmodified FBE (9.2 mm) and

(b) unmodified FBE with a 150 m (6 mil) primer layer containing 15 wt% microencapsulated additions (4.7 mm).

Coating thickness was 350 m (14 mils) in both cases.

13

A

B


14/15

Figure 6: Typical EIS spectra for an unmodified FBE and the microcapsule containing material after 24 hours.

Note the presence of an additional time constant indicative of the inhibitor film in the case of the microcapsule

containing material.

Figure 7: Typical EIS spectra for an unmodified FBE and the microcapsule containing material after 360 hours.Note that the additional time constant is still present for the microcapsule containing material, illustrating its

persistence.

14

0 15000 30000 45000 60000

-70000

-55000

-40000

-25000

-10000

Scotchkote 413SG

Modified FBE

10-3

10-2

10-1

100

101

102

103

104

105

102

103

104

105

10-3

10-2

10-1

100

101

102

103

104

105

-90

-65

-40

-15

Real Impedance (Resistive)

ImaginaryImpedance(Capacitive)

Frequency (Hz)

Frequency (Hz)

PhaseAngle

Magnitude24 Hours

pH 5, 3.5% NaCl

Additional Time

Constant

Real Impedance (Resistive)

ImaginaryImpedan

ce(Capacitive)

Frequency (Hz)

Frequency (Hz)

PhaseAngle

Magnitude

0 2500 5000 7500 10000 12500 15000 17500

-17500

-15000

-12500

-10000

-7500

-5000

-2500

0

Scotchkote 413SG

Modified FBE

10-3

10-2

10-1

100

101

102

103

104

105

101

102

103

104

105

10-3

10-2

10-1

100

101

102

103

104

105

-90

-75

-60

-45

-30

-15

0

360 Hours

pH 5, 3.5% NaCl

Additional Time

Constant


15/15

Figure 8: Typical results for impact damaged coatings exposed in 60C (140F), pH 5, 3.5% NaCl solution for

(a) an unmodified FBE and (b) a coating containing the microencapsulated materials. The microcapsules

dramatically increased the time to corrosion initiation in this qualitative test (from 4 hours to nearly two weeks).

15

Severe corrosion

initiation

Minor

corrosion

initiation

A

B

a high performance, damage tolerant fusion bonded epoxy coating

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