The Shop-Coated Pipeline That CrackedFrom JPCL, September 2011 | Free Product Information More items for Coating Materials 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 as the 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 of Pittsburgh 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 to chemicals in soil and excellent impact resistance, which means less damage during 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 films are 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” shopapplied 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. In This Article Background Laboratory Investigation Conclusions Recommendations Valerie D. Sherbondy, Senior Chemist, KTA-Tator, Inc 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 shopapplied coatings were discovered. Inspection of the joint areas indirectly extended to the neighboring 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. 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. The average coating system thickness measurements revealed a range of 54. It was reported that only four or five initial blisters were observed in the field before the pipe sections were installed and welded. The primer was specified to be applied to achieve a dry film thickness (DFT) of 16–20 mils. As the surface cooled. The total FBE thickness around defective areas was measured using a nondestructive electronic coating thickness gage. and the topcoat was brown. cracks at field bend locations were holiday tested and repaired in the field shortly after the bending procedure. The topcoat was to be applied to achieve a DFT of 30–36 mils. This testing was performed to determine if the cracks in the coating sample extended through the FBE coating film to the substrate. with an average of 18 mils. Once prepared for coating. additional blisters formed in the FBE coating 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. Near-White Blast Cleaning. was to be applied immediately after the first coat. and that the resultant profile be angular with a depth of 1. Additional blisters were observed on the pipe sections after field installation. The blisters were repaired in the field. The primer was green. Properly heated and cured control samples of the specified primer and topcoat materials were provided by the coating manufacturer.Background The specification provided for coating the pipe sections required that the steel surfaces be prepared in accordance with SSPC-SP 10. It was confirmed that the cracks did extend through the coating.6 mils. or outer jacket. During the plasma cutting process. The pipes were prepared and coated in a shop and then shipped to a single location for installation. High voltage holiday testing was performed on the pipe sections received by the laboratory prior to sectioning for laboratory testing. 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. The nondestructive measurements were consistent with the overall thickness determined by microscopy and confirmed that the total system thickness exceeded the specified range of 46–56 mils.8–60. The laboratory used a plasma cutter to section the pipe samples and isolate the areas exhibiting defects for examination. The thickness readings were obtained in a minimum of six areas on each pipe sample. In addition. the pipe sections were to be heated to between 460 F and 500 F. not exceed 500 F. Laboratory Investigation Coated samples were cut from larger pipe sections at the field site by the contractor and submitted to the laboratory. with the exception of those on a blistered pipe section sent to the laboratory for examination. The topcoat. A two-coat FBE coating system was specified. most of the 2 . It had been noted that in some instances cracks were not apparent after bending and had appeared the following day. The total system DFT was specified to be in the range of 46–56 mils.5 to 3.5 mils. or at least sufficiently deep enough to result in detection of the discontinuity. and pipeline operating conditions require the use of advanced FBE-based worldclass coatings to protect the pipe exterior. 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. in addition to effectively dictating the lifetime of the pipeline.R. Damage Tolerant Fusion Bonded Epoxy Coating D. History. J. Thus. storage. and capacity upgrades. As the times and exposure conditions have changed. INTRODUCTION Corrosion is a global problem. which may occur on the job site. TX 78726 USA ABSTRACT A novel technique has been developed which significantly improves the damage tolerance of epoxy coated components in a variety of corrosive environments. pumping energy. heat curable. and a tough. FBE coatings have been in use since 1960 to protect pipelines from corrosion. Background.A High Performance. FBE coatings have offered an effective solution to these problems for nearly 40 years. consuming three to four percent of gross national product in the developed countries of the world. 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. FBE coatings have evolved as well. increased levels of carbon dioxide (CO2) and other factors contribute to a pipeline environment that increases levels of internal corrosion. It is a material that utilizes heat to melt and adhere to a metal substrate. installation. Corrosion protection is essential to prevent leaks. fire and explosion. Guilbert 3M Company Corrosion Protection Products Dept. environmental disasters. thermosetting epoxy resin powder. personal injury. Austin. the corrosion prevention system also significantly influences the pipelines operational costs such as general maintenance. C. 3 . improved field application technology provides comparablequality same-system coatings for the girth weld. Enos. Furthermore.G. smooth finish resistant to abrasion and chemicals.[1] Selecting economical and effective techniques for minimizing the effects of corrosion is a critical design decision for pipeline systems. The quality of the protective coating is thereby maintained. and corrosion protective linings and coatings. they represent only a small fraction of the overall long-term cost of a pipeline system. FBEs have been formulated to operate in these very harsh service environments. Hydrogen sulfide (H2S).A. Today. More demanding transportation. and Advantages of FBE Linings and Coatings An FBE is a one part. Although these protective measures are critical. despite minor damage. There are many possible solutions to these problems including use of corrosion resistant alloys. In addition. excellent adhesion. this improved corrosion performance enhances cathodic disbondment (CD) performance while the impact resistance and flexibility of the fusion-bonded epoxy (FBE) coating are unaffected. 3M Austin Technical Center 6801 River Place Blvd. inhibitors. It provides a coating with no trapped solvents. service disruption and costly maintenance. It is estimated that over sixty thousand miles (ninety-five thousand kilometers) of FBE coated pipelines are installed around the world. Kehr. instead of trying to prevent it. hard FBE coating provides reduced friction compared to uncoated or concrete-lined pipe. are encapsulated within a seamless. and water pipeline industries. FBE provides a thinner lining than competing materials such as concrete. considerably larger quantities of the fill material may be added to a coating without adversely affecting its properties. 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. and the coating remains structurally sound. More recently. Unfortunately. and fittings in water districts for both water and sewer systems in California for nearly thirty years. with coating on over two hundred thousand square meters [6]. it has been used in sour crude pipelines [4]. this coating is considerably more damage tolerant than traditional FBE coatings. the material to be encapsulated. irrespective of the pipe coating condition. 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 []. It has been applied 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. The solution to this problem is seemingly quite simple: if the FBE coated pipe is treated properly. What follows is a brief description of the coating technology under evaluation. it has protected drinking water pipework since 1978. enabling smaller pipe sizes and reduced bulk and weight during handling and installation of pipe. FBE has been used in high-sand-content seawater cooling pipework for ten years and is still in excellent condition. microcapsules are between 5 µm to 200 µm (0. This results in more efficient flow. or the abuse level. or is the result of rock damage occurring during backfill [7]. Specific formulations meet the drinking-water requirements in many countries. Nevertheless. and. The smooth. As a result. Similarly. along with promising preliminary results. defects caused by mishandling or misuse of the coated pipe significantly reduce it’s ability to provide the superior corrosion protection required for many applications. pH. and even more difficult to verify. once encapsulated. Fill materials may be either aqueous or non-aqueous in nature. Microencapsulation is a technique through which liquid materials.g. impact. and lower-installed pump or compressor investment. Policing jobsites and preventing the use of questionable construction practices is problematic at best.2 mils to 8 mils) in size with wall thicknesses on the order of 1 µm to 2 µm (0. the type of damage which is causing the problems discussed above is nearly impossible to avoid. liquid-based fill materials behave as a solid. The mechanical damage which weakens conventional coatings instead ruptures the microcapsules which in turn “heal” the FBE coating. Damage Tolerant FBE Coatings Although FBE coatings are extremely effective corrosion protection materials in a wide variety of environments. design the coating to survive it with much of its corrosion-preventive properties intact. A wide variety of shell wall materials are available – the appropriate choice is determined by a combination of the application. It has been used on valves. It is better to assume that damage to the coating is inevitable. What is important to note is that. FBE is the favored primary coating for three-layer polyolefin corrosion coatings. As illustrated below. solid shell. In the water industry. In general. where it has been in use since 1979. or solution chemistry). it still needs to get the job done—preventing the onset of corrosion and subsequent structural problems. In this study. solving both erosion-corrosion problems as well as general corrosion [5]. gas. the potential savings are over four million dollars in compressor equipment cost and an annual energy savings of about a million dollars.04 mils to 0. Through the addition of microencapsulated materials. Coating damage frequently occurs during the handling and installation of a pipeline.08 mils). their overall effectiveness is still closely tied to the quality of the applied coating. reduced energy costs. preserving its barrier properties. the pipeline should readily meet or exceed its design life.. Using the six percent figure on an eight-hundred mile (thirteen-hundred kilometer). pumps. and the desired stimulus to rupture the capsule (e. preventing rock damage during backfill is nearly impossible. 4 . In the UK. In addition to its use as a stand-alone exterior coating. DN 750 (NPS 30) pipeline with a discharge pressure of 140 kPa (960 psig) and a compressor station every eighty miles (one-hundred-thirty kilometers). As with nearly all barrier coatings. a self-healing FBE coating has been designed. It is in use protecting brine-pit piping systems. such a coating is pursued. such as oils.FBE is currently specified in the oil. An example of microencapsulated oil is presented in Figure 1. preserving the protective benefits of the FBE. This damage may be the result of an impact to the coating. Coating thickness was verified using a magnetic thickness gauge. Also illustrated in Figure 2 is the manner in which the coating is designed to function. releasing their fill and locally discoloring the coating (e. In this example. The microcapsules contain approximately 80% active fill. However. etc. Although placing the microcapsules in the primer layer is the simplest embodiment of this coating concept. only very limited concentrations of a liquid additive may be added before the powder begins to clump and hinder application. and coated in the topcoat bed. the dye capsules would rupture. Microcapsule containing coatings were produced by first depositing a primer layer 150 µm (6 mils) in thickness which consisted of 85% unmodified FBE + 15% microcapsules. Upon damage. Once damaged. in the case of a powder coating such as an FBE. it is not the only one. The coating will behave the same as a traditional FBE until it has been subjected to mechanical damage. a series of different microcapsules could be envisioned. then grit blasted to a near-white metal finish in accordance with NACE No. the fill material reseals the coating and prevents the onset of corrosion. In the topcoat. consisting essentially of combinations of corrosion inhibiting materials and sealants. where large additions of an inhibitor may hinder cure of the coating or degrade physical properties. A two-step coating was accomplished by first dipping the sample into the primer bed. each serving a different purpose. Control samples were coated with 400 µm (16 mils) in a single coating operation. the coating consists of two layers. after which they were coated via a fluidized bed system. as illustrated in Figure 2. The two layers were applied sequentially (i. EXPERIMENTAL METHODS Coating Composition and Preparation Prior to coating.2/SSPC-SP 10.As an example. large concentrations of the inhibitor may be added with little or no detrimental effect on the handling or application of the coating material. If that same liquid is encapsulated prior to addition to the powder. In addition. suppose a liquid inhibitor has been demonstrated to effectively halt corrosion of the metal to be coated. ensuring their delivery directly to the metal surface. flexible FBE. mild steel bars were degreased in 2-butanone (MEK) and isopropanol.. or the topcoat. turn a green coating red). the microcapsules release their protective fill. Figure 3 illustrates a coating that has microencapsulated additions in both the topcoat and the primer layer. easing the identification of damage sites along the pipe for later repair with appropriate patch materials. The coating formulator then makes the decision that the inhibitor should be added to the current coating formulation. a series of modified coatings were formulated and produced. The epoxy matrix of the primer layer is an unmodified. The FBE coatings investigated in this study were based on a flexible fusion bonded epoxy resin. they are able to deliver their protective fill directly to the regions near the metal surface where they are needed. their purpose being to reseal the damage site and hold in place the inhibitive materials released from the primer layer. Once released. is composed entirely of an unmodified FBE. More details on the actual formulation may be found below in the Experimental Methods section. after which the sample was immediately transferred to. microcracking of the coating during bending on the job site. no additional preheating). By placing the microcapsules close to the steel surface in the primer layer.. Each bar was preheated for 45 minutes to a temperature of 400°F (205°C).e. microcapsules containing a dye could also be incorporated into the topcoat. In this study. Samples were left in each fluidized bed for sufficient time to allow the coating to build to the desired thickness. As can be seen in the figure. A similar scenario holds for liquid-based coatings. and are approximately 50 µm (2 mils) in size. followed by a 250 µm (10 mils) top coat of unmodified FBE.g. capsules containing sealants could be used. The first layer is a primer layer containing the microcapsules. A variety of fill materials have been investigated. Electrochemical Testing 5 . Microcapsules containing corrosion inhibiting materials could be placed in the primer layer. The second layer of the coating. 44 VSCE for the CD experiments. RESULTS Cathodic Delamination Testing Cathodic delamination testing was performed for traditional FBE coated samples as well as for the microcapsule loaded coating. Figure 5 illustrates the typical results for the two coatings. The samples were then placed in the cell pictured in Figure 4. a saturated calomel reference electrode. electrochemical impedance spectroscopy was used to qualitatively evaluate changes occurring at the damage site. Corrosion initiation tests were conducted in mildly acidic. To further demonstrate the ability of the modified coating to provide increased protection.25 inch) defect in the center of a 11. samples were prepared as described above. samples were subjected to an impact of 80 in-lbs (9 Nm) with a 0. then placed into a pH 5. Next.2mm (0. All solutions were prepared using distilled water and reagent grade chemicals. This second time constant represents the newly sealed layer resulting from the ruptured microcapsules. Note the minor attack visible on the modified FBE coating as compared to the severe attack visible on the conventional coating.5% NaCl solution for 30 days. The cathodic delamination testing solution was made in accordance with ASTM G8 [8] and contained 1% each of sodium chloride. Electrochemical Impedance Spectroscopy. Upon completion of the test. Four replicates of both the control and microcapsule containing coatings were investigated. and about the open circuit potential for the impact-damaged samples. 3.). In the case of the modified FBE coated samples. Experiments were performed about a DC bias of –1. The perturbation frequency was scanned between 106 Hz and 1 mHz.38 inches) for the traditional FBE to 4.17 inches) for the capsule loaded coating. Throughout the testing. 3. rust blooms were observed within the damage site for all conventional FBE coated samples.5 inch) coated panel. Neither coating was discolored. the solution was added and the samples polarized for 30 days at –1. or observably swelled after the 30-day experiment. coated samples were damaged as discussed above and placed into a mildly acidic.5 wt% NaCl solution at 60°C (140°F). Inc. Cathodic Delamination (CD). 3. Four replicates of each coating were evaluated. A waveform of 25 mVRMS was used in all cases. There was very little variation among the four replicates of each coating. Samples were prepared by machining a 6 mm (0. On an area basis. Following coating. the samples were placed into a pH 5. and sodium sulfate.8mm (0.9-mm) diameter tup. no corrosion initiation was observed within the defect for two weeks. After 6 weeks. blistered. high chloride solution.44 V vs. Next. the delaminated area was reduced by 68%. periodic electrochemical impedance spectra were taken from each sample. Corrosion Initiation from a Damage Site To determine if the microencapsulated additions actually prevent the onset of corrosion.5 inch x 4. Impact Corrosion Testing. As can be seen in the figure. Four replicates of both the control and the capsule containing samples were investigated.4 cm x 11. aerated.Solution Preparation. the coating around the intentional holiday was removed with a knife and the delamination radius measured in accordance with ASTM G8. the delamination radius was reduced by 60% from 9. a second time constant is present in the case of the modified coating.4 cm (4. All experiments were conducted under software control via ZPlot (Scribner Associates. The sodium chloride solutions were first made to the desired concentration after which the pH was adjusted (via HCl) to 5. Figures 6 and 7 present a comparison of impedance data for the conventional and modified FBE coatings. more significant corrosion was visible on the 6 . Based on this information. it may be inferred that the modified coating is providing increased protection compared to the standard FBE coating. EIS testing was performed utilizing a PAR Model 273A Potentiostat in combination with a Solartron 1255 FRA and two PAR Model 314 Multiplexers. Periodic electrochemical impedance spectroscopy (EIS) spectra were taken from each sample throughout the 30 days. As is clearly evident in the figures. While in the bath.625-inch (15. A holiday detector was utilized to verify that the coating had been disrupted and that bare metal was exposed. Throughout the time of the test it can be seen that the polarization resistance of the modified FBE coating remained significantly higher than that of the conventional FBE coating. Within a matter of hours. This is illustrated in Figures 8a and 8b. sodium carbonate.5 wt% sodium chloride solutions. no new technologies must be invested in and learned by applicators. The only change required is the addition of another 7 . This is in contrast to the typical procedures followed when using inhibitors. The system above alleviates many of the problems of using inhibitors – so. The microcapsule containing coating also provides additional benefits when used in conjunction with a cathodic protection system. These protective fill materials may include corrosion inhibiting materials as well as sealants for the coating. In other words. it is much more than that. Perhaps most important. modified FBE coating. electrochemical testing to determine if the microcapsules increase the corrosion resistance of a damaged coating revealed that the onset of corrosion was delayed considerably. one of the primary factors dictating operational cost and overall effectiveness is the total defect area present in the coating. DISCUSSION/SUMMARY To summarize. However. protection of the external surface of a pipe is possible. a protective material is delivered to and held in place at the steel surface within a damage site. the amount of cathodic protection current required to protect those areas increases – thus increasing the cost of operation. while very little of the material is wasted. Experiments were conducted on coatings containing a wide variety of microcapsule types and fill materials. When such a system is utilized. a significant improvement in performance was observed. the damaged coating is sealed. In addition. Although this approach appears to be simply the addition of corrosion inhibitors to a coating. such a coating will also reduce the cost and help maintain the effectiveness of a cathodic protection system as well. the effective throwing power of the CP system decreases. though. in an industry standard cathodic disbondment test. a coating could be produced that. 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. This self-healing characteristic is achieved through the use of microencapsulated additions that are positioned close to the metal/coating interface. there is no need to continuously augment the system with additional inhibitor. In the case of external protection of the pipe. due to IR drop. the corrosion of the conventionally coated sample was again more severe then the microcapsule containing. In addition. in addition to possessing the self-healing capabilities described above. as the overall cathodic protection current increases. In addition to the benefits described above. and the protective nature of the coating is preserved. since the inhibitor is confined to the coating. By maintaining a form that is handled in the same manner as conventional FBE coatings. Preliminary results for one of the more promising combinations were presented above.modified FBE coated sample. 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. the newly sealed layer formed by the ruptured microcapsules further enhances the performance of the patch. the entire stream must be treated. Another advantage of a modified FBE coating as presented above is its similarity in performance and handling to traditional FBE coatings. providing a more effective barrier to the external environment. a larger portion of the applied potential will be comprised of IR drop – unless compensated. In addition. This indicator would enable more efficient repair of damage areas via an appropriate patch material. In the particular example presented in this paper. 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. insufficient cathodic protection will be applied. The modified FBE coating may be applied via electrostatic spray or through a fluidized bed. the microcapsules are designed to rupture and release their protective fill when the FBE coating is subjected to mechanical damage. the modified FBE coating offers a number of advantages over similar corrosion prevention technologies. For example. As a result. When protecting the internals of a pipe system.e. through the use of dye capsules.. As was discussed previously. would positively indicate where damage occurred. Since the overall effect of the coating described above is to minimize the amount of damage experienced by the pipe. the use of inhibitors is typically not possible due to environmental concerns. As the total defect area increases. By sealing the inhibitive materials in place at the damage site. even though only that portion which is in contact with the steel needs to have inhibitor present – the remainder is waste). 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. a modified FBE coating has been presented which possesses an extraordinary self-healing ability. In addition to aiding the patch process. Since the coating behaves identically to a conventional FBE coating.series of spray guns in the existing equipment (this assumes. 8 . of course. that a multi-layer coating is applied). no new pipeline construction practices or procedures need be adopted. CONCLUSIONS In conclusion. Implementation of this technology will be facilitated by the fact that the same technologies are used in its application. 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. Upon being damaged in a manner that would compromise a conventional FBE. No new technologies must be mastered by coating applicators – the modified FBE can be readily applied with existing equipment and methods. releasing their protective chemistry. this coating reduces operation costs associated with the use of a CP system. The modified FBE coating presented in this study possesses superior resistance to cathodic delamination compared to conventional FBE coatings. increased maintenance requirements or expensive equipment that is subject to failure in the field does not accompany this increased resistance to corrosion. Unlike cathodic protection. The overall effect of this coating is the reduction of defect area on a coated pipe. the microcapsules are ruptured. the damaged FBE coating is healed. • 9 . in this study a robust FBE coating has been designed through the application of microencapsulated additions. retaining much of the protective properties that it possessed prior to damage. As a result. Since the cost to operate a CP system is a direct function of the defect area. 2. Moavin. “Corrosion Control Report: Internal Pipe Coatings are a Wise Investment.” Materials Performance.36.. REFERENCES 1. March 1993. 7. D. Thomas.” unpublished. 3. 1993. Jr. “Condition Evaluation of Reinforced Concrete Structures: A Case Study. “New Developments in Coatings for the Internal Protection of Water Industry Line Pipe. February 1982. 3 (1993). Rupert F.” Paper No. Ron E. Corrosion ‘95.” ASTM Standard G8-96. “Standard test Methods for Cathodic Disbonding of Pipeline Coatings. “Yates Field Crude Line Coated Internally. NACE National Corrosion Conference. D. “Fusion-Bonded Epoxy Pipe Coatings – 10 Years’ Experience...” Pipeline and Gas Journal. pp. “Fusion-Bonded Epoxy Coatings for Pipeline Corrosion Protection.” Pipeline and Gas Journal. 10 . Gray. Read. Langford.. 67-69. 4. Externally.. 32. 8. NACE 1992 Annual Corrosion Conference. 5. p.” 1981.. Carlson. 6. Norman. Vol. Islam.ACKNOWLEDGEMENTS The authors gratefully acknowledge the technical support provided by Susan Weiland and Stephen Daniell in the 3M Corrosion Protection Products Department. Paul.” Paper No. Strobel. 521. Dr. 27. No. “Internal Pipeline Corrosion Coatings Case Studies and Solutions Implemented. 3M Company publication. 11 .Figure 1: Micrograph of typical microcapsules containing a protective fill. FBE Damage Steel Self Healing Newly Sealed Layer Figure 2: Schematic illustrating the function of a single primer layer containing corrosion-preventative microencapsulated additions. Damage Steel Damage Indicator Self Healing.). etc. impact testing. CE RE Clamping System Acrylic Cell Body WE Defect O-Ring Seal Coated Sample 12 .e. Indicating Newly Sealed Layers Figure 3: Schematic illustrating the function of a coating in which both the primer and top layer contain microencapsulated additions.. primer provides corrosion inhibiting materials. By careful selection of the fill materials. Figure 4: Schematic of electrochemical cell used for the testing and evaluation of the FBE coated plates (i.g. the function of the top and bottom layers may be tailored (e. while the top layer provides materials which seal the damage site and possibly provide a visual indication of the damaged area. CD testing.. A B 13 .7 mm).44 VSCE for (a) unmodified FBE (9.2 mm) and (b) unmodified FBE with a 150 µm (6 mil) primer layer containing 15 wt% microencapsulated additions (4.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. Coating thickness was 350 µm (14 mils) in both cases. 5% NaCl Scotchkote 413SG Modified FBE 104 103 102 10-3 Imaginary Impedance (Capacitive) -55000 -40000 10-2 10-1 100 101 102 103 104 105 Frequency (Hz) -25000 -90 Phase Angle -65 -40 -15 10-3 10-2 10-1 100 101 102 Additional Time Constant -10000 0 15000 30000 45000 60000 103 104 105 Real Impedance (Resistive) Frequency (Hz) Figure 6: Typical EIS spectra for an unmodified FBE and the microcapsule containing material after 24 hours. 14 .-70000 105 Magnitude 24 Hours pH 5. Note the presence of an additional time constant indicative of the inhibitor film in the case of the microcapsule containing material. 3. Scotchkote 413SG Modified FBE -17500 105 Magnitude Imaginary Impedance (Capacitive) -15000 360 Hours pH 5. Modified FBE Note that the additional time constant is still present for the microcapsule containing material.5% NaCl Scotchkote 413SG Modified FBE 104 103 102 101 10-3 10-2 10-1 100 101 102 103 104 105 -12500 -10000 Frequency (Hz) -7500 -90 -5000 Phase Angle -75 -60 -45 -30 -15 0 10-3 10-2 10-1 100 101 102 103 104 105 -2500 Additional Time Constant 0 0 2500 5000 7500 10000 12500 15000 17500 Real Impedance (Resistive) Frequency (Hz) Scotchkote 413SG Figure 7: Typical EIS spectra for an unmodified FBE and the microcapsule containing material after 360 hours. 3. illustrating its persistence. Figure 8: Typical results for impact damaged coatings exposed in 60°C (140°F).5% NaCl solution for (a) an unmodified FBE and (b) a coating containing the microencapsulated materials. A Severe corrosion initiation B Minor corrosion initiation 15 . 3. pH 5. The microcapsules dramatically increased the time to corrosion initiation in this qualitative test (from 4 hours to nearly two weeks).
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