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C-1 APPENDIX C LITERATURE REVIEW REFERENCES AND SUMMARIES* No. References Comments R. Avery, "Application of Thermal This paper discusses the advantages of thermal spray coatings in comparison with conventional air dry coatings Sprayed Coatings in a Shop systems. Some of these advantages include resistance to mechanical damage, provisions for barrier and sacrificial 1 Environment Some Practical protection, low VOC emissions, and rapid turnaround. However, the author cautions that quality control, surface Considerations," SSPC International preparation, and operator training are necessary to provide superior long-term performance. Compared with air dry Conference, 1995. coatings, application of TSMCs is more cost competitive with respect to labor, material and schedule costs. This paper provides a general overview of the use of thermal spray coatings (zinc and aluminum) and sealers on steel. In waters where carbonate hardness is high, zinc is generally recommended. In waters where chloride content is high, aluminum is the recommended coating. In comparing combustion spraying versus electric arc spraying, the author J. C. Bailey, "Corrosion Protection of states that the latter provides application at higher deposition rates, hotter particles and higher coating adhesion 2 Welded Steel Structures by Metal strengths. The author notes that since the corrosion product of zinc coatings is often readily removed, they benefit Spraying," Metal Construction, 1983. greatly from the use of a sealer. The corrosion products of aluminum coatings, on the other hand, are generally more corrosion resistant and adherent and, thus, benefit less so than zinc coatings from the application of a sealer. Recommended sealers include vinyl chloride/acetate copolymers, phenolic resins, silicone modified alkyds, silicone resins or polymers, and, for higher temperatures, aluminum pigmented silicone resins. J. C. Bailey, F. C. Porter, and M. This paper discusses metal spraying of zinc and aluminum on bridges in the U.K. The authors conclude that zinc is 3 Round, "Metal Spraying of Zinc and preferable in alkaline conditions while aluminum is preferable in slightly acidic conditions and at high temperatures. Aluminum in the United Kingdom." This paper provides significant experimental data on the relationship between adhesion and surface profile: · Arc spraying of aluminum provides about 3x the bond strength to a steel substrate vs. flame spraying of zinc or aluminum, or arc spraying of zinc. Grit type also makes a large difference, with angular iron grit preferred over copper slag or silica sand. E. Bardal, "The Effect of Surface · This work was for low thickness coatings, 0.15 to 0.25 mm (9 mils). Preparation on the Adhesion of Arc and · Adhesion was found to increase with measured reflectivity, as compared to a standard light gray tile. This also Flame-Sprayed Aluminum and Zinc 4 Coatings to Mild Steel," Norwegian correlated to a degree with improving from a Sa 2 to 2 to a Sa 3 standard of cleanliness. Institute of Technology, University of · The paper also shows that cleanliness is not the only factor. Adhesion values also increase with Ra x n where Ra is Trondheim, Trondheim, Norway. the center-line average of roughness times the number of peaks, and also with an electrochemically determined value of total surface area. Ra is defined by (1/L)* integral (o to L) of y dx. N is the number of peaks in the profile length. The electrochemical principal is based on the assumption that Rp is a material constant in a passivating solution, thus differences in Rp will be related to different surface areas in contact with the electrolyte. Rp values are compared on blasted steel substrates vs. polished surfaces of the same material. V. Begon, J. Baudoin, and O. Dugne, This paper discusses the metallographic process, describing it as the primary way to evaluate thermally sprayed "Optimization of the Characterization coatings. The management and organization of a metallographic process is of prime importance to keep the process 5 of Thermal Spray Coatings," both repeatable and expedient. The paper defines a complete method for metallographic preparation based on a International Thermal Spray pragmatic approach. Conference, 2000. Alfred D. Beitelman, "Evaluation of The U.S. Army Corps of Engineers uses 85-15 zinc aluminum alloy arc-sprayed coatings on hydraulic structures Surface Preparation and Application exposed to corrosive environments. Premature failure of these coatings has been attributed to poor surface preparation 6 Parameters for Arc-Sprayed Metal and application procedures. This study evaluated various materials used for metallizing, specifically the effects of Coatings," USACERL Technical Report surface preparation and application parameters on adhesion, cavitation, erosion, porosity, and oxide content. 99/40, April 1999. This program evaluated the suitability of seven two-wire arc-spray systems to apply coatings of zinc, aluminum, 85-15 Zn-Al and 90-10 Al-Al2O3. The authors found that only three of the seven units tested were capable of continuously applying 85-15 Zn-Al. The average adhesion values, performed in accordance with ASTM D4541-93, for the combustion wire coatings of zinc, 85-15 Zn-Al, aluminum, and 90-10 Al-Al203 were 200, 435, 200, and 400 psi, respectively. The authors discuss some potential factors that may affect adhesion: Thomas Bernecki, "Final Report to U.S. · Unlike combustion, wire arc has no open flame to remove moisture and preheat the surface of the substrate. Army-CERL: Evaluation of Two-Wire 7 This may be factor in applications involving structures in water. Electric Arc Systems," February 26, · ASTM C633 is based on the measurement of normal forces. The presence and magnitude of a surface profile 1996. may affect the accuracy of the measurement. Also the porosity at the surface could also affect measured adhesion values. · Power settings define initial particle size and velocity. Stand-off distance can affect final impact velocities. Low velocities and/or large particles can result in lower temperature on impact, thereby affecting the splatting characteristics of the coating. This paper reviews the use of wire arc spray zinc vs. galvanizing on ski lifts. The authors discuss a case study in M. Bhursari and R. Mitchener, "Ski- which painted lifts required repainting every 3 years, hot dipped lifts showed signs of corrosion in fewer than 5 years Lift Maintenance: Wire Arc Spray vs. 8 and thermal sprayed ski lifts exhibited no corrosion after 5 years. It was estimated that the wire arc-spray zinc coating, Galvanizing," SSPC International depending upon the thickness, would have a life expectancy of 20 years with minimal maintenance. The authors Conference, 1998. concluded that thermal spray coatings were more resistant to abrasion and wear than thin galvanized coatings. This paper provides a brief compilation of information on thermal spray standards set by various professional M. M. Bhusari and R. A. Sulit, societies, including American Society for Testing and Measurement (ASTM), American Welding Society, American "Standards for the Thermal Spray 9 Water Works Association (AWWA), International Association of Corrosion Engineers (NACE), and Society of Industry," International Thermal Spray Protective Coatings (SSPC). These efforts have the ultimate objective of making the coating system performance Conference, 2000. more reliable and predictive. * References and Summaries not verified by TRB.
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C-2 No. References Comments This report presents the results of a 19-year study of the corrosion protection afforded by wire-flame-sprayed aluminum and zinc coatings applied to low carbon steel. The program was initiated in July, 1950 by the Committee on Metallizing (now the Committee on Thermal Spraying) of the American Welding Society. The first panels were exposed in January, 1953. This report presents the results of an inspection of the flame-sprayed coated steel panels made after all panels had been exposed for 19 years. J. Bland, "Corrosion Testing of Flame- Aluminum-sprayed coatings 0.003 in. to 0.006 in. (0.08 mm to 0.15 mm) thick, both sealed and unsealed, gave Sprayed Coated Steel 19 Year 10 complete base metal protection from corrosion in sea water and also in severe marine and industrial atmospheres. Report," American Welding Society, Where aluminum coatings showed damage such as chips or scrapes, corrosion did not progress, suggesting the Miami 1974. occurrence of galvanic protection. The use of flame-sprayed aluminum and zinc coatings is recommended as a means to extend the life of such iron and steel structures as bridges, highway or street light poles, marine piers or pilings, ship hulls, storage tanks, industrial structures, etc. Corrosion is thereby combated, and the natural resources needed in the manufacture of iron and steel are conserved. This paper discusses an exposure test of mild steel panels coated with wire-sprayed aluminum, powder-sprayed aluminum, wire-sprayed zinc, powder-sprayed zinc, hot-dipped aluminum, hot-dipped zinc, powder-sprayed 65 w/o Zn-35 w/o Al and electrodeposited 60 w/o Zn-40 w/o Fe. The five exposure sites used were located in rural, marine, and industrial environments. Metallographic examination revealed that the powder-sprayed coatings of aluminum and zinc were significantly more porous and less uniform than the wire-sprayed coatings. The powder-sprayed 65 w/o P. E. Bonner, "The Corrosion of Zinc, Zin-35 w/o Al coating was the least uniform of the sprayed-metal coatings, being of variable quality and somewhat 11 Zinc Alloy and Aluminum Coatings in discontinuous. After 6 months of exposure, the zinc-aluminum alloy coatings at all sites were in excellent condition the Atmosphere." and showed little corrosion product. Even after 2 years, only a few white areas of corrosion product were visible on some of the Zn-Al specimens. The paper goes on to discuss metallographic examinations of the coatings following these exposure tests. Pores were observed in the sprayed aluminum coatings where corrosion product was visible. A few pores were also observed in the sprayed zinc coatings, but with little or no corrosion product. Very few corrosion product filled pores were observed in the zinc-aluminum alloy coatings; however, some corrosion product was visible in some of the surface valleys when exposed to the more aggressive environments. This paper discusses case histories involving zinc thermal spray coatings. The author discusses advantages of TSMCs J. M. Brodar, "Blundering Towards over paint type coatings, including no cure time; durability; no VOC; and a single coating method for immersion, 12 Success with Metal Spray," SSPC atmospheric, and alternating wet and dry exposures. The author emphasizes the need for a high zinc-to-steel surface International Conference, 1995. area ratio in excess of 100,000:1 for freshwater immersion. This paper summarizes some metallizing applications for the maintenance and repair of the infrastructure and provides a general overview of metallizing technology. The authors provide data on aluminum and zinc spray rates and coverage of arc-spray machines, a comparison of vinyl and zinc metallized coating life cycle cost (LCC) to include maintenance interval, current cost and so forth, and applications. T. Call and R. A. Sulit, "Protecting the Thermal sprayed aluminum and zinc provide the long-term corrosion control coatings. However, its initial application Nation's Infrastructure with Thermal- is usually more expensive than painting or galvanizing if thermal spraying (metallizing) is not integrated into the 13 Sprayed Coatings," AWS International design and fabrication phases of new construction and repair projects. Aluminum and zinc metallized coatings are Welding Exposition. tough enough to withstand fabrication, transportation, and assembly operations. The improved capabilities and productivity of metallizing equipment for aluminum and zinc spraying are a major factor in their current cost competitiveness. The net result is that the costs of metallizing, paint, and galvanizing are getting closer every day. Even though the initial application cost of metallizing may be higher, the life cycle cost (LCC) and average equivalent annual costs are lower than paint coating systems. Metallizing LCCs, when properly engineered into the construction schedule, are equal to or less than paint coating LCCs. This book discusses corrosion and its control in marine environments. Topics discussed include forms of corrosion, K. A. Chandler, Marine and Offshore 14 material selection, coatings (paint and metallic), and steel pilings (although no discussion of metallic coatings on steel Corrosion, 1985. pilings). This is a brief technical paper outlining the performance features of thermal spray applied aluminum coatings. W. Cochran, "Thermally Sprayed Pertinent issues from this paper include the following: 15 Aluminum Coatings on Steel," Metal Coatings are applied to white metal substrates at 37 mils. Sealers are useful for cosmetic concerns, primarily to Progress, December 1982. reduce dirt build-up. TSA coatings have been used in freshwater supply systems by a Texas utility for over 25 years. This is a comprehensive document which attempts primarily to review the U.S. Navy's approach to the use of metallizing for corrosion control on Navy ships. The report does provide several major conclusions that seem meaningful with respect to the subject contract. · TSA coatings are known to be excellent corrosion control coatings for below-deck applications. However these coatings perform inconsistently on the weather deck. This is attributed to the lack of consistent application and Committee on Thermal Spray Coatings quality control, which is especially evident in the more harsh environments. for Corrosion Control, "Metallized · Long-term performance data for TSA materials are based on coatings applied using best practices with extensive Coatings for Corrosion Control of QA. It is not clear that the same level of QA is achieved in production applications. The report notes that there Naval Ship Structures and Components, 16 are not good NDT techniques available for finding critical defects such as excessive porosity, bond-separation, National Materials Advisory Board," local coating penetrations, and excessive oxide inclusions. This is where future research should focus. National Academy of Sciences, · Risk factors can be mitigated by the use of a good seal coat. These are especially good at mitigating porosity. Washington, D.C., Report NMAB-409, · The report suggests that TS pure aluminum is the best material for marine use. February 1983. · The report suggests that humidity and surface cleanliness during application are key and need to be carefully specified and controlled during material application. · While it is clearly understood that low bond strength of TSM reduces performance, high bond strength does not guarantee good performance. There is no demonstrated minimum acceptable bond strength to guarantee performance. This paper discusses the benefits of thermal spray coatings, as well as quality control parameters, surface preparation, T. Cunningham, "Quality Control of and application technique. The author concluded that while TSMCs have relatively high initial applied costs, they can Thermal Spray Coatings for Effective 17 provide economical long-term protection because of their long service life. Ideal coating characteristics include low Long-Term Performance," SSPC porosity, a smooth surface, closely controlled DFT, and good adhesion. Quality control measurements should International Conference, 1995. examine surface profile, film thickness, coating adhesion, and porosity.
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C-3 No. References Comments This paper describes specific experiences with TSA on offshore components: · Wellhead support structures SP-5, 12 mils TSA; little mechanical damage and a few blisters after 5 years of T. Cunningham and R. Avery, exposure. "Thermal Spray Aluminum for · Riser pipe 8 to 10 mils TSA plus 0.6 mil conventional sealer (aluminum pigmented silicone or thinned epoxy; 18 Corrosion Protection: Some Practical concern for overspray contamination in the weld bead). Experience in the Offshore Industry," · Flotation chambers Large structures (63 ft long) were coated with TSA applied by an automated process. SSPC International Conference, 1998. · Sealers traditionally either vinyl or aluminum pigmented silicone. Silicone exhibits superior performance, but is intended to be heat cured and is difficult to see. This paper summarizes findings on the performance of sealers on thermal spray coatings in offshore environments. Two thermal spray coating sealers are commonly used: aluminum-pigmented silicone (for high temperature T. Cunningham and R. Avery, "Sealer applications) and vinyl etch primer. While the performance of the silicone sealer is reportedly better than that of Coatings for Thermal Sprayed 19 vinyl, the aluminum silicone sealer is virtually invisible and requires heat cure. The lack of visibility causes Aluminum in the Offshore Industry," difficulties for sprayers and inspectors. Epoxy sealers are available in any color, but there is occasionally an adverse Materials Performance, January 2000. reaction to the visual appearance of a thin sealer. The authors recommend that the two-pack epoxy be thinned, suggesting that more than half of the applied materials should be thinner. The Research Division of the Connecticut Department of Transportation, sponsored by the FHWA, completed an 8- K. DuPlissie, "Lessons Learned of the year project to evaluate the performance of zinc-based coatings for abrasive blast-cleaned structural steel. This study I-95 Thermal Spray Project in concluded that 20 Connecticut," Fifth World Congress on · In order for the coating to adhere to a steel surface, an anchor tooth (jagged) surface profile is necessary. Coating Systems for Bridges and Steel · Performance of a bend test is important because Structures, 1997. 1. It enables adjustment of equipment to proper settings and proper techniques. 2. It allows the inspectors to test the blast and the coating prior to the actual application. This paper discusses the results for the first 8 years of a long-term evaluation of various coating and cathodic protection systems. These systems include nonmetallic coatings, metallic pigmented coatings, nonmetallic coatings on metal-filled coatings, nonmetallic coatings on metallic coatings, metallic coatings and cathodic protection on bare and coated piles. With 25 systems tested, the following conclusions were made: · Above the high-water line was the most corrosive zone on bare steel samples, on the order of 8 to 12 mils per year; some pitting was visible above and below the mudline. · Coal tar epoxy coatings exhibited severe damage below the water line due to sand impingement; general attack and some undercutting were visible in the atmospheric zone; undercutting resistance was improved in the tidal E. Escalante, W. P. Iverson, W. F. zone, but general attack was still visible; coatings were susceptible to mechanical damage during installation. Gerhold, B. T. Sanderson, and R. L. · Electrochemical measurements indicated that phenolic mastic and polyester glass flake exhibited good resistance Alumbaugh, "Corrosion and Protection to deterioration; the phenolic mastic was good over the entire surface of the pile after 6 years of exposure little 21 of Steel Piles in a Natural Seawater pitting in the erosion zone, maximum corrosion rate of 0.15 mpy just below the mean high-water line, moderate Environment," Institution for Materials undercutting in the atmospheric zone with a maximum penetration of 1 in., some coating failure at the flange Research, National Bureau of edge; the polyester glass flake, with an average coating thickness of 32 mils, exhibited minor pitting, little coating Standards, June, 1977. breakdown, difficult to remove coating by sandblasting, minor deterioration at the flange edges in the erosion zone, little damage in the atmospheric or splash zones, and undercutting of up to 1 in. in the atmospheric zone. · Polyvinylidene chloride, when compared with phenolic mastic and polyester glass flake, exhibited a significantly higher degree of deterioration corrosion rate of 5 mpy in the erosion zone, average corrosion rate of 2.4 mpy over entire pile, considerable deterioration in the atmospheric zone, undercutting of up to 0.3 in. in the tidal zone and 2 in. below the mudline. · Aluminum pigmented coal tar epoxy exhibited high electrical resistivity, very little deterioration, some coating damage in the erosion zone with a corrosion rate of less than 0.1 mpy, minor pitting over most of the pile, less than 1.2 in. of undercutting and some rust staining in the atmospheric zone, 0.1 in. of undercutting in the tidal zone, no undercutting or coating deterioration below the mudline; the aluminum pigmented coal tar epoxy system with a 30% thinner coating thickness exhibited more damage overall, little deterioration at the flange but some deterioration and pitting 2 to 3 in. from the edge, average corrosion rate of 0.2 mpy over the entire pile, undercutting of 1.5 in. in the atmospheric zone and as much as 2 in. below the mudline, and minor coating damage in the tidal zone. · Nonmetallic coatings on metal-filled coatings were also tested; coal tar epoxy over zinc rich organic primer performed well, exhibited an average corrosion rate of 0.2 mpy, severe coating damage with undercutting of almost 2 in. in the atmospheric zone, minor undercutting in the tidal zone, negligible damage below the mudline; epoxy polyamide over zinc rich inorganic primer exhibited good resistance with an average corrosion rate of less than 0.1 mpy, some deterioration in the erosion zone, negligible damage below the mudline, good undercutting resistance in all zones with less than 0.5 in. in the atmospheric zone, some blistering below the mudline; coal tar epoxy over zinc rich inorganic primer exhibited good resistance to deterioration, no metal loss near the flange, minor pitting, undercutting of 0.6 in. in the atmospheric zone, minor undercutting in the tidal zone, no measurable undercutting below the mudline; vinyl over zinc rich inorganic primer exhibited general attack over the pile length with more attack in the erosion zone, an average corrosion rate of 0.2 mpy, undercutting of less than 0.5 in. with some edge deterioration in the atmospheric zone, undercutting of less than 0.1 in. but extensive general deterioration in the tidal zone, undercutting of less than 0.1 in. below the mudline; vinyl mastic over zinc rich inorganic primer exhibited an average corrosion rate of less than 0.25 mpy, little attack and undercutting of less than 0.1 in. in the atmospheric zone, general deterioration with undercutting of less than 0.1 in. in the tidal zone, and undercutting of 0.2 in. with some blistering below the mudline. · Nonmetallic coatings on metallic coatings: vinyl sealer over flame-sprayed aluminum exhibited an average corrosion rate of less than 0.05 mpy, a small amount of metal loss in the erosion zone, practically insignificant pitting, excellent corrosion resistance in the atmospheric zone, visible general coating failure and immeasurable undercutting in the tidal zone, some coating deterioration below the mudline; polyvinylidene chloride over flame- sprayed zinc developed a nonconducting film over time which gradually improved the coating performance, exhibited an average corrosion rate of less than 0.1 mpy, little and uniform metal loss, minor scattered pitting, minor damage in a few areas in the atmospheric zone, significant blistering of the topcoat (but the zinc coating still provided protection) in the tidal zone; vinyl-red lead over flame-sprayed zinc exhibited the most deterioration of the three systems with the topcoat beginning to fail during the first year of exposure followed by the gradual deterioration of the zinc (the total coating thickness of this system was only 50% of that of the polyvinylidene chloride over zinc flame spray).
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C-4 No. References Comments zone, no undercutting or coating deterioration below the mudline; the aluminum pigmented coal tar epoxy system with a 30% thinner coating thickness exhibited more damage overall, little deterioration at the flange but some deterioration and pitting 2 to 3 in. from the edge, average corrosion rate of 0.2 mpy over the entire pile, undercutting of 1.5 in. in the atmospheric zone and as much as 2 in. below the mudline, and minor coating damage in the tidal zone. · Nonmetallic coatings on metal-filled coatings were also tested; coal tar epoxy over zinc rich organic primer performed well, exhibited an average corrosion rate of 0.2 mpy, severe coating damage with undercutting of almost 2 in. in the atmospheric zone, minor undercutting in the tidal zone, negligible damage below the mudline; epoxy polyamide over zinc rich inorganic primer exhibited good resistance with an average corrosion rate of less than 0.1 mpy, some deterioration in the erosion zone, negligible damage below the mudline, good undercutting resistance in all zones with less than 0.5 in. in the atmospheric zone, some blistering below the mudline; coal tar epoxy over zinc rich inorganic primer exhibited good resistance to deterioration, no metal loss near the flange, minor pitting, undercutting of 0.6 in. in the atmospheric zone, minor undercutting in the tidal zone, no measurable undercutting below the mudline; vinyl over zinc rich inorganic primer exhibited general attack over the pile length with more attack in the erosion zone, an average corrosion rate of 0.2 mpy, undercutting of less than 0.5 in. with some edge deterioration in the atmospheric zone, undercutting of less than 0.1 in. but extensive general deterioration in the tidal zone, undercutting of less than 0.1 in. below the mudline; vinyl mastic over zinc rich inorganic primer exhibited an average corrosion rate of less than 0.25 mpy, little attack and undercutting of less than 0.1 in. in the atmospheric zone, general deterioration with undercutting of less than 0.1 in. in the tidal zone, and undercutting of 0.2 in. with some blistering below the mudline. · Nonmetallic coatings on metallic coatings: vinyl sealer over flame-sprayed aluminum exhibited an average corrosion rate of less than 0.05 mpy, a small amount of metal loss in the erosion zone, practically insignificant pitting, excellent corrosion resistance in the atmospheric zone, visible general coating failure and immeasurable undercutting in the tidal zone, some coating deterioration below the mudline; polyvinylidene chloride over flame- sprayed zinc developed a nonconducting film over time which gradually improved the coating performance, exhibited an average corrosion rate of less than 0.1 mpy, little and uniform metal loss, minor scattered pitting, minor damage in a few areas in the atmospheric zone, significant blistering of the topcoat (but the zinc coating still provided protection) in the tidal zone; vinyl-red lead over flame-sprayed zinc exhibited the most deterioration of the three systems with the topcoat beginning to fail during the first year of exposure followed by the gradual deterioration of the zinc (the total coating thickness of this system was only 50% of that of the polyvinylidene chloride over zinc flame spray). · Metallic coatings: hot-dipped galvanized steel pile exhibited a decreasing corrosion current for the first 3 years of exposure followed by a steadily increasing corrosion current (approaching that of bare steel) for the next 5 years, exhibited an average corrosion rate of 0.15 mpy, significant corrosion in the erosion zone, some corrosion in the atmospheric zone, coating failure in the form of pits above the high-water line, pitting and undercutting in the tidal zone, thin and no coating below the mudline; flame-sprayed aluminum exhibited a steadily increasing corrosion current (approaching that of bare steel as the aluminun deteriorated), exhibited some metal loss in the erosion zone, virtually no pitting, minor corrosion damage in the atmospheric and tidal zones, and extensive coating damage below the mudline. · Cathodically protected steel piles: electrochemical measurements indicated corrosion rates much lower than similar piles without cathodic protection; in general, the anodes located below the mudline provided more protection than similar anodes above the mudline. This paper discusses the performance of thermal sprayed aluminum after 8 years of service on offshore TLP risers and Karl P. Fischer, William H. Thomason, tethers. The authors believe that a 30-year service life is achievable with a 200 micron TSA coating with the use of Trevor Rosbrook, and Jay Murali, specific sealer systems. The authors concluded that a silicone sealer adequately fills the pores of the TSA coating and 22 "Performance of Thermal Sprayed prevents the formation of blistering. After 8 years of service, the TSA coating on the Hutton TLP production risers Aluminum Coatings in the Splash Zone and tethers was in good condition. The splash zone area was indistinguishable from the remainder of the inspected and for Riser Service," NACE 1994. components. This paper studies the electrochemical behavior of flame-sprayed aluminum (FSA) coating in natural seawater. The authors concluded that FSA generally performs well in both the submerged and splash zone exposure, primarily as a K. P. Fischer, W. H. Thomason, J. E. very strong barrier-type coating. The free corrosion potential of the FSA coating in strongly flowing seawater was Finnegan, "Electrochemical 930 to 950 mV vs. Ag-AgCl at ambient temperature. The authors claim that the use of a silicone sealer paint on the Performance of Flame-Sprayed 23 FSA coating will increase the service life of the system. An FSA coating with silicon sealer paint will have some Aluminum Coatings on Steel in reduced anodic capabilities, yielding a current density output of 30 to 200 mA/m2 in a potential range of 950 to 850 Seawater," Materials Performance, mV. For FSA coating without sealer, the current output can be up to 500 mA/m2 in an initial exposure period. September 1987. However, at a high constant current density, the aluminum coating will be consumed during a few months of exposure. This article provides an introduction to the uses of thermal sprayed metal coatings as corrosion protection for steel, as an alternative to paint coatings. Arc spray, when compared with flame spray, has been shown to give faster output and superior adhesion. Flame spray may be favorable in areas that are difficult to access. Aluminum and aluminum alloys are used and an alloy with 5% magnesium is currently widely specified, although Fitzsimons is not convinced it provides the best protection offshore. Aluminum-5% magnesium is highly efficient for offshore platforms and ship topsides, where the anodic advantages of the metal are shown. Although experience has Brendan Fitzsimons, "Thermal Spray shown that sealers are of benefit on exposed aluminum coatings, areas not exposed to driving rain (e.g., undersides of Metal Coatings for Corrosion 24 platforms and bridges) may be better left unsealed to reduce the effect of "sweating" or condensation. Protection," Corrosion Management, December 1995/January 1996. Sprayed aluminum has been shown to be effective against corrosion under insulation, which might have become wet due to leakage of rainwater through the weather cover. Thermally sprayed aluminum works well on plant operating at elevated temperatures, coated with epoxy sealers for use up to 120°C and with a silicone aluminum sealer above that temperature. Fitzsimons also discusses the advantages and disadvantages (cathodic vs. anodic, cost, adhesion, etc.) of different coatings (aluminum, zinc, tin, lead, etc.). M. Funahashi and W. T. Young, "Development of a New Sacrificial This interim report studies aluminum and zinc alloys as anodes to cathodically protected steel embedded in concrete. Cathodic Protection System for Steel 25 Laboratory studies indicated that a series of aluminum-zinc-indium alloys outperformed both pure zinc and pure Embedded in Concrete," Report aluminum as anodes. FHWA-RD-96-171, FHWA, Washington, DC, May 1997.
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C-5 No. References Comments This paper studies the performance of thermal spray (arc and flame spray) coatings of Al, AlMg, and ZnAl for 18 months in seawater. The arc-sprayed specimens exhibited better adhesion than the flame-sprayed specimens. The P. O. Gartland and T. G. Eggen, authors concluded the following: "Cathodic and Anodic Properties of · Al and AlMg were acceptable barrier coatings in combination with a sacrificial anode system. ZnAl exhibited 26 Thermal Sprayed Al- and Zn- Based blistering at low potentials and high corrosion rates at higher potentials. Coatings in Seawater," Corrosion 1990, · The use of a silicone sealer significantly improves the barrier properties of the thermal spray coatings. The Paper Number 367. corrosion rate at the free corrosion potential was reduced by a factor of two to three. At higher potentials, the corrosion rate is not affected. · Coating thickness and surface preparation had only a minor influence on coating properties. N. D. Greene, R. P. Long, J. Badinter and P. R. Kambala, "Corrosion of Steel This paper discusses case histories of pile corrosion, as well as theoretical and experimental analyses. The authors 27 Piles," Innovative Ideas for Controlling concluded that pile corrosion is the result of macrocell activity along the pile surface. Different oxygen concentrations the Decaying Infrastructure, NACE can lead to rapid localized corrosion. Paper No. 95017, 1995. This publication contains papers presented at the Second Symposium on Corrosion Testing in Natural Waters in 1995 in Norfolk, Virginia. Some of the papers include: · Ashok Kumar, Vicki L. Van Blaricum, Alfred Beitelman, and Jeffrey H. Boy, "Twenty Year Field Study of the Performance of Coatings in Seawater." Steel H piles were coated with various coatings including coal tar epoxy, Robert M. Kain and Walter T. Young, polyurethane and flame-sprayed zinc and aluminum. Electrochemical techniques (polarization resistance and Corrosion Testing in Natural Waters 28 Tafel plots) were periodically utilized. Long-term coating evaluation showed that flame-sprayed aluminum with a (Second Volume), ASTM Rep. No. STP topcoat sealer performed best at the cooler temperatures in Massachusetts waters (Buzzards Bay, Cape Cod) and 1300, 1997. polyester glass flake performed best in Florida waters (La Costa Island) · R. E. Melchers, "Modeling of Marine Corrosion of Steel Specimens." This paper proposes a conceptual model for immersion corrosion, tidal corrosion, and atmospheric corrosion for steel under marine conditions. Diffusion and kinetic theory are utilized in the development of phenomenological modeling. W. R. Kratochvil and E. Sampson, This paper discusses the deposition of two wire diameters (1/8" and 3/16"), three wire materials (Al, Zn/Al, and Zn) "High Output Arc Spraying Wire and and two spray rates (rated at 300A and 450A). The authors concluded that 3/16" wire, when compared with 1/8", 29 Equipment Selection," SSPC exhibits higher deposition rates and deposits over 60% more material for Al, 32% more for Zn/Al, and 34% more for International Conference, 1998. Zn. The stiffness of the thicker wire affects operator comfort, range of motion, and fatigue levels. S. Kuroda and M. Takemoto, "Ten Year Interim Report of Thermal The thermal spray committee of the Japan Association of Corrosion Control (JACC) has been conducting a corrosion Sprayed Zn, Al and Zn-Al Coatings test of thermal sprayed zinc, aluminum, and zinc-aluminum at a coastal area since 1985. Arc-spray and flame-spray Exposed to Marine Corrosion by Japan coatings were applied to steel piping at varied thicknesses and subjected to various post-spray treatments. No 30 Association of Corrosion Control," significant changes were observed in the coating systems after 5 years of exposure. After 7 years, zinc coatings with International Thermal Spray and without sealing exhibited degradation in the immersion zone. However, the aluminum and zinc-aluminum Conference, 2000. coatings still exhibited excellent corrosion resistance. The test is scheduled to continue until 2001. F. L. LaQue, Marine Corrosion Causes This book discusses the various mechanisms involved in marine corrosion. The author describes an experiment 31 and Prevention, 1975. involving continuous and isolated specimens in seawater to demonstrate the effects of macrocell corrosion. This paper evaluated flame and electric arc-sprayed coatings of zinc, aluminum, zinc-15 wt% aluminum and duplex layered coatings onto mild steel substrates. These systems were exposed to a variety of corrosive conditions in a 3.0 wt% sodium chloride solution and in natural sea water. The sprayed coatings were sealed with an epoxy polyamide to reduce surface porosity. Eric S. Lieberman, Clive R. Clayton, Electrochemical, salt spray, immersion, and adhesion tests were utilized to evaluate the coating systems. The authors and Herbert Herman, "Thermally- concluded that because of zinc's strong electrochemical activity, zinc does not afford as long-lasting protection as Sprayed Active Metal Coatings for does aluminum. Zinc-15 wt% aluminum, although electrochemically similar to zinc, provides barrier protection 32 Corrosion Protection in Marine similar to aluminum, while still maintaining zinc's degree of protection. The zinc-aluminum coatings exhibit strong Environments," Final Report to Naval corrosion protection, high adhesive strength, and a high coating density. A duplex-layered coating of aluminum Sea Systems Command, January 1984. sprayed onto zinc-coated steel proves to be effective in reducing crevice attack of the aluminum coating. Electric arc-sprayed deposits, when compared with flame-sprayed deposits, were less porous, exhibited higher adhesive strength and superior corrosion resistance. Studies on the microstructure of electric arc-sprayed coatings of different wire diameters revealed that as the wire diameter is decreased, a more dense coating will arise due to better atomization. R. T. R. McGrann, J. Kim, J. R. Thermal spray coatings are used for dimensional restoration of worn parts during aircraft overhaul. Residual stress, Shandley, E. F. Rybicki, and N. G. tensile bond strength, porosity, oxides, impurities, and hardness affect the performance of thermal sprayed parts. An Ingesten, "Characterization of Thermal understanding of the relation of these coating characteristics to process variables (material selection, spray process, 33 Spray Coatings Used for Dimensional spray angle, and coating thickness) is needed. The authors studied four nickel alloys applied by plasma spray and high Restoration," International Thermal velocity oxy-fuel (HVOF) using different spray angles and coating thickness ranges. The authors investigated how the Spray Conference, 2000. thermal spray process variables affect the thermal spray characteristics. This book discusses the use of protective coatings for corrosion control. One specific case that the book references is C. G. Munger, Corrosion Prevention by 34 the use of galvanizing and inorganic zinc in tidal seawater conditions. The galvanized test panels exhibited significant Protective Coatings, NACE, 1984. pinpoint rust, while the inorganic zinc-coated panels exhibited no visible corrosion after 2 years of exposure. P. Ostojic and C. Berndt, "The Variability in Strength of Thermally This paper shows the variation in tensile adhesion test data for TS coatings. The authors conclude that adhesion 35 Sprayed Coatings," National Thermal values based on the average of several tests are meaningless. The data seem to fit a standard Weibull distribution, and Spray Conference Proceedings, ASM thus such an analysis needs to be conducted to adequately characterize this critical QA parameter. International, September 1987, p. 175. Timothy D. Race, "Evaluation of Seven This study evaluated seven sealer systems for zinc and aluminum metallized coatings in fresh and salt waters. Sealer Systems for Metallized Zinc and Conclusions: 36 Aluminum Coatings in Fresh and Salt · For zinc in fresh and salt waters, recommend epoxy and epoxy with wash primer. Waters," Final Report for HQUSACE, · For aluminum in fresh water, recommend pigmented urethane or white pigmented vinyl. September 1992. · For aluminum in salt water, none of the tested sealers performed adequately.
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C-6 No. References Comments This paper evaluates metallized coating and sealer systems for highly abrasive environments. Four thermal spray materials were evaluated, including aluminum-bronze (89Cu, 10Al, 1Fe), stainless steel (18Cr, 8Ni), zinc-aluminum Tim Race, Vince Hock, and Al (85Zn, 15Al), and pure zinc. The authors concluded that coatings anodic to mild steel, such as 85-15 zinc-aluminum Beitelman, Performance of Selected 37 and pure zinc, are possible alternatives to conventional paint coatings for use in highly abrasive environments. Metallized Coatings and Sealers on However, a performance evaluation is required to establish the service lives of these materials. They also concluded Lock and Dam Facilities, August 1989. that coatings cathodic to mild steel, such as aluminum-bronze and stainless steel, are not recommended for such environments. This paper provides an overview of the variables that determine spray rate with the twin wire arc-spray process. A F. S. Rogers, "Benefits and Technology U.S. patent for spraying wire larger than 3.2 mm (1/8 inch) has resulted in surprising improvements in deposit Developed to Arc Spray 3/16 Inch (4.8 efficiency and spray rates. The authors also discuss some other design improvements, such as mm) Diameter Wires Used for 38 · a new innovative nozzle system that atomizes and distributes the spray into a desirable spray pattern, Corrosion Protection of Steel," · a new patented electrical design mastered arc starting by automatically gapping the wire at the end of each spray International Thermal Spray cycle, and Conference, 2000. · wire straighteners that prevent kinks and bends. F. S. Rogers and W. Gajcak, "Cost and Effectiveness of TSC Zinc, This paper discusses the advantages of 3/16" wire feedstock over 1/8". These advantages include higher spray rate at Zinc/Aluminum and Aluminum Using 39 lower amperages, better deposit efficiency, higher quality, lower labor costs, lower material cost, lower equipment High Deposition Low Energy Arc maintenance cost. Spray Machines," SSPC International Conference, 1997. This article reviews the in-service performance of FSA on subsea components of the Hutton Tension Leg Platform in T. Rosbrook, W. H. Thomason, J. D. the North Sea. While some blistering was observed after 2 years in service, the rate of consumption was not Byrd, "Flame Sprayed Aluminum excessive, and it was concluded that the coating would exceed the 20-year design life. The blisters were believed to 40 Coatings Used on Subsea be the result of inadequate sealing of the aluminum by the vinyl sealer. Although the silicone type sealer may not Components," Materials Performance, crosslink without a high temperature cure, it penetrates the porosity of the FSA and provides a good barrier to water September 1989. penetration. The authors recommend the use of chilled iron grit (grade C17/24) to overcome the possibility of contamination from the use of aluminum oxide abrasives. M. M. Salama and W. H. Thomason, "Evaluation of Aluminum Sprayed This paper discusses corrosion protection methods for offshore structural high-strength steel to avoid problems with 41 Coatings for Corrosion Protection of fatigue and hydrogen embrittlement. Offshore Structures," Society of Petroleum Engineers, 1984. E. R. Sampson and P. Sahoo, "New Arc The increasing use of arc-spray systems in the overhaul of aircraft engine components has created a demand for new Wire Approvals for Aircraft Power wire approvals. This paper discusses some historical background of the arc-spray process, materials that are presently 42 Plant Overhaul," International Thermal approved and those that have been submitted for approval. The paper discusses advances in arc-spray systems that Spray Conference, 2000. make them suitable replacements for plasma spray and HVOF coatings. This paper attempts to correlate analytical techniques to characterize the microstructures of thermal spray coatings to Brian S. Schorr, Kevin J. Stein, and understand in-service properties. The authors focus on cermet thermal spray coatings and show the breakdown of Arnold R. Marder, "Characterization of 43 carbides during spraying. This breakdown produces a mixture of oxides and various carbides. The authors also Thermal Spray Coatings," Materials reference other papers that discuss metallographic preparation and routine analysis of thermal spray coatings to avoid Characterization, 1999. erroneous porosity readings. This testing was designed to illustrate the marine performance of various thermal spray alloys. Pure zinc and aluminum were control materials. The Zinc-Aluminum alloys of interest were intended to be of nominal 85/15 (weight %) zinc-aluminum. These alloys were sprayed from either a pre-alloyed 85/15 mixture or via feeding controlled amounts of each material (a pseudo-alloy) during the thermal application. Key points include: · The 85/15 wt.% ratio provides for 32 vol.% of aluminum in the alloy. · The porosity levels in the pure aluminum coatings range from 5 to 15% vs. 5% for the zinc. The lower melting point for the zinc allowed for more material "flow" before freezing on the steel substrates. This higher liquid-time tends to reduce the material porosity. · There is a drastic difference in the material microstructure between the pseudo-alloy and the pre-alloyed materials. The average material grain size is drastically smaller with the pre-alloyed material. It consists of a fine dispersion of zinc-rich and aluminum-rich areas as opposed to the larger, distinct areas of zinc and aluminum in the pseudo- alloy. B. A. Shaw and P. J. Moran, · For the pseudo-alloy, there were wide variations in local material content and little true alloying in the matrix. "Characterization of the Corrosion Wight percentage variations ranged from 85% zinc/15% aluminum to 40% zinc/60% aluminum. 44 Behavior of Zinc-Aluminum Thermal · All of the coatings stilled showed areas of imbedded grit and voids extending to the substrate--details that must Spray Coatings," DTNSRDC/SME- be minimized in any thermal spray application. 84/107. · In seawater immersion, after 6 months, the panels with pure zinc had significantly less fouling than those coated with pure aluminum. · At 6 months of seawater immersion, the pseudo-alloy showed areas of inter-coat blistering, not at the coating- substrate interface. This appeared to be attributed to attack of the zinc material and protection of the aluminum material. This would be in accordance with the expected material passivation behavior. Chloride was found to have permeated to these sites. · For the pre-alloyed materials, the coatings started as whitish-silver materials and turned a charcoal gray. These coatings also exhibited flaking and blistering. Blisters as large as 5 mm were noted. Again, the blisters were within the coating, not at the substrate. Corrosion product was noted within the blisters. In atmospheric exposure, 2 of 15 panels showed some flaking of the thermal coating. With both exposure conditions, the attack does seem to occur along oxide layers. · For the electrochemical testing, materials were applied to both PTFE and 1018 steel substrates. There was little difference in material performance as a result of the substrate. For the aluminum, the Ecorr values stabilized at 800 mV ±50mV. For the zinc and the alloy materials, the potential was nominally in the range of 1.0 to 1.05 volts. All potentials are vs. SCE. Reported exposure periods are only 30 days. Anodic polarization data were obtained after 1-hour and 14-day immersion. After 14 days, the aluminum was found to be in a passive state. The zinc and zinc alloy materials were more active. Thus, at this time in the test, the aluminum would not be expected to provide much cathodic current vs. the zinc and zinc alloy materials.
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C-7 No. References Comments · The report conclusions of note include the following: (1) the pseudo-alloy provided the best overall protection-- on the basis of being able to provide current to bare steel areas at scribes, (2) the pre-alloyed 85:15 wire is not suitable for immersion service due to accelerated attack along the material oxide boundaries. This paper provides an evaluation of the corrosion behavior of zinc-15% aluminum pre-alloyed wire coating and zinc- aluminum pseudo alloy coating of approximately the same composition. This evaluation consisted of corrosion field B. A. Shaw and P. J. Moran, exposures, electrochemical testing, and coating characterization (optical microscopy, scanning electron microscopy, "Characterization of the Corrosion electron probe microanalysis and X-ray diffraction). After 6 months of atmospheric and splash and spray exposure, 45 Behavior of Zinc-Aluminum Thermal the pseudo alloy coatings provided the better overall corrosion performance. Zinc-aluminum (and aluminum-zinc) Spray Coatings," Corrosion 85, Paper coatings appear to be capable of combining the long-term protection provided by aluminum and the sacrificial No. 212. protection provided by zinc. However, in order to obtain long-term protection, an alloy with a more coherent aluminum rich phase than the zinc-15% aluminum pre-alloyed wire and a more even distribution of phases than the pseudo alloy coating is needed. H. D. Steffens and Dr. Ing, This paper evaluates the electrochemical behavior of zinc and aluminum thermal spray coatings in seawater and "Electrochemical Studies of Cathodic sulfuric acid. Adhesion tests indicated that the adhesion of aluminum was twice that of zinc. The authors concluded 46 Protection Against Corrosion by Means that electric arc spraying, compared with flame spraying, of aluminum was more economically sound and led to better of Sprayed Coatings." adhesion. Robert A. Sulit, Ted Call, and Dave This paper discusses the use of Duralcan 90/10 aluminum composite nonskid coating for AM-2 Mats which are Hubert, Arc-Sprayed Aluminum interlocking aluminum extrusions. The aluminum composite is composed of 90 vol% Al + 10 vol% Al2O3 (8 to 10 47 Composite Nonskid Coatings for AM-2 microns in diameter). The authors concluded that the Duralcan 90/10 nonskid coating, when compared with existing Landing Mats, June 1993. epoxy nonskid coating systems, exhibited superior wear resistance and a 30% less 20-year life cycle cost. R. A. Sulit, F. West, and S. L. Kullerd, This paper discusses the installation and operation of Corrosion-Control (CC) Shops in Navy Shore Intermediate "Wire Sprayed Aluminum Coating Maintenance Activities (SIMAs) to deliver wire sprayed aluminum (WSA) coating services. The Navy-specified 48 Services in a SIMA Corrosion-Control ambient temperature WSA coating system consists of an anchor tooth profile of 2 to 3 mils coated with 7 to 10 mils Shop," National Thermal Spray WSA, sealed with one thinned epoxy polyamide, two coats of epoxy polyamide barrier, and two coats of silicone Conference, September 1987. alkyd topcoats for a total thickness of 16 to 20 mils. Herbert E. Townsend, "Twenty Five This paper discusses the results from a long-term atmospheric corrosion test of steel sheets hot-dipped and coated with Year Corrosion Tests of 55% Al-Zn 49 various aluminum-zinc alloy compositions. The author concluded that coatings composed of at least 44.6% aluminum Alloy Coated Steel Sheet," Materials exhibited a longer service life than conventional galvanizing. Performance, April 1993. This paper discusses the use of zinc and aluminum coatings on offshore (both fresh and salt water) pilings. Trifel concluded that thermal diffusion zinc coatings outperform thermal spray zinc coatings with respect to adhesion and service life. Thermal diffusion zinc coatings are applied by covering the tubes with zinc powder and increasing Mark Trifel, "The Use of Metallic temperature to 680°F (360°C) for twelve hours. An average coating thickness of 4.7 mils (0.12 mm) is deposited on to 50 Protective Coatings in the Soviet the tubes. In splash zones, this coating has a service life greater than 17 years w/o sealer (25 to 30 years w/sealer). Union," News from the Field. The author also concluded that aluminum coatings provide more corrosion resistance than zinc and are well suited for river water immersion. Electric arc metallizing produces more heat than flame spray and improves the adhesion of the lining. A. Tsourous, "The Restoration of the This paper discusses the use of thermal spray zinc coating on an existing bridge superstructure. The project specified Historic Trenton Non-Toll Bridge an SP-10 surface preparation and a minimum DFT of 8 mils. Deposition efficiency was approximately 75%. The 51 Using Field Applied Thermal Spray material cost was $0.80 per ft2 and direct labor cost was approximately $4.32 per ft2. The author concluded that while Coatings," SSPC International application costs typically exceed those of traditional high-performance coating systems, metallizing's life cycle cost Conference, 1998. far outperforms most of these systems. D. J. Varacalle and D. P. Zeek, This paper studies twin wire electric arc spraying of 1/8" diameter Zn and 85:15 wt% Zn-Al wire and the suitability of "Corrosion Resistance of Zinc and such systems for anticorrosion applications. In general, the 85:15 wt% Zn-Al coating, when compared with Zn, 52 Zinc/Aluminum Alloy Coatings," SSPC exhibited higher bond strength, higher hardness, and higher deposition efficiency. The Zn coating exhibited higher International Conference, 1998. corrosion resistance (salt spray) and higher density. J. Wigren, "Grit-Blasting as Surface This is a general paper with several interesting conclusions: Preparation Before Plasma Spraying," · The paper focuses on TSA adhesion as a function of surface roughness parameters. 53 National Thermal Spray Conference · The research shows that excessive blasting and particle embedment are concerns. Proceedings, ASM International, · The paper concludes that the as-coated adhesion does not correlate with adhesion in service--as is the case with September 1987, p. 99. most coatings. American Welding Society References 180-page training manual discusses the results of a National Shipbuilding Research Program performed by Puget 54 Thermal Spray Manual, 1996. Sound Naval Shipyard. Covers the fundamentals of thermal spraying: sequencing the job, processes, safety, and so forth. Guide for the Protection of Steel with Thermal Sprayed Coatings of 30 pages provide a guide to select, plan, and control thermal sprayed coatings over steel. Discusses quality control 55 Aluminum and Zinc and their Alloys checkpoints, maintenance and repair, job control records, and operator certification. and Composites, 1993. Guide for Thermal Spray Operator 56 9 pages discuss recommended thermal spray operator qualification procedures. Qualification, 1992. Thermal Spraying: Practice, Theory 181 pages discuss thermal spraying and selection of suitable processes. Emphasis on practical shop and field 57 and Application, 1985. procedures. Other References Metals Handbook - Desk Edition, ASM 58 International, Materials Park, Ohio. NACE International Publication 1G194, "Splash Zone Maintenance Systems for 59 Marine Steel Structures," NACE International, Houston, TX, 1994. SSPC Volume I Good Painting Practice, Fourth Edition, Chapter 4.4 60 Thermal-Spray (Metallized) Coatings for Steel, SSPS: The Protective Coatings Society, Pittsburgh, PA.