Thermally Sprayed Metal Coatings to Protect Steel Pilings: Final Report and Guide (2004) / Chapter Skim
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From page 4... ...
Ideally, the alloy should have a very low self-corrosion rate and be an efficient and effective sacrificial anode. Aluminum TSMCs have been found to protect steel well under seawater immersion conditions (3)
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From page 5... ...
It was anticipated that the work plan would consist of laboratory tests designed to provide information to supplement the literature in the areas of surface preparation, sealers, and application parameters. Task 4 -- Interim Report The interim report presented the results of Tasks 1 through 3.
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From page 6... ...
. The lower corrosion rates in the immersed and intertidal zones are believed to be, in part, the result of the attachments of various organisms and marine growth.
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From page 7... ...
. Other studies have also concluded that macrocell corrosion is involved in the corrosion of steel in the tidal zone (25)
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From page 8... ...
The literature suggests corrosion rates of 0.13 mpy (3.3 µm/yr) for aluminum TSMC.
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From page 9... ...
Historically, appropriate sealer coats are often listed as reducing the tendency for these types of defects. Several thermal spray systems were reviewed for testing under this program.
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From page 10... ...
However, according to the AWS "Corrosion Test of Flame-Sprayed Coated Steel -- 19 Year Report," unlike aluminum, the service life of zinc thermal spray coatings is dependent on coating thickness (28)
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Figure 5 shows the complex test panel used in the corrosion testing. Aluminum TSMC Zinc TSMC Figure 3.
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This included visual Aluminum TSMC Zinc TSMC Figure 4. TSMC application at Corrpro's laboratory.
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TABLE 5 General test matrix TEST Testing Objective Th ic kn es s Pr of ile B en d ad he sio n Te ns ile ad he sio n Co rro sio n D ro p w ei gh t im pa ct M ic ro - st ru ct ur e Sealers X X X X X X X Abrasive mixes X X X X X X Spray parameters X X X X X Effect of steel hardness X X X X HSLA1 steel v. carbon steel X X2 Edge geometry effects X X X X Coating defects X X X Surface contamination X X X X 1 HSLA = high-strength, low-alloy.
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From page 14... ...
DFT measurements were made on samples after preparation and cure (after cooling for TSMC samples and a minimum of 7 days after sealer coats were applied)
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From page 15... ...
Adhesion is commonly used to monitor coating quality. MIL-STD-2138A specifies that a "good" aluminum TSMC should have a minimum adhesion strength of 1,500 psi (10.3 MPa)
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From page 16... ...
Corrosion Tests Laboratory tests consisting of alternate wet-dry seawater exposure and constant immersion were performed to evaluate Figure 8. Pneumatic adhesion test apparatus.
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From page 17... ...
The test methods used for these evaluations are presented in Table 8. For analytical purposes, the ASTM D714 rating is converted to a composite blistering rating.
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From page 18... ...
This cycle was used to simulate the tidal action of natural waters, which can accelerate the corrosion of structures with their wet-dry cyclic actions. This test was conducted in the same tank used for constant immersion, with test samples placed just above this environment.
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From page 19... ...
Adhesion Comparison of tensile adhesion strength with each of the five sealers tested showed similar ranges as those observed for aluminum and zinc TSMC samples applied over a 100-percent grit-blasted substrate. However, the primary failure location for the sealed samples varied from substrate to adhesive failures.
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From page 20... ...
Chemical indicator solutions are easily employed and can be implemented in field evaluations, but the reaction of the sodium hydroxide solution on the aluminum TSMC may prevent an accurate measurement of exposed metal. The data presented in Table 12 suggest that most sealers provided near complete coverage of the aluminum and zinc TSMCs, with the possible exception of Devoe 167 Preprime and Carboline Rustbond on the aluminum TSMC.
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From page 21... ...
Optically stimulated electron emission (OSEE) was tested to quantify the coverage of the sealer coats over aluminum and zinc TSMCs.
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From page 22... ...
The overall corrosion rating for unsealed zinc TSMC was 8, and the rating for unsealed aluminum TSMC was 9. Overall corrosion ratings for sealed aluminum and zinc TSMCs were 9 to10.
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From page 23... ...
Tensile adhesion of zinc TSMC versus abrasive mix (panels prepared by CSI, 1 psi = 6.89 KPa)
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From page 24... ...
Average values and 95-percent confidence ranges for RA, RY, RZ and RQ profilometer data on A36 panels prepared with different abrasive mixes (1 mil = 25.4 µm)
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From page 25... ...
Tensile adhesion for aluminum and zinc TSMCs on A36 steel versus abrasive mix and applicator (1 psi = 6.89 KPa)
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. Corrosion Tests Comparing Abrasive Mixes The aluminum TSMC in cyclic immersion tests appeared to be tolerant of the use of various shot/grit mixture ratios in the constant immersion test.
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From page 27... ...
(15.2–25.4 cm) Corrosion Tests Comparing Application Parameters The aluminum TSMC in constant immersion displayed a corrosion rating and composite blister rating of 10 for all of the application parameter variables.
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From page 28... ...
No discernable difference was observed in the adhesion of the zinc or aluminum TSMCs on A36 and Grade 50 samples prepared by grit, shot, or the mixtures tested. 29 Corrosion Tests Comparing Steel Hardness In the constant immersion tests, the overall corrosion ratings of both alloys were similar, differing by less that 1 unit for all of the abrasive mixes used.
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From page 29... ...
A panel coated with aluminum TSMC and a panel coated with zinc TSMC, each with equal areas exposed in an electrochemical test apparatus, were used for testing. In tests, the coated panel was coupled to freshly blasted Grade 36 and Grade 588 steel panels through individual wire connections.
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From page 30... ...
Sacrificial current flow monitoring has demonstrated that after 2 to 5 days in tests, a measurable sacrificial current is generated by both TSMC materials to protect the A36 and A588 bare steel panels. Current flow to these samples is mar31 ginally reduced for A588 steel compared with A36 steel, suggesting that this more corrosion-resistant alloy requires less sacrificial protection.
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From page 31... ...
Galvanic current, aluminum TSMC versus A588 steel.
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From page 32... ...
However, with the exception of the aluminum TSMC samples, no substrate corrosion was observed on these samples. Some substrate corrosion (red rust)
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From page 33... ...
The end of the chamfer can create a sharp corner, as this is where the relieved and flat edges meet. The observed reduction in the zinc TSMC is consistent with the observations on the chamfered edge of the aluminum TSMC.
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From page 34... ...
Figure 36. Zinc TSMC photomicrographs, rounded edge.
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From page 35... ...
Some corrosion of the holiday area has occurred on most samples, suggesting that such large defects are not fully protected by the exposed TSMC surface area. Similar to the constant immersion samples above, minimal deterioration of the TSMC on the cyclic immersion samples has been observed.
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From page 36... ...
In cyclic immersion tests, the aluminum TSMC had corrosion ratings of 9.3 at 5 µg/cm2 with a holiday, 7.7 at 5 µg/cm2 without a holiday, and 9 at 10 µg/cm2 with or without a holiday. The composite blister ratings for aluminum TSMC were 10 at 5 µg/cm2 with a holiday, 8.7 at 5 µg/cm2 without a holiday, 8.6 at 10 µg/cm2 with a holiday, and 10 at 10 µg/cm2 without a holiday.
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From page 37... ...
immersion panels with circular holidays after 6 months in test (zinc TSMC on left and aluminum TSMC on right)
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From page 38... ...
Zinc TSMC should be considered for areas where salt contamination is present because of its relative insensitivity to salts. Where aluminum must be used, the surface preparation should include provisions for thorough washing of the surface to remove chlorides.
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From page 39... ...
It is further recommended that the Tri-Society (AWS/NACE/SSPC) Thermal Spray Committee on Corrosion Protection of Steel be addressed to assist in the dissemination of the guide.
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From page 40... ...
2.3. The aluminum TSMC appeared to be insensitive to the abrasive mixes tested in this study based on the 12-month corrosion tests.
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From page 41... ...
42 9.2. Aluminum is more tolerant to chloride contamination than zinc TSMC in corrosion tests, showing better overall corrosion performance, but it has more tendency to blister.
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From page 42... ...
"The Effect of Surface Preparation on the Adhesion of Arc and Flame-Sprayed Aluminum and Zinc Coatings to Mild Steel." Norwegian Institute of Technology, University of Trondheim, Trondheim, Norway.
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From page 43... ...
Takemoto. "Ten Year Interim Report of Thermal Sprayed Zn, Al and Zn-Al Coatings Exposed to Marine Corrosion by Japan Association of Corrosion Control." Presented at the International Thermal Spray Conference, Montreal, 2000.
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From page 44... ...
October 1, 1998 ISO 14922-1 Thermal Spraying – Quality Requirements of Thermally Sprayed Structures Four parts discuss the quality requirements for thermal spraying for application by the manufacturers using the thermal spraying process for coating new parts, for repair and for maintenance. June 15, 1999 NACE Standard RP0287-95 Standard Recommended Practice, Field Measurement of Surface Profile of Abrasive Blast Cleaned Steel Surfaces Using a Replica Tape Provides a procedure to measure the surface profile of abrasive blast cleaned steel.
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From page 45... ...
2 Near-White Blast Cleaning A near-white blast cleaned surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter, except for staining. Staining shall be limited to no more than 5% of each unit area of surface.
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From page 46... ...
Properties and property determination of powders for thermal spraying include: • Sampling and sample splitting, • Chemical composition, • Particle size range, • Particle size distribution, • Manufacturing process and particle shape, June 1996 Swedish Standard • Apparent density, • Flow properties, • Microstructure, and • Determination of phases. Safety Standards for Metallizing Steel Structures STANDARD TITLE SCOPE DATE COMMENTS SSPC PA-3 A Guide to Safety in Coating Application This guide defines methods and practices which are most practical in maintaining safety during application of protective coatings on steel structures.
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From page 47... ...
U.S. Army COE Manual EM 1110-2-3401 SSPC SP-5 2.0- to 3.0-mil profile, depending on TSMC material and thickness Hard, dense, angular blast media such as aluminum oxide, iron oxide and angular steel grit
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From page 48... ...
B-2 TSMC Application STANDARD HOLDING PERIOD ENVIRONMENTAL CONDITIONS COATING THICKNESS SPRAY PARAMETERS ANSI/AWS C2.23-XX Typically within 6 hours of blasting, depending on environmental conditions 5°F above dew point Ref. AWS C2.18 below To be validated at each crew change with a bend test Draft #2 ANSI/AWS C2.18-XX SSPC CS 23.00A-XX NACE TPC #XA Typically within 6 hours of blasting, depending on environmental conditions 9°F above dew point For 10- to 20-year life in salt water immersion: Zinc – 14 to 16 mils Aluminum – 10 to 12 mils Zinc/Aluminum – 14 to 16 mils Several perpendicular overlapping passes EN 22063 Typically within 4 hours of blasting, depending on environmental conditions 5°F above dew point Varies Zinc – 2 to 10 mils Aluminum – 4 to 12 mils Zinc/Aluminum – 2 to 8 mils None specified ISO 2063 Shall not exceed 2 to 12 hours, depending on environmental conditions 5°F above dew point Varies Zinc – 6 to 14 mils Aluminum – 4 to 10 mils Zinc/Aluminum – at least 6 mils 2-ft square block pattern JIS H 8300 JIS H 8301 None specified None specified Varies Zinc – up to 12 mils Aluminum – up to 16 mils None specified MIL-STD-2138A(SH)
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From page 49... ...
ASTM C 633 EN 22063 Uniform without blisters or bare patches and free from non-adhering metal and defects Not specified None specified Grid test and tensile test ISO 2063 Uniform without blisters, bare patches, non-adhering metal and defects Not specified None specified Grid test, adhesive tape and/or tensile test JIS H 8300 JIS H 8301 Free from blisters, cracks and other harmful defects Zinc – not specified Aluminum – IAW JIS H 8663 None specified Zinc – IAW JIS H 8661 Aluminum – IAW JIS H 8663 MIL-STD-2138A(SH) Uniform appearance with surface defects limited to small nodules not greater than 0.025 in.
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From page 50... ...
or application of a paint system ISO 2063 Aggressive environments, such as industrial or marine PVB primers or paints with a single vinyl component; paints based on chlorinated rubber or epoxy systems JIS H 8300 JIS H 8301 Not specified None specified MIL-STD-2138A(SH) Not specified High temperature: heat resistant aluminum paint IAW TT-P-28 or equivalent seal coat Low temperature: MIL-P-24441 Polyester powder U.S.
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From page 51... ...
Maintenance and Repair STANDARD SURFACE PREP TSC/SEALER APPLICATION TOUCH-UP ANSI/AWS C2.23-XX Not specified Inspect and maintain on a periodic basis, before maintenance repair and recoating is required Not specified Draft #2 ANSI/AWS C2.18-XX SSPC CS 23.00A-XX NACE TPC #XA Solvent clean; scrape off loosely adherent paint; hand brush, abrasive brush blast, power tool and abrasive blast; feather and lightly abrade As specified Spray can degreasing and spray can painting may be used for temporary repairs EN 22063 Not specified Not specified Not specified ISO 2063 Not specified Not specified Not specified JIS H 8300 JIS H 8301 Not specified Not specified Not specified MIL-STD-2138A(SH) Solvent clean; scrape, brush, blast, abrade – depending on level of damage As specified Paint coating may be replaced when TSC facilities are unavailable U.S.
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From page 52... ...
In comparing combustion spraying versus electric arc spraying, the author states that the latter provides application at higher deposition rates, hotter particles and higher coating adhesion strengths. The author notes that since the corrosion product of zinc coatings is often readily removed, they benefit greatly from the use of a sealer.
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From page 53... ...
E Bonner, "The Corrosion of Zinc, Zinc Alloy and Aluminum Coatings in the Atmosphere." 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.
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From page 54... ...
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.
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From page 55... ...
• 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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From page 56... ...
ZnAl exhibited blistering at low potentials and high corrosion rates at higher potentials. • The use of a silicone sealer significantly improves the barrier properties of the thermal spray coatings.
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From page 57... ...
Diameter Wires Used for Corrosion Protection of Steel," International Thermal Spray Conference, 2000. This paper provides an overview of the variables that determine spray rate with the twin wire arc-spray process.
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From page 58... ...
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 temperature to 680°F (360°C)
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From page 59... ...
This paper discusses various methods to apply thermal spray coatings. Methods discussed include Union Carbide's D-gun and Stoody Deloro Stellite, Inc.'s JET KOTE II hypervelocity oxy-fuel (HVOF)
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From page 60... ...
This paper discusses the suitability of zinc and aluminum coatings, applied by a twin-wire arc process, for corrosion protection. The authors performed a sequential regression analysis to establish a relationship between process parameters (orifice diameter, gun pressure, current, and spray distance)
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