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51 7 REPAIR AND MAINTENANCE 7.1 Introduction Deterioration and damage to the TSMC can occur under several circumstances, including damage during installation, impact by foreign objects, abrasion, and corrosion. Damage that occurs during installation should be identified by the inspector and repaired according to the specifications. Repair to installation damage can vary from complete replacement of the coating to minor touch-up depending on the extent of the damage. This section can be used for minor repairs as defined by the specification or agreement between the owner and applicator. Damage that occurs during service requires periodic inspection to identify the need to repair TSMC systems. 7.2 Assessment The first step in the repair of TSMCs is an assessment of the type of thermal spray coating system under evaluation and the nature of the damage or wear. Steps in assessing the need to repair a thermal spray coating system are listed below. 7.2.1 Identification of the Type of Thermal Spray and Sealer Material Originally Applied Historic records should be reviewed for information on the type of TSMC and sealer used as well as any previous repairs. Chemical analyses may also be used. The experienced observer may also be able to distinguish between the various types of thermally sprayed materials. 7.2.2 Identification and Documentation of the Type and Extent of Deterioration 188.8.131.52 Test methods for quantifying coating deterioration. The following test methods have visual standards for quantifying coating deterioration: · ASTM F1130, "Standard Practice for Inspecting the Coating of a Ship" (useful for standardizing the method of reporting the extent of corrosion and coating deterioration). · ASTM D610, "Test Method for Evaluating Degree of Rusting on Painted Steel Surfaces" (provides standard charts for quantifying the amount of rusting on a steel surface). · ASTM D3359, "Test Method for Measuring Adhesion by Tape Test." · ASTM D714, "Test Method for Evaluating Degree of Blistering of Paints." · ASTM D4214, "Test Method for Evaluating Degree of Chalking of Exterior Paint Films." · ASTM D660, "Test Method for Evaluating Degree of Checking of Exterior Paints." · ASTM D661, "Test Method for Evaluating Degree of Cracking of Exterior Paints." · ASTM D662, "Test Method for Evaluating Degree of Erosion of Exterior Paints" (a standardized reporting form should be developed and kept on file for the structure for future reference). 184.108.40.206 Identification of sealer defects. Sealer defects are difficult to identify unless a topcoat has been used. Sealer and topcoat defects include disbondment from the substrate, cracking,
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52 checking, and mechanical damage. These will expose the thermally sprayed metal to the environment, which can reduce its service life. Lesser defects include discoloration and chalking, which do not necessarily indicate that the substrate is exposed, but do indicate eventual exposure of the substrate. 220.127.116.11 Identification of defects in thermally sprayed metal. Defects in the thermally sprayed metal include worn coating (indicated by general or localized thickness reductions); coating oxidation (evident by the presence of a powdery residue on the coating surface); the presence of rust and bare steel; and cracked, blistered, and delaminated areas. 7.3 Determination of Repair and Recoat Intervals 7.3.1 TSMC The need to repair or replace the metal coating depends on how much corrosion the structure can tolerate, the type of corrosion that can be tolerated, and the corrosion rate of the structure in the environment. For example, pitting on a pile often can be tolerated because it does not affect the structural integrity of the structure. On the other hand, a pit in a sheet pile might not be acceptable since a perforation would affect the ability of the structure to hold back water. In that case, even small pits must be repaired quickly. The corrosion rate of the structure should be monitored at defects in the coating and repairs scheduled when it is determined that the amount of corrosion is threatening to reach the critical thickness. In a corrosive environment (e.g., seawater), repairs to the coating will have to be more frequent than in a less corrosive environment (e.g., freshwater). 7.3.2 Sealer and Topcoat One approach to determining the time to repair and recoat detailed in G. H. Brevoort, M F. Melampy, and K. R. Shields, "Updated Protective Coating Costs, Products, and Service Life," Materials Performance, February 1997, pp. 3951: Maintenance painting can take the following sequence: Action % Breakdown Occurrence Original coating Initially Spot touch-up and repair 510* 33% of expected life Maintenance repaint (spot prime and full coat) 510* 50% of expected life Full recoat 510* 100% of expected life * before active rusting of substrate 7.4 Repair Methods 7.4.1 Standards for Repair and Maintenance The American National Standards Institute (ANSI) and the American Welding Society (AWS) have published a standard for the repair and maintenance of TSMCs. The TSMC
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53 repair procedures used depend on the type and extent of degradation and the presence or absence of sealer and paint topcoats. ANSI/AWS C2.18-93, "Guide for the Protection of Steel with Thermal Sprayed Coatings of Aluminum and Zinc and Their Alloys and Composites," addresses the maintenance and repair of TSMCs. This section summarizes the types of repairs that might be encountered and the procedures available. 7.4.2 Repair Procedures 18.104.22.168 Increasing TSMC thickness. Unsealed TSMCs that are worn thin or that were applied to less than the specified thickness may be repaired by repreparing the surface and applying more metal. If the coating was recently applied, it may be possible to simply apply additional coating directly onto the original coating. If the coating is oxidized, the abrasive brush blast procedure should be used prior to application of additional TSMC material. 22.214.171.124 Repair of small (<1 ft2 [<0.1 m2]) damaged areas with steel substrate not exposed. Repair by solvent cleaning, scraping with a flexible blade tool, wire brushing, edge feathering, lightly sanding to abrade the cleaned areas, and sealing and painting. 126.96.36.199 Repair of large (>1 ft2 [>0.1 m2]) damaged areas with steel substrate not exposed. Repair by solvent cleaning, abrasive brush blasting, edge feathering, and sealing and painting. 188.8.131.52 Repair of TSMCs with steel substrate exposed. Either of two procedures may be used to repair TSMCs damaged to the extent that the steel substrate is exposed. One method uses a rapid "paint only" repair procedure that is useful in emergency situations, and the other utilizes a TSMC plus sealer and paint coats procedure that is far more durable. The emergency repair procedure should always be followed by the more permanent repair when conditions permit. 184.108.40.206.1 The rapid "paint only" repair procedure. The rapid "paint only" repair procedure includes solvent cleaning, scraping with a hard blade tool, power tool cleaning, edge feathering, sealing, and topcoating. 220.127.116.11.2 The thermal spray repair procedure. The thermal spray repair procedure includes solvent cleaning, scraping with a hard blade tool, abrasive blast cleaning to near white metal, edge feathering, TSMC application, sealing, and topcoating. 7.4.3 Description of Repair Procedure 18.104.22.168 Solvent cleaning. Grease and oil should be removed by solvent cleaning. The solvent may be applied by wiping, brushing, or spraying. The following cleaning solvents may be used: Super Hi-Flash Naphtha, Type I (ASTM D3734) and n-Butyl Alcohol (ASTM D304). Precautions should be taken to protect any parts that may be affected by the solvents, and all appropriate safety precautions must be taken. 22.214.171.124 Flexible-blade scrape to bonded TSMC. Use a 1-in. (25-mm) flexible-blade paint scraper to remove loose paint and TSMC around damaged or worn areas until the tightly adherent paint and TSMC is reached. Care should be taken not to gouge or further damage the TSMC.
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54 126.96.36.199 Hard-blade scrape to bonded TSMC. Use a hard-blade paint scraper to push the blade underneath the loose TSMC, and push and scrape away all loosely adherent paint and TSMC until reaching a well-bonded area. 188.8.131.52 Hand brush clean. Use a stiff hand-held stainless-steel or bristle brush to vigorously brush away loose debris. Power tools should not be used as they will polish the thermally sprayed coating and may wear through the thermally sprayed coating to the substrate. 184.108.40.206 Abrasive brush blast. Clean abrasive blasting media, such as fine mesh (3060) angular iron oxide grit or aluminum oxide, may be used to abrasive brush blast away loose paint. Use low enough blasting pressures to minimize abrasion and removal of thermal spray coating, but high enough pressure for reasonable paint and loose TSMC removal and the development of a sufficient anchor-tooth pattern for sealers and topcoat paints. 220.127.116.11 Power-tool cleaning per SSPC-SP-3. For power-tool cleaning, hand-held power cleaning tools (e.g., disc sander with 80-mesh abrasive paper and stainless steel rotary brushes) should be used, using light pressure to clean and roughen the surface for painting. Do not polish the surface smooth. 18.104.22.168 Abrasive blast to near-white-metal finish and 2.5-mil (63-µm) profile. The surface should be abrasively (or mechanically) blasted to a near-white-metal finish with a 2.5-mil (63-µm) profile. The blasting nozzle should be kept perpendicular ± 10 degrees to the work surface; angle blasting into the TSMC/steel bond line may debond the bonded TSMC from the substrate. 22.214.171.124 Feathering. A 2- to 3-in. (50- to 80-mm) border should be feathered into the undamaged paint and TSMC area. Feathering is the operation of tapering off the edge of a coating. 126.96.36.199 Light abrasion. The prepared surface and the feathered area around the exposed TSMC should be lightly abraded with sand/grit paper to provide a mechanical bonding surface for the sealer or sealer and topcoat. 188.8.131.52 TSMC application. The thermal spray repair metal should be the same as that originally applied. Flame sprayed coatings should be repaired only by the flame spray technique. Wire- arc spray has a greater energy (particle impact velocity and temperature) and may delaminate marginal flame sprayed coatings. Wire-arc sprayed coatings may be repaired using either wire-arc or flame spray. 184.108.40.206 Sealers and topcoats. Apply the sealer and/or topcoat using proper application techniques. 7.5 Quality Control Quality control provisions apply to the various repair procedures as detailed in the corresponding sections of the guide regarding · Ambient air conditions, · Surface temperature,
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55 · Surface cleanliness, · Surface profile, · Adhesion, · TSMC thickness, · Sealer thickness, and · Topcoat thickness.