PAINT BASICS AND CORROSION IN METAL AIA103 Basic Composition of Paint Solvents (Liquids) Pigments Additives Resins (Binder)
2 Prime Pigments Titanium Dioxide (TiO2) provides excellent hiding power and whiteness available as a solid (powder) or liquid (slurry) Zinc Oxide controls mildew resists ultra-violet light resists yellowing Titanium dioxide is the world's primary pigment for providing whiteness, brightness and
opacity. 3 Resins Types: Latex, Alkyd, Epoxy, Polyurethane Binds or glues ingredients (pigments and additives) of paint together Resin provides adhesion to the substrate Resin provides durability & resistance properties: U-V resistance Moisture resistance Chemical resistance
Stain resistance Fade resistance Chalk resistance Block resistance 4 Gloss/Sheen Levels Gloss or Sheen of paint refers to reflectivity or how shiny the dry paint film is. There is lack of standards and confusion in the paint industry related to gloss or sheen levels. Gloss is measured at 60 for flat to gloss ranges. Sheen is measures at 85 between flat to eggshell
Some paint manufacturers use different terms to define products between flat and semi-gloss: silk, suede, satin, velvet, eggshell, low sheen, low luster, pearl, etc. 5 Gloss/Sheen Levels Term Gloss @ 60 Sheen @ 85
75+ 6 Alkyd Resin Technology ALKYD (Oil-Based) A synthetic resin made by reacting alcohols and fatty acids Soya bean, linseed, tung-oil oil commonly used
Benefits of alkyds: - Superior brushing characteristics - Abrasion resistance - Excellent flow and leveling - Good adhesion - Used in rust preventative paint Alkyds have limited availability and use in California. 7
9 Acrylic vs. Alkyd Paints These paints have been exposed to the elements for 46 years. Over that time, the PVA (and the alkyd) paints have disintegrated. The 100% acrylic paint remains in remarkably good shape. The paint film is essentially intact, and, while it has chalked and faded, it retains its original green color.
Top left: Alkyd paint Top right: Vinyl-Acrylic paint Bottom left: Alkyd paint Bottom right: 100% acrylic paint 10 Acrylic vs. Alkyd Paints The paint on the left half of each board is acrylic, the paint on the right half, an alkyd. The colors of the paints were identical when applied. After 15 years of weathering, the
appearance of the alkyds has changed dramatically. All have lost gloss, faded, and chalked. The acrylic paints, in contrast, have proven remarkably durable with good color retention. 11 Premature Coating Failure DEFINITION: The deterioration of the coating system, or corrosion of the coated surface, more rapidly than would normally be expected under the service conditions.
12 Corrosion Simply put, corrosion is created when two dissimilar metals at atomic levels come into contact with each other and create a chemical reaction. The new compound is called oxide. In iron it is called Iron oxide. In aluminum, aluminum oxide and in copper, copper oxide. These metals will not rust or corrode unless a conductor between the two metals or atoms is present. Water or oxygen in contact with the metal for a longer period of time is
normally the conductor that starts the rusting or corrosion process. Salts in the water will accelerate the process. 13 Galvanized Metal White Rust Pure water (rain, dew, condensation) contain no dissolved salts or minerals.
Pure water will react with zinc hydroxide quickly to create white rust. Acid or acid rain, will accelerate the deterioration of the zinc finish. Passivators are a coating applied at time of manufacture to protect the zinc. 14 Causes Of Paint Film Failures (New )
Faulty Products 2 - 5% Unforeseen Circumstance 10-15% Improper Specification 25-30% Improper Prep/Application 45-55% 15 THERE ARE TWO (2) MAJOR CAUSES FOR IMPROPER COATING SPECIFICATIONS 16
1. Inadequate or incomplete project information 2. Lack of product knowledge 17 PROJECT INFORMATION NEEDED. 18 CUSTOMER CUSTOMER NEEDS
NEEDS DETERMINE COATING SYSTEM DETERMINE DETERMINE SURFACE SURFACE PREPARATION PREPARATION EVALUATE THE
ENVIRONMENT EVALUATE SERVICE REQUIREMENTS EVALUATE EXISTING SURFACE CONDITIONS 19 What are the Goals of Surface Preparation?
To provide a surface suitable for painting by: Removing contamination Providing a surface profile Removing or smoothing irregularities (pits, projections, sharp edges) Removing tightly bound mill scale & rust 20 What Surfaces Require Preparation? Iron and Steel Galvanized Metal Aluminum
Copper Miscellaneous metals Pre-Coated Metal Siding Previously Painted 21 CORROSION ! HOW MUCH ? 22 23
Results of Pin Hole Rusting of the Primer 24 What is the Environment? Type P Type M
Type C or Type A 25 Type P: Protected Architectural
26 Type P: Protected Architectural Not subject to chemical contaminants Normal humidity range
Normal industrial interior Corrosion of steel or galvanized surfaces negligible 27 Type M: Moderate 28 Type M: Moderate
Exterior weathering Normal industrial atmosphere Moderate concentrations of chemical fumes Corrosion of steel < 3 mils / year and galvanized substrates negligible Concentrations of chemical interior light to moderate fumes without humidity 29 Type C: Corrosive 30
Type C: Corrosive Moderately aggressive chemical fumes, mists or dust Corrosion of steel 3 - 6 mils / year and galvanized substrates < 1 mil per year Adjacent to Type A: but at least 30 yards away 31 Type A: Aggressively Corrosive 32 Type A: Aggressively Corrosive
Immersion service Excessive exposure to aggressive chemical fumes, mists dusts or contaminates Corrosion of steel > 6 mils / year and galvanized substrates > 1 mil per year
Usually confined to an area within 30 yards from corrosion source 33 Application Apply the coating system using one manufacturer Apply according to the manufacturers recommendations Apply to the Dry Film Thickness (DFT) as stated by the manufacturer
Recoat within the window specified by the manufacturer The finish system shall be a solid uniform finish free of voids and pinholes. 34 Factors Affecting Coating Performance Protectio n Structural Design (We cant control)
l p p A n o i t ica Surface Pre p.
Des ig n Surface Preparation g n i t a Co
Coating Selection 35 A Poor Design 36 Other Design Considerations Surfaces should be smooth (e.g. welds) Welding preferred to riveting All surfaces should be well drained Stiffening members should be on the outside surface of tank or vessel
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