PAINT BASICS AND CORROSION IN METAL AIA103

Basic Composition of Paint

Solvents (Liquids) Pigments Additives Resins (Binder) 2

Prime Pigments

• •

Titanium Dioxide (TiO 2 )

•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.

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• • • •

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.

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Gloss/Sheen Levels

Term Gloss @ 60°

Flat 0-5 Velvet/Low Luster Eggshell 5-10 10-20 Low Sheen Semi-Gloss Gloss 20-30 55-70 75+

Sheen @ 85

0-5 5-15 15-25 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.

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Latex Resin Technology

LATEX (water-based) Synthetic polymers Main resins 100% Acrylic Styrene Acrylic Vinyl-Acrylic Acrylic Copolymer Vinyl Acetate Ethylene 8

Latex Resin Technology QUALITY Latex paint benefits include: * Ease of application * Yellowing resistance * Chalk resistance * Low odor * Color retention * Gloss retention * Washability * Durability * Good flow & leveling * Flexibility * Excellent adhesion * Improved adhesion * Scrub resistance * Water clean-up 9

Acrylic vs. Alkyd Paints Top left: Alkyd paint Top right: Vinyl-Acrylic paint Bottom left: Alkyd paint Bottom right: 100% acrylic paint 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.

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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.

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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.

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• • • • White Rust

Galvanized Metal

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.

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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

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1. Inadequate or incomplete project information 2. Lack of product knowledge 17

P R O J E C T I N F O R M A T I O N N E E D E D … … .

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CUSTOMER NEEDS DETERMINE COATING SYSTEM EVALUATE THE ENVIRONMENT DETERMINE SURFACE PREPARATION EVALUATE EXISTING SURFACE CONDITIONS EVALUATE SERVICE REQUIREMENTS

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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 ?

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Results of Pin Hole Rusting of the Primer

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What is the Environment?

• • • • • Type – P Type – M Type – C or Type – A 25

Type P: Protected Architectural

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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

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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

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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

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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 manufacturer’s 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.

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Factors Affecting Coating Performance

Protection

• • • Structural Design (We can’t control) Coating Selection Surface Preparation 35

A Poor Design

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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 37

THANK YOU

PROVIDER J476