PAINT BASICSAND

CORROSION IN METAL AIA103

Provider J476

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Basic Composition of Paint

Solvents (Liquids)

PigmentsAdditives

Resins (Binder)

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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.

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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

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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° Sheen @ 85

Flat 0-5 0-5

Velvet/Low Luster 5-10 5-15

Eggshell 10-20 15-25

Low Sheen 20-30

Semi-Gloss 55-70

Gloss 75+

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Alkyd Resin TechnologyALKYD (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 TechnologyLATEX (water-based)

Synthetic polymers

Main resins

- 100% Acrylic

- Styrene Acrylic

- Vinyl-Acrylic

- Acrylic Copolymer

- Vinyl Acetate Ethylene

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QUALITY Latex paint benefits include:

* Ease of application * Low odor

* Yellowing resistance * Color retention

* Chalk resistance * Gloss retention

* Washability * Durability

* Good flow & leveling * Flexibility

* Excellent adhesion * Scrub resistance

* Improved adhesion * Water clean-up

Latex Resin Technology

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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 paintTop right: Vinyl-Acrylic paintBottom left: Alkyd paintBottom right: 100% acrylic paint

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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.

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Premature Coating FailureDEFINITION:

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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• 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.

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.

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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.

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• Faulty Products 2 - 5%

• Unforeseen Circumstance 10-15%

• Improper Specification 25-30%

• Improper Prep/Application 45-55%

Causes Of Paint Film Failures (New )

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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

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PROJECT INFORMATIONPROJECT INFORMATION

NEEDED NEEDED…….…….

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DETERMINEDETERMINE COATING COATING SYSTEMSYSTEM

EVALUATE EVALUATE EXISTING SURFACE EXISTING SURFACE

CONDITIONSCONDITIONS

CUSTOMERCUSTOMERNEEDSNEEDS

CUSTOMERCUSTOMERNEEDSNEEDS

EVALUATEEVALUATETHETHE

ENVIRONMENTENVIRONMENT

EVALUATEEVALUATESERVICESERVICE

REQUIREMENTSREQUIREMENTS

DETERMINEDETERMINESURFACE SURFACE

PREPARATIONPREPARATION

DETERMINEDETERMINESURFACE SURFACE

PREPARATIONPREPARATION

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• Removing contamination

• Providing a surface profile

• Removing or smoothing irregularities(pits, projections, sharp edges)

• Removing tightly bound mill scale & rust

To provide a surface suitable for painting by:

What are the Goals of Surface Preparation?

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What Surfaces Require Preparation?

• Iron and Steel

• Galvanized Metal

• Aluminum

• Copper

• Miscellaneous metals

• Pre-Coated Metal Siding

• Previously Painted

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CORROSION !CORROSION !

HOW MUCH ?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

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Type P: Protected Architectural

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• Not subject to chemical contaminants

• Normal humidity range

• Normal industrial interior

• Corrosion of steel or galvanized surfaces negligible

Type P: Protected Architectural

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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 andgalvanized substrates negligible

• Concentrations of chemical interior – light to moderate fumes without humidity

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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

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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

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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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Surf

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Pre

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Desi

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Applic

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ProtectioProtectionn

Factors Affecting Coating Performance

• Structural Design(We can’t control)

• Coating Selection

• Surface Preparation

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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

THANK YOU

PROVIDER J476