Paint Basics and Corrosion in Metal

7/28/2019 Paint Basics and Corrosion in Metal

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PAINT BASICSAND

CORROSION IN METALAIA103


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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 Oxidecontrols mildew

resists ultra-violet light

resists yellowing

Titanium dioxide is the world'sprimary pigment for providing

whiteness, brightness andopacity.


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Resins Types: Latex, Alkyd, Epoxy, Polyurethane

Binds or glues ingredients (pigments andadditives) of paint together

Resin provides adhesion to the substrate

Resin provides durability & resistanceproperties:U-V resistance

Moisture resistance

Chemical resistance

Stain resistanceFade resistance

Chalk resistance

Block resistance


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Gloss/Sheen Levels

Gloss or Sheen of paint refers to reflectivity or howshiny the dry paint film is.

There is lack of standards and confusion in the paintindustry related to gloss or sheen levels.

Gloss is measured at 60for flat to gloss ranges.

Sheen is measures at 85 between flat to eggshell

Some paint manufacturers use different terms todefine 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 5-15Eggshell 10-20 15-25

Low Sheen 20-30

Semi-Gloss 55-70

Gloss 75+


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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


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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 theelements for 46 years. Over that time,the PVA (and the alkyd) paints havedisintegrated.

The 100% acrylic paint remains in

remarkably good shape. The paintfilm is essentially intact, and, while ithas chalked and faded, it retains itsoriginal 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 theright half, an alkyd.

The colors of the paints wereidentical when applied. After 15years of weathering, the

appearance of the alkyds haschanged dramatically.

All have lost gloss, faded, andchalked. The acrylic paints, incontrast, 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 twometals or atoms is present.

Water or oxygen in contact with themetal for a longer period of time isnormally the conductor that starts

the rusting or corrosion process.Salts in the water will accelerate theprocess.

Corrosion Simply put, corrosion is created when two dissimilar metals at

atomic levels come into contact with each other and create achemical reaction. The new compound is called oxide. In iron itis called Iron oxide. In aluminum, aluminum oxide and incopper, copper oxide.


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Galvanized Metal White Rust

Pure water (rain, dew,condensation) contain nodissolved salts or minerals.Pure water will react with zinchydroxide quickly to create

white rust. Acid or acid rain, will accelerate

the deterioration of the zincfinish.

Passivators are a coating

applied at time of manufactureto 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 CAUSESFOR IMPROPER

COATING SPECIFICATIONS


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1. Inadequate or incomplete project

information

2. Lack of product knowledge


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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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DETERMINECOATINGSYSTEM

EVALUATEEXISTING SURFACE

CONDITIONS

CUSTOMERNEEDS

EVALUATETHE

ENVIRONMENT

EVALUATESERVICE

REQUIREMENTS

DETERMINESURFACE

PREPARATION


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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 !

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 chemicalcontaminants

Normal humidity range

Normal industrial interior

Corrosion of steel or galvanizedsurfaces 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 galvanizedsubstrates < 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 chemicalfumes, mists dusts or contaminates

Corrosion of steel > 6 mils / year andgalvanized substrates > 1 mil per year

Usually confined to anarea within 30 yards

from corrosion source


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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 ofvoids and pinholes.


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Protection

Factors Affecting Coating

Performance

Structural Design(We cant 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 oftank or vessel


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THANK YOU

PROVIDER J476

Documents

Paint Basics and Corrosion in Metal