1. CLEANING AND PAINTING OF STRUCTURAL STEEL THE BASICS
FRANK D. REA PCS, NACE

2. CORROSION
WHAT - gradual destruction of a metal or alloy by chemical or electrochemical reaction.
WHY - metals are in an unstable state.
HOW – electrons travel from a negative area (anode) of the metal to a positive area (cathode) through an external conductive intermediate (electrolyte) and then returns to the anode through the metal itself to complete the corrosion cell.

3. PROTECTIVE COATINGS
BARRIER
INHIBITIVE
SACRIFICIAL
COMBINATION

4. BARRIER COATINGS
Protection by preventing water, oxygen and electrolyte from coming in contact with the metal substrate.

5. INHIBITIVE COATINGS
STOP
Contain chemicals which hinder the corrosion process. They react with the cathode, anode or other components (oxygen, electrolyte, acid).

6. 4/1/2017
SACRIFICIAL COATINGS
Provide galvanic protection. They corrode (sacrifice) in preference to the substrate, providing electrons which reverses the corrosion cell and transforms anodes to cathodes.
MENTION GALVANIZING

7. THE INGREDIENTS OF PAINT
VEHICLE
RESIN (non-volatile)
SOLVENT (volatile)
PIGMENT
INHIBITIVE
SACRIFICIAL
OPACITY (HIDING)
ADDITIVES
A. VISCOSITY
B. ANTI-FOAMING

8. PAINTS ARE USUALLY DESCRIBED BY THE RESIN
4/1/2017
PAINTS ARE USUALLY DESCRIBED BY THE RESIN
RESIN ESTABLISHES THE CHEMICAL AND PHYSICAL PROPERTIES OF THE PAINT.
THE RESIN ESTABLISHES THE CHEMICAL AND PHYSICAL PROPERTIES OF THE PAINT.

9. TYPES OF PAINTS BY RESIN
ACRYLICS (Latex) B, I
ALKYDS B, I
EPOXIES B, I
COAL TAR EPOXIES B
EPOXY MASTICS B
ZINC RICH
A. ORGANIC B, S
B. INORGANIC B, S
5. POLYURETHANES B, I, S

10. INORGANIC ZINC RICH (IOZ)
Solvent borne self-curing inorganic zinc rich ethyl silicate.
Used as a primer for steel, primarily in the fabrication shop.
ADVANTAGES: Excellent abrasion, heat and severe
Environment resistance. Fast-drying. Can be used without
a topcoat. Applied properly can last more than 20 years.
DISADVANTAGES: Requires a very clean, blasted surface;
user unfriendly; difficult to topcoat (porous); high initial
cost.

11. 4/1/2017
ALKYDS
Modified drying oil paints which include silicone alkyds, epoxy esters, uralkyds and oleoresinous phenolics. Machinery, touch up, dowel rod assemblies.
ADVANTAGES: User friendly, surface tolerant, expand and contract with substrate.
DISADVANTAGES: Can contain high amounts solvent, slow drying, tack. Only oleoresinous phenolics can be used in severe environments.
User friendly – one part, wet out

12. EPOXIES
Two-component thermosetting materials which cure chemically. Consist of a base and a curing agent (catalyst). FDOT uses polyamide epoxies as the intermediate coat in a three coat Inorganic Zinc system.
ADVANTAGES: Bond well to properly cleaned steel and concrete, very durable in most environments. Excellent barrier coating.
DISADVANTAGES: Pot life limitations, chalk (poor gloss and color retention), inflexible.

13. EPOXY MASTICS Higher solid version of epoxies with added pigment
and less solvent. Aluminum epoxy mastic used as touch-up
primer, overcoat primer and in some cases a finish coat.
ADVANTAGES: Very surface tolerant, can be applied to
marginally cleaned steel. Compatible with most coatings, low VOCs, durable, good adhesion.
DISADVANTAGES: Pot limitation, overspray, chalk, lack of flexibility, topcoating problems (short recoat window)

14. COAL TAR EPOXIES An epoxy which has been fortified with coal tar.
Immersion service, sheet piling.
ADVANTAGES: lower cost, improved water
resistance and greater film build.
DISADVANTAGES: Become brittle in sunlight,
pot life, toxic effects, high solvent content.

15. POLYURETHANES
Also a two-component thermosetting coating. Consists of an
isocyanate and a polyol. Aliphatic polyurethane used as finish coat
of three coat inorganic zinc rich system.
ADVANTAGES: Best gloss and color retention, protects
epoxy intermediate coat from UV, hard but flexible.
DISADVANTAGES: Highly toxic (need personal protection),
lose gloss when applied in high humidity, user unfriendly,
pot life limitation, more expensive than an epoxy.

16. 4/1/2017
LATEX ACRYLICS
Emulsion of resin in water used to coat wood, masonry, and steel. Cure by coalescence, leaving a semi-permeable coating which “breathes”. Intermediate and topcoats.
ADVANATAGES: Excellent flexibility, ease of overcoat and repair; and gloss/color retention. User friendly.
DISADVANTAGES: Poor immersion resistance, difficulty bonding to smooth surfaces. Can only be used when ambient temperature is above 50ºF.
User friendly – overspray, one-part

17. SURFACE PREPARATION (removal of surface contaminants) Cleaning
Pre-Cleaning
(removal of surface contaminants)
Cleaning
Profiling

18. SURFACE PREPARATION Why is it so important?
Poor surface preparation is the most frequent cause of premature coatings failure.
Surface preparation is the
most expensive operation
of a painting project.

19. PRE – CLEANING Abnormalities
STEEL
Remove sharp edges, weld splatter
CONCRETE
Patch, Caulk

20. PRE – CLEANING Surface Contaminants
Types
Loose Rust
Loose Paint
Salts
Dirt and Dust
Oil and grease
Chalk
Efflorescence (cement only)
Latence (cement only)
Removal Methods
Solvents
Steam
Potable Pressurized Water

21. CLEANING HAND TOOLS (Stainless Steel or Aluminum) POWER TOOLS
VACUUM POWER TOOLS
ABRASIVE BLASTING
SAND
RECYCLABLE STEEL SHOT AND GRIT
SLAG (Black Beauty)
SPONGE
WATER BLASTING OR JETTING
CHEMICAL STRIPPING

22. DEGREE OF CLEANILINESS
SSPC SURFACE PREPARATION STANDARDS
SP1 Solvent Cleaning
SP2 Hand Tool Cleaning
SP3 Power Tool Cleaning
SP5 “White Metal” Blast (NACE 1)
SP6 “Commercial” Blast (NACE 3)
SP7 “Brush-Off” Blast (NACE 4)
SP10 “Near White” Blast (NACE 2)
SP12 High and Ultrahigh (NACE 5)
Pressure Water Jetting

23. PROFILE (ANCHOR PATTERN)
CORRECT
TOO DEEP
TOO ROUND

24. PROFILE (ANCHOR PATTERN)
FOUR FACTORS DETERMINE THE SHAPE AND
DEPTH OF THE PROFILE OF BLASTED SURFACES
Size of the Particle
Shape of the Particle
Hardness of the Particle
Velocity of the Particle

25. SUMMARY CORROSION TYPE OF COATINGS DIFFERENT PAINTS
SURFACE PREPARATION