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CLEANING AND PAINTING OF STRUCTURAL STEEL THE BASICS

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HOW electrons travel from a negative area (anode) of the metal to a positive ... SPONGE. WATER BLASTING OR JETTING. CHEMICAL STRIPPING. DEGREE OF CLEANILINESS ... – PowerPoint PPT presentation

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Title: CLEANING AND PAINTING OF STRUCTURAL STEEL THE BASICS


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
  1. BARRIER
  2. INHIBITIVE
  3. SACRIFICIAL
  4. 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
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.
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
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
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.
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
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.

17
SURFACE PREPARATION
  • 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
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