Presentation on theme: "CLEANING AND PAINTING OF STRUCTURAL STEEL THE BASICS"— Presentation transcript:
1CLEANING AND PAINTING OF STRUCTURAL STEEL THE BASICS FRANK D. REA PCS, NACE
2CORROSIONWHAT - 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.
4BARRIER COATINGSProtection by preventing water, oxygen and electrolyte from coming in contact with the metal substrate.
5INHIBITIVE COATINGSSTOPContain chemicals which hinder the corrosion process. They react with the cathode, anode or other components (oxygen, electrolyte, acid).
64/1/2017SACRIFICIAL COATINGSProvide galvanic protection. They corrode (sacrifice) in preference to the substrate, providing electrons which reverses the corrosion cell and transforms anodes to cathodes.MENTION GALVANIZING
7THE INGREDIENTS OF PAINT VEHICLERESIN (non-volatile)SOLVENT (volatile)PIGMENTINHIBITIVESACRIFICIALOPACITY (HIDING)ADDITIVESA. VISCOSITYB. ANTI-FOAMING
8PAINTS ARE USUALLY DESCRIBED BY THE RESIN 4/1/2017PAINTS ARE USUALLY DESCRIBED BY THE RESINRESIN ESTABLISHES THE CHEMICAL AND PHYSICAL PROPERTIES OF THE PAINT.THE RESIN ESTABLISHES THE CHEMICAL AND PHYSICAL PROPERTIES OF THE PAINT.
9TYPES OF PAINTS BY RESIN ACRYLICS (Latex) B, IALKYDS B, IEPOXIES B, ICOAL TAR EPOXIES BEPOXY MASTICS BZINC RICHA. ORGANIC B, SB. INORGANIC B, S5. POLYURETHANES B, I, S
10INORGANIC 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 severeEnvironment resistance. Fast-drying. Can be used withouta topcoat. Applied properly can last more than 20 years.DISADVANTAGES: Requires a very clean, blasted surface;user unfriendly; difficult to topcoat (porous); high initialcost.
114/1/2017ALKYDSModified 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
12EPOXIESTwo-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.
13EPOXY MASTICS Higher solid version of epoxies with added pigment and less solvent. Aluminum epoxy mastic used as touch-upprimer, overcoat primer and in some cases a finish coat.ADVANTAGES: Very surface tolerant, can be applied tomarginally cleaned steel. Compatible with most coatings, low VOCs, durable, good adhesion.DISADVANTAGES: Pot limitation, overspray, chalk, lack of flexibility, topcoating problems (short recoat window)
14COAL TAR EPOXIES An epoxy which has been fortified with coal tar. Immersion service, sheet piling.ADVANTAGES: lower cost, improved waterresistance and greater film build.DISADVANTAGES: Become brittle in sunlight,pot life, toxic effects, high solvent content.
15POLYURETHANESAlso a two-component thermosetting coating. Consists of anisocyanate and a polyol. Aliphatic polyurethane used as finish coatof three coat inorganic zinc rich system.ADVANTAGES: Best gloss and color retention, protectsepoxy 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.
164/1/2017LATEX ACRYLICSEmulsion 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
17SURFACE PREPARATION (removal of surface contaminants) Cleaning Pre-Cleaning(removal of surface contaminants)CleaningProfiling
18SURFACE PREPARATION Why is it so important? Poor surface preparation is the most frequent cause of premature coatings failure.Surface preparation is themost expensive operationof a painting project.
20PRE – CLEANING Surface Contaminants TypesLoose RustLoose PaintSaltsDirt and DustOil and greaseChalkEfflorescence (cement only)Latence (cement only)Removal MethodsSolventsSteamPotable Pressurized Water
21CLEANING HAND TOOLS (Stainless Steel or Aluminum) POWER TOOLS VACUUM POWER TOOLSABRASIVE BLASTINGSANDRECYCLABLE STEEL SHOT AND GRITSLAG (Black Beauty)SPONGEWATER BLASTING OR JETTINGCHEMICAL STRIPPING
22DEGREE OF CLEANILINESS SSPC SURFACE PREPARATION STANDARDSSP1 Solvent CleaningSP2 Hand Tool CleaningSP3 Power Tool CleaningSP5 “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