CLEANING AND PAINTING OF STRUCTURAL STEEL

THE BASICS

CORROSIONWHAT - 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.

SURFACE PREPARATION Pre-Cleaning (removal of surface contaminants)

Cleaning

Profiling

SURFACE PREPARATIONWhy 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.

PRE CLEANINGAbnormalities STEEL Remove sharp edges, weld splatter

CONCRETE Patch, Caulk

PRE CLEANINGSurface 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

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

DEGREE OF CLEANILINESS SSPC SURFACE PREPARATION STANDARDS

SP1Solvent Cleaning SP2Hand Tool Cleaning SP3Power Tool Cleaning SP5White Metal Blast(NACE 1) SP6Commercial Blast(NACE 3) SP7Brush-Off Blast(NACE 4) SP10Near White Blast(NACE 2) SP12High and Ultrahigh(NACE 5) Pressure Water Jetting

Kinds of Abrasive

COPPER SLAG.

CONTAMINATED COPPER SLAG.

GARNET.

METALLIC GRIT

METALLIC SHOT

METALLIC GRIT AND SHOT MIX.

PROFILE(ANCHOR PATTERN)CORRECT

TOO DEEP

TOO ROUND

PROFILE(ANCHOR PATTERN)FOUR FACTORS DETERMINE THE SHAPE ANDDEPTH OF THE PROFILE OF BLASTED SURFACES

Size of the ParticleShape of the ParticleHardness of the ParticleVelocity of the Particle

PAINTINGSince freshly blasted surfaces are subjected to immediate corrosion, particularly areas of high humidity or salt atmospheres such as marine environments, no more surfaces shall be blast cleaned than can be primed coated before visible or detrimental re-rusting occurs. Blasted surfaces shall be prime coated no later than the end of the same workday.

PAINTINGOil, grease, salt deposits, soil dust or foreign matter deposited on the surface after surface preparation has been completed shall be removed prior to painting. If rusting occurs after completion of surface preparation, the surface shall be re-cleaned in accordance with the original method.Paint can be applied by one, or a combination of the following methods:1.Brushing2.Roller Coating3.Air Spraying4.Airless spraying5.Paint mitt ( for small-diameter piping and similar applications)The method of application shall be governed by the paint material Manufacturers recommendations for particular paint being applied. For general application techniques, requirements and precautions, SSPC PA1 shall be used as reference. A strip coat shall be applied to all welds, corners, and edges after the application of prime coat and before the next full coat. The strip coat shall be brushed or rolled.

PAINT DEFECTS

PAINT FAULTS, BITTINESSINCLUSIONS, EITHER AIRBORN OR FROM THE PAINT ITSELF. COULD BE PARTIALLY CURED PAINT, OUT OF SHELF LIFE.

COATING FAULTS BLEEDINGTHE SOLVENT FROM THE TOP COAT SOFTENS THE UNDER LYING MATERIAL AND ALLOWS IT TO PASS INTO AND THROUGH THE LAYER, CAUSING DISCOLOURATION. BROWN FOR BITUMEN, YELLOW FOR COAL TARS.

COATING FAULTS BLISTERINGBLISTERS CAN BE FILLED WITH GAS, LIQUID OR CRYSTALS

COATING FAULTS CHALKINGDEGRADATION OF A BINDER DUE TO DISRUPTIVE FACTORS IN THE ENVIRONMENT

COATING FAULTS CISSINGCAUSED BY INADEQUATE SURFACE PREPARATION.A DIFFERENCE IN SURFACE ENERGY CAUSES LOCAL LACK OF ADHESION.

COATING FAULTS CRACKINGCOATING AGE AND DIFFERENTIAL EXPANSION

COATING FAULTS CRATERINGBOWL SHAPED DEPRESSIONS. CAUSED BY ESCAPING SOLVENT OR GASES. PAINT IS OF TOO LOW A VISCOSITY TO FLOW AND FILL THE DEPRESSIONS

COATING FAULTS CURTAINS, SAGS, RUNS AND TEARSCAUSED BY OVER APPLICATION. REMOVE OFFENDING EXCESS MATERIAL, LIGHTLY ABRADE, RECOAT.

COATING FAULTS FLAKINGMATERIAL PROGRESSIVELY GETS BRITTLE WITH AGE, CRACKS AND BEGINS TO DETACH

COATING FAULTS HOLIDAYSDEFINED AS BEING :- A VOID, A MISS, OR AN UNCOATED AREA

COATING FAULTS LIFTINGCAUSED BY SOLVENT STRENGTH AND ALSO LACK OF OBSERVANCE OF STATED OVERCOATING TIME

ORANGE PEELSIMILAR APPEARANCE TO A CITRUS FRUIT SKINCAUSED BY PAINT VISCOSITY PROBLEMS OR BY APPLICATOR TECHNIQUE

COATING FAULTS ROPINESSBRUSHMARKS

Kinds of Testing

Holiday TestThe Holitech DC Holiday Detector tests and detects pinholes and flaws in insulated coatings on conductive substrates.Operation is by a test voltage being applied to the coating by moving a brush electrode across the surface and where there is either a pinhole or flaw, the voltage will spark through the coating, a red indicator will flash and an audible alarm will sound. The detected flaw can be marked for subsequent repair, and testing resumed for the remaining surface area.

DFTDry Film Thickness is a critical measurement in the coating application process. It provides vital information as to the expected life of the substrate, the products fitness for purpose, its appearance and ensures compliance with a host of International Standards.

Quality systems, such as those described in ISO 9000, ISO 17025 and Guide 25, require that gauges be properly controlled, logged and in calibration. Increasingly, users are specifying that the readings taken by gauges are traceable to National Standards.

DFTDigital coating thickness gauges are the most widely used due to their high level of accuracy and they can be used to measure the coating thickness on almost any substrate, whether ferrous or non-ferrous

ADHESION TESTTape TestThe X-cut tape test is primarily intended for use at job sites. Using a sharp razor blade, scalpel, knife or other cutting device, two cuts are made into the coating with a 30 45 degree angle between legs and down to the substrate which intersects to form an X. A steel or other hard metal straightedge is used to ensure straight cuts. Tape is placed on the center of the intersection of the cuts and then removed rapidly. The X-cut area is then inspected for removal of coating from the substrate or previous coating and rated.

Pull-Off TestA more quantitative test for adhesion is the pull-off test where a loading fixture, commonly called a dolly or stub, is affixed by an adhesive to a coating. By use of a portable pull-off adhesion tester, a load is increasingly applied to the surface until the dolly is pulled off. The force required to pull the dolly off or the force the dolly withstood, yields the tensile strength in pounds per square inch (psi) or mega Pascals (MPa). Failure will occur along the weakest plane within the system comprised of the dolly, adhesive, coating system, and substrate, and will be exposed by the fracture surface

Inspection Check PointsPre-Surface PreparationExamples of inspection check pointsContractor submittalsSurface preparation mediaCoatings materialsContainment and ventilationWaste managementSurface contaminationOil, grease and debrisSoluble salts

Post Surface PreparationExamples of inspection check pointsAmbient conditionsSurface preparation mediaRemoval of surface contaminationSurface cleanlinessSurface profileSurface imperfectionsWaste management

Coating ApplicationExamples of inspection check pointsCoatings materialsMixing, thinning and strainingAmbient conditionsWet film thicknessCoatings application defectsPerformed for each coating applied

Post Coating ApplicationExamples of inspection check pointsCoating thicknessAmbient conditionsRecoat window/free of contaminationPerformed for each coating applied

Post Curing of CoatingExamples of inspection check pointsCoating application defects (each coat)Dry film thickness (each coat)Pinhole/holiday detection (buried/immersion service)

Final InspectionExamples of inspection check pointsRepair and touch-upWaste removalSite restorationVerification of corrective action implementation