SCIENTIST PROTECTIVE COATINGS GROUP ... DESIGN AND TESTING By Dr . S. SYED AZIM SCIENTIST PROTECTIVE...

COATINGS DESIGN AND TESTING

By

Dr . S. SYED AZIMSCIENTIST

PROTECTIVE COATINGS GROUPCORROSION TESTING & EVALUATION DIVISION

CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTEKARAIKUDI-630 006

First Training Course on Surfaces, Coatings and Corrosion ProtectionIIM HRDC-KC, March 6&7, 2009, IIT Madras

MAJOR AREAS OFRESEARCH AND DEVELOPMENT

ElectrochemicalMaterialScience

Electrodics,Electrocatalysis

Electro Metallurgy

ElectrochemicalsOrganic & Inorganic

Batteriesand

Fuel Cells

CECRI

Industrial MetalFinishing

Centrefor

Education

ElectrochemicalInstrumentation

Corrosion Science andEngineering

PollutionControl


MAJOR AREAS OFRESEARCH AND DEVELOPMENT

Cathodic Protection Protective Coatings

Failure Analysis

Marine CorrosionAnd its Control

Concrete Corrosionand its Control

Corrosion Inhibition

Corrosion TestingAnd Monitoring

CORROSIONSCIENCE

ANDENGINEERING

Basic Aspects ofCorrosion

Corrosion Education Corrosion Map ofIndia


AGENDA

• Definition• Coating design• Surface Preparation• Coating specifications

- Steel Structures Testing & Evaluation


Corrosion of metals and alloys poses greatproblems from the point of view of conservation ofmetals, operational costs and pollution hazards.One of the most successful methods forcontrolling corrosion is by the application of paintcoatings.


A protective coating is a material composed of synthetic resins orinorganic silicate polymers which, when applied to a suitable su bstratewill provide a continuous coating, that will resist industrial o r marineenvironments. In order to provide corrosion protection, the pro tectivecoating must also.

1. Resist the transfer or penetration through the coating of ions f romsalts, which may contact the coating.

2. Resist the action of osmosis.

3. Expand and contact with underlying surface, and

4. Maintain a good appearance, even under extreme weather condition s.


Protection by coating mainly depends upon three factors

1. The material

2. Surface preparation and

3. Application

If any one of the three is weak, protection value isaffected to that extent


Impermeability

• The ideal impermeable coating should becompletely unaffected by the specificenvironment it is designed to block, be it mostcommonly humidity, water or any othercorrosive agent such as gases, ions orelectrons.

• The ideal impermeable coating should have ahigh dielectric constant and also have perfectadhesion to the underlying surface in order toavoid any entrapment of corrosive agents.


Inhibition• In contrast with coatings developed on the basis of

impermeability, inhibitive coatings function by reactingwith a certain environment to provide a protective filmor barrier on the metallic surface.

• The concept of adding an inhibitor to a primer has beenapplied to coatings of steel vessels since these vesselshave been first constructed.

• Such coatings were originally oil based and heavilyloaded with red lead.


Cathodically protective pigments• As with inhibition, cathodic protection in

coatings is mostly provided by additives in theprimer.

• The main function of these additives is to shiftthe potential of the environment to a lesscorrosive cathodic potential.

• Inorganic zinc based primers are goodexamples of this concept.


Surface Preparation Standards

National Association of Corrosion Engineers

(NACE)

Steel Structures Painting Council (SSPC)

Swedish Standards (Sa,St)


National Association of CorrosionEngineers (NACE)

NACE 1 White metal Blast Cleaning

NACE 2 Near- White Blast Cleaning

NACE 3 Commercial Blast Cleaning


Steel Structures Painting Council (SSPC)

SP-1 Solvent CleaningSP-2 Hand Tool CleaningSP-3 Power Tool CleaningSP-4 Flame CleaningSP-5 White Metal Blast CleaningSP-6 Commercial Blast CleaningSP-7 Brush-Off Blast CleaningSP-8 PicklingSP-9 Weathering Followed By Blast CleaningSP-10 Near-White Blast Cleaning


Swedish Standard (St,Sa)

St 2 Hand Tool CleaningSt 3 Power Tool CleaningSa 1 Brush-Off Blast CleaningSa 2 Commercial Blast CleaningSa 2 1/2 Near-White Blast CleaningSa 3 White Metal Blast Cleaning


Surface preparation in descending order ofeffectiveness

1. White Sandblast NACE # 1, SSPC SP 5 -63, SA-32. Near-White Sandblast NACE # 2, SSPC SP10 -63. SA 2.53. Commercial Blast NACE # 3, SSPC SP 6 -63, SA 24. Brush Blast NACE # 4, SSPC SP 7 -63, SA 15. Acid pickling SSPC SP 8-636. Flame Cleaning SSPC SP 4 -637. Power Tool Cleaning SSPC SP 3 -638. Chip &Hand Wire Brush SSPC SP 2 -639. Solvent Wipe SSPC SP 1-63

Each lower grade in the list allows greater amount of contaminat ion to be lefton the surface prior to the coating


Shot blasted steel surface


ANCHOR PATTERN OR SURFACEPROFILE

1. Surface texture of a metal, produced by abrasive blasting,to assist the adhesion of a coating, is called anchorpattern or surface profile.

2. Most paint systems, especially inorganic zinc coatings,require an anchor pattern-characterised by a surfaceroughness and a roughness profile to obtain properadhesion.

3. It is usually assessed by standardised comparator viz.Rugotest No.3 and Keane-Tator Surface ProfileComparator. Anchor pattern obtained depends on thetype of abrasive used for blasting.

4. Using fine sand of mesh size 80, maximum height ofprofile is found to be 35-37 microns whereas with ironshot of mesh size 14, it is found to be 90 microns


Inspection of surface preparation

Inspection of surface preparationincludes the following: ISO 8501•Cleanliness. Solvent cleaning to removesalt, oil, grease and dust/dirt•Evaluation of present condition (rustgrade)•Evaluation of surface (preparation gradeand roughness)•Remaining contamination acceptable?


Anchor Pattern• The anchor pattern or profile is extremely important to

protective coatings in that it provides for excellentcoating adhesion.

• Anchor pattern can be thought of as tiny peaks andvalleys in the substrate being blasted.

• The depth of these “valley’s” is determined by the size,type and hardiness of the abrasive being used; by theair pressure; and by the distance and angle of thenozzle to the surface.

• Too much anchor pattern wastes coating and allowssubstrate to show through; too little anchor patternreduces the bonding surface between the material andthe substrate.


General guidelines to achieve specific anchor patterns.Assumption is 90PSI nozzle pressure, 2 feet from surface

30-60 Jetmag, 16 garnet, 16aluminum oxide, 16 steel grit

3.0 Mil

30-60 Jetmag,36 garnet, 24aluminum oxide, 25 steel grit

2.5 Mil

32-B4 Jetmag, 36 garnet, 36aluminum oxide, 40 steel grit

2.0Mil


1.5 Mil


1 Mil

120/150 Jetmag, 100 garnet,120 aluminum oxide

0.5 Mil

BLAST MEDIAANCHOR PATTERN


Abrasive sizes vary and a tolerance of 10% should be maintained to expect these results


Coating Type Min. Sur. Pre.

Alkyd NACE # 3CoalTar Enamel NACE # 3Vinyl NACE # 2Chlo. Rub NACE # 2Epoxy NACE # 2CoalTar Epoxy NACE # 2Urethane NACE # 2Organic Zinc NACE # 2Inorganic Zinc NACE # 2

Minimum Surface Preparation Requirements


1. The purpose of coating application is to developa continuous highly adherent film with an eventhickness over the substrate.

2. To achieve this, various factors have to beconsidered such as type of coatings and weatherconditions, application methods etc.

3. It is advisable to avoid painting below 10 0C andabove 400C,

4. If the relative humidity is above 80%, during therainy weather and wind velocity is above 24km/hror else freezing will occur before the paint dries.


Application Methods

• Brush• Air Spray• Airless Spray• Hot Spray• Hot Airless Spray• Roller


Factors Affecting Application of Paint

• Temperature• Humidity• Cover• Damage• Thickness• Recoating


Fan too narrow for normal work.May be used for narrow areassuch as small angles

Fan too wide - edges causeover spray

Normal fan - Approximately 8”wide used for most sprayapplication. Hold gun within 10 ”


Method of application SQ.M

Brush 65Roller 120-260Air spray 200-600Airless spray 300-800

Area coverage per day


CONVENTIONAL Vs AIRLESS SPRAY

CONVENTIONAL AIRLESS SRAY

COVERAGE sq.m/day 400 -800 600 -1000

OVERSP RAY % 20 - 40 10 -15

PORTABILITY Fair Excellent

DIRECT DRIVES No YES

HOSES 2 Usually 2

MASKING Considerable Moderate

PENETRATION OF Fair Good

CORNERS & VOIDS

THINNING BEFORE SPRAY Usual Sometimes

FILM BUILD PER COAT Lower Higher

MOISTURE(Compressor ) Possible N one

PAINT CLOGGING Slight Possible


Main Ingredients for paint formulation

Polymer (Binder)PigmentSolventAdditives

Properties of the coatings can be changed bychanging ingredients.


PROTECTIVE COATING SYSTEM

Primer Undercoat Topcoat Finish coat


Primer

The primary function of a primer over steel is to providecorrosion protection. The primer is in direct contactwith the metal surface and must therefore provide a firmbond between the metal and the subsequent coats ofpaint. The primers may well be classified as follows onthe basis of the working principal.

a. Inert primer (primer containing only inert pigments)

b. Inhibitive primer (primer containing inhibitive pigments)

c. Galvanic primer (primers containing zinc or aluminum

pigment)


Undercoat

Undercoats are highly pigmented high build paints possessinghigh impermeability, which follow the primer and providenecessary ground for the finishing coat. In addition an underco atshould posses the following properties.

a. Fairly rapid set to avoid sagging and pulling away from sharpedges

b. Very high impermeability to ions, moisture and air

c. Good adhesion to primer and topcoat.


Top coat

The topcoat completes a paint scheme and serves as the first lin e of

defense against the corrosive environment whilst providing

decoration. At the same time, a good finish coat should offer

adequate protection and be capable of retaining its decorative e ffect

(measured in terms of color and gloss) for a long period. The t opcoat

also protects the entire paint scheme from UV degradation.


6

ROLE OF BINDERS

Alkyds - Can be used in mild atmospherePhenolics - Has got high electrical resistanceAcrylics - Has got good resistance against acids

and alkaliesEpoxies - good in very aggressive atmospheres

except strong acidsAliphaticPolyurethane - Very stable against ultra violet radiations.


Schematic representation of Tortuouspath formed by glass flakes


SEM OF TiO2 PIGMENT


SEM of glass flakes


Typical Protective Coating Specifications

Coat Material Thickness(mm)

PrimerEpoxy ZincPhosphate

75

Barrier Epoxy MIO 125

Finish Polyurethane 50


a) Conventional Epoxy specification


b) Zinc rich epoxy specification

Coat Material Thickness(mm)

Primer Epoxy Zinc Rich 40





COATINGS FOR MARINE STRUCTURES

Atmospheric zone

1. Vinyl system (3 to 4 coats) - 200 - 250 µm

2. Epoxy-zinc phosphate primerEpoxy -polyamide undercoat - 300 µmEpoxy-polyamide topcoat

3. Inorganic zinc silicate primerEpoxy polyamide undercoat - 325 µmEpoxy polyamide topcoat

4. Chlorinated rubber primerChlorinated rubber topcoat

- 250 - 300 µm

(Contd.,)First Training Course on Surfaces, Coatings and Corrosion ProtectionIIM HRDC-KC, March 6&7, 2009, IIT Madras

Splash zone:

1. Coaltar epoxy - 300 µm

2. Epoxy polyamide primerEpoxy polyamide topcoat

Underwater:

1. Epoxy polyamide -200 - 300µm

2. Epoxy coal tar - 400µm + Cathodic protection

3. Bitumen - 1 mm

- 300 µm


COATINGS FOR ACID ATMOSPHERE

1. In many plants it is a common thing to have acidsreleased to the atmosphere and also spillage ofacids.

2. The main points to be taken care of in this case isthat the binder should not be disintegrated whenreacted with acids.

3. Pigments used for paint formulations includingextenders should be non-reacting type.

4. If the acid concentration is comparatively high,special pigments are to be incorporated whichwould take care of the adverse reactions.


TYPES Types of Tanks TANKS Floating roof tanks

Storing volatile products

Crude, HSD, SK, MS, Naphtha.

Fixed roof tanks

Storing heavy products

FO, LSHS, VGO, Bitumen.

Floating cum fixed roof tanks

Storing volatile products with stringent quality.

ATF, JP5.

COATINGS FOR TANKS


COATING SYSTEM IN USE

ORDINARY EPOXY COATING. DFT APPLIED 200 to 300 MICRONS. LIFE 3 TO 4 YEARS. TANKS DECOMMISIONED AT INTERVALS OF

6 TO 8 YEARS.


Coatings for underground pipelines

1. Coal tar enamel

2. Polyethylene tapes- Manual/ Power drivenapplicators.

3. Fusion bonded Epoxy coatings

4. Three Layer Polyolefin coatings (PE/PP)


PrimerTop Coat

Oleoresinous Alkyd Silicon

e alkyd Vinyl Chlorinatedrubber

Epoxy(2 pack)

Coaltar

epoxyurethane

Oleoresinsc c c NR NR NR NR NR

AlkydC C C NR NR NR NR NR

Siliconealkyd

C C C NR NR NR NR NR

Phenolresin

C C C NR NR NR NR NR

VinylC C NR C C C C NR

Chlorinatedrubber

C C C C C NR NR NR

EpoxyNR NR NR C C C C C

Coal tarepoxy

NR NR NR NR NR C C NR

Zinc-richepoxy

NR NR NR NR C C C NR

Inorganiczinc

NR NR NR C C C NR NR

UrethaneNR NR NR NR NR NR NR C

Compatibility of Different Paints


TESTING ANDEVALUATION OF PAINTS


Evaluation Methods

• Wet film thickness (WFT)• Dry film thickness (DFT)• Hardness• Flexibility• Adhesion• Abrasion• Impact• Accelerated Tests• Electrochemical tests


Wet Film Wheels• Wet film Wheels consists of three circles.

• The central circle is of smaller diameter and iseccentric of the two outer circles.

• By rolling the gauge through a wet coating, thecenter disc eventually touches the film.

• This point on the scale indicates the thickness.

• If the volume to solids ratio of the coating is known,then the wet film thickness can be used to predictthe dry film thickness.


Wet Film Wheel

Various measurement ranges are available from 0 to 25 µm to 0 to 3000µm (0 to1mil - 0 to 40mils) are available


Dry film thickness (DFT) Many methods are used for DFT measurements.

They are destructive & non destructive

Magnetic thickness gauges are based on the principlethat the attractive force between a permanent magnetand magnetic metal is inversely proportional to thedistance between them.

The principal limitations are

(i) the film must not be indented by the load and

(ii) the film must not be tacky.


Dry film thickness (DFT) meter


Eddy-current thickness gage

1. Eddy-current thickness gage is designed tomeasure the thickness of non -conductive coatingson non-ferrous substrates.

2. A probe coil energized by an alternating currentinduces eddy current creates an opposingalternating magnetic field in the substrate thatmodifies the electrical characteristics of the coil.

3. The magnitude of these changes is influenced bythe proximity of the substrate, that is, by thethickness of the coating, and is registered on thegage meter.


Hardness and related Properties

Organic coating hardness is difficult to define. Theformulations of the coatings are so designed as toimpart a certain amount of flexibility and elasticity.

In this context, the hardness can only be defined asthe film to indentation or scratching or damping.

A number of methods and instruments are availablebut the common methods are scratch by a pointedtip, using pendulum-rocker type instruments, usingindentor.


Scratch hardness (ASTM B-7027-05)

1. A number of instruments are available for the study of scratchhardness.

2. In all the cases the basic principle is to decide that amount ofload required by a sharp tip or edge to cut through the film.

3. In bare essentials the instrument consists of balanced beam,on one arm of which are a short knife or a pointed stylus anda post upon which weights can be placed.

4. The scratch is examined for the exposure of the base metal.

5. The weights are added or removed to determine exactlyunder what load the tip scratches through the film.


Scratch hardness Tester


Abrasion resistance

1. Abrasion resistance may be defined generally as theability of the material to withstand mechanical actionsuch as rubbing, scrapping or erosion, that tendsprogressively to remove materials from its surface.

2. The result of an abrasive action will be loss of coatingmaterials, loss of gloss or the surface may be marred.

(i) The falling abrasives method and

(ii) The use of rotating wheels .


Taber abrasion (ASTM D 4060)1. The specimen in the form of a 4 inch dia or a 4" x 4" sq. is

mounted on a turn table that rotates at 60 rpm under a pair ofabrading wheels in such a manner as to case side slip betweenthe abrading wheel and the surface of the test specimen.

2. 'calibrase' wheels No C.S. – 10 or C.S. – 17 are used. Abrasionresistance of coatings is expressed in terms of weight loss perspecified number of revolutions (e.g. 1000 revolutions) under astated load (e.g. 1000 g).

3. This is the wear index or wear rate. Alternatively, abrasionresistance may be expressed in terms of number of revolutionsrequired to wear through the coating to the substrate under agiven set conditions and this is called wear cycles or amount ofwear.


Taber Abraser


Adhesion

1. Adhesion testing procedures involve themeasurement of the force required for theremoval of the coating substrates.

2. Basically the methods of adhesion testingof the coating involves the cutting,scrapping, scratching, pulling etc.


Cross cut adhesion tester


Elcometer 106 Adhesion Tester(ASTM D-4541 Pull off)


Flexibility (ASTM D-522) Paint and varnishes films must have sufficient elasticity so

that they will not split or crack following upon shrinkage of th efilm or movement of the substrate due to whether or serviceconditions.

The flexibility of films may be evaluated by studying thetensile and elastic properties of the free films or by subjectin gthe coated films to bend tests.

The bending tests of the coated specimens are carried outusing a range of mandrels.

The elongated and the tensile strength of the free films aretested using tensile strength apparatus like instron.


Conical mandrel apparatus


Tubular Impact Tester• The falling weight method provides reliable

evaluation of the coatings resistance to impact.

• A mass (with or without indenter, depending onstandards) guided by a graduated tube, fallsfrom variable heights up to 1 m onto the samplepanel firmly clamped onto a die.

• The pass/fail height or force to failure can bedetermined on the tube scale


Tubular Impact Tester


Accelerated testsLaboratory Performance Tests

i) Cyclic corrosion tests (CCTs) Accelerated cyclic corrosiontests are fast becoming the industry norm for the evaluationof the anti-corrosive behavior of atmospheric coatingsystems. Traditional salt fog test ASTM B117,ISO 7253.

ii) Norsok Cyclic Test

Based on NACE TM0184, 72 hours Salt Fog (ASTM B117,ISO 7253) with artificial sea water (ASTM D1141)16 hoursdry out (23ºC) 80 hours UV at 60ºC/ condensation at 50ºC,4 hours/ 4 hours cycle (ASTM G53) Total duration = 25weeks.


ASTM D5894

ISO 23168 hours Prohesion (ASTM G85, Annex A5) 168 hours UV at60ºC/ condensation at 50ºC, 4 hours/ 4 hours cycle (ASTM G53) Totalduration = 24 weeks(blend of Sodium Chloride and Ammonium Sulphate)

Draft NACE (Based on Shell)

168 hours Prohesion (ASTM G85, Annex A5) with artificial sea water(ASTM D1141) 168 hours UV at 60 ºC/condensation at 50ºC, 4 hours/ 4hours cycle (ASTM G53) Total duration = 12 weeks.

Draft 040

72 hours Salt Fog (ASTM B117, ISO 7253) 24 hours freeze at –20ºC 72hours UV at 60ºC/ condensation at 50ºC, 4 hours/4 hours cycle (ASTMG53) Total duration = 25 weeks


Salt Spray CabinetFirst Training Course on Surfaces, Coatings and Corrosion Protection

IIM HRDC-KC, March 6&7, 2009, IIT Madras

Accelerated Weathering Test(ASTM G-53)

1. Simulated aggressive weather conditions can beobtained within a confined space by suitablyassembled equipments.

2. The natural weather condition includes, ultravioletradiation, heat radiation, humidity condensation, wind,rain etc.

3. The simulated weather apparatuses are capable ofproducing one or more of the weather conditions insidethe test chamber.

4. A typical apparatus is called Weathrometer.


Weathrometer


ELECTROCHEMICAL METHODS FORCOATING EVALUATION

Potential- Time M---> M n+ +e-

Electrochemical Impedance

Potential – time measurements were carried out to find outthe corrosion protection capability of the paints formulated.

In this method 6” x 4” painted panels are used. A glasstube of approximately 1sq.cm was fixed on the paintedpanel using araldite.

3% sodium chloride is used as the electrolyte. The opencircuit potential (OCP) was measured with respective to asaturated calomel electrode using a salt bridge.


Potential –Time measurementset up


VARIATION OF POTENTIAL WITH TIME

-600

-500

-400

-300

-200

-100

00 5 10 15 20 25 30 35

DURATION IN HOURS

POTE

NTI

AL

IN m

V Vs

SC

E

CONTROL

SYSTEM A

SYSTEM B


Electrochemical Impedance Method

Electrochemical impedance methods forcoating testing are based upon the well -established theory of electronic AC circuitanalysis.

By determining the "Equivalent -circuit"behaviour can be characterized.

The most common data presentation stylesare the Bode and Nyquist plot.


Setup used for Impedance measurements

1 Coating2 Working Electrode3 Glass tube 1cm2

4 Pt auxiliary electrode5 Ref. electrode (SCE)6 Electrolyte


Impedance Measurement Set -up


A metal covered with an undamagedcoating generally has very high impedance.

The equivalent circuit for this situation isgiven below

Perfect Coating


Typical Bode Plot for an Excellent Coating


Most coatings degrade with time, resulting in more complexbehavior.

After a certain amount of time, water penetrates into the coatin gand forms a new liquid/metal interface under the coating.Corrosion phenomena can occur at this new interface.

Equivalent Circuit for a Damaged Coating


Bode Plot for a Damaged Coating


Bode plot


COATING RESISTANCE WITH TIME

0.00E+00

2.00E+10

4.00E+10

6.00E+10

8.00E+10

1.00E+11

1.20E+11

1.40E+11

0 5 10 15 20 25 30 35

DURATION IN MONTHS

CO

ATI

NG

RES

ISTA

NC

E IN

OH

MS

CONTROL

SYSTEM A

SYSTEM B


Modern instrumental methods

Spectroscopic methods

Fourier transform infra red (FT -IR) spectroscopy

35

40

45

50

55

60

65

70

75

80

85

90

95

100

%T

rans

mitt

ance

500 1000 1500 2000 2500 3000 3500 4000W avenumbers (cm -1)


Chromatographic methods1. Gas chromatography is the most widely used

analytical technique.

2. Both gas chromatography and liquidchromatography play prominent roles for theanalysis of paints and related materials.

3. GC is useful in the analysis of individual resincomponents e.g. polyols, fatty acids, dicarboxylicacids either as raw materials or

4. Chemical degradation of the respective resins, inthe form of pyrolysis GC.


X-ray diffractionQUALITATIVE ANALYSIS

Identification of pigments, extenders and othercrystalline phase by x-ray diffraction is done bymatching the peaks of the diffraction pattern ofa sample under analysis with the sets ofdiffraction peaks exhibited by referencesamples of known composition. X -ray will notprovide away chemical information about thetest sample


Diffraction pattern of dried paint film

P o s i t i o n [ ° 2 T h e ta ]

2 0 3 0 4 0 5 0 6 0 7 0 8 0

C o u n ts

0

2 0 0

4 0 0

A z i m _ 3


Limitations

Misidentification can occur when the samplecontains several crystalline phase producing acomplex pattern and diffraction in the onlytechnique used for the analysis

(e.g.) peaks of red lead, quartz and zinccoupled d – values – 3.38, 3.34 and 3.31 A.


THANK YOU


SCIENTIST PROTECTIVE COATINGS GROUP ... DESIGN AND TESTING By Dr . S. SYED AZIM SCIENTIST PROTECTIVE...

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Transcript of SCIENTIST PROTECTIVE COATINGS GROUP ... DESIGN AND TESTING By Dr . S. SYED AZIM SCIENTIST PROTECTIVE...