Corrosion PPT

CORROSION & ITS CONTROLCORROSION & ITS CONTROL

BY

SURENDRA SINGH

Corrosion Control Cell

Energy for the World

Discussion PointsDiscussion Points• Corrosion Types• Corrosion Control MethodsCorrosion Control Methods• Corrosion Testing Methods


C iCorrosion

Corrosion is defined as “the chemical or electrochemical reaction between a metal and its environment resulting in the loss of the mate ial and its p ope ties ”the loss of the material and its properties.”


Ship Corrosion (Marine)Ship Corrosion (Marine)


Corrosion in Machinery (Industrial)Corrosion in Machinery (Industrial)


Electrochemical cellElectrochemical cell2• Anode : 2Fe 2Fe2+ + 4e-

• Cathode : O2 + 2H2O + 4e- 4OH-

Net Reaction: 2Fe +0 + H O Fe O + H2Fe +02 + H2O Fe2O3 + H2

• An electrical connection between• An electrical connection between anode and cathodeA l t l t• An electrolyte


Corrosion RateCorrosion Rate

• Corrosion rate is defined in two form

Short Duration TestMil K W / A T DMils per year = K x W / A x T x D

L D ti T t Long Duration Testmm/yr = Thickness loss / time


P t i fl i i tParameter influencing corrosion rate

• Atmospheric exposure– Humidity– TemperatureTemperature– Concentration of salts

A t f i ll ti id i di t d t t– Amount of air pollution, acid rain, dirt, dust etc– pH


T f iTypes of corrosion

• Uniform Corrosion • Corrosion Fatigue• Galvanic Corrosion• Pitting Corrosion

• Stress Corrosion Cracking• Pitting Corrosion

• Crevice Corrosion

Cracking• Erosion Corrosion

• Microbiological Corrosion

• Hydrogen Induced CrackingCorrosion g


Uniform CorrosionUniform Corrosion

• Uniform corrosion is a form of corrosionin which a metal is attacked at about the same rate over the entire exposed surface.

• Uniform thickness loss


St l ith ill S l d R tSteel with mill Scale and Rust

Mill scale is yellow brownish color in nature and it is loosely adherance with the base metal.

After further exposure mill scale leads to formation ofscale leads to formation of rust.


Assessment of RustAssessment of Rust

Rust Grade A, as per ISO 8501 1

Rust Grade B, as per ISO 8501 1ISO 8501-1 ISO 8501-1

Rust Grade C, as per Rust Grade D, as per ISO 8501 1


ISO 8501-1 ISO 8501-1

G l i C iGalvanic Corrosion• Galvanic corrosion is an

electrochemical action of two dissimilar metals in the presence of an electrolyte and an electron conductive path.

• It occurs when dissimilar metals are in contact with each other.


Galvanic SeriesGalvanic Series


Severity of corrosion depends on conductivity of electrolyte and anode-cathode area ratio

Cathode is more noble than anode and electrolyte with

y

anode and electrolyte with good conductivity

C th d i bl thCathode is more noble than anode and electrolyte with poor conductivity

Unfavorable area ratio, Small anode area corrode very rapidly


Pitting CorrosionPitting Corrosion

Pitti i i l li d tt k• Pitting corrosion is a localized attack on a material.

• The passive film may be destroyed mechanically or by aggressive ions in an electrolytey gg y


• Pitting corrosion occur when the amount of corrosion at one or more points on metal is much greater then the average amount of g gcorrosion.

• Susceptibility of metals to pitting corrosionSusceptibility of metals to pitting corrosion can be detected by ASTM G48 Standard.


Crevice CorrosionCrevice CorrosionIt occurs mainly in theycrevices at the junction oftwo metals exposed inaggressive environmentaggressive environment.

Accelerated attack occurs because of a differential in oxygen concentration.

Susceptibility of matels to crevice corrosion can beSusceptibility of matels to crevice corrosion can be detected by standard ASTM G48.


Intergranular CorrosionIntergranular Corrosion

Alloys such as austenitic stainless steel & some alloys, when inadequately heat treated duringinadequately heat-treated during welding results chromium carbide precipitation over grain boundaries.p p gChromium concentration variationbetween grain vicinity & grainb d hi h i i i iboundary, which initiate corrosionprocess. ASTM No. 7 100X


• Susceptibility of austenitic stainless steel can be detected by ASTM A262be detected by ASTM A262

• PreventionU l b i 304L 316L– Use low carbon content i.e 304L, 316Linstead of SS304, 316.

– Use Ti or Nb grade SS such as 321, 347.


E i C iErosion Corrosion• The combined action involving corrosion

and erosion of metals in the presence of a moving corrosive fluid or a materiala moving corrosive fluid or a material moving through the fluid, leading to accelerated loss of material

• The most significant effect of erosion-corrosion is the constant removal of protective film from the metal surface


Sharp corners creates turbulence, leading to erosion corrosion

This corrosion mainly occurs in bends, elbows, valves, pumps, blowers, impellers, nozzle etc.


Stress Corrosion CrackingStress Corrosion Cracking

The phenomenon of stress corrosion cracking is defined ascorrosion cracking is defined as the occurrence of microscopic brittle fracture in metal due to thebrittle fracture in metal due to the combined action of tensile stress (residual or applied) some(residual or applied), some specific environment.


SCC causes premature cracking of metals in certain environmentsmetals in certain environments

Copper or Brass : Ammonia solutions water vaporCopper or Brass : Ammonia solutions, water vapor Stainless steel : Seawater, Acid chloride, H2S Carbon steel : Nitrate solutionsCarbon steel : Nitrate solutionsNickel Alloy : Caustic soda or NaOH Solution

Susceptibility of metals to SCC can be detected by ASTM G36/NACE TM0177y


T l d i t l SCCTransgranular and intergranular SCC


Scanning Electron MicroscopScanning Electron Microscopy

I t l SCCTransgranular SCC Intergranular SCC


C i F tiCorrosion FatigueCorrosion fatigue can beCorrosion fatigue can be defined as a materials failure mechanism which depends on the combined action of repeated cyclic stresses and chemically reactive environment.

Corrosion fatigue is a special case of stress corrosion caused by the combined effects of cyclic stress andcaused by the combined effects of cyclic stress and corrosion.


Hydrogen EmbrittlementHydrogen EmbrittlementHydrogen Embrittlement (HE) causes ductility loss and result in brittle fracture of susceptible materials under applied and residual tensile stresses.

T il iblTensile stresses, susceptiblematerial, and the presence of h d thydrogen are necessary to cause hydrogen embrittlement.


H drogen Ind ced CrackingHydrogen Induced Cracking• The four essential factors

for cracking to occurS tibl i– Susceptible grain structure: MartensiteHydrogen >15ml/100gm– Hydrogen >15ml/100gm of weld

– Temperature less than– Temperature less than 200oC

– StressStress


HIC MacrostructureHIC Macrostructure

Prevention of HICPrevention of HIC

Use low hydrogen welding process B k h h ldi l d b f ldi Bake or heat the welding electrode before welding Preheat the metal to remove moisture Reduce stress by heat treatment


Mi bi l i l C iMicrobiological Corrosion

•Microbial corrosion is caused by the presence and activities of microbesand activities of microbes.

• The microbes can be• The microbes can be bacteria & fungi.


Corrosion Control MethodsCorrosion Control Methods• Better Material Selection

Materials inherently resistant to corrosion in certainenvironments

• Corrosion Control by design• Barrier Protection

Li id P i t– Liquid Paints– Powder Coating

Galvanizing (HDG)– Galvanizing (HDG)• Cathodic Protection

Impressed current– Impressed current– Galvanic Sacrificial Anode

• Use of Inhibitors and Chemical Additives


Use of Inhibitors and Chemical Additives

Better Material SelectionBetter Material Selection• Use material which is not susceptible of corrosion or p

use high chromium content such as Stainless Steel, Nickel alloy instead of carbon steel or mild steel.y

• Selection process depend on– Expected service lifeExpected service life– Reliability or safety– Material costMaterial cost– Fabrication cost– Maintenance and Inspection cost– Maintenance and Inspection cost

• Test the material prior to its usage as per ASTM / ASME Section II / NACE Standard


ASME Section II / NACE Standard

Corrosion Control by designCorrosion Control by designLiquid trap

C t

Bad Design Bad Design

Concrete

Good Design Bad Design Concrete

Good Design Good Design


Paint Application• It acts as a barrier between the susceptible corrosive

metal and the particular environment such as chemical, moisture, sunlight and rain.

• Not so costly method and easily applied on the y ysubstrate.

• Better Aesthetics.Better Aesthetics.• High degree of adhesion with the substrate.

Sufficient thickness can be applied (greater the• Sufficient thickness can be applied (greater the thickness better the corrosion resistance).


C iti f P i tComposition of Paints


Paint SystemPaint System• Selection of paint to be appliedSelection of paint to be applied• Surface Preparation• Mixing and thinning of paint• Application techniqueApplication technique• Primer layer• Intermediate layer• Top layer• Top layer• Thickness to be achieved


Type of coatingType of coatingLacquers are solutions of natural or synthetic– Lacquers are solutions of natural or synthetic resins (Vinyl chloride, rubber and acrylic)W t l i (l t ) C ti– Water emulsion (latex) Coating

– Oil based Coatings– Epoxy Coatings– Coal tar Epoxy CoatingsCoal tar Epoxy Coatings– Polyurethanes (isocynate and polyol)

O i Z i h ti– Organic Zn rich coating


Paint/Coating TestPaint/Coating TestSl No. Paint Properties Paint Test Standard

1Adhesion Cross Cut or Cross Hetch ISO 2409

Pull-Off Adhesion D 4541

2 Abrasion/Erosion Taber Test D 4060

3 UV-Resistant UV-A (340nm) and UV-B (313nm)

D 4587UV B (313nm)

4 FlexibilityConical Bend Test ASTM D 522

Cylindrical Bend Test ASTM D 522yImpact Test D2794

5 Paint continuity Pinhole/Holiday Test ISO 5162


Coating system in Enercon WEC componentsComponent Name Existing Paint System Maintenance Paint

system

Coating system in Enercon WEC components

Steel TowerInterzinc 52Intergard 400

Interplus 256Interthane 990 g

Interthane 990 (RAL 7038) Shade - RAL 7038

Cast Parts / Intergard 251I t d 400

Interplus 256I t th 990Stator carrier Intergard 400

Interthane 990 (RAL 7035)Interthane 990

Shade - RAL 7035

St t Ri / F-93 varnish Interplus 256Stator Ring / Disc Rotor

F-93 varnishResicoat R4-ES HLF 16R

Interplus 256Interthane 990

Shade - RAL 7035

TransformerCongard200F & Congard 50FPipcothane MT-300DACRO-65

Interplus 256Interthane 990

Shade - RAL 7038


Powder coatingPowder coating• Powder coating is a finishing g g

technology where a decorative and highly protective coating g y p gcan be applied to a wide range of products. p

• The process involves spraying finely ground electro-staticallyfinely ground, electro statically charged particles of pigment and resin onto a surface to beand resin onto a surface to be coated.


Powder TypesPowder Types• Thermoplastic:

• Powder melts and flows to form a film. • Continues to have the same chemical composition when it solidifies• Continues to have the same chemical composition when it solidifies• Will re-melt when heated.• Thick coating surface

E l• Examples » Polyethylene » PVC

Th tti• Thermosetting: • Powder melt flow and cross-link chemically to form film.• Cured coatings have different chemical composition than the basic

iresins. • Will not re-melt when reheated• Can produce thin paint like coating of 0.001 – 0.003 inch thick.• Examples

» Epoxy » Acrylic Urethane


Why powder coatingWhy powder coating• Superior Appearance p pp• Corrosion Resistance• Solvent Resistance• Solvent Resistance • Highly durable• Coating does not drip or sag• Ready to use and require no mixing solventsReady to use and require no mixing, solvents,

or hardners.• Less wastage


G l i i (HDG)Galvanizing (HDG)• Iron metallurgically reacts with molten zincIron metallurgically reacts with molten zinc

and form a tightly bonded inorganic coating.• Zinc coating forms an even and uniform• Zinc coating forms an even and uniform

thickness applied to edges and flat surfaces. C i t ti h i• Corrosion protection mechanism– Zn layer acts as barrier coating – Zn is more active than steel and corrode

first to protect the cathodic area of the pstructure.


Coating thickness of Gal anisingCoating thickness of Galvanising


HDG ProcessHDG Process


HDG Coating InspectionHDG Coating Inspection

• Coating Thickness – magnetic gauges, optical microscopy (Micron)

• Coating Weight – weigh-strip-weigh (g/m2, Oz/ft2)• Finish and Appearance – visual inspectionFinish and Appearance visual inspection • Additional Tests

Adherence stout knife• Adherence – stout knife • Bending – bend 180o, diameter = 4Thk


Service Life of HDGService Life of HDG


1mil = 25.4µm = 0.56oz/ft2 Coutesy by AGA(USA)

Cathodic ProtectionCathodic ProtectionA technique to control the corrosion of metalA technique to control the corrosion of metal surface by making that surface cathode of an electrochemical cellelectrochemical cell.

Corrosion Control can be achieved in two ways:1) Sacrificial Anode2) Impressed current

Cathodic protection is commonly applied on pipelines underground storage tanks ships and oilpipelines, underground storage tanks, ships and oil platforms.


Sacrificial AnodeSacrificial Anode

• Type of sacrificial anodes –Zinc, Al, Mg.• Used on small structures• Anodes welded or bolted to fixtures• Need regular checks for wastage


Impressed CurrentImpressed CurrentInvolves the use of an external power source – metal to be protected is made cathodic to its surroundings

Very costly to run –mainly used in marine applications – oil rigs –large anodes placed approximately 100mapproximately 100m away.


Corrosion Testing Methods


Crevice corrosion as per ASTM G48Crevice corrosion as per ASTM G48

• Mainly used to determine resistance of Stainless Steels and related alloysrelated alloys

• Specimen Size 50mm x 25mm x T mmmm

• Test Solution : Ferrric Chloride• Test Temperature: 22 ± 2 or 50 ±• Test Temperature: 22 ± 2 or 50 ±

2oC• Test Duration: 72hrsTest Duration: 72hrs• Measure weight loss after cleaning


Pitting corrosion as per G48Pitting corrosion as per G48• Mainly used to determineMainly used to determine

resistance of Stainless Steels and related alloysy

• Specimen Size 50mm x 25mm x T mm

• Test Solution : Ferrric Chloride• Test Temperature: 22 ± 2 or 50Test Temperature: 22 ± 2 or 50

± 2oC• Test Duration: 72hrs• Test Duration: 72hrs• Measure weight loss after

cleaning


cleaning

Intergranular Corrosion as perIntergranular Corrosion as per ASTM A262

• Mainly used to determine resistance of austenitic stainless steel to IGC

• Extra low carbon grades, and stabilizedExtra low carbon grades, and stabilized grades, such as 304L, 316L, 317L, 321, and 347 are tested after sensitizing heat347, are tested after sensitizing heat treatments at 650 to 675°C for 1hr.


Practice A Oxalic Acid Etch TestPractice A—Oxalic Acid Etch Test

• Cutting • PolishingPolishing• Etching Solution

– 10% Electrolytic oxalic Acid • The etched surface is examined on aThe etched surface is examined on a

metallurgical microscope at 250 X to 500 X500 X.


•

Classification of Etch StructureClassification of Etch Structure

Step Structure Dual Structure

Dit h St t


Ditch Structure

Practice B—Ferric Sulfate-SulfuricPractice B—Ferric Sulfate-Sulfuric Acid Test

• Specimen Size 25mm x 15mm x T mmT t S l ti F i S lf t• Test Solution : Ferrric Sulfate-Sulfuric Acid

• Test Temperature: Boiling Solution• Test Temperature: Boiling Solution• Test Duration: 120hrs• Measure weight loss W after• Measure weight loss W after

cleaning and drying• Corrosion rate:• Corrosion rate:

Millimeter per month = 7290 x W / A x t x d


P ti C Nit i A id T tPractice C—Nitric Acid Test• Specimen Size 25mm x 15mm x Spec e S e 5 5

T mm• Test Solution : 65 ± 0.2 % by y

weight Nitric Acid • Test Temperature: Boiling

Solution• Test Duration: 48 x 5 = 240 hrs• Measure weight loss W after

cleaning and drying• Corrosion rate:

Millimeter per month = 7290 x W / A x t x d


= 7290 x W / A x t x d

Practice E—Copper-Copper Sulfate-Practice E Copper Copper SulfateSulfuric Acid Test

• Specimen Size 100mm x 15mm x 10 mm

• Test Solution : Copper-Copper Sulfate-16 %Sulfuric Acid

• Test Temperature: Boiling Solution

• Test Duration: Min. 24 Hrs• Bend test & Dia : 180O, 4T • Observe the bend surface for

cracks, fissure etc.


SCC as per ASTM G36SCC as per ASTM G36• This test method describes procedure for conducting

stress-corrosion cracking tests in a boiling i hl id l imagnesium chloride solution

• This test method is applied on cast and welded stainless steel material

• Test Specimen Size: 100mm x 9mm x 3mm• Test Solution: Magnesium Chloride • Test Temperature: 155 ± 1oC• Test Duration: Min. 96hr Max. 500Hrs • Periodically observe the specimen for crack initiation• Periodically observe the specimen for crack initiation

using 20X.


SCC Test as per NACE TM0177SCC Test as per NACE TM0177• Used to detect susceptibility of Used to detect suscept b ty o

SS to H2S atmosphere.• 75-85% UTS is applied to tensile pp

specimen• Test Duration 720 Hrs• Purge H2S gas through inlet tube

throughout the test duration• Test temperature 90oC and

pressure 16bar• Report the failure of metal


Hydrogen Induced Cracking TestHydrogen Induced Cracking Test as per NACE MR0284

• Used to detect pipeline and pressure vessel steel for susceptibility to HICsusceptibility to HIC

• 3 Specimen of each material of size 100mm x 25mm x T mm• Immersed specimen in mixture of 5 wt% NaCl and 0 5%Immersed specimen in mixture of 5 wt% NaCl and 0.5%

CH3COOH. Initial pH 2.7 ± 0.1.• Purge H2S gas through inlet tube throughout the test durationg 2 g g g• Test duration: 96hrs• Cut each specimen in four part and observe for internal cracks Cut eac spec e ou pa t a d obse e o te a c ac s

using microscope.


S lt S T t ASTM B117Salt Spray Test as per ASTM B117• Widely used corrosion test • Test specimen type, size, duration, evaluation p yp

method depends on client requirement• Test Solution: 5% NaClTest Solution: 5% NaCl• Test Chamber Temperature: 35 ± 2oC

If bare specimen: Calculate weight loss• If bare specimen: Calculate weight loss• If Coated specimen: Observe for blistering,

rusting.

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Corrosion PPT