Corrosion Protection. Ing. Petr Drašnar, Ph.D.

Transcription

1 Corrosion Protection Ing. Petr Drašnar, Ph.D.

2 Surface Treatments Surface treatment is one of the basic manufacturing technology that affects all manufacturing sectors. The chosen technology affects: Reliability Quality Sales Added value

3 Purpose of using surface treatment Improve appearance Corrosion resistance Chemical resistance Wear resistance Hardness Electrical conductivity Etc.

4 Corrosion Corrosion is a natural process, which converts a refined metal to a more stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials by chemical reaction with their environment.

5 Corrosion of metals = The most of the metals is unstable and has a tendency to revert to more stable mineral forms Oxidation of metals = Oxidation is loss of electrons Nature Oxides Sulfides Industry Metal Alloy ŽELEZNÁ RUDA OCEL KOROZNÍ PRODUKTY

6 Corrosion reciprocity = material, environment & their interaction Factors affecting corrosion: Material Corrosion Aggressivity Corrosion Rate Additional effects (UV, erosion, abrasion, etc.)

7 Types of Corrosion 1. Corrosion proces Chemical Electrochemical (Galvanic) 2. Reaction medium Atmosphere Liquids Gases Soil Soil corrosion of the pipe

8 Types of Corrosion 3. Form of corrosion General Localized 4. Corrosive agents Stray current corrosion Stress corrosion Fretting corrosion Bacterial fretting corrosion

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10 Chemical corrosion Chemical reaction between surface and reaction medium Non-conductive - without electrolyte Motion of a particle over a distance of atoms Causes: Electrically non-conductive and low-conductive materials Corrosion of metals in gases at higher temperatures - SCALES Metals in reducing gases H 2 embrittlement Metals in a non-conductive organic environments

11 Scales Hydrogen embtittlement Corrosion of glasss Scales

12 Galvanic corrosion Different metals and alloys have different electrochemical potentials (or corrosion potentials) in the same electrolyte. Conductive - with electrolyte Causes: Metals in water and aqueous solutions Atmospheric corrosion Corrosion in Soils Corrosion in Melts

13 Corrosion on the surface Sective corrosion of Zinc in brass Corrosion of Copper Steel tube

14 Standard Electrode Potential Anodic half with respect to hydrogen electrode Cathode with respect to hydrogen electrode

15 Galvanic corrosion Galvanic corrosion Galvanic corrosion

16 Atmospheric Corrosion Causes: The formation of the electrolyte layer on the metal surface by the condensation of atmospheric moisture Thickness in real conditions µm

17 Reaction with oxygen and water

18 Corrosion Aggressivity of Atmospheres

19 Lookout tower in C2 environment Anchor chain in C5 M environment

20 Liquids Conductive Salt solutions, acids Electrochemical reaction Non-conductive Liquefied gases (N 2, O 2 ), Alcohols, Crude oil, Petrol Chemical reaction

21 Gases Reducing atmosphere H 2, N 2, NH 3 reaction with non-metallic components inside the material Hydrogen embrittlement

22 Oxidizing atmosphere O 2, CO 2, SO 2 Rreaction with the base material Steel spring in Oxidizing atmosphere Copper foof in Oxidizing atmosphere

23 Corrosion Protection Modification of corrosive environment Type of material Surface treatment Construction Galvanic protection

24 Methods of Corrosion Control Barrier Protection Cathodic Protection Corrosion Resistant Materials Construction

25 Cathodic Protection Eternal source of direct current power is connected (or impressed) between the structure to be protected and the ground bed (anode). Cathode: Fe Anode: Al, Zn, Mg Sacrificial Anode Pieces of an active metal such as magnesium or zinc are placed in contact with the corrosive environment and are electrically connected to the structure to be protected Using the external power source Use: Pipelines, hot water tanks, underground storage tanks, ships

26 Cathodic Protection Sacrificial Anode Sacrificed Hg anode of hot water tank

27 Corrosion Protection Surface Treatment Cathodic protection e.g. zinc coatings Barrier protection e.g. paints Inhibitors It is necessary to ensure: Adhesion Wholeness

28 What do we expect Corrosion protection Functional properties Visual properties What must be ensured: Environmental resistance Adhesion Service life Health safety

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30 Pretreatments

31 Contaminants on the surface EXTERNAL, Dirts, oil contaminants, dust INTERNAL, Reaction of surfave and atmosphere / corrosion products, scales/

32 DEGREASING AGENTS ORGANIC DEGREASERS WATER DEGREASERS NON FLAMMABLE FLAMMABLE ALKALINE TENZIDE EMULSIVE CHEMICAL ALKALINE ELEKTORLYTIC NEUTRAL ACIDIC

33 Degreasing Dipping Spraying High pressure spraying Electrolytic degreasing Degreasing in steam

34 Parameter with infuence on cleaning Chemical agent, mechanical energy, temperature, time

35 PICKLING Remove and dissolve metal oxides and hyrated oxides from surface. Mostly used: mineral acids (hydrochloric acid, sulfuric acid) Pickling of Zn and Al alkaline solutions Activation Special type of pickling (before Zn elctroplating) Removing thin oxidic layers and activation of surface

36 Mechanical pretreatment Mechanical pretreatment Tumbling Grinding Blasting Polishing Brushing Special forms

37 Tumbling Tumbling machine and tumbling elements

38 Blasting what to ensure Clean Adhesion Corrosion resistance Appearance Mechanical properties

39 Classification of blasting machines By principle: Compressed air blasting mechanical blasting By mobility: Stationary Mobile By mode: Manual Automatic By purpose: Laboratory Industry

40 compressed air blasting compressed air (cca 0,2 0,8 MPa) Speed m/s

41 Mobile blasting machine Blasting

42 Mechanical blasting More productive 16 kg/s, speed 80 m/s. Bigger series Blasting unit

43 Mechanical blasting

44 Abrasives blasting agent By material: metal Non metal By origin: natural syntetic By shape: Sharpshaped grit Round shaped granulate

45 Types Cast iron Steel Corundum Ballottini Plastic abrasives Sand

46 Lifetime of organic coatings on different types of pretreatment technologies /removing corr. products/ pretreatment 4 coatings of organic coating system lifetime /years/ 2 coatings of organic coating system Manual brushing 2,3 1,2 Pickling 9,6 4,6 Blasting 10,3 6,3

47 Barrier vs. Cathodic protection Barrier protection of steel (pasive protection) Cathodic protection of steel - (active protection)