Paint School

Paint School Training Course Handouts Course held by Jotun Marine Coatings Sandefjord 10 -11 January 2001

Jotun Paint School

Course Handouts Contents Chapter Title

Page

1

Introduction

2

2

What is Paint?

3

3

Generic Paint Types

8

4

Steelwork

15

5

Pre-treatment

19

6

Paint Application

26

7

Inspection and Control

33

8

Paint Failures

41

9

Antifouling

47

10

Safety, Health and Environment (SHE)

53

11

Corrosion

59

12

Cathodic Protection

65

Jotun Paint School

Course Handouts

Page 1

1. Introduction Why paint? There are two main reasons for painting. For many people, the most important reason is that we want pleasant surroundings (decorative painting). In other contexts, paints are applied because it is financially very important to protect structures against corrosion. For these purposes, corrosion-protective paints are used. A good paint system will be a cost-effective method of protecting the structure: The life of the structure is extended, maintenance costs are reduced and the risk of accidents which affect people and the environment is reduced.

Painting and cathodic protection For most applications, painting has been found to be the simplest and most economical way of protecting structures, regardless of the exposure environment and your location in the world. When a structure requires protection, it is important to select a paint system suitable for the purpose. Paint is a semi-finished product and the protection will be no better than the quality of the finished coating. The human factor applies during both pre-treatment and application. A paint system is also often exposed to mechanical wear, which can cause weakness/damage to the paint film. Where damage occurs, the substrate (normally steel) begins to rust. Jotun has therefore developed a concept called the "Single Source Solution". This concept enables us to provide cathodic protection as a back up for corrosion-protective paints. The aim is to ensure optimum cost solutions for protecting structures exposed to water. Cathodic protection protects damaged areas in the paint film.

Jotun Jotun is one of the world's leading suppliers of corrosion-protective paints for industry, shipping and oil-related sectors. We also supply paints for decorative purposes and powder products, based on a worldwide network of factories and companies. To support customers, we have established a wide range of services. This ensures that the customer receives the right paint products from our corrosion-inhibiting systems at optimum cost.

Jotun Paint School As part of our service, Jotun arranges paint courses. These can be courses of more general character or specific customer-related courses. They focus on the practical use of paint. To find out more about these courses, contact your local Jotun office for more information.

Course Handouts The course handouts contain a brief introduction to the main topics of paint technology. Each section consists of an introductory section and a copy of selected overhead slides. Not all topics in the handout will necessarily be discussed on the course you follow.

Welcome to the Jotun Paint School !

Jotun Paint School

Course Handouts

Page 2

2. What is Paint ? Definition of paint and varnish Paint is a product in liquid or powder form which contains pigments and which is applied to a substrate to form an opaque film. The film has protective and/or decorative properties and can also be given special functions as required. Paint is described as opaque if it hides the substrate completely. Varnish is a product which, when applied to a substrate, gives a solid transparent film and has protective, decorative or special properties. Varnish does not contain covering pigments and is therefore regarded as "clear paint".

What is paint made of? The main constituents of paint are binder, pigment, extender (filler), solvent and additives (auxiliary substances). The binder is the most important component of paint. The binder gives the paint most of its properties such as adhesion to the substrate, resistance to weathering, water, chemicals, temperature etc. Binders can be divided into groups (generic types) depending on the drying or curing process which takes place after the paint has been applied to the substrate. The first group are known as oxidatively drying, as the paint absorbs oxygen from the air and dries. Example: alkyd paints. The next group are called physically drying. When the paint is applied to the substrate, the solvent simply evaporates. Examples: chlorinated rubber and acrylic. The third and final group contains chemically curing paints. These paints are usually twocomponent, e.g. epoxy. Pigments in a paint can be colour pigments which give the paint opaqueness, the desired shade etc. Colour pigments, both organic and inorganic, are available in many shades. Titanium dioxide is a strong colouring, white pigment with good opaqueness and is used in white and pale colours. Rust-inhibiting pigments include zinc (cathodic protection) and zinc phosphate (inhibiting protection). Such pigments are used only in primers (first coat). Extenders or fillers such as dolomite, talcum etc. have little or no opaqueness and are transparent in the binder. They have different forms e.g. balls, needles, fibres etc. and are used to give a sealed film, the right gloss etc. In antifouling paints, for example, copper oxide is used as a pigment to prevent fouling of ships’ hulls. Solvents are added to the paint to adjust the viscosity so the paint can be applied by brush, roller or spray gun. Different binders require special solvents or solvent mixtures to be able to dry or cure in such a way that the paint properties are not damaged. Additives are a small, but important, part of the paint. Such substances include antisettling agents (to prevent fouling), thickeners (to prevent sagging / running), antifoaming agents (to prevent air entrapment), etc.

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How does paint protect the substrate ? Paint protects the substrate in three main ways: barrier effect, inhibitor effect and galvanic effect. Paints which have a barrier effect only form a barrier between the substrate and the environment and no rust-inhibiting pigments are added. Most paints come under this group: many primers, all intermediate coats and top coats. Aluminium and glass flakes are often used in primers to increase the barrier effect. Paints which use the inhibitor effect contain inhibiting pigments e.g. zinc phosphate. Such pigments are only used in primers. Paints in this group are not suitable for use under water. Paints with a galvanic effect contain pure zinc pigments and are used only as primers. The basic principle is that the zinc makes metallic contact with the steel so that the zinc can act as an anode. If the paint system is damaged, the zinc pigments will protect the exposed steel cathodically (see section on Cathodic Protection).

What does a paint system consist of? In most cases, a paint system consists of 2 to 4 coats and is built up from a primer coat, one or two intermediate coats and a top coat. The three main constituents in the paint system can be three different paints, but it is not unusual to use a particular paint as both primer and intermediate coat. Each part of the system has a specific function and it is therefore important to follow the instructions of the paint manufacturer and the recommended system structure to achieve the best possible result. The main purpose of primers is to ensure good adhesion of the system to the substrate. Intermediate coats usually ensure that the system is sufficiently thick to create a good barrier from the surrounding environment. The top coat gives the surface the right colour, a good durable gloss and protection against the external environment. A paint system can include more coats than stated above. In brief: • • •

Shop primer, primarily for the temporary protection of steel from production through to the construction stage. Tie coat, which is applied to porous surfaces to prevent pinholes or to ensure good adhesion between coats (tie coat). Mid coat. More than two are used for paints which cannot be applied in thick coats.

Personal notes

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Chapter:

What is Paint ? The properties of a paint will be decided by the binder

Paint consist of:

•

• Binder • Colour pigments • Extenders • Solvents • Additives

• • •

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Curing mechanism of binders Oxidising • Alkyd Physically drying • Chlorinated rubber • Vinyl • Acrylic • Asphalt • Tar

Describes the type of paint/coating Bind pigments and extenders to a solid film Provides the adhesion to the substrate Provides the water, chemical, solvent and UV resistance

Curing (drying) through oxidation

Chemically curing • Epoxy • Polyurethane • Polyester • Silicate

Solvents evaporating

Oxygen enter. Reaction starts:

Polymer molecules linked together through chemical bonds

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Physical drying. Solvent borne paints

Physical drying Waterborne paints

Solvents evaporating

Water evaporating

= Dispersed droplets

Polymer molecules are packing:

Droplets melt together, co-solvents evaporate

Polymer molecules stick together (no chemical bonds):

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Droplets are packing

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Chapter:

What is Paint ? The surface tolerance depends on the penetrating properties of the binder

Curing mechanism of two -pack paints

Vinyl Chlorinated rubber Epoxy Polyurethane

Solvents evaporating

= Polymer

= Curing agent (hardener)

Urethane alkyd

Polymer & hardener molecules reacted to form a new chemical substance:

Surface tolerant paint: Epoxy Mastic

Alkyd Boiled linseed oil Raw linseed oil

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The Gloss of a paint depends on the PVC (Pigment - Volume - Concentration)

Pigments, examples Rust preventing pigments: • Red Lead • Zinc • Zinc Chromate • Zinc phosphate

Coloured pigments (hiding power / opacity): • Inorganic; red, yellow, brown, black • Organic, all colours • Titan dioxide (white)

Binder Colour pigments

Glossy PVC 15 -25

Extenders Semigloss PVC 30 - 40

Extender pigments (non/limited hiding/opacity properties): • Talcum • Barium sulphate • Microdol (dolomite)

Flat PVC 35 - 50

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Solvent or diluent

Solvents / diluents Solvent

• •

• Dissolve the binder • Give lower viscosity • Give application properties for brush, roller, spray

Single or blended Disolves the binder completely (Forms a solution)

Diluent • Single or blended • Does not dissolve the binder (Forms a “mixture”)

• Used in conjunction with solvents Paint School

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Chapter:

What is Paint ? Additives

Addition of thinner Evaporation rate and solubility of a thinner will influence a paint’s: • Drying time • Film-forming properties • Quality of the film

• Wetting agent • Anti-foam • Anti-settling • Anti-skin • Anti sagging • Catalysts • UV-absorbers

❶ Most paints are ready to be applied as supplied by the manufacturer.

❷ Never add an unspecified thinner to a paint,

etc.

it may lead to disastrous results

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An impervious coating serves as an inert barrier to protect the surface

Corrosion protection by paints

Impervious to ions, oxygen, carbon dioxide

For corrosion prevention with paints, three main principles are employed:

Low moisture transmission 2nd coat 1st coat

• Barrier effect • Inhibitor effect • Galvanic effect

Primer Steel No voids at interface Strong adhering to accumulate water coating thoroughly wets steel surface Physical as well as Clean surface - no salts to create osmotic blistering chemical adhesion

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Inhibition

Cathodically protective pigments Damage in coating to steel surface

Moisture Absorption

Moisture allows Zinc to ionize, cathodically protecting the steel.

Ionisation of Inhibitor Reaction with Steel Surface

Superior adhesion prevents coating undercut

Passive layer forms

2nd Organic Topcoat

2nd Coat 1st Coat Inhibitive Primer

Zn

Inorganic Zinc Primer

Steel

Steel

An inorganic Zinc primer reacts to protect the steel substrate when the topcoat is damaged.

Moisture may penetrate to reach the inhibitive primer where the reactive pigments are activated, which in turn passivate the metal substrate at the coating/metal interface. Paint School

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3. Generic Paint Types It is not possible to develop a "universal" paint which fulfils all possible functions. Paints are therefore developed for different jobs. As a result, each paint has a different set of properties. Paints are often grouped according to the chemical composition of the binder, which we refer to as ‘generic paint types’. To ensure that you choose the right paint or paint system with the right properties, it is important to know the strengths and weaknesses of the various generic types.

Alkyd paints Alkyd paints are made from alcohol and acid with the addition of fatty acid or oil. The addition of fatty acid and/or oil can be varied to give alkyds with different properties. Alkyd paints can only be used above water (not submerged) as the water resistance is poor. They are not used on zinc primer or galvanised steel as a chemical reaction - saponification would occur with the binder, with subsequent blistering and flaking. The drying/curing process is also temperature-dependent. This is because alkyd paints dry or cure by absorbing oxygen from the air. This is a chemical reaction and such reactions are always influenced by temperature. The degree of pre-treatment required for the substrate can vary from St 2 to Sa 2½, depending on the purpose of the paint and the environment to which the paint is exposed. By modifying the alkyds for example with styrene or silicon, other properties can be achieved.

Physically drying paints The group of physically drying paints contains generic types such as chlorinated rubber (CR), vinyl and acrylic-based paints. These are being withdrawn from the market due to the high content of volatile organic compounds (VOC). The chlorinated compounds in CR paints also give off chlorine on ageing. Physically drying paints are single-component, and dry by pure evaporation of the solvents. This means that these paints are not so sensitive to the ambient temperature during application and drying (does not apply to waterborne acrylic). They are also resoluble by other paints which contain strong solvents or in contact with thinners. CR paints are used outdoors both above and under water. Vinyl-based paints are used only above water. Acrylic is used as a top coat, as it retains its gloss better than chlorinated rubber or vinyl in such systems. acrylic is also used as primers in waterborne systems.

Chemically curing paints Chemically curing paints are thermosetting plastics, unlike physically drying paints which are thermoplastics. Thermosetting plastics are more resistant to chemicals than thermoplastics as they form an insoluble three-dimensional network after curing.

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These paints are normally two-component. The supplier provides these paints in two separate containers, one for the base and the other for the curing agent. We often refer to these as component A and component B. Before painting, the two components must be mixed. It is particularly important to mix the components in the correct ratio and to ensure good agitation. The curing process is a chemical reaction between the base and curing agent, so application and curing are temperature-dependent. It is equally important to apply the paint to the substrate before the chemical reaction has proceeded for too long after mixing of the components. We often talk of the usage time (potlife) of paints. When the potlife has elapsed, the paint becomes dry and finally completely hard and cannot be applied.

Some chemically curing paint types Epoxy paints have excellent chemical resistance, particularly to alkalis. They have good adhesion both to steel and concrete and good water resistance. Epoxy can be modified using phenol, coal tar and hydrocarbon resin to give special properties, e.g. better chemical resistance, better penetration, better water resistance etc. One drawback with many epoxy paints is that they contain large quantities of solvent. However, other types have now been developed with a high solids content (mastic products) with excellent "all round" properties. There are also a solvent-free epoxy paints which are used for drinking water tanks. Waterborne Epoxy paints are increasingly being used today because they give a better working environment. Chemical resistance however is slightly reduced. Zinc epoxy (organic) or zinc ethylsilicate (inorganic) are used as cathodic protective primers on blast-cleaned substrates. Zinc ethylsilicate (solvent-based) and alkali silicate (waterborne) are also often used inside storage tanks for solvents because of the extremely good solvent resistance. Polyurethane paints are also thermosetting plastics. They are used as top coats on epoxy (which chalks in sunlight) as they have excellent weather-resistance and durable gloss. Polyester paints are thick coat paints used in areas where a high degree of wear resistance is required. For example gangways, production decks, dam walls (concrete) for power stations etc. These paints are applied in thick coats (e.g. 2 x 750 µm) and cure quickly (a few hours). They also have good chemical resistance. Vinylester is also a thick coat paint (2 x 750µm). It has good chemical resistance and is often used inside storage tanks for chemicals. Such paints can be used on both steel and concrete. Personal notes

Jotun Paint School

Course Handouts

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Chapter: Alkyd paints

Alkyd paint

Properties

Where to use

Advantages

Limitations • Poor chemical resistance

• Good application • • • • • • •

Generic types

properties 1-component Good weather durability Good wetting properties Good recoatability Good levelling properties Good gloss retention Dry heat resistant up to 120 ºC.

• • • • •

(especially against alkaline) Limited water resistance (submerged) Limited solvent resistance Limited film thickness per coat Poor adhesion to CR Never to be used on Zinc

Segments

• Ships • Industry

Objects

• Newbuildings / Maintenance • All exterior and interior objects • Only above water

Surface preparation

• St 2 to Sa 2½ or shop primed steel

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Chlorinated Rubber paints

Chlorinated Rubber paints

Properties

Where to use

Advantages • Physically drying • Not temperature

Limitations • Poor solvent resistance • Low solid content • Relatively poor wetting

dependent

• Easy to recoat • One component • Very good water

properties

• Thermoplastic • Dry heat resistant up to

resistance

• Ships • Offshore • Industry

Segments

Objects

• Newbuildings / Maintenance • Below and above water • All external surfaces

Surface preparation

• Blast-cleaned to Sa 2½ or shop

approx. 70 °C

• Relatively good chemical resistance

primed steel Paint School

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Vinyl paints

Vinyl Tar - Modified type

Properties

Properties

Advantages • Physically drying • Good chemical resistance • Good water resistance • Quick drying • Not temperature dependent • One-component

Advantages

Limitations

• Higher content of

• Low solid content • Poor resistance against

solids • Higher water resistance • Better wetting properties • Cost advantages

strong solvents

• Dry heat resistant up to approximately 80 ºC

Used for: Exterior objects above water Offshore on top of Zinc-ethylsilicate

• Bleeding • Dark colours • Tar on cancer list

Used for: Under water areas

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Disadvantages

Handouts

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Chapter:

Generic types

Pure Epoxy paints

Pure Epoxy paints

Properties

Where to use

Advantages

Limitations

• Chemical curing • Very good chemical resistance • High alkali resistance • Moderate resistance to acids • Good adhesion • Very low permeability • High mechanical strength • Dry heat resistant up to 120 °C

• Chalking • Temperature dependent • 2 - component • Requires blast cleaning • Overcoating time

Segments

• Ships • Offshore • Industry

Objects

• Newbuildings / Maintenance • Chemical cargo tanks

Surface preparation

• Blast-cleaned to Sa 2½ or shop primed steel

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Epoxy Coal Tar

Epoksy - acrylic

Properties

Properties

Advantages:

Positive

Limitations:

• Chemically curing • More flexible • Excellent water resistance • Better wetting properties • Dry heat resistant up to 90 °C

• Dark colour • Temp. dependent • 2-component • Recoating interval • Bleeding when overcoated • Coal Tar is carcinogenic

Limitations

• Very good weather • • • • •

resistance Very good gloss retention Very good chemical resistance Very good solvent resistance Cures down to 0 °C Potlife (24 timer)

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• 2-pack • Overcoating time

Epoksy - acrylic pints

Epoxy Mastic paints

Where to use

Properties

Segments

Objects

Surface preparation

Advantages

• Ships • Offshore • Industry

• Chemically curing • Surface tolerant • Light colours • Very good water resistance • Very good wetting properties • Good chemical resistance • High solid content • High build (Thick coats) • Winter curing agent • Dry heat resistant up to 90 ° C

• Newbuildings / Maintenance • Above water • Indoor and outdoor • Top coat on Epoxy, Epoxy • Mastic, Polyester glass flake

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Limitations • Chalking • Temperature dependent • Not to be applied on thick coats of physically drying paints • Minimum DFT 150 µm by airless spray

Page 11

Chapter:

Generic types Experience When using Epoxy paints

Epoxy Mastic paints

Where to use • Ships • Offshore • Industry

Segments

Objects

• Newbuildings / Maintenance • Ballast tanks and Cargo tanks • All exterior and interior surfaces,

Surface preparation

• St 2 to Sa 2½ or Water jetted,

• • • • • • •

above and below water

Correct mixing ratio Good mixing Potlife Induction time Correct pre-treatment Correct film thickness Adequate ventilation

Magnesium descaled or shop primed steel Paint School

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• • • •

• • • • •

Temperature dependent curing Avoid high humidity Minimum and maximum curing times Time for fully cured Use epoxy thinner Health and epoxy

Polyurethane paints

Polyurethane paints

Properties

Where to use

Advantages

•

•

Limitations

Very good weather resistance Excellent gloss durability Very good chemical resistance Very good solvent resistance Cures down to 0 °C

• • •

2-pack May cause skin irritation Overcoating time

Segments

• Ships • Offshore • Industry

Objects

• Newbuildings / Maintenance • All exterior substrates above

Surface preparation

• On top of Epoxy, Epoxy Mastic

water (Also internal at times) and Polyester coatings

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Zinc Epoxy

Zinc Epoxy paints

Properties

Where to use

Advantages • • • • • •

Chemically curing Good corrosion protection Good adhesion Require min. Sa 2 ½ Good mechanical strength May be recoated with all types of paint, except Alkyd • Dry heat resistant up to 120 ºC

Limitations • • • •

Temperature dependent 2-component Film thickness: 25 - 50 µm Not acid- and alkaline resistant (Resistant between pH 5-9)

Segments

• Ships • Offshore • Industry

Objects

• Newbuildings / Maintenance • All exterior and interior objects above and below water (as holding primer for underwater use 20-30 microns).

Surface preparation

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• Blast-cleaning to minimum Sa 2½

Page 12

Chapter:

Generic types

Zinc Ethylsilicate paints

Zinc Ethylsilicate paints

Properties

Where to use

Advantages

Limitations

• Very good solvent resistance • Very high heath resistance oC)

(max 400 • Very high mechanical strength • Very good adhesion to blast cleaned steel • Relatively good recoatability

Segments

• Ships • Offshore • Industry

Objects

• Newbuildings / Maintenance • All exterior objects above the

• Requires humidity for curing

• 2-pack • Max. DFT: 100 µm At higher DFT tendency of mud-cracking or checking

waterline.

• Tank coating and Water ballast tank (No paint on top) Surface preparation

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Aluminium Silicone paints

Waterborne acrylics

Properties

Advantages and Limitations

• Pure aluminium silicone:

• •

Resistant up to approximately 600°C

• Modified aluminium silicone: • • • • • •

Resistant up to approximately 400°C

• To be applied in thin coats only (20 µm) Heavier coats may give blistering

Remember: To be applied on Sa 2 ½ Overcoating only on fully cured Zinc silicate

•

Advantages Good corrosion protection Reduce the emission of solvents Low VOC content Flash point above 100 ºC Water as thinner / cleaner Good water resistance Good UV - resistance Good adhesion to other generic type of paints No risk of saponification

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•

Limitations

• Due to water-soluble

• • • •

groups, more sensitive to aqueous solutions (more blistering/earlier corrosion) Slower drying compared to solvent based types at high relative humidity Need good ventilation Need good pre-treatment Less chemical resistance

Waterborne epoxy

Waterborne paints

Advantages and limitations

Conditions during application

Limitations

Advantages

• • • • • • • •

• Blast-cleaning to minimum Sa 2½

Good corrosion protection Reduced emission of solvents Low VOC content Flash point above 100 ºC Water as thinner / cleaner Good water resistance Cures down to 5 ºC Good adhesion to steel, galvanized steel, Aluminium and concrete Good sprayability

Relative humidity (%) 100

• Need good ventilation at high humidity

• •

80 70

solvent borne The same health hazards as solvent borne Epoxies Due to water-soluble groups, more sensitive to aqueous solutions

Application and drying possible

60 50 40

Application not recommended

30 20 10

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Recommended conditions during application and drying

90

• Must be stored above 0 ºC • Shorter potlife compared with

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20 30 40 50 Temperature ( oC)

60

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Chapter:

Generic types Glassflake Reinforced Polyester

Glassflake Reinforced Polyester • • • • •

Properties

For protection of steel and, in certain cases, Aluminium and concrete. The glass-flakes are 3-5 microns thick and 400 microns across. Potlife : Approximately 45 minutes. Curing time: Approximately 3 hours. Thickness 600 - 1500 microns per coat.

Advantages

Limitations

• • • • •

Quick curing Variable curing time Application with airless Excellent mechanical strength

• Temperature dependent • Short potlife • Recoating interval

Glass-flakes reduce shrinkage, increases mechanical strength and water resistance.

• Bad curing may be

2 - 12 hours experienced on Zinc primers and galvanised surfaces.

• Very good chemical resistance Paint School

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Glassflake Reinforced Polyester (Styrene free)

Vinyl ester coatings

Properties Limitations

Advantages

• Styrene free • Dry to handle in 2 hours • Cures down to 5 ºC (2-component pump)

• Excellent mechanical

• Cures down to 10 ºC (normal airless spray)

Glass-flake reinforced Vinylester coating for protection of steel and concrete in aggressive environments.

• Short potlife • Recoating interval 1 hour to 2 weeks (23 ºC )

• Require Sa 2 ½ and a roughness

strength

of 50-100 microns • Very good adhesion • curing may be experienced • Very good water resistance. Bad on Zinc primers and galvanised surfaces. • Very good chemical resistance Paint School

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Application of Polyester and Vinyl ester coatings

Vinyl ester coatings

Advantages and limitations Advantages

• Very fast curing • Very good adhesion • Very good abrasion • • • •

resistance Very good chemical resistance Very good solvent resistance Can be applied by normal airless spray Glassflakes improve abrasion resistance

Limitations

• Capacity of pump, min.

• Very fast curing • Very good adhesion • Very good abrasion • • •

• • •

resistance Very good chemical resistance Very good solvent resistance Can be applied by normal airless spray

• •

12 l/min (airless) Material hose: 3/8” Use teflon gaskets Nozzle: 0,035-0,053 Angle 40 - 80 o Remove filters Check the W.F.T.

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• Check ventilation, light etc. • Thinner No. 17 or 15, • • •

Acetone for flushing or cleaning Only on blast-cleaned steel Proper mixing Short potlife

Page 14

4. Steelwork Before a structure is painted, a number of operations must be performed on the substrate. The initial work required is generally known as "steelwork". Steelwork is a very important part of the surface treatment and must be carried out before cleaning and priming of the steel. Good steelwork will ensure that the life time of the paint system meets expectations. In practice, it is impossible to achieve a long life time for a paint system if the steelwork is omitted or poorly performed. The requirements for preparation will always be part of the paint specification. A steel structure should be designed so that all parts of the structure are accessible for cleaning, pre-treatment and painting. It is particularly important to ensure that these requirements are taken into account at the newbuilding / construction stage. Designers often forget that structures require maintenance. Steelwork involves the following stages before cleaning and priming: 1. 2. 3. 4. 5. 6.

All sharp edges are rounded to a radius of at least 2 mm by grinding. All welding beads and slag are grinded off. Surface defects such as lamination etc. are removed by grinding. Undercutting in the weld is repaired before priming. Rough manual welds to be grinded. Gas-cut edges are to be grinded before priming.

To avoid contamination and damage to the coating, steelwork should be performed in the welding shop and not in the paintshop. Production times will also be reduced if sharp edges in notches, manholes etc. are rounded before welding work is performed. All welds should be inspected and if necessary repaired before cleaning is carried out. The welds must be free from weaknesses such as undercut, hole, craters and welding splashes. Notched, drainage holes etc. should have a radius of at least 50 mm to ensure good priming and correct paint application.

Personal notes

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Page 15

Chapter:

Steel work Steel preparation

Pre-blasting preparation involves the following activities

Edges and weld spatters

Rounding or smoothing of: Sharp edges Corners Welds Grinding of: Laminations Flame cut edges Weld spatter Notches minimum diameter: 30 mm Inspected and approved before cleaning

Sharp edge

Gas cut edge

A. Remove by grinder or disc sander.

A

B

B. Rolled steel sections normally have round edges. Therefore can be left untreated.

A

A. Remove visible spatter before gritblasting with grinder or chipping hammer.

B

B. For spatter not readily removed, remove using grinder/disc.

Weld spatter

See ISO 8501 “Visual assessment of surface cleanliness” Paint School

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Grinding of sharp edges, welds etc. Disc sander and disc grinder

Pre-blasting preparation

Rounding sharp edges Coating applied to a square-cut section

Sander for removing mill scale, paint and rust

Sharp edge

Grinder for heavy grinding, such as edges and weld beads

Reduced coating thickness at sharp edges due to tension created during drying / curing

Coating

Steel

Rounded edge Even coating thickness

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Steel support after blast-cleaning to Sa 2 ½

Steel support after blast-cleaning to Sa 2 ½ The sharp edges have been rounded prior to blast-cleaning: Good !

The sharp edges should have been rounded prior to blast-cleaning

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Chapter:

Steel work Severe corrosion due to a combination of several effects

Manholes in a tank

• Sharp edges • Rough welds (not grinded) • Missing stripe coating

• Section manholes • Well grinded edges

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Steel preparation

Grinding of notch with rotating file

Weld spatter, welding smoke

Easy access with a rotating file Weld spatter

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Weld Areas at risk

Disc grinding of weld beads, sharp edges etc. by means of a disc grinder.

Steel substrate after disc grinding

Other types of discs are available. Some of them will reduce the amount of sparks.

Weld beads etc. has been removed to form an acceptable substrate for the paint system

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Chapter:

Steel work

Pre-blasting preparation

Unacceptable weld. Too rough and full of pinholes / pores

Laminations, undercuts, welding seams

• Weld spatters close to weld • Rewelding and grinding must be carried out

Lamination

prior to reblasting and painting

Remove using grinder

Undercut Undercuts exceeding classification ruling should be repaired by welding and grinding.

Manual weld bead Sharp profile peaks to be smoothed using grinder

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Early corrosion of welds in a water ballast tank

Paint on a very poor weld. Pinholes and holidays visible after second stripe coating

• Neither rewelding nor grinding have been carried out prior to application

• Remedial Actions: Reblasting, rewelding,

• Rough weld seams.

grinding and blast -cleaning: COSTLY

• •

Should have been grinded Probably in combination with poor stripe coating Mud can be seen, particularly on the bottom

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Spot welding leads to crevices which are susceptible to corrosion

Sharp edge an spot welds. Early corrosion attack

Not recommended solution for exposure to severe / aggressive environments

• Construction newly painted

• Exposed to humid atmosphere

• Corrosion initiates after a short period of time on weak areas: Sharp edges, crevices and spot welds

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5. Pre-treatment After the steelwork on the steel structure has been completed, inspected and approved, pretreatment can begin. The purpose of preparation is to ensure that the substrate is suitable for application of the paint, i.e. the steel is sufficiently clean and rough. Contaminants such as oil, grease and salts for example cannot be removed by blast-cleaning. Before preparation begins, the steel must be properly cleaned. Cleaning removes contamination and impurities such as oil, grease, salt, dust and dirt. Salts from a marine atmosphere which are deposited on the structure, and welding fumes from manual welding are examples of salts which should be washed off before preparation. Salts can cause osmotic blistering and oil will reduce the adhesion of the paint. Salts must be removed with plenty of fresh water. Oil and grease cannot be removed with water alone; strong alkali washing agents and solvents must be used. Once the substrate is clean, pre-treatment can begin. There are countless methods which can be used, all of which have advantages and disadvantages. Here is a brief list of some methods: Blast-cleaning. To ensure maximum paint adhesion, a rough surface is required. In view of this, blast-cleaning is the best preparation method. Blast-cleaning removes old paint, rust and scales and gives a clean rough surface. Possible blast-cleaning methods are dry blast-cleaning, slurry blast-cleaning (addition of water) and wet blast-cleaning (water with addition of abrasives). Dry blast-cleaning gives a clean dry surface and the required roughness but causes considerable dust which contaminates the immediate environment. Slurry and wet blastcleaning give a rough, clean surface without dust, but create flash rust. It has been found that much of the abrasives remain on the substrate after blast-cleaning. Such contaminants may on some alloys cause a risk of corrosion at these points. For preparation of stainless steel, aluminium and galvanised steel, it is important to use non-metallic abrasives. Ultra high-pressure water cleaning. This preparation method is becoming increasingly common. The method consists of removing contamination, corrosion products and old paint by applying water to the substrate under extremely high water pressure (up to 2500 bar). The method has two essential advantages: no cloud of blasting dust is created to contaminate the immediate environment as in traditional blast-cleaning, and water-soluble salts are removed from the substrate. It is important to use clean water so that the substrate is not contaminated by the water used. The method gives a clean surface but will not give any extra roughness to steel. The original roughness of the steel is retained where intact paint is removed, but the corrosion pattern on corroded areas will be considered as roughness where corrosion has occurred. One disadvantage with water cleaning is that the tendency to form flash rust on the steel will increase as moisture is added to the substrate. The degree of flash rust depends on the relative humidity, the temperature of the steel and atmosphere, and the cleanliness of the surface. Mechanical cleaning. Use of mechanical cleaning tools such as steel brushes, grinding equipment or machining, does not achieve the same degree of cleanliness and roughness as blast-cleaning and the adhesion between the substrate and the paint system will therefore be reduced. Needle guns for example often cause excessive roughness or break-up of the substrate.

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Electrolytical descaling. There is a special preparation method where magnesium strips are used to remove rust. This has proved particularly useful in severely corroded ballast tanks on sailing ships where thick rust layers can be removed at sea. However, the procedure requires a knowledge of how to calculate the number of anodes needed, installation of the anodes, treatment periods and cleaning after the procedure. Such treatment should therefore be carried out in collaboration with Jotun. The method to be used will be described in the paint specification and is primarily selected on the basis of:





Purpose of the structure Exposure conditions Required life time Restrictions related to environmental requirements and safety.

One essential element of the entire pre-treatment process is care when performing the work. Today, the inspection is performed with reference to various standards. The most common standards are ISO 8501 which gives a visual description of the appearance of a steel surface both before and after blast-cleaning and wire brushing. For water-blasting/water-jetting, separate standards have been prepared by ISO and SSPC/NACE.

Personal notes

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Chapter:

Pretreatment

Surface treatment may include the following operations

Work to be carried out in the cleaning shop

• Steel work (Pre-blasting preparation) • Removal of: – Rust and mill scale – Salt – Grease, oil, dirt – Old / unwanted paint • Flattening of glossy paint • Special pre-treatment of new aluminium

Remove prior to pre-treatment:

• Salt and soil:

Clean water

• Oil - grease:

Solvent with emulsifying agent or alkaline cleaner

and galvanised surfaces Paint School

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Equipment contaminating the surface

Degreasing side bottom with emulsifying detergent to remove oil, grease etc.

Oil contamination from grinder

• Should always be carried out before blast-cleaning • The detergents must be removed by ”Low pressure

Reasons may be: • Oil leaking out of equipment • Equipment has been stored with oil • Lack of oil trap. (Air from compressor contains oil)

water cleaning, LPWC” (Around 250 - 300 bar)

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Must be removed prior to surface preparation

Blisters close to weld, probably due to welding smoke remaining on the the steel

Welding smoke is water soluble and can only be removed by water

• Welding smoke is resoluble in water and will Welding smoke

Area washed with water

create osmotic blistering

• Galvanic difference between steel plate and weld may aggravate the attack

• Solvents will not •

remove the welding smoke completely If not removed, osmotic blistering may occur.

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Chapter:

Pretreatment

Pre-treatment

Rotary impact or scarifying tools

Evaluation of methods Blast cleaning Power grinding Power wire-brushing Manual wire- brushing. Needle hammer Power chiseling Manual scraping

Ideal Not as good as blast cleaning, but best alternative. Great risk of unwanted polishing. Not recommended. Very poor. Usable, but risk of unwanted rough surface, Good in combination with other methods Usable in combination with other methods.

Equipment with rotating abrasive head

• • •

Rotary impact tools is the best choice for removing coatings

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Steel substrate treated by hand and mechanical power tool cleaning equipment

Grinders and sanders • • •

Coated abrasive discs - To remove paint, mill scale and rust Non-woven abrasive discs - To remove paint and rust and for feathering of paint Wire brushes - To remove loose rust (tends to polish surface)

Mechanical wire brush approximately St 3

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Pre-treatment

Advantages

Disadvantages

• •

• • •

•

Surface remains dry Good anchor pattern for paint No pre-rusting profile

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Handouts

Hand wire brush, approximately St 2

Dry blasting Benefits and limitations

Illustration of various blasting methods

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Peening flaps (Roto-Peen) - Creates a surface profile, 25 to 75 microns Rotary hammers - cutters Nylon non-woven abrasive wheels

Does not remove salt Does not remove oil Creates dust

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Chapter:

Pretreatment

Blast cleaning

Blast - cleaning

Factors influencing the production rate

Measure the air pressure at the nozzle Pressure gauge

• Productivity is directly proportional to: Pressure at Nozzle Capacity of the air compressor

Nozzleholder

Nozzle

• Pressure at Nozzle

7 kg/cm² = 100% productivity Air

• Pressure at Nozzle 5,6 kg/cm² = 66% productivity • Pressure at Nozzle 4,2 kg/cm² = 50% productivity

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Blast cleaning: Effect of nozzle pressure on cleaning rate.

Blast Cleaning

Rule of thumb: To avoid loss of pressure

Nozzle pressures, Kg / cm²

The blast hose shall have an opening which is 3-4 times bigger than the orifice of the nozzle.

Hose opening

Nozzle opening 3 - 4 times

Cleaning time: 2 minutes Source: Clemtex Ltd.

Remaining Removed

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Blast cleaning Impact damages may destroy overlapping zone

Blast cleaning

Abrasives will damage the coating Cracks due to direct impact by abrasives

Corroded area. Subsequent spot blasting Solid coating

3-Coat paint

Originally corroded area

Area require feathering

Steel

Impact by abrasives Feathered required

Area with reduced adhesion

(SOURCE: Munger, C.G. Practical aspects of Coating Repair.

Corroded and blast cleaned

Materials Performance, Vol. 19, No 2 p. 46 (1980)

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Chapter:

Pretreatment

Blast cleaning

Blast cleaning

Abrasives will damage the coating

Correct and incorrect sweep blasting

Impact of abrasive

Star crack areas

Abrasives approx. 0.5 mm Pressure approx 2-3 kg / sqcm

3-coat paint system

Star cracks

Areas with reduced adhesion

Often abrasives of 0.2 - 1.4 mm and too high pressure is used

Steel May be caused by direct impact or rebounding abrasives (ricochet) Paint School

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Corrosion has taken place Almost the total area has been spot blasted

Loose edges resulting from spotblasting carried out some time ago • Edges has not been feathered prior to application of the paint • The edges are weak points in the paint film • Corrosion attack initiates on such areas

• Spot blasting in this way result in many loose edges that needs to be feathered

• Recommendation: Blast - clean larger areas Top coat Bare steel Antifouling

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Surface has not been well cleaned Over painting grit or foreign matters • • • •

Poor cleaning of ballast tanks

Weak point in paint film Entrapped air Less adhesion Corrosion will develop rapidly

• Abrasives remaining from blast cleaning • 300 µm Coal Tar Epoxy • Blistering and rust penetration after 10 months of exposure

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Chapter:

Pretreatment

Slurry and wet blasting Benefits and limitations Advantages

Disadvantages

•

•

• •

Surface profile is achieved Removes salt Creates no dust.

Water-jetting Advantages • Salt level on steel surface drastically reduced. • No dust produced. • No grit cost (water is usually cheaper).

Flash rust may develop on surface

• • •

Grit blasting uses 55 kg/m², costing £ 63,-/ton = 3,46/m². Ultra High Pressure Water Jetting, UHPWJ needs 130 l/m², costing £ 0,80/ton = £ 0,10/m²). Close working of other trades possible. Abrasives can be introduced if improved surface profile is required. Lower noise level than with grit blasting.

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Pre-treatment of Stainless steel

Pre-treatment of Aluminium • Degreasing and washing • Sweep blasting with non-metallic abrasive

• Degreasing and washing • Sweep blasting with non-metallic abrasive • Abrading through other means, e.g.

or

• Abrading through other means, e.g. mechanical tools, emery paper etc or

mechanical tools, emery paper etc

• Washing with a strong alkaline cleaner followed by washing with clean water or

• Wash primer (Not in combination with Epoxy paint) Paint School

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Pre-treatment of hot-dip galvanised steel. • • • •

Electrolytic de-scaling. Working process • • • • • •

T-wash Sweep blasting Etch primer, single or two - pack Natural weathering for at least twelve months

• • • • Paint School

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Empty the ballast tank Mount the Magnesium strips Fill the tank with seawater Ballasting period of 1-2 weeks Empty the tank Remove calcareous deposit immediately (Water pressure: 250 to 300 bar) Remove loose rust and scale Remove iron cores Dry the tank Start application of paint

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6. Paint Application It is important to understand that paint is a semi-finished product. Only once the paint has been applied to a structure will the real properties of the paint system become apparent. How well a system works largely depends on the skill of the painter. The protective properties of a paint can be significantly reduced if the paint is applied incorrectly.

Application technique To apply the paint to achieve the optimum properties, it is important to select the right application tool and method. Generally application tools are selected according to the size of the object, complexity, accessibility, type of paint and environmental aspects. Painting always begins with "stripe coating". Stripe coating means applying an extra coat of paint on areas where experience has shown that it is difficult to achieve the specified film thickness by spray. Typical areas which should be stripe coated are sharp edges, notches, welds (particularly manual welds) and areas which are difficult to reach with a spray gun. This is a very important job but it is often skipped or done badly as it is a time-consuming process. Stripe coating on bare steel should always be carried out with a round or oval brush and not a roller. The aim is to ensure good wetting of the substrate. Stripe coating should also be used between each coat. A stripe coat can be applied with a roller on the previous coat where suitable. The film thickness achieved using brushes or rollers is normally in the range of 35 - 40 µm. Airless spraying is the most effective and cost-saving application method. It is possible to paint large areas in the minimum of time and paint can be applied in greater and more even film thicknesses per coat than with a brush and roller. The application technique and experience of the painter are very important for achieving a good result. This includes factors such as the right distance between the gun and object (normally 30 to 60 cm), the right angle to the object (normally 90 degrees), good overlapping (approx. 50% overlap) and sensitivity in use of the trigger. When spraying, the paint is applied at as low a pressure as possible to achieve an even spread. Too high a pressure leads to dry spraying and a lot of dust.

Checks to be carried out during application The painter only has one instrument available for checking the film thickness during application: wet film gauge (comb or wheel). It is important to use the cam regularly. This ensures good checking during the entire application process so that the correct film thickness is achieved over the entire structure. The atmospheric conditions should always be checked during application of paint, and the correct ventilation ensured, especially in tanks. These conditions must be monitored throughout the application process and whilst the paint is drying / curing.

Mixing and thinning Do not add unnecessary quantities of thinner to the paint as this causes slower drying and you will have to apply the paint in greater wet-film thicknesses to achieve the same dry film. Use Jotun Paint School

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of the correct (specified) thinners is important as adding the wrong thinner can cause poor results in terms of corrosion protection. When applying two-component paints, the mixing process itself is also important. Use mechanical agitators and not stirrers. Good agitation or mixing of the two components and the correct mixing ratio are important. Follow the instructions on the technical data sheet for the product. Plural component spray (two-component spray) are also available for applying special two-component paints, where the components are mixed in the correct ratio in the unit itself.

Health The painter is exposed to solvents and various other components in the paint. Make sure that approved protective equipment is used and that ventilation is adequate. Personal notes

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Chapter: Paint Application Application

Tools for mixing of paints • Always use mechanical

Cleanliness and good housekeeping before, during and after application are one of the most important factors to have a good result

• •

agitator to ensure proper mixing. Proper mixing will not be achieved by a stirrer A stirrer may also contain dirt and loose parts that may contaminate the paint and clog the spray equipment

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Consequence of inferior mixing: Poor coating performance

Methods for paint application

• To the right: Correct mixing and mixing ratio. • To the left: Insufficient mixing and / or incorrect mixing ratio.

Airless spray: Good Paint brush: Good Roller: Poor, particularly for the first coat

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Application by paint brush

Application by roller

Benefits

Benefits

• Good wetting of the substrate • Forces the paint into the surface • Better than roller on the first coat • Good on areas with poor accessibility

• Application speed is faster than with paint brush • Good on areas with poor accessibility

Limitations

• Poor wetting of the substrate • Never use for the first coat • May incorporate air and pinholes

Limitations

• Gives low film thickness, many coats required • Creates an uneven film • Application speed is slow

in the paint film

• Gives low film thickness, many coats required

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Chapter: Paint Application Stripe coating of superstructure between first and second full coat

Application

Stripe coating prior to each full coat

Note the contrasting colours. Excellent work

Stripe coat with paint brush:

• Where difficult access with spray • Profiles • Inside edges • Holes, notches • Corners, angles • Sharp edges • Manual welding seams

• • • •

Pipes Supports Windows Reeling

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Poor workmanship: Stripe coated welding seam

Rules when spraying

• Many holidays • The paint must be worked properly into the rough

• Correct distance between spray gun

Paint application.

substrate using several strokes with the paint brush.

and substrate: (30-60 cm)

• Correct angel (90°) • Overlapping (50% or cross application)

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Seek to keep the gun at a right angle to the substrate

Paint application. Airless spraying with overlap

The distance should be between 30 and 60 cm. The optimal distance will vary, among other things with wind, temperature, pressure at the nozzle and viscosity of the paint .

50 % Overlap

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Overlapping ensures an even film thickness

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Chapter: Paint Application Application with a spray gun.

Formation of a paint film

Stroke and triggering

• As the coating droplets hit the

Structure

substrate they will become flat.

• Then, they will overlap and form a continuous paint film

Start stroke → Pull trigger

→

Release trigger →

End stroke

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Incorrect application technique. Waving with the gun

Overspray or dry-spray Dry-spray will develop at the edges of a wide spray fan. This may give a rough film and pinholes Outside area of effective spraying: • Low impact • Poor flow of paint • Result: Dry-spray

Result:

• • • •

Area of effective spraying

Uneven paint film Dry-spraying will occur The loss factor will be high The roughness will increase

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Spraying of a ship’s bottom. Very poor application technique

Incorrect use of airless spray equipment will result in: • A rough surface • Too much paint dust • Pinholes in the paint film • Entrapped air • Entrapped solvents • Too high paint consumption

• Too long distance • Dry spraying • Uneven film thickness Running water along side the ship while painting. (Scupper plug missing)

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Chapter: Paint Application Poor application technique serves nobody

Spot-blasting and poor application technique. Direction of application

• Contamination of • • •

• Loose paint edges • Application has been

the environment High loss factor Poor corrosion protection Waste of money

•

done in only one direction Corrosion has developed on shadow sides shortly after application

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Application Technique With Spray Gun

Spray application technique. Apply one extra coat to corners Wrong

Positioning of the spray gun Correct Wrong Parallel

Perpendicular

Over spray

Arcing

Heavy

Correct

Tilting Light

Light Source: Corr. Control Principles and Metodes, Sect. 7, Ameron Inc., Monterey Park, Ca.)

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Application of inside corners Air cushion is formed

Application of inside corners • Spray each side of the corner separately • Use a vertical spray pattern • This will give an even film thickness

Area with thin layer of paint

2 3 4

Area with thick paint film

5

Application directly into the corner gives an uneven film thickness, but may still be satisfactory for many types of service

1 (Source: Industrial Maintenance Painting, National Association of Corrosion Engineers; Houston TX, p 88, 1973)

(Source: Industrial Maintenance Painting, National Association of Corrosion Engineers; Houston TX, p. 88, 1973.)

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Chapter: Paint Application Inside a tank Runs leading to cracking of paint

Application technique:

Surfaces with deep pits

• Paint has collected in the corner

• Several mm thick paint

• The paint cracked, corrosion will develop Air will be compressed in pits and push the paint back. This makes use of airless spray on such areas almost impossible Paint School

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What factors influence the drying / curing process ?

Paint not applied according to the specification. Close up of paint film (2 of 2) • Specification : 50 µm • Thickness of topcoat:

• Relative humidity, % • Ventilation • Temperature • Film thickness • Number of coats • Evaporation speed of solvents

100 - 150 µm Result: • Entrapped air • Entrapped solvents • Porous film • Blisters and delamination will occur in future Paint School

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Temperature and humidity of air used for drying.

Main rule for pre-treatment and paint application: •

Temperature of substrate should be at a temperature of

•

min. 3oC

• • •

above dew point of the air in the vicinity

Supply of heated air immediately after application may lead to skin drying and entrapped solvents Cold air will keep the film open longer and ensure proper evaporation Avoid high air temperature (especially epoxy) High humidity will slow down the drying time Exhaust from heating equipment using propane or paraffin oil contain water and Carbon dioxide and may create Amine sweating

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7. Inspection and Control The human factor is an important element in the process to ensure the specified quality of the paint system. It is therefore very important to inspect and control all work performed in connection with surface treatment. During the manufacture of a structure, inspections and control should be performed at the following critical phases: • • •

Steelwork Pre-treatment Before, during and after application.

For all activities, the inspector should verify and document that the work complies with the specification and has been performed professionally, and that the paint supplier's instructions for use of the product have been followed.

Steelwork Activities which are normally included in the preparation are described in chapter 4. The inspector should verify that the steelwork has been performed according to specification or ISO 12944-3. In particular, this includes the rounding of edges, grinding of welds, removal of weld spatters and grinding of laminations.

Pre-treatment The inspector must check and ensure that the structure is free from oil, grease and salt and that the washing procedure has been followed. Visual assessments shall be made of the degree of rust on the steel before preparation and the condition of the structure after preparation. Standards ISO 8501-1 or ISO 8501-2 (for repair work) apply. Before and during pretreatment, the atmospheric conditions are checked according to ISO 8502-4. Other checks to be performed usually include inspection for invisible contamination on the surface such as salts (ISO 9502-6 and 9), dust (ISO 8502-3) and specified roughness (ISO 8503). All data and records shall be entered in a daily log.

Application of paint The inspector's task during application of the paint is to ensure that all work proceeds in the specified manner. This includes all work operations from opening of the paint tin to the application of the final coat. It is important to have a good overview of all technical documentation. Check technical data sheets and check for use of the right thinners, the right curing agent for the base, mechanical agitators and a good mix when using two-component paints. Check the specified pre-reaction time if given in the technical data sheet. Check that stripe coating has been performed properly before application of the full coat by spraying. Ensure that the painter carries out careful checks with using wet film gauge so that the specified wet film thickness is applied. The atmospheric conditions should be monitored during the painting work. Ensure adequate ventilation to remove solvents. All data and records must be entered in a daily log. Jotun Paint School

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Drying / curing After drying / curing, the dry film thickness is checked (ISO 2808). Pay particular attention to areas where access with an airless spray gun is difficult, and ensure that the dry film thickness lies within the specified limits. Check that the overpainting intervals are observed for the paints, and that the surface is clean before overpainting. After a structure is painted, the total film thickness should be checked. Individual specifications also require adhesion testing for example to ISO 4624, or holiday detection to ASTM G62-85. It is very important to have good test routines and enter all data and records in a daily log.

Personal notes

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Chapter:

Inspection and Control

What is QA - QC ?

An inspector’s work includes: • Be capable of interpreting the specifications

QA = Quality Assurance (A documented management system)

• Understand the objective • • • •

QC = Quality Control (Inspection and testing routines)

of the inspection Inspect all structures to be painted Ensure that all specified requirements are met Document the results from the inspections In case of non-conformance: Issue written reports

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Daily logs • • • • • • •

Steel temperature Air temperature % Relative Humidity Dew point Object no. and name Exact specification Pre-treatment, specified and actually conducted.

An inspector needs to know

• Film thickness (to be • • • • • •

• All paints that will be used • All relevant inspection

measured also at spot repair) Area, m² Product name, place of production and batch no. Name of relevant persons What was discussed Non conformance report (remember signatures) Other comments

methods and inspection tools

• Relevant standards • Relevant TDS and MSDS • Methods involved in cleaning, pre-treatment and paint application

• The equipment used for pre-treatment and application: Benefits and limitations

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Inspection of steel work (Pre-blasting preparation)

What needs to be inspected ? If relevant, the following stages of the production need to be inspected

The following items need to be inspected during construction

• Shop-priming of the steel • The steel work

• Rounding of sharp edges. • Smoothing of rough welding seams. • Removal / grinding of weld spatter

(Pre-blasting preparation) and surface preparation prior to paint application • Application of paint • The applied paint film and its curing/drying conditions.

and beads.

• Cleaning

• Cracks and pittings. • Surface faults like laminates etc. • ISO 12944 - 3 , or ISO 8501 - 3

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Chapter:

Inspection and Control

Inspection of cleaning and surface preparation prior to application

ISO 8501 - 1

Surface preparation

If relevant, the following conditions must be inspected / verified

• • • • •

Cleanliness (salt, oil, grease and dust/dirt) Evaluation of present condition (rust grade) Surface preparation (e.g. blast cleaning) Cleanliness of prepared surface (salts, oil, grease, dust and dirt) Climatic conditions (temperature, relative humidity etc.)

•

Visual assessment of surface cleanliness after blast cleaning, hand or power tool cleaning or flame cleaning

• •

Rust grades and preparation grades of uncoated steel Photographic examples of steel when blast cleaned with different abrasives

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ISO 8501 - 2

ISO 8501 - 2

Surface preparation

Standard for deciding preparation grades

PSa : Localised blast cleaning (grades 2, 2 ½ and 3)

As for ISO 8501-1, but: For steel where previous coating has been removed locally, not completely.

PSt

: Localised hand and power tool cleaning (grades 2 and 3)

PMa : Localised machine abrading (one grade) Paint School

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ISO 8502

ISO 8502

Assessment of surface cleanliness (1 of 2)

Assessment of surface cleanliness (2 of 2)

Part 1 Field test for soluble iron corrosion products

Part 6 Extraction of soluble contaminants for analysis. The Bresle method.

Part 2 Laboratory determination of chloride on cleaned surfaces.

* Part 9 Conductometric measurements of soluble salts .

Part 3 Assessment of dust on steel surfaces prepared for painting (pressure- sensitive tape method)

*

Part 4 Guidance on the estimation of the probability of condensation prior to paint application.

* Part 7, 8 and 10 are not prepared

Part 5 Measurement of chloride on steel surfaces prepared for painting. Ion detector tube method. Paint School

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Chapter:

Inspection and Control

Atmospheric conditions. Requirement during blasting and painting

Ambient temperature and steel temperature Is the temperatures important ? YES !

• Ambient temperature will influence: – shelf life – pot life – viscosity/sprayability – steel temperature • Steel temperature will affect: – speed of cure – degree of cure – recoating interval – service life of the coating

Surface temperature of the structure must be minimum 3 °C above the dew point of the surrounding atmosphere

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ISO 8502 - 6

ISO 8502 - 9 Conductometric measurement of soluble salts.

The Bresle method. A method for extraction of soluble contaminants on steel substrates for analysis:

Field method for measuring soluble salts by conductivity (µ S) of solutions containing water soluble salts

The Bresle method This is a quantitative test

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Instruments for measuring surface roughness

Calculation of salt level on the substrate

• • • • •

Formula: (L2 - L1) x 6 = mg salt per m2 L2 = µS after cleaning L1 = µS before cleaning Water sample, ml.: 10 Constant in formula: 4

15 6

20 8

50 20

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Stylus instruments Elcometer Mod. 123 Testex Press-O-film Microscope Comparator – Rugotest No. 3 – ISO 8503 etc.

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Chapter:

Inspection and Control

ISO 8503 Surface roughness

Inspection during application The following must be verified, inspected or tested:

• Example of a reference • • • •

• • • • • • • • •

comparator Surface profile comparator comprising four segments. Grit (G) Shot (S) Check if the profile is according to specification and the paint manufacturer’s recommendation

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Information to be found from the technical data sheet, TDS • Product description – Generic type etc. • Recommended use – Where to use the product • Technical information – Solids by volume, WFT, DFT

• Application data – Methods, mixing, potlife • Surface preparation – Different methods given

Record name of coating and batch no. Ensure proper mixing of 2-pack paints Ensure use of the correct thinner Measuring the wet film thickness (WFT) Number of coats as given in the specification Cleanliness between coats (salts, dust, oil etc.) Drying time / recoating intervals Control of equipment: Pressure, nozzle etc. Climatic conditions (Ventilation, Air and steel temperature and the relative humidity)

ISO 2808 - 97

Determination of film thickness (1 of 2)

• Conditions during application

Method 1:

Determination of wet film thickness.

Method 2:

Determination of dry-film thickness by calculation from mass Measurement of dry-film thickness by mechanically contacting method Measurement of dry-film thickness by the profilometer method Measurement of dry-film thickness using microscope method

• Drying and overcoating time at different temperatures

• Typical recommended • • • •

Method 3:

system Storage Handling Packing control Health and safety – Details in MSDS

Method 4: Method 5:

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Calculations : Paint Abbreviations

ISO 2808 - 97

Determination of film thickness: (2 of 2) Method 6:

Magnetic method

Method 7:

Eddy current method

Method 8:

Non-contact methods

Method 9:

Gravimetric method (dissolving methods)

Method 10:

Determination of dry-film thickness on blast-cleaned steel substrates

WFT DFT % VS LF DV

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= = = = =

Wet Film Thickness Dry Film Thickness Percent Volume Solids Loss Factor Dead Volume

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Chapter:

Inspection and Control

Formula for determining the DFT Formula: DFT

Consumption of Paint with loss To be painted: Tank, area of 500 m2 , 40 % loss

WFT x % VS 100

=

40 % loss implies that only 60 % will remain on the surface. The correction factor, Loss factor, will be 0.6

Example:

Area, m2 x DFT 10 x % VS x loss factor

Formula: WFT =

250 µm

% VS =

50 %

DFT

250 x 50 100

=

=

125 µm

Epoxy mastic

500 x 200 10 x 85 x 0,6

= 196 litre

Polyurethane topcoat

500 x 50 10 x 50 x 0,6

= 83 litre

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Dead volume increases the volume of paint required

How much paint should we order ? calculation of paint consumption with loss A loss of 40 % means that only 60 % will be applied on the surface

Smooth (polished) steel surface Even film thickness

Example: 100 litre is needed, loss is 40 % We have to order

Steel Specified thickness Uneven steel surface Paint will fill the valleys

100 x 100 60

Dead volume

100

= 0,6 (loss factor) = 167 litre

Not 100 litre + 40 % extra = 140 litre Steel Paint School

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ISO 2808 - 97

Inspection after application

Determination of film thickness Method No. 10 - On blast cleaned steel substrates

After application the following must be checked

• Electromagnetic instruments • Calibration on a smooth steel surface min. 1,2 mm thick • For DFT measurement, not less than 25 and preferably

• Climatic conditions (Ventilation, • • • •

Temperature and humidity) Curing / drying of the film Dry film thickness (DFT) Adhesion Holiday detection (if required)

above 50 microns

• Number of readings, as a guide: – 1 reference area: At least 3 readings evenly – 2 reference areas for every square meter for flat plates – 4 reference areas for every length for a web – 2 reference areas every metre length for a flange – 2 reference areas every metre length for a pipe

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Chapter:

Inspection and Control

ASTM D 3359-87 Adhesion testing by knife and adhesive tape

ISO 2409

Cross-cut test Cutting tool Single bladed knife or Multi-blade cutting tool with 6 cutting edges spaced 1 mm or 2 mm apart

• There are two test methods • The method to select depends on the DFT Method A: DFT above 125 microns Method B: DFT below 125 microns (Above 125 if wider cuts are used)

Spacing of cuts 0 - 60 microns: 0 - 60 microns: 60 - 120 microns: 121 - 250 microns:

Method A: X - cut. Tape test Method B: Cross - cut. Tape test

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1 mm spacing, hard substrates 2 mm spacing, soft substrates 3 mm spacing, hard/soft substrates 3 mm spacing, hard/soft substrates

ISO 4624

ASTM G 62 - 85 Method A

Pull-off test for adhesion

Pinhole detection. Low voltage.

Procedure:

• • • • •

• Low voltage: < 75 V DC • To detect pinholes, voids or metal particles to be

Test dollies glued onto the coating Adhesive: Cyano-acrylate or solvent free epoxy Remove adhesive and coating around the dollies Pull off test-dollies vertical to the surface Read adhesion value and report the type of fracture

in the range of 25-250 microns. • Effective for paint films up to a DFT of 500 microns if a wetting agent is used in the water. • This is a non-destructive test.

Fractures:

• Adhesion failure - fracture between coats or substrate and 1. coat • Cohesion failure - fracture within a coat Paint School

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ASTM G 62 Method B

ISO 12944

Holiday detection. High voltage.

General standard for corrosion protection: Paints and varnishes - Corrosion protection of steel structures by protective paints systems.

High voltage: 900 - 20.000 V

Part 1 Part 2 Part 3 Part 4 Part 5 Part 6 Part 7 Part 8

Used to detect pinholes, voids and areas with thin paint films This is a destructive test.

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General introduction. Classification of environments. Design considerations. Types of surface and surface preparation. Protective paint systems. Laboratory performance test methods. Execution and supervision of paint work. Development of specifications for new work and maintenance.

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8. Paint Failures As we have already said, paint supplied in containers is a semi-finished product. The finished product only exists once the paint has been applied to the structure in a complete paint system. This is where we see how good the protection is. The most important and most common paint failures occur as a result of poor or insufficient steelwork, preparation or application. Some of these faults are revealed during or shortly after application but some only appear after a certain period in service. The most common failures during and just after application are: • • • • •

Insufficient film thickness Sags / runs Dry spraying Pinholes Amine sweating

Insufficient film thickness is often the result of non-systematic application and inadequate checks with a wet film gauge. Sags / runs occur when the paint is applied too thickly or too much thinner has been added to the paint. This is probably because the specification has not been followed. Occasionally, faults are also found in the paint. The inspector must note the production number in the daily log. Sags / runs should be repaired immediately with a brush. Dry spraying is normally a result of poor application or difficult weather conditions. The most common application fault is too great a distance between the spray gun and the structure. High temperature combined with low relative humidity will also contribute to dry spraying as the solvents evaporate en route from the gun to the object. Strong wind or strong ventilation also contributes to an increased risk of dry spraying. Pinholes often occur on porous substrates, for example zinc silicate. On these substrates, it is important to apply a thin layer of paint, normally called a tie coat or by using the mist coat full coat technique. Pinholes are also found if there is too strong ventilation during application. Amine sweating can occur on epoxy paints during curing in particularly humid environments. The phenomenon results in a sticky surface, occasionally visible as white stains. These must be removed before overpainting using rags and tepid water (thinners for some paints). The risk of amine sweating is reduced by observing the specified induction time after mixing the two-component paint and ensuring good atmospheric conditions during application and curing. The most common paint faults after exposure are: • • • • •

Blistering Rust penetration Cracking Flaking Chalking

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Such faults can be assessed using standard ISO 4628. Blistering is normally an adhesion-related problem and is due to poor cleaning before application of the paint. The most common cause of blistering is the application of the paint to a substrate contaminated with salt (osmotic blistering). After blisters have formed, they burst and the underlying unprotected material begins to rust if rust formation has not already started. Osmotic blistering occurs on exposure under water or in areas with heavy condensation. In particular, the salts sodium chloride and ferric chloride, and welding smoke, cause blistering. Other causes of blistering can be dust or grit on the surface (reduces adhesion), voids between the steel and the paint or trapped air in the paint film. Blistering is evaluated according to ISO 4628-2. Rusting occurs after a blister in the paint film bursts. The failure will occur most quickly where the paint film is too thin. Particularly susceptible areas are sharp edges, rough welds and places which are difficult to access for application. If rusting occurs after a very short time without prior blistering, there will be an opening through to bare steel, i.e. a pinhole. Rust penetrationevaluated according to ISO 4628-3. Cracking occurs after a certain ageing of the coating. The causes can be: • • • •

The top coat is harder than the coats underneath Excessively thick system combined with temperature variations Excessively fast curing of two-component systems Excessively thick zinc silicate gives "mud cracking".

There are various degrees of cracking. Cracks can either form in the top coat only or throughout. The time before the fault occurs can vary. Mud cracking occurs immediately after application but cracking occurs only after a certain time. Cracking is evaluated according to ISO 4628-4. Flaking is normally the result of a poorly cleaned substrate (oil, grease) or the paint being applied onto condensation or surfaces with amine sweating. Paint will frequently flake off from areas with blistering or cracking and occurs where adhesion is poorest. Flaking is evaluated according to ISO 4628-5. Chalking is an ageing problem. The binder is degraded by UV radiation from the sun and the pigments appear as dust on the surface. The paint's ability to resist chalking will vary according to the binder used. Epoxy will chalk in sunlight after just a few months whereas polyurethane will retain its gloss for many years. Chalking is evaluated according to ISO 4628-6. Personal notes

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Chapter:

Paint Failures Sags and runs

Most common paint failures • • • • • • • •

Holidays, too low DFT Sags and runs Orange peel Dry spraying Overspray Pinholes, popping Fish-eyes Wrinkling / lifting

• • • • • • • • •

Sweating (Amine) Blushing Poor drying / curing Blisters Rust penetration Cracking Flaking Chalking Discolouration/bleeding

Appearance

• Paint running or hanging like curtains on vertical surfaces Caused by

• Too high Wet film thickness • Too much thinner added to the paint • Airless spray gun too close to surface Repair

• Avoid above • Use paint brush to smoothen or remove excessive paint

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Orange peel Appearance

• Paint surface is rough, like an orange peel

Caused by

• Poor flow / levelling properties of the paint

Dry spray Appearance • Porous, sandpaper like surface of the paint Caused by • Poor atomisation of the paint • Spray gun too far away from the object • High air temperature and low relative humidity: Too fast

(Paint too thick or too low temperature)

evaporation of the solvents

• Poor atomisation of the paint • Too fast evaporation of the thinner • Airless spray gun too close to surface Repair

• Strong wind during application • Inorganic Zinc: Re-blast and apply new paint • Physically drying paints: Apply thinner on the painted

Repair

surface and apply a new coat

• Oxidativly drying paints: Remove loose dust and apply

• Improve application technique • Use correct thinner • Grind surface and apply new paint

topcoat

• Two-pack paints: Remove loose dust, sandpaper to smooth surface, apply topcoat

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Pinholes

Pinholes / popping Appearance

Appearance • Tiny holes through one or more coats, or even down to the substrate, as if perforated by a needle Caused by • Dry spraying • Entrapped solvents or air • Porosity of previous coat • Incorrect application technique or viscosity of the paint Repair • Grind top layer of the paint • Recoat

Caused by

• • •

Repair

• Reduce film thickness or ventilation and adjust application technique (Tie coat / mist coat technique.

• Remove paint on painted surfaces and repaint

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Solvents or air try to evaporate through the upper part of the film, which has already nearly dried, leaving small bubbles /craters on the surface Very porous substrate (e.g. Zinc silicate primer) Entrapped solvents or air in the paint film Usually in connection with too high film thickness, too long application distance or too strong ventilation.

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Chapter:

Paint Failures

Fisheyes

Wrinkling

Appearance • Spots of paint on the surface with no wetting of the surface around the spots. Appearance of a fisheye. Caused by • Paint applied on oil, silicone or other contaminants • Painted on incompatible paint (Glossy paint giving poor wetting) Repair • Grind top layer of the paint • Recoat

Appearance • Small wrinkles through or partly through the paint film Caused by • Skin drying of the paint film, which is usually applied too thick Repair • Grind top layer of the paint • Recoat

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Sweating and carbonisation (Amine blooming)

Lifting Appearance • Small wrinkles through the paint film Caused by • Softening and raising or swelling of a previous coat by the application of an additional coat • Normally when overcoating Alkyd • Lifting often caused because the solvents in the new coat is too strong for the previous coat Repair • Remove the paint • Recoat

Appearance • Tacky and sweating film, often with white stains Caused by • High humidity, particularly on Epoxies during curing • Poor ventilation • The Amines react with CO2 and humidity and form Amine carbamate. • Too low temperature Repair • Wash with warm water or thinner, using rags Preventive measure: Induction time before application start

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Bloom and blush (Blushing)

ISO 4628

Content of the Standard The standard consists of six parts

Appearance

• Surface looks milky Caused by

• Condensation on cold steel surfaces at high humidity • Air pollution, sulphur dioxide (SO2) and ammonia forming ammonium sulphate on the paint film.

• “Fast “ thinners Repair

• Grind top layer of the paint • Recoat

Part 1 Part 2 Part 3 Part 4

General principles and rating schemes Designation of degree of blistering Designation of degree of rusting Designation of degree of cracking

Part 5 Part 6

Designation of degree of flaking Designation of degree of chalking

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Chapter:

Paint Failures

ISO 4628 - 2

ISO 4628 / 3 Designation of degree of rusting

Degree of blistering

Rating Designate the degree of rust formation by reference to the pictorial standards

Blisters of size 5

Degree Density 2

Density 3

Density 4

Density 5

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Area rusted %

Ri 0

0

Ri 1

0,05

Ri 2

0,5

Ri 3

1

Ri 4

8

Ri 5

40/50

ISO 4628 / 3

Pinpoint rusting

Designation of degree of rusting Test report:

Appearance

The test report shall contain at least the following information: a) the type and identification of the product tested b) a reference to this International Standard (ISO 4628/3) c) the numerical rating of the rusted area d) the numerical rating of the size of the rust spots, if desired, for example: Rust: Ri 3 (S4) = rusted area, as a percentage of rust, approximates standard 3, the sizes of the individual rust spots of the order of a few millimetres. e) the date of the examination

• Points of rust Caused by

• Small pores (pinholes), openings or defects in the paint film down to bare steel

• Holidays due to overspray, dry spraying etc. • Too high substrate roughness Repair

• Grind down to bare steel • Recoat

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ISO 4628 - 4

ISO 4628 / 4 Designation of degree of cracking

Evaluation of cracking

Test report:

Quantity

a) the type and identification of the product tested b) a reference to this International Standard (ISO 4628/4) c) the numerical rating of the quantity of cracking d) the numerical rating of the size of cracking e) the depth of cracking (a. b. or c), where possible, for example: cracking 2 (S3) b

1

2

3

4

5

If necessary, the standard assessment may be amplified in words, for example “linear cracking”. The use of such comments shall, however, be avoided wherever possible e) the date of the examination Paint School

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Chapter:

Paint Failures ISO 4628 - 5

ISO 4628 / 5 Designation of degree of flaking

Evaluation of flaking. Quantity

Test report 1

The test report shall contain at least the following information: a) b) c) d) e)

2

3

4

5

the type and identification of the product tested a reference to this International Standard (ISO 4628/5) the numerical rating of the quantity of flaking the numerical rating of the size of flaking the depth of flaking (a or b), for example: flaking 3 (S2) a

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Chalking

Bleeding

Appearance • Almost like dust on top of the coat

Appearance

• Discolouration of a paint, particularly in

Caused by

• Coloured ingredients in a previous coat or on

topcoats

• The gloss will be reduced Caused by

• • • • Repair

Pigments and extenders exposed on the paint surface, due to Exposure to sun / UV light Degradation of the binder Weathering of the paint Insufficient mixing of the paint

Repair

• Grind and/or wash top layer of the paint • Recoat

Note: Bleeding may continue through additional coats unless source is removed

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Delamination (Adhesion failure)

Mud-cracking

Appearance • Loss of adhesion: – Intercoat delamination: Between coats – Substrate delamination : Between primer and substrate Caused by • Primer not compatible with subsequent coat • Contamination of substrate or between coats • Recoating interval too long • Blooming / sweating Repair • Remove loose paint layer or down to substrate • Recoat

Appearance • Cracks occurring during the drying process of the paint • Appearance of the surface of cracked mud Caused by • Particularly for inorganic Zinc applied at a too high film thickness Repair • Re-blast to Sa 2½ or grind off • Apply the inorganic Zinc

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• • • •

the substrate is dissolved by solvents in the subsequent coat, e.g. Soluble pigments (Poor solvent resistance) Tar, Bitumen, etc. Surface contaminants (coloured) Re-blasting and re-application

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9. Antifouling All surfaces exposed to seawater will be "attacked" by marine organisms. When these organisms attach and grow, they cause a significant increase in surface roughness. On a ship's hull, this results in greater friction resistance and hence increased fuel consumption. It is therefore extremely important to prevent marine fouling when assessing a ship's fuel economy. The types of organisms and their growth rates vary with the temperature of the seawater, salinity and the light intensity in the sea. Plant organisms are normally diatoms or green/brown algae, whereas the most common animal organisms are Cirripedia (barnacles), bryozoa and hydroids. The most common way of preventing the fouling of marine structures is to apply a preventative coating or antifouling as we often call it. This contains one or more toxins (biocides) which are normally sufficient to make the antifouling effective against most organisms. Antifouling paint can be divided into three categories: conventional, long life and selfpolishing antifouling paints. 1. Conventional antifouling paints – also known as "soluble matrix" antifouling paint, have been in use for many years. The main binder is resin, a natural product which dissolves very slowly in seawater. The Resin is brittle but although these formulations contain various additives, this type of antifouling often takes the form of a very weak film and the paint can only be applied in relatively low film thickness. The effective protection against fouling varies from 12 to 18 months. 2. Long life antifouling paints are also known as "insoluble matrix". The binder is not completely insoluble in seawater. The active components (biocides) and resin are released but the binder remains on the structure as a porous frame. The porous film left after the biocides have been released forms a weak substrate for a new coat of paint. It is therefore recommended that a sealer coat be applied at each dry docking to create a better substrate for the new antifouling. One risk with this type of antifouling is that year after year, coat after coat, many layers of paint are built up. This build up of layers can cause the paint to break away from the surface or from earlier coats, which increases the roughness of the hull. This condition is called "sandwich coating" and, after fouling, is the main cause of increased roughness on a ship's hull. Long-term antifouling paints are effective for about 24 months. 3. Self-polishing antifouling paints – hydrating type are based on a mixture of watersoluble and water-sensitive binders. These react with seawater to form a soft layer which dissolves relatively easily in water. This type of antifouling was first developed when the need arose for tin-free antifouling paints. The effective life is about 36 months. In today's market, conventional, long-term and self-polishing hydrating antifouling paints are largely tin-free. 4. Self-polishing antifouling paints – hydrolysing type contain a binder which is initially insoluble in seawater. When the paint film is exposed to seawater, a thin layer on the surface of the film absorbs water and a chemical reaction occurs between the binder and the water (hydrolysis). This is the main difference compared with other antifouling paints. The reaction product is water-soluble and will slowly dissolve or be washed away. Thus fresh, new Jotun Paint School

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antifouling paint is constantly being exposed. This results in a linear/predictable rate of biocide release which ensures a highly effective antifouling action. This type of antifouling is available both tin-free and with tin. Both variants can give effective protection for up to 60 months. One very important reason for using self-polishing antifouling paints is to avoid the "sandwich coating", which often occurs when using conventional or long-term antifouling paints. With a self-polishing antifouling paint, the surface will not become porous and it is not normally necessary to use sealers. When a ship is in dock, the hull is rinsed with fresh water to remove slime and other contamination, and the new antifouling paint is then applied directly onto the old paint film. Self-polishing antifouling paints are often based on copper with tin and/or other biocides. Those based on tin are restricted in most countries due to the environmental effects in the sea and will be prohibited from use within a few years. Copper-based products are more "environmentally friendly".

Personal notes

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Chapter: What is fouling ?

Antifoulings What is fouling ?

(1 of 2)

(2 of 2)

There is an estimated 4 - 5000 fouling species and these can be classified into: Fouling is the settlement and growth of marine plants and animals on manmade structures in the sea

➨

Microfouling

– generally referred to as slime, a complex viscous mixture of bacteria and microscopic organisms

➨ Macrofouling – which includes animals and plants Paint School

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What is the consequence of fouling

Why do ships need anti-fouling systems?

On a ship’s hull Increased fuel consumption

Fouling leads to an increase in fuel consumption of up to 40%, due to the increase in drag resistance

On a marine structure Increased drag Structural failures

Heavier load on the structure

Seawater pipe systems – Increased corrosion – Reduced pipe diametres

A clean ship sails faster and with less energy Fouling will eventually damage the primer system

Pump failures

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Selection of Antifoulings • • • • •

Legislation / Environment Type of ship Speed Trade / Voyage factor Dry-docking interval: – Conventional antifoulings: – TBT-containing antifoulings (tributyltin): – TBT-free, self polishing antifoulings:

Hull roughness Roughness can be divided in two main groups

• 1 - 2 years

•

5 years 3 years

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Permanent roughness – welding seams, valve openings, bulging plates etc. Temporary roughness – flaking, dry spray, cracking, sagging, fouling etc.

Page 49

Chapter:

Antifoulings Antifoulings and hull economy

Frictional resistance depends on: • The speed of the ship • The area of the underwater hull • The shape of the hull • The roughness of the hull

Calculation example: Panamax vessel Antifouling – 7,000 litres at a cost of $ 40,000 - $ 50,000 ➡ 10% saving represents $ 4,000 - $ 5,000 Fuel cost – 10,000 HP at $ 100 / ton, sailing 250 days a year ➡ Would save 5% or $ 100,000 in the same period

Hull roughness is the only one of these factors which can be varied to a significant degree

➡ 20-25 times better return

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Application faults •

•

Antifouling challenges

Typical application faults that increase roughness: – Overspray – Sagging – Dry spray – Paint spatter Poor application has a greater ill effect on the drag of a hull than wear and tear

•

Main threat on sidebottom is fouling

•

Main threat on flatbottom is roughness

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Main types of antifoulings

Development of Antifoulings Influencing factors the past thirty years:

1. Conventional Antifouling

➊ Demands from shipowners for better performance with economy ➋ Increased emphasis on surface roughness and hull performance ➌ Increases in fuel oil prices over the period ➍ Technological achievements by many antifouling manufacturers ➎ The trend to extend periods between dry-dockings ➏ The increasing awareness of environmental issues

2. Long-life Antifouling 3. Selfpolishing Antifouling

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Chapter:

Antifoulings Conventional Antifoulings

The composition of Antifoulings • • • • • •

Binder Biocide Extenders Pigments Solvents Additives

• • • • •

?

Soluble matrix paints Rosin as a binder Approximately 12 months protection Binders dissolves in water and biocide is released Often called: Tropic, Super Tropic etc. NOTE: Danger of cracking and flaking Needs to be quickly immersed in water

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Self polishing Antifoulings

Long-life Antifouling • • • • • • •

Insoluble matrix paints Only biocides are released Effective protection is up to 24 months Leaves weak substrate for subsequent coat Sealer coat normally required Binder: CR, Vinyl (possible to add small amount of colophonium) Often called Sargasso etc.

• • • • • •

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Selfpolishing Antifouling with TBT • • • • • • •

Self-polishing Antifouling - Tin free

Introduced in the 1970’s Contains chemically bound organotin Released by hydrolysis in seawater In addition, biocides like cuprous oxide (Cu2O) and organic boosters are used The rest of the copolymer is water soluble and is worn off, usually by friction Reduce hull roughness No sealer coat required for recoating

• Blend of water soluble and water sensitive binders or hydrolysable binders.

• With respect to performance the early ‘ablative’ •

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Predictable performance Extended dry docking period Control of roughness and smoothing No “sandwich coatings” problems Fouling control due to linear biocide release Lifetime directly proportioned with dry film thickness

Handouts

antifoulings have been refined close to those containing tin. Not identical to tin based antifouling in performance yet.

Page 51

Chapter:

Antifoulings Why is hydrolysis so important ?

Release rate for Anti-foulings Anti-foulings

Release rate (µg/cm2 / day)

Comparison of release rate of biocide for different A/F-types

Because:

• 40

Conventional A/F 30

Long life A/F

• •

Minimum release level for fouling protection

Selfpolishing A/F

30

•

10

1

2

3

Linear erosion rate assures long term antifouling property No skeletal layers means good adhesion Continual smoothing of the surface ensures good fuel efficiency Hard film maintains its good appearance

Time, years

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Rules and regulations •

New tin-free technology SeaQuantum SeaQuantum-- Advanced Advanced tin-free tin-freeanti-fouling anti-fouling

MEPC approved a draft assembly resolution in November 1998 agreeing that:

Based on a unique hydrolysing silyl polymer Meets the draft IMO regulations for 2003 and 2008

The Theapplication applicationof ofall allanti-fouling anti-foulingsystems systemscontaining containingTBT TBT should shouldbe beprohibited prohibitedthroughout throughoutthe theworld worldby by1.1.2003 1.1.2003

Matches tin-containing selfpolishing performance With performance that exceeds what has gone before

AAcomplete completeprohibition prohibitionon onthe thepresence presenceof ofTBT TBTantiantifouling foulingsystems systemson onship’s ship’shulls hullsto tobe bein inplace placeby by1.1.2008 1.1.2008

With a track record of success in newbuilding and drydocking

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New tin-free technology Why is hydrolysis so important?

Anti-fouling for Aluminium hulls

• Because linear polishing rate • • •

assures long term antifouling property Because no skeleton layer means good adhesion Because continuous smoothening of the surface ensures good fuel efficiency Because hard film maintains its good appearance

Special requirements:

• Must be free from Copper • Must perform at speeds up to 50 knots • Preferably selfpolishing

Steel hull Newly applied

Can also be used on steel hulls:

• When port calls are frequent • When service distances are short • For laid up ships

Steel hull After exposure in the sea

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10. Safety, Health and Environment (SHE) In recent years, awareness of SHE-related matters has increased. This is reflected in legislation and by companies and individuals becoming involved in such matters. At the Paint School, we have decided to focus on health problems in connection with the surface treatment of structures. General guidelines During the preparation and use of paint, it is important to be aware of the risks associated with the activity. In brief: • • • • • •

Follow current legislation from local and national authorities. Read the safety data sheets for all products. Know the risks and how to protect yourself. Obtain the necessary training in the use of the products and equipment to be used. Use the necessary protective equipment to protect the respiratory system, eyes, skin and hearing. Inspect all areas where work will take place to reveal possible SHE faults. Ensure correct storage and handling of products and associated thinners before, during and after the work. The products should be collected in a specially allocated area.

Safety Safety aspects are particularly important in connection with the use of solvent-based paints. Solvents are flammable and in the right environment and under unfavourable conditions can cause both fire and explosion. Be aware that solvents are heavier than air and will sink down to areas which lie below the painting work. In general, the following aspects should be checked in connection with painting work. • Plan the work and co-ordinate this with other activities in the area. • Inspect the area where the work is to be performed. Shut off the areas affected. Remember areas which are lower than that where the painting is to be performed. • Check the equipment to be used, including safety and protective equipment. • Closed rooms must be declared gas-free before work begins. • Take extra safety precautions when painting in tanks and confined areas: Adequate ventilation, explosion-proof working lights and equipment, an assistant with a line and adequate breaks in fresh air.

Health Surface treatment represents a health risk. The risk can however be reduced to a minimum if the operators and people in the vicinity of areas where such work is in progress proceed as follows: • Read the safety instructions and SHE documentation for the product (safety data sheet) • Follow the instructions given. In particular: use adequate approved protective equipment e.g. fresh air masks, gloves, protective goggles and anti-static footwear/clothing. The most serious health risks are associated with the following:

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Solvents • Irritation of the skin, eyes and respiratory organs • Can be absorbed through the skin. Degrease the skin. Can cause eczema • Negative effects on the liver, kidneys, respiratory organs, blood, central nervous system and reproductive organs • Can cause headaches, dizziness and fatigue Epoxy • Irritation of eyes and skin • Causes skin allergy • For sensitive persons: epoxy allergy can be life-long Isocyanates • Irritation of eyes, skin and respiratory organs • Causes allergy to the skin and respiratory organs • For sensitive people: allergies can be life-long • At high temperature: toxic gases such as free isocyanates can be emitted Heavy metals: Dust and vapours Metals harmful to health are mainly: chromium (IV), lead, iron, cadmium, cobalt, copper, zinc and nickel. The organs which can be affected (examples of symptoms/effects): • Respiratory organs (metal fever) • Skin (eczema) • Blood cells (anaemia) • Nervous system (fatigue) • Heart (irregular pulse) • Kidneys (reduced function) • Bone structure (accumulation) Dust Dust is a factor which must be taken into account both during pre-treatment and spray application. Dust is inhaled through the nose and mouth and can cause lung damage (dust disease, silicosis) and irritation of the eyes. Dust on the skin can also cause irritation depending on what the substance contains. Noise Noise is primarily linked with steelwork and preparation. Many tools produce noise levels over 100 decibels. A lower limit for the use of ear protectors is often set at around 80 decibels. Personal notes

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Chapter:

SHE

Many risks are involved when working with paints

Safety hazard: Solvents Solvents are heavier than air

Safety – Explosion and Fire Health – Manufacturing and Surface treatment Environment – Emission to air (VOC) – Emission to water (Maintenance) – Emission to soil (Waste handling)

• A fire may start in lower areas or compartments

• Ignorant personnel below can be affected

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Safety risk: High pressure equipment

How can we reduce the possibility for accidents to happen ?

Surface treatment involves equipment with very high pressures

•

• Blast cleaning

•

- Mixture of air and particles • Water Jetting - Water up to above 2500 Bar • Airless spray application - Paint

• •

Never point any high pressure unit at another person or at yourself !! Paint School

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Read the Safety Data Sheet and follow the given precautions and advices Check the surrounding areas for nearby activities, particularly welding, machining etc. (remember lower levels) Ensure proper ventilation and check the direction where solvents may move Always use approved and sufficient personal protection equipment of approved type

Precautions when painting in confined spaces.

How flammable is a paint ? The “Flash point” tells how flammable a Paint is.

• Ensure good ventilation • Exhaust points for fumes / solvents must be close

The flash point is the lowest temperature at which the fumes from the solvents ignite or explode

• • • • • • •

Classification:
Extremely flammable: Flash point below 0 °C
Highly flammable: Flash point between 0 and 21°C
Flammable: Flash point between 21 and 55 °C

to the bottom Start application from the bottom and up Always use non-sparking tools Use antistatic clothing with hood Use masks with air supply Use boots and gloves Never smoke Safety lines or use naked flames ! Sufficient rest periods

This information can be found in the Safety Data Sheet Paint School

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Chapter:

SHE

Symbols Fire and explosion hazards

Symbols Health hazards

These symbols can be found in Safety Data Sheets and on the paint tin label

These symbols can be found in Safety Data Sheets and on the paint tin label

E

O

Explosive

Oxidizing

F

T+

T

Highly flammable

Very Toxic

Toxic

F+

Extremely flammable

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Xn

Corrosive

Xi

Harmful

Irritant

Evaporation of solvents during application of an object

Types of information to be found in the safety data sheet (16 points). 1. Identification of the company 2. Composition and ingredients 3. Hazard identification 4. First aid measure 5. Fire fighting Measures 6. Accidental release measures 7. Handling and storage 8. Exposure control and personal protection

C

Area: Dry Film thickness:

Litres of Solvents

9. Physical and chemical properties 10. Stability and reactivity 11. Toxicological information 12. Ecological information 13. Disposal considerations 14. Transport information 15. Regulatory information 16. Other information

20.000 m² 300 microns

5000 4000 3000 2000 1000 0

Mastic

Vol. % Solids 82 % Paint School

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General precautions for surface treatment (1 of 3)

Tar Epoxy 65 %

Alkyd 50 %

CR 40 %

General precautions for surface treatment (2 of 3)

Before the work starts During work

• Do not start the work without proper training or experience • Know all safety routines and where to find • • • • •

• Always use appropriate, approved personal protection equipment

necessary equipment if an accident should occur Read and understand all Safety and Technical Data Sheets Know all the hazards involved (R phrases) Know all protective measures requires (S phrases) Availability of appropriate, personal protection equipment Evaluate the work place regarding - Other nearby activities, warning signs, mixing station, first aid kits, ventilation, housekeeping

• Use the tools and equipment correctly to avoid injuries to others or to yourself

• Keep all containers / tins closed • The work can be exhausting: Take sufficient rests • Keep the work place tidy during the work

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Chapter:

SHE

General precautions for surface treatment (3 of 3)

Filter types Dust P1: Lowest degree of protection P2: Medium degree of protection P3: Highest degree of protection

After work • • • • • •

Close all Containers / tins Clean the equipment properly Store unused paint and thinners safely (Paint store) Throw waste in designated containers. (Hazardous waste) Clean the personal protection equipment and store it properly to avoid contamination Clean yourself with water and cleaning cream

Gas from organic solvents A1 Lowest degree of protection A2 Medium degree of protection A3 Highest degree of protection

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Health hazards from solvent exposure

Health hazards when using paints. paints. Binders • Skin contact. • Particularly Epoxy, Amines and Isocyanates may cause skin irritation and Allergic reactions Solvents: May enter the body in three ways:

Acute effects

Long term effects

• Headache • Abnormal tiredness • Dizziness • Nausea

• Irritability • Loss of memory • Organ damages

• By inhalation • Skin contact • Ingestion

(kidneys, liver, CNS)

• Reduced reaction ability • Reduced evaluation ability Skin irritations

Other constituents: • Tar, Heavy metals

• Eczema • Dry and cracked skin

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Health hazard: inhalation of solvents

Health hazard: Skin contact with solvents

The most dangerous hazard • Solvents will be transported by the blood stream to internal organs of the body. • Amount absorbed and the effect on the body will depend on: Type of solvent, period of exposure, concentration and work load. • May cause damage to: Central nervous system, respiratory system, liver, kidneys and reproductive systems,

The most frequently occurring health effects • Causes: - Reddening - Swelling - Drying and cracking of skin - Absorption through intact skin: Some, like Xylene - Absorption through damaged skin: Several, like White Spirit Protective measures: Avoid direct contact Protective clothes, gloves and boots

Protective measures: Proper ventilation. Use approved, protective mask Paint School

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Other types might be required for products classified as corrosive.

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Chapter:

SHE

Health hazards when working with Epoxies. Epoxies.

Health hazards when working with tar containing paints. paints. Hazards
The main hazard with tar containing paints is the risk for developing cancer, especially when exposed to strong sunlight
Long term exposure to vapours may damage internal organs, cause heritable genetic defects and birth defects
Short term exposure to fume and vapours may cause irritation to nose, throat and eyes
Splashes to skin causes irritation Protective measures
Protective mask to avoid breathing vapours
Protective clothes covering the whole body and gloves

Hazards :
Eczema and allergic reactions on the skin
Liquid Epoxies with low molecular weigths (below 700) are most likely to give an allergic reaction
An allergic reaction to Epoxy is irreversible.
Hyper-sensitive persons must stay away from epoxies. Protective measures
Protective clothes covering the whole body and gloves
Proper cleaning with water, soap and cleaning cream
Use disposable overalls

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Health hazards when working with paints containing Isocyanates. Isocyanates.

Health hazards when working with paints containing heavy metals. metals.

The monomer is more volatile than the pre-polymer and is therefore more dangerous
Isocyanates are found in Polyurethane paints Hazards
Irritation of eyes skin and airways
Sensitization by inhalation and skin contact
Asthma Protective measures
Protective mask to avoid breathing of vapours
Protective clothes covering the whole body, boots and gloves

Some times used in pigments, additives or driers. Hazards (Metal fumes,dust from hot work)
Zinc. Dust and fumes: Zinc fever, chills, coughing, irritation
Copper. Fumes: Metal fever and chills
Lead. Dust and fumes. Damage blood cells, Anemi, skeleton, reduced fertility and central nervous system
Chromium. Dust and fumes: Sensitisation, cancer
Nickel / Cobalt. Sensitisation General Protective measures
Protective mask to avoid breathing of vapours
Protective clothes covering the whole body, boots and gloves




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Health hazards when working with antifoulings. antifoulings.

How dangerous is a chemical or a paint ? Different persons will respond differently In general the hazard will depend on:

• Antifoulings are generally looked upon as Toxic • Some antifoulings contain Tin • Tin may cause irritation to skin and eyes the central

The toxicity and amount of the compound

nervous system and effect the immune system General Protective measures Protective mask to avoid breathing of spray mist / droplets
Protective clothes covering the whole body, boots and gloves

The concentration and risk of exposure

The contact period with the chemical




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11. Corrosion What is corrosion? To give materials satisfactory protection against corrosion, it is important to understand what corrosion is. Only once we know when, how and why a material corrodes (rusts) can we specify the right material and give the material a cost-effective protection. Corrosion is defined as "a material’s reaction with the surrounding environment during the formation of corrosion products". From this definition, it is clear that it is not enough to know the properties of the material, we also need knowledge of the exposure environment. This means that we need to know how corrosive the environment surrounding the material is. To illustrate the different material properties, consider the following example: gold will not corrode in seawater and therefore we call this an inert material in this environment. Zinc however is far from inert. Similarly a particular material will have a totally different longevity in two different environments: unprotected steel corrodes quickly in seawater but will be almost everlasting in a dry indoor atmosphere.

The corrosion process The corrosion process is caused by the supply of energy to metals when they are produced and processed. This is an undesirable energy state and the metal will try to return to its natural condition. This can involve the material dissolving into metal ions and electrons. For such a reaction to occur, the metal must form part of a corrosion cell. A corrosion cell consists of two different materials connected together via a conductive electrolyte and a metal conductor. A conductor can be another conductive material or it can be a direct contact between the two metals. The conductive electrolyte can for example be seawater or condensation with some form of contamination or salts which make the condensation conductive. If we regard the corrosion process as an electrical circuit, it is easy see that we can stop or at least reduce the corrosion by either breaking the electrical circuit or by increasing the resistance in the circuit. This is the principle behind the use of many paints as corrosion protection. When paint is applied to the metal, we apply an insulating layer and it becomes more difficult for the conductive ions in the electrolyte to reach the surface of the metal. The ohmic resistance in the circuit increases. Another method is to change the surrounding environment. We can for example prevent condensation forming by changing the temperature of the metal or by ensuring better ventilation.

Corrosion types There are many different forms of corrosion. Although we will not discuss all of them, we should briefly mention the two most common types on steel structures: galvanic corrosion, general corrosion and crevice corrosion. Galvanic corrosion occurs when two different alloys are connected together in an electrical circuit, as described for corrosion cells. In such a circuit, it is always the most negative metal which corrodes. This metal is called the base metal or the anode in the circuit. The noble Jotun Paint School

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metal or cathode will actually acquire a certain degree of protection (see cathodic protection). Typical examples of galvanic corrosion are aluminium which corrodes when connected to steel or a cast iron valve which is connected to an aluminium-brass pipe. In principle, general corrosion is very similar to galvanic corrosion except that the corrosion process occurs on one metal only. The galvanic cell occurs when either various alloy elements or contaminants are present in the metal or the metal surface is uneven. The corrosion will occur on the most base elements on the alloy surface. Crevice corrosion is a type of corrosion which is mostly found on passive materials such as stainless steels. The attack takes place in narrow gaps or crevices. Critical crevices for initiation of corrosion are between plates, pores in welds, between gasket and flange in pipe systems, under various types of settlements (marine mud) and contamination (paint splashes). The reason for the attacks is that the environment inside the crevice is different from the environment outside. A corrosion cell will be formed between the two areas. A ondition that will increase the risk of attack even furter is the presens of aggressive ions such as chlorides found in seawater. Once initiated the crevice corrosion attack may propagate at a very high speed and cause rust penetration within a surprisingly short period of time. Personal notes

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Chapter:

Corrosion Production and degradation of steel

Definition of Corrosion

Reaction between the material and the surrounding environment takes place

Corrosion is a reaction between

Plates, pipes, profiles, etc.

Material and Surrounding environment

W ate r Ox /hu yg mi en dit y

g gy in er tur En fac u an M Raw material Iron ore

under formation of corrosion products

Rust

The presence of water / humidity and Oxygen is a pre-requisite for corrosion of steel Paint School

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Freely corroding steel

How is rust formed ?

Electrolyte (Water or soil) Painted surface exposed to humidity

The water molecules penetrate the paint Due to osmotic forces blisters are formed

Paint Steel

The blisters break and corrosion is initiated

Anode Cathode

Cathode Paint School

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A galvanic cell

Pre-requisites for corrosion

2e-

A galvanic cell consists of: Cathode: Steel

• A Cathode: • • •

-

Anode: Zinc

O2

- 2OH ½ O2 + H2 O + 2e - =

In seawater, a calcareous deposit is formed on the steel surface

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2+

Zn = Zn + 2 e

The noble metal / alloy (or part of metal) An Anode: The less noble metal / alloy An electrical connection between the two metals. Conducting electrical current (by electrons) An electrolyte: Conducting electrical current (by ions)

Handouts

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61

Chapter:

Corrosion

Corrosion speed differ when exposed to the same environment

Galvanic potentials in seawater

In a strong alcaline environment Aluminium and Zinc will corrode rapidly, while steel will be passive Aluminium Zinc

Steel

Protective Iron oxide pH > 10

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How to measure the corrosion potential of a structure

Steel in Seawater Potential versus Zinc & Ag/Ag Cl ref. electrodes Ag / Ag Cl

Potentials in volt

Zinc

Cu / CuSO4

Volt meter Rapid corrosion - 0.55

+ 0.50

- 0.60

+ 0.25

- 0.85

+ 0.0

-1.10

- 0.25

- 1.35

Structure

+

-

General corrosion Some corrosion

- 0.80

100% Cathodic protection -1.05

- 1.30

Increasing polarisation Overprotection

Reference electrode

Sea water

Possible coating damage Paint School

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Elements influencing the corrosion speed of metals

pH-scale

Submerged materials

• Temperature • Salinity • Oxygen content • Water velocity • Acidity (See below) • Type of electrolyte ( e.g. cargo or chemicals) • Content of contaminants / pollution that

Acidic

Neutral

Alcaline

promotes corrosion • Micro-organisms. Paint School

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Chapter:

Corrosion

Parametres influencing the corrosion speed. Atmospheric corrosion

Apart from using paint and CP: How to protect against corrosion ? Corrosion protection can be achieved in many ways

• Humidity • Temperature • Concentration of salts • Amount of air pollution,

• • • • • • • • •

including acid rain, soot and dust particles

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Avoid stagnant water at bottoms of tanks and containers Better

Corrosion Properties of the materials • •

Best solution

x

x

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Most frequently occurring types of corrosion

Most frequently occurring types of corrosion

On carbon steel

• • • •

Uniform corrosion Uneven corrosion (deep pits) Galvanic corrosion Stress corrosion cracking

Stainless steels

Titanium

• Crevice corrosion • Pitting corrosion • Stress corrosion cracking

• Hydrogen embrittlement

Copper based alloys

• Pitting corrosion • Galvanic corrosion

• Erosion corrosion

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Handouts

• Fatigue

Aluminium

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All materials have their strong sides But, they also have their weak points

Knowledge is required for selecting the correct material for a given application

x

Unfortunate

Good design Avoid corrosion traps Improved accessibility - maintenance Proper materials selection Insulate between dissimilar materials Change the surrounding environment Remove water / humidity Apply metallic coatings Use corrosion inhibitors (closed systems)

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63

Chapter:

Corrosion Crevice corrosion occurs under paint spillage or plates

Steel with mill scale

Crevice corrosion occurs in narrow gaps where the oxygen concentration is lower than on the freely exposed part of the material

Outdoor exposure • The mill scale cracks • Corrosion will develop on the steel Mill scale is more noble than steel

Seawater Mill scale

Corrosion

Ingress of seawater Paint

Plate

Stainless Steel Steel

Steel

Corroded areas Paint School

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Galvanic corrosion is to a large extent determined by the conductivity of the electrolyte

Pitting corrosion •

The corrosion attack decreases with increasing distance from the cathode due to an increased ohmic resistance

•

Corroded area

•

Pitting corrosion

Electrolyte (Seawater)

Anode

Pitting corrosion is a localised attack on a material normally protected by a passive film The passive film may be destroyed mechanically or by aggressive ions in an electrolyte Severe corrosion may take place beneath the passive layer Passive layer

Cathode Stainless steel Seen from above

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Corrosion fatigue

Cross section

Stray current corrosion

Corrosion Fatigue is a combined effect of an aggressive environment and dynamic loads on a structure

Welding transformer

Welding on board

- +

Load

Stray current Pontoon

Quay

Fatigue only

No failure above line

To earth Corrosion

Corrosion fatigue

Seawater

No. of dynamic cycles Paint School

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12. Cathodic Protection Basic conditions Cathodic protection (CP) is one of the most common forms of corrosion protection. To understand how this method works, you need to be familiar with a few basic facts. The first is the mechanism behind the corrosion process (see the section "Corrosion"). Remember that the very occurrence of the corrosion process means that when a metal corrodes (rusts), the metal breaks down into ions and electrons are released. It is also necessary to understand what an electrochemical cell (corrosion cell) is. This is a conductive circuit which consists of a noble metal (cathode) and a base metal (anode) in metallic contact with each other. In addition, the metals must be in contact with each other via a conductive electrolyte (for example seawater). In such a circuit, it is always the anode which corrodes, while the cathode will be protected.

Which metal will corrode in a cell ? When two metals are connected together, we can predict which will corrode and which will be protected. This is due to the electrochemical voltage level of the metal, or corrosion potential. The potential for a metal can be measured by putting the metal in seawater and measuring the voltage between the metal and a reference electrode. When we have measured the potential of several metals, we can classify them. The most noble is placed at the top of the list and the most base at the bottom. This classification is called the ‘Galvanic series’. In a connection between two metals, the most negative metal will be the anode whilst the metal higher up in the table will be the cathode.

Principle of cathodic protection Cathodic protection is based on preventing a metal from dissolving. By ensuring that electrons cannot be released from the metal we want to protect, the corrosion can be limited or stopped. This is done by connecting a more negatively charged metal (e.g. aluminium) to the metal we want to protect (e.g. steel). Aluminium will release electrons more readily and will have enough power to propel the electrons into the steel and thus prevent dissolution. Aluminium is therefore the anode and will corrode instead of the steel. The aluminium is sacrificed, hence the name sacrificial anode. When the negatively charged electrons enter the steel, the steel will of course have a more negative potential than it has in its free state. It is this change in potential which protects the steel. To ensure protection, the steel must fall below a certain negative potential level. This level is called the protection potential and is specified as a design criterion. The protection potential is normally of the order of -800 mV relative to a silver/silver chloride reference electrode. An anode can only release a certain number of electrons before it is consumed. To ensure that the anodes work as long as necessary, we must calculate how many anodes are required. These calculations are called ‘designing a cathodic protection system’. A design requires Jotun Paint School

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knowledge of some important parameters. The most important ones are the area to be protected, the type of material to be protected, the type of anode to be used, the lifetime of the system and the area of the structure which has been painted. A painted structure requires fewer anodes than an unpainted one. Finally: cathodic protection can be achieved by a forced voltage system. These systems supply DC current to the steel in the same way as anodes.

Personal notes

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Chapter:

Cathodic Protection

Corrosion of a metal or alloy

How to protect a structure

• Corrosion is a reaction between the metal and the surrounding • •

Corrosion Protection can be achieved by : • Sacrificial Anode Cathodic Protection System • Impressed Current Cathodic Protection System

environment The corrosion rate depends on the properties of the metal and the corrosivity of the environment. Corrosion is dissolution of the metal, among other things involving the release of electrons:

Fe → Fe

2+

Both systems supply electrons to the structure. The structure will become more negative and metal dissolution will be prevented

+ 2e

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Marine Objects to be protected: protected:

Type of sacrificial anodes •

•

•

Zinc – Noranode – Coral Z Aluminium – Coral A – Coral A high grade Magnesium

• • • • •

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The principle of cathodic protection. protection. potentials vs. vs. different reference electrodes

Offshore and industry (Norwegian sector). sector).

Objects to be protected: • Offshore platforms – Fixed/floating – Concrete/steel • Subsea installations – Templates/manifolds/ •

modules. Subsea pipelines

Cu /

• Harbour facilities – Piles – Sheet piles • Buried tanks and

Zn

pipelines (onshore)

• Above ground storage

mV

CuSO4

+ 500

- 600

+400

- 700

+300

- 800

+200

- 900

+100

- 1000

0

- 1100

Freely corroding steel

Mixed potential

tanks

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Ships FPSO / FSU Mobile rigs Floating dry-docks Barges

Handouts

Freely corroding Zinc

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Chapter:

Cathodic Protection

Cathodic Protection Steel protected by a sacrificial anode

Corrosion potentials in seawater Zinc, Zinc, Ag/Ag Cl and Cu/CuSO Cu/CuSO4 Reference electrodes Ag / Ag Cl

Potentials in volt

Zinc

Cu / CuSO4

Rapid corrosion - 0.55

+ 0.50

- 0.60

+ 0.25

- 0.85

+ 0.0

-1.10

- 0.25

- 1.35

General corrosion

Electrolyte (Water or soil)

Some corrosion

- 0.80

100% Cathodic protection -1.05

Overprotection

- 1.30

Cathode

Possible coating damage

Anode

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Reduction of corrosion rate of steel by cathodic protection. protection. Moving seawater

Marine Design criteria • • •

Free corrosion

100 Corrosion rate (per cent) 50

• • •

Full cathodic protection

10 -600 -650 +500 +450

-700 +400

-750 +350

- 800 +300

mV -850 Cu / CuSO4 +250 Zn

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Current density requirement depends on:

Protective

Design criteria • • • • • •

A. Environmental parameters • Sea water composition and salinity • Sea water temperature • Resistivity of sea water • Sea water flow velocity • Other factors, marine growth

Design lifetime Coating system and condition Protection potential Anode capacity Electrolyte resistivity Environmental conditions/impacts

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Design lifetime Coating system and condition Current density (Coating type and damages) Electrolytic resistivity Environmental conditions / impacts Ballasting period.

Handouts

B. Steel surface Painted / not painted Steel temperature Coating system, if any Condition of coating system

• • • •

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Chapter:

Cathodic Protection Comparison of cathodic protection systems general advantages: advantages:

Sacrificial anode material selection

Main Types Zinc Aluminium Magnesium

• • •

Anode material selection • Chemical composition • Electrochemical performance - Anode potential - Stable current - Consumption • Anode corrosion pattern • Price • Class requirements

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Comparison of cathodic protection systems general limitations Sacrificial anode systems • Large weight for large capacity, long life systems.

• • • • • • •

Impressed current systems • Relative complexity of system demands high level of design expertise.

• In-service operator surveillance required.

• Hydrodynamic loadings can

• Vulnerable to component

be high (Seawater drag)

failure or loss of power.

• Flexibility under widely varying operating conditions

• Weight advantage for large capacity, long life systems

• Low friction (reduced sea water drag)

• Low life cycle cost (LCC)

Why choose an ICCP system on hull

• Response to varying operating conditions is limited.

Impressed current systems

Sacrificial anode systems • Simple, reliable and free from in-service operator surveillance • System installation is simple • Low installation cost for short term protection

Smooth hull, no drag Flexible dry-docking intervals Low cost for long term operation Long lifetime, minimum of maintenance No welding required at dry docking No risk of damaging internal Paint systems Fully automatic corrosion protection

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Ship hull: Current density at different paint damage

Why choose a SACP system on hull

Paint damage, %

• Simple installation

100

• Maintenance free between dry docking

80 60

• Low cost for short term operation

40

• World-wide availability

20 0

20

Anodes Paint School

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40

60

80

ICCP

100

120

140

160

180

Current density, mA/m²

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Chapter:

Cathodic Protection Corrosion in broken blister Passivation by CP

Principle : Effect of using CP Corrosion Curves depend on - Coating condition - CP-design Corrosion

Without Cathodic Protection Seawater CP and coating at newbuilding

Rust

Paint Steel

CP installed

With Cathodic Protection

Coating breakdown

Seawater

Anode current

Anode

Paint Time

Steel

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Ships hull: Current density as function of coating breakdown

Sacrificial anode system ➊ Aluminium alloy anodes ➋ Zinc alloy anodes (technically equal)

Coating breakdown Current density 2-5% 5-10 % 10-15 % 15-20 % 20-25 % 25-30 %

Calcareous layer

10 mA/m2 15 mA/m2 20 mA/m2 30 mA/m2 40 mA/m2 50 mA/m2

Aluminium is recommended prior to Zinc because: ☛ Aluminium anode weight is approx. 1/3 of Zinc ☛ Total price for equal protection: Al. anodes approx 1/2 of Zinc anodes

☛ Lower installation costs due to weight difference

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Location of Pitguard anodes

Cathodic protection ❶ ICCP - Impressed Current ❷ SACP - Sacrificial Anodes ❸ EAF - Electrolytic Antifouling System for

Web frame Tank bottom

seawater systems (CUPROBAN)

❹ Slip ring arrangement for propeller shaft

Web frame

Seawater Anode

Coatings and Cathodic Protection Water level

➡ The Single Source Solution Paint School

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