Khanna A.S. (Ed.) High-Performance Organic Coatings: Selection, application and evaluation

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Organic coatings for marine and shipping applications 357

mechanism of almost all these products is obtained by copper oxides or

organisms not covered by copper are added. As far as is known and also

from the authors’ experience, some alternatives are performing satisfacto-

based antifoulings.

Fouling Release Coatings (FRCs) are free from biocides, so they can be

considered as one of the most environmentally friendly solutions. Their

with the substrate is critical and requires a ‘sealer’ or tie coat. Moreover,

the mechanical properties during utilization are delicate. Application and

repair demand particular expertise. This all makes the coating rather expen-

sive as compared to conventional antifouling coatings. Finally, these coat-

ings do not really prevent fouling, but lower the adherence of the marine

organism to the coating. Nowadays all known antifouling paint manufactur-

ers offer also Fouling Release Coatings. Their application in practice is

satisfactory, at least for certain types of vessels: those with a limited ‘non-

sailing time’ and with the possibility of sailing faster than 15 knots.

Development is still on-going and particular attention is also being given

of the possibility of lowering the drag resistance by adapting the surface

16.5 Inspection, monitoring and maintenance

16.5.1 Protection against corrosion

Introduction

When discussing the effectiveness of the protective action against corrosion

of coating systems, it is imperative that design objectives of these systems

for durable performance and the actual performance under practical condi-

tions are realistically compared. Of course, this would normally only be

possible after quite some years of exposure to practical conditions. It would

coating system is not suitable for the chosen application. Therefore we need

inspection and monitoring methods with an early warning capability and,

on the other hand, accelerated testing and evaluation procedures that can

reliably predict long-term behaviour based on laboratory experimental

data.

In ideal cases the testing methods used for monitoring can also be used

under careful control for laboratory experimentation with predictive prop-

erties. In these cases the measuring techniques are so sensitive that informa-

tion on very limited degradation not resulting from accelerated testing, but

obtained under mild exposure conditions similar to those found in practice,

salts. In addition other active compounds with toxic properties for specific

rily; however, their efficacy and lifetime do not meet those of the TBT-

development and optimization, however, is more difficult. The adherence

profile of these coatings in practice.

be unacceptable and costly to conclude only after say five years that the

358 High-performance organic coatings

extrapolation to long-term behaviour becomes possible. These techniques,

such as electrochemical impedance spectroscopy, electrochemical noise and

mechanical delamination testing, although available in principle, have yet

to be improved to be adopted for general use as lifetime predictive tools

[32].

Design for lifetime

Design for lifetime prediction, reaching out for durable coating systems,

should always be part of a total performance approach as given in Fig. 16.5.

In this chapter we will focus on the second step in this system: we aim at

application of the coating such that its lifetime is optimized (within the

limitations of the lifetime of the total structure), while monitoring its poten-

tial degradation and taking the appropriate maintenance measures if

needed. In most cases the normal lifetime of a coating system is lower than

that of its protected structure. This means that we can focus on the exten-

sion of the lifetime of the coating in use based on proper knowledge of

the coating’s performance-related parameters such as adhesion, thickness,

porosity, ionic transport properties, barrier action, permittivity, water

uptake, blistering, etc.

type, generic coating type, cover thickness, curing conditions and allowable

Production

Construction

Energy and

raw materials

‘Processing’

Rest materials

End of

service

life

Recycle

Application

Degradation

Maintenance

Conservation

Energy and

raw materials

Impact on

surroundings

Environmental

measures

Impact on

surroundings

Energy and

raw materials

prolong

postpone

Impact on

surroundings

Impact on

surroundings

Environmental

measures

Environmental

measures

Environmental

measures

16.5 The concept of the total performance approach.

becomes quantitatively available such that under well- defined conditions

Often the service life of a construction is not specified. It is then implicit

by referring to specifications using standards for raw materials, metal alloy

Organic coatings for marine and shipping applications 359

crack width: a long service life is assumed to result. If long-term proven

records of similar structures exist this may work well. Then testing and

service life calculations are not needed. In other cases it may lead to unac-

ceptable early failure.

Explicit design for service life using performance-based design has

become more important nowadays. First, better comparison of different

material classes becomes possible, while also product standards do not

necessarily apply in new and different ambient conditions (Middle and Far

East vs. Europe; Europe vs. Florida; etc.). Also a great variety of new

materials, including new combinations, has arisen in the last 15 years, while

environmental issues render some materials obsolete. Last but not least,

the responsibility for product performance has shifted to the manufacturer,

which increases awareness. For performance based design we need proper

data based on practical experience with materials and constructions, either

from exposure sites or directly from practice. Alternatively we need repre-

sentative testing results, either as a result of monitoring under conditions

cedures in the laboratory.

Assessment of performance

In Section 16.3 we described the various damage and degradation scenarios

encompassing blistering and cathodic delamination. Different degradation

processes demand different measuring techniques for proper evaluation of

the coating properties. In this subsection we will give a short summary.

substrate and environment is to actually expose coated substrates to the

environment in which the coating will ultimately be applied [15, 16, 34–40].

This is generally done by mounting coated panels to exposure rigs as shown

in Fig. 16.6. Although long-term exposure to the actual environment offers

a good representation of the actual service life, ‘natural’ degradation of

modern protective coating systems is extremely slow. Outdoor exposure

tests frequently require 10–20 years before reliable conclusions can be

drawn. Consequently, results are not provided in a commercially acceptable

time period [35, 38, 39, 42–44]. A second drawback to this approach is the

variability of the ‘natural’ environment. No time period or location is the

same as any other and thus exposed materials are degrading in constantly

service life prediction [35, 43–45].

Many researchers have attempted to speed up the natural coating deg-

radation process by increasing the physical and chemical stresses (e.g. by

altering temperature, humidity, pH, salt concentrations and the intensity of

UV radiation) in so-called accelerated tests. Ideally, the stresses only cause

in use, or as a result of accelerated testing or refined sensitive testing pro-

The most reliable way of studying the suitability of a coating for a specific

changing rates and fashions. This greatly influences the accuracy of the

360 High-performance organic coatings

the system to fail faster than it normally would, while the mechanism of

failure remains the same as in the non-accelerated conditions [36, 46–49].

The ability to relate the performance of a coating exposed in such tests to

then it should be possible to greatly reduce the time-to-market for new

products by substituting short-term laboratory exposure results for results

The most widely used accelerated test for coating evaluation is the salt

spray test [35, 54–58]. This has been true despite severe criticisms this type

of testing has received [35, 48, 52–64]. Salt spray tests are cabinet tests

where a salt solution is pumped into a nozzle where it meets a jet of humidi-

salt spray tests ASTM B117 and ISO 9227 continuously subject test speci-

mens to a fog of salt particles (5 wt% NaCl) at an elevated temperature of

coating system that will resist these test conditions should also perform well

in aggressive service environments. The assumption was that the mecha-

nisms of corrosion and degradation in service would be similar to those in

the test cabinet [54]. However, many examples can be found in the litera-

ture suggesting that little, if any, correlation exists between the results from

salt spray tests and in-service performance. Most remarkably, negative cor-

relations have been observed quite regularly [37, 57, 61–66].

ering tests were developed. Incorporation of cycling steps seems intuitively

16.6 Typical setup for outdoor exposure of coated panels in a coastal

environment.

the field performance is a universal need. If such a linkage can be made,

from long-term field exposures [35, 50–53].

fied compressed air, forming a droplet spray. The standardized pH-neutral

35°C. The justification for these extreme conditions has always been that a

To overcome the deficiencies of continuous salt spray tests, cyclic weath-

justified, considering that coatings exposed to the outdoor environment

Organic coatings for marine and shipping applications 361

undergo similar effects on a frequent basis [39]. Indeed, many have claimed

the superiority of cyclic tests over conventional salt spray tests, as these

relation to actual environments [33, 35, 56, 62, 64, 67]. Test chambers in

which specimens are exposed to ultraviolet radiation (UV) are widely used

to obtain weathering data for a wide range of polymer products, including

coatings. Commercially available UV chambers already began to appear in

[68].

While cyclic testing was seen as an important advance, it was also sus-

pected that ultraviolet radiation (UV) plays an important role in natural

weathering of coated metals. This led Skerry and his co-workers to inves-

that the corrosion performance characteristics of organic coatings were

markedly affected by the UV-weathering factors in the test [58]. Furthermore,

the combined cyclic salt fog/UV test showed an improved reproduction of

coating performance ranking and failure modes observed in practice [36,

48, 52, 54, 58, 59]. In this respect, this cyclic salt fog/UV test is superior to

continuous salt fog, or even cyclic salt fog alone. In Table 16.3 the most

important test methods are summarized. Testing should be encompassed

by proper evaluation methods. Coating degradation is usually evaluated

using standardized methods; the common methods are given in Table 16.4.

Unfortunately the majority of these methods are based on visual observa-

tion [69], rendering them rather subjective. There has been considerable

effort to develop evaluation methods for organic coatings that are numeri-

cal, reproducible and accurate [70–72]. The use of electrochemical tech-

niques, in particular electrochemical impedance spectroscopy (EIS), has

been shown to be very valuable. EIS not only provides results in a short

time but the obtained data can give indications on the actual corrosion

mechanisms. In addition, corrosion and coating damage may be determined

prior to its visual manifestation [33, 41, 49, 63, 73–80]. This coincides with

the present trend towards the development of methods which enable early

prediction of coating performance, even before the occurrence of any sub-

stantial changes in its appearance [33, 41, 73, 76–78, 80].

Electrochemical noise measurement (ENM) for corrosion studies was

apply ENM to the study of organic coatings [82] and were soon joined by

other laboratories. It was found that changes of the noise resistance with

time were in general agreement with the known performance of several

coating systems. However, Mansfeld and co-workers emphasized the need

for analysis of noise data not only in the time domain, but also in the fre-

quency domain in order to obtain mechanistic information [83]. Therefore,

the spectral noise resistance, obtained through Fast Fourier Transforms

tests produce failures more representative of field results, with better cor-

about 1920 and since then numerous modifications in have been made

first described by Iverson in 1968 [81]. Eden and Skerry were the first to

tigate the influence of an added UV weathering cycle. The results indicated

362 High-performance organic coatings

Table 16.3 Overview of some (standardized) accelerated tests

Test method Conditions

Continuous salt spray tests

ASTM B117

ISO 9227 (NSS)

DIN 50021 SS

JIS Z 2371

(NSS)

Continuous, pH-neutral salt spray (5% NaCl at

35 °C).

Immersion test

ASTM D870

Coated specimens are partially or completely

immersed in distilled or demineralized water

at ambient or elevated temperatures.

Humidity tests

ASTM D2247

ISO 6270

Coated specimens are exposed to atmo-

sphere maintained at approximately 100%

relative humidity with the intention that

condensation forms on the test specimens.

Cyclic tests

ASTM G85 Annex 5

Wet and dry cycling (1 h of fog (0.05 wt%

NaCl + 0.35 wt% (NH

)

) at ambient

temperature and 1 h of drying at 35°C).

ASTM G 154

ISO 4892–3

Coated specimens are exposed to alternating

UV/condensation cycles.

Advanced cyclic tests

ASTM D5894

ISO 20340

Alternating UV/condensation cycles and wet/

dry salt-spray cycles. ISO 20340 includes an

optional freeze cycle.

Automotive tests

GM 9540P/B (General

Motors)

Wet/dry and humidity cycling. Electrolytic

solution: 0.9% NaCl, 0.1% CaCl

, 0.25%

NaHCO

, pH: 6–8.

Total cycle time: 24 h. The typical duration of

the test is 80 cycles (1920 h).

CCT-I, IV (Nissan)

Wet/dry and humidity cycling. Electrolytic

solution: 5% NaCl.

The typical duration of the test is 200 cycles

(1600 h) for CCT-I and 50 cycles (1200 h) for

CCT-IV.

VDA 621-415

Wet/dry and humidity cycling. High time-of-

wetness, poor correlation for zinc pigments

and galvanized steel. Also used for testing

heavy infrastructure paints.

Organic coatings for marine and shipping applications 363

Test method Conditions

HCT (Hoogovens Cyclic

Test)

Based on actual weathering conditions in the

Netherlands. The test simulates two years of

exposure including daily and seasonal

variations in 1680 hours. The temperature

and relative humidity are varied from

respectively 25 to 50°C and 50 to 98%. Test

specimens are periodically dipped in an

electrolyte. The composition of the electrolyte

differs during winter and summer

simulations.

VICT (Volvo Indoor

Corrosion Test)

Different variants exist. Stresses used are

temperature, humidity and salt solution

(spray or submerged). Tends to produce

duration of the test is 12 weeks.

SAE J2334

24 h cycle consisting of: 6 h 100% relative

humidity at 50°C, 15 min salt application

(0.5% NaCl + 0.1% CaCl

+ 0.075% NaHCO

)

and 17 h 45 min drying at 60°C and 50%

relative humidity. The typical duration of the

test is 60 days.

Other tests

Kesternich:

ASTM G87

ISO 3231

DIN 50018

8 h exposure to water vapour and sulphur

dioxide at elevated temperature and humidity

levels, followed by 16 h of ambient labora-

tory conditions. Test originally designed for

bare metals exposed to a polluted industrial

environment.

SCAB (Simulated

Corrosion Atmospheric

Breakdown) test:

ISO 11474

Accelerated outdoor corrosion test. Test

specimens exposed outdoors are periodically

sprayed with a salt solution.

ASTM International – American Society for Testing and Materials

ISO – International Organization for Standardization

DIN – Deutsches Institut für Normung e.V

JIS – Japanese Standards Association

Corporate standard

SAE International – Society of Automotive Engineers

Table 16.3 Continued

not only allows one to evaluate the frequency dependence of noise data,

but also enables a direct comparison with the modulus of impedance

obtained with EIS. This practice has been successfully applied by several

workers [82–84]. ENM and related analysis methods are only starting to

filiform corrosion at scribes. The typical

(FFT) of potential and current fluctuations, was introduced. This method

364 High-performance organic coatings

Table 16.4 Common standardized evaluation methods of specimens subjected

to accelerated tests

Standard Aspect Description

ISO 4628-2,

ASTM

D714

Blistering These standards describe a method for

assessing the degree of blistering of

coatings by comparison with pictorial

standards.

The ISO standard has adopted the pictorial

standards from ASTM and includes the

correlation between the ISO and ASTM

rating systems.

ISO 4628-3,

ASTM

D610

Rusting These standards describe a method for

assessing the degree of rusting of coated

steel surfaces by comparison with pictorial

standards.

The ISO standard includes the correlation

between the ISO and ASTM rating systems.

ISO 4628-4,

ASTM

D661

Cracking These standards describe a method for

assessing the degree of cracking of

coatings by comparison with pictorial

standards.

ISO 4628-5,

ASTM

D772

Flaking These standards describe a method for

coatings by comparison with pictorial

standards.

ISO 4628-6,

ISO 4628-7,

ASTM

D42148

Chalking These standards describe methods for

assessing the degree of chalking of

coatings by comparison with pictorial

standards.

ISO 4628-8,

ASTM

D1654

Delamination

and corrosion

These standards specify methods for

assessing delamination and corrosion

around a scribe in a coating on a test panel

or other test specimens. The ISO standard

describes one method which involves the

use of pictorial standards. Both standards

include numerical rating of failure.

mature, but this technique appears very promising for the study of organic

coatings.

Maintenance and repair

Maintenance and repair are extremely important in achieving design life-

chapter. Therefore we restrict ourselves to the objectives and we give some

time. However, it is a field in itself and somewhat out of the scope of this

assessing the degree of flaking (scaling) of

Organic coatings for marine and shipping applications 365

are:

• Prevention of needless corrective measures during service life, e.g. by

proper and regular cleaning procedures

• Repairing in the best possible way, as quickly as possible, at the lowest

costs, with little inconvenience to users

• Optimizing maintenance costs, minimizing non-operational time, opti-

mizing life-cycle costs of the structure.

Important issues are:

• Accessibility to inspection and action

• Built-in, easy to apply test devices (intelligent pig, corrosion samples/

electrodes, capacity sensor)

• Maintenance manuals

• Expert diagnosis.

16.5.2 Protection against fouling

Assessment of performance

The most common way to determine the performance of antifouling coat-

ings is to expose panels with antifouling in a natural sea location (Fig. 16.7).

However, this is time consuming, especially if long-term activity is expected,

and not suitable for development purposes. On the other hand, because of

the quiescent situation, this test can be considered as more severe than in

conditions encountered in practice. A practical test is the use of test patches

on ships. This test is suitable for products that are already developed.

For development purposes and prediction of performance a number of

laboratory tests have been developed. For example, rotor tests according

to ASTM D4939–89 are used to determine erosion rates of self-polishing

coatings in natural seawater under different conditions (5–25 knots and at

a temperature of 10–35°C). The erosion rate is a measure of biocide release,

giving reliable indications for long-term performance. The same equipment

is used for accelerated ageing of coated panels, which can then be subjected

to bioassays with barnacle larvae or raft exposure. In this way additional

information on long-term performance of coatings is obtained (Fig. 16.8).

As stated in Section 16.4, Fouling Release Coatings are non-toxic coat-

ings that do not prevent settlement but provide fouling organisms a bad

surface to adhere to. For such coatings static immersion testing is inade-

quate. For example, ASTM D5618-94 is a standard test method for mea-

determination. Comparison of adhesion strengths on newly coated and

(raft) aged panels gives valuable information on long-term coating perfor-

surement of barnacle adhesion strength in shear that is used for efficacy

important issues to reflect on. The objectives of maintenance and repair

366 High-performance organic coatings

16.7 Test discs on the raft in a natural sea location: the harbour of

Den Helder, The Netherlands.

16.8 Combined rotor and bioassay test to assess the ageing and

speed at which fouling organisms detach from the surface. Such critical

speeds can be determined using rotary equipment with coated panels or

discs that are subjected to various rotation times and regimes. Figure 16.9

shows an example of a rotary apparatus suitable for measuring critical

speed and drag in resistance. Combining this with ageing procedures gives

valuable information on long-term performance of FRC.

efficacy.

mance. Another criterion for efficacy assessment of FRC is the critical