Corrosion Protection Evaluation of Some Organic Coatings Incorrosion Protection Evaluation

8/11/2019 Corrosion Protection Evaluation of Some Organic Coatings Incorrosion Protection Evaluation

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CORROSION PROTECTION EVALUATION

OF SOME ORGANIC COATINGS IN

WATER TRANSMISSION LINES1

Anees U. Malik, Shahreer Ahmad, Ismail Andijani

Fahad Al-Muaili, T.L. Prakash and John OHara

Research & Development Center,

Saline Water Conversion Corporation

P.O. Box # 8328, Al-Jubail 31951, Kingdom of Saudi Arabia

SUMMARY

As an alternative to cementitious materials, organic polymeric materials have long been

considered for pipe coatings. This is due to their good corrosion resistance, imperviousity to

water/air, resistant to salinity, immunity to large variations in pH and chemical and physical

stabilities at moderately high temperatures. Keeping in view the viability of organic coatings

as promising area of water research, a project proposal entitled Corrosion Protection

Evaluation of Some Organic Coatings in Water Transmission Lines was formulated by the

Corrosion Department of R&D Center, Al-Jubail which was subsequently sponsored and

funded by King Abdul Aziz City for Science and Technology (KACST) as a one year short

project.

The project encompasses short and long terms testing of three types of organic coatings, viz.,

polyethylene (PE), polyurethane (PU) and fusion bonded epoxy (FBE) on steel in order to

determine the corrosion behavior in aqueous environment with special reference to product

water. The work of the project was divided into seven tasks, namely, Task-I: litera ture survey,

Task-2 : establishment of facilities, Task-3: mechanical testing, Task-4 : wet tests, Task-5:

impedance studies, and task-6: data analysis and report preparation. Coating materials,

namely, FBE-Scotchkote-206N, PUAqualine-600A, PU-Irathane-155 and 3 layer PE were

used for the studies. Wet tests consisting of salt fog, autoclave and close circuit corrosion

loop were carried out to study the corrosion behavior of coating, water uptake or permeation

1

Issued as Technical Report No. TR 3804/APP 95009 in November 1999.

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and stability of coating under high temperature and pressure. The mechanical testing

consisted of adhesion, bending and cathodic disbonding tests provided information about the

adhesivity or bonding of the coating to the substrate, resistance to cracking, disbonding,

delamination or other mechanical damage as a result of bending. Cathodic disbondment testprovides adhesion assessment and determines resistance of the coating to C.P and current

flow. AC impedance measurements evaluate quantitatively the water uptake by the coatings

and non-destructive determination of cathodic disbondment.

The results of accelerated tests (salt fog tests) showed that in the scribed-coated samples, the

creepage increases with increasing exposure time. FBE, 3 layer PE and Irathane-155 (PU)

show no blistering after 100 days exposure in salt spray cabinet but Aqualine-600A (PU)show blistering on scribed and unscribed surfaces. Autoclave tests were carried out to

determine the behavior of coatings under high temperature and pressure. The results of the

tests indicate that FBE, Aqualine-600A and 3 layer PE coatings are quite resistant to waters

at 40oC and 1500 psi but Irathane155 shows decrease in thickness in liquid as well as vapor

phases and also exhibits slight decoloration, swelling and texture appearance in both phases.

This is an indication of degradation of Irathane-155 in water under high temperature and

pressure. Close circuit loop test results of 4 weeks exposure in water indicate no markedchange in the color and texture of the coating. There was no perceptible change in weight

during 1 month exposure to water at 25oC.

The results of adhesion tests on coatings showed that the binding between the metal substrate

and the coating was more than the coating and the dolly. The pull off adhesion tests carried

out on coated samples after autoclave tests showed that adhesive strength of all the coating is

greater than 500 psi. The flexibility (bending) tests carried out on coatings show no defect orpresence of holidays at the bending site. On the basis of radial disbondment measurements

from cathodic disbondment tests, the decreasing performance of the coatings can be

represented as :

FBE > 3 layer PE > Aqualine 600 > Irathane 155

It is important to note that during cathodic disbondment tests at 25C and 40C, Aqualine 600

and Irathane 155 were found swelled and sticky.

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The results of AC impedance tests carried out on all the coatings in 3% NaCl indicate no

water uptake by the coatings even after 6 months of exposure.

A detailed analysis of the results from immersion, electrochemical and mechanical studies

carried out on four organic coatings indicates that only FBE appears to have right

combination of properties which make it viable for consideration as an internal coating for

pipes. The results of cathodic disbondment tests show that as external coatings both FBE and

PE can be employed under cathodic protection conditions.

1. INTRODUCTION

In recent years, there are several cases of pipe failures in the form of leakages, bursting or

cracking of the pipelines [1-4]. In majority of cases the failures have been attributed mainly to

rebar corrosion, which is caused by permeability of chloride from low resistivity soil. The

problem is acute in areas where the soil, besides having high chloride contents, has

intermittent dry and wet spells. As a possible alternative to cementitious materials, in recent

years, a number of olefin, vinyl and epoxy based polymer coating have appeared in the market.

Epoxy based paints or coatings have been employed as internal linings as well as external

coatings in considerable number of pipelines in the Kingdom. The epoxy paints are quite

impervious to water/air and are resistant to salinity; large variations in pH and temperatures

but surprisingly their performance record have not been consistently satisfactory [1]. Fiber

reinforced plastics (FRP) have been used on limited scale in desalination plants for distillate

transmission and in seawater intake [5]. However, FRP pipelines have never been used in

large diameter long distance water transmission system perhaps due to their fabrication

limitation and strength factors. Fusion bonded epoxy (FBE) and fusion bonded polyurethane

(FBU) based coatings have been used for internal and external applications for transmitting

potable water though on limited scale [6]. Polyethylene coatings have been used as external

coatings but constitute one of the 3 layers of olefin based internal linings [7-8]. These coatings

appear to have characteristic properties required for application in water transmission system

but performance data about these coatings are sketchy and therefore, a detailed and systematic

performance evaluation is essential.

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Keeping in view this background, a project proposal entitled Corrosion Protection Evaluation

of Some Organic Coatings in Water Transmission Line had been formulated and which was

subsequently sponsored by King Abdul Aziz City for Science and Technology (KACST) as a

one-year short project. The proposed studies encompass accelerated and short term testing ofsome polymer coatings (polyethylene, polyurethane and fusion bonded epoxy) on steel in

order to determine the corrosion behavior in aqueous environment with special reference to

product water. There is paucity of data regarding the behavior of these coatings in product

water and the results of the studies are likely to provide data, which would be useful in

selection of pipe coating materials for water transmission system.

1.1 Organic Coatings

Organic coatings, applied on properly pretreated surfaces, are the most common and most

effective mode of corrosion protection for metallic objects and structures. The exterior

surfaces of corrodible metals such as iron and steel are effectively protected from their

environment by a coating system. Organic coatings have also been used for protection of

porous refractory surfaces such as cement mortar or concrete structures, which are pervious to

moisture or gases.

Despite the fact that the pipeline coating represents only about 5% of the total cost, the choice

of the most effective coating is a key point to guarantee the life of the installed pipelines. A

recent survey [9] of the failures of the protective coatings on pipeline indicates that 48.8%

failures are attributed to delamination, 26.8% to blisters; loss of gloss, solvent entrapment and

pinholes account 9.7% each (the total exceeds 100% because some of the cases show

combined multiple failure phenomena). For failure avoidance, considerations ofenvironmental factors and nature of flow medium are most important issues for selection of

suitable coating materials.

A large variety of organic polymeric materials belonging to different functional groups have

been used as external coatings for open air or buried pipelines. Asphalt mastic and asphalt

enamel, coal tar epoxy, extruded polyethylene, fusion bonded epoxy, multilayer polyolefin

coating systems including polyethylene or polypropylene and polyurethane are some of themost widely used organic pipe coatings for external applications. Polyethylene coatings

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having an FBE primer and a 2-layer polyethylene based material extruded over it has been

used extensively through out the world in recent years [10, 11]. In such coatings, the epoxy

provides good adhesion to steel and good cathodic disbonding characteristics, which are

combined with water barrier and good mechanical properties of polyethylene. Thecombination has better adhesion, cathodic disbonding resistance, hydrolytic stability and

impact strength than either coating used by it self. For internal coatings, fusion-bonded epoxy

(FBE) and fusion bonded polyurethane (FBU) based coatings are promising materials as

internal coatings and have been used for transmitting water though on limited scale.

1.2 FBE as I nternal Coatings for Water Transmission

Cement concrete and fusion-bonded epoxy (FBE) is the two major types of internal lining

used in steel pipes for potable water transmission purposes. The literature is abounded with

references on the technology and application of cement concrete pipes. The cement concrete

internal lined pipes appear to have best performance under positive Langelier index conditions

when protective carbonate scales are formed on the lining. FBE has many advantages over

cement concrete, which include:

(i) Saving in pipe thickness (or material).

(ii) Chemical inertness over a broad range of pH.

(iii) Presence of smooth and chemically inert surface.

(iv) High friction resistance surface.

(v) Ease in coating of complex shapes.

(vi) Ease in field welding.

(vii) Ease in transportation of large size pipes and consequent saving in cost.

FBE linings have been extensively used by SAUDI ARAMCO in their water injection systems

and appear to be performing satisfactorily [12]. FBE internally lined pipes have been used for

water transmission purpose in U.K., U.S.A and other parts of the world for the last several

years [12]. For example, Scotch 206N (FBE) internal lined pipes have been used since 1978

in U.K for drinking water pipelines and no failure has been reported so far [13]. In U.S.A.

East Bay Municipal Utility has been using Scotckote fusion epoxy 134, 203 and 206N as

external and internal coatings in their potable water system for more than 20 years [14].

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1.3 Ef fect of Chlori de Contamination on FBE Coating Perf ormance

Soluble salt contamination can cause premature failure on virtually all types of coatings.

Amongst the anions, chloride is the single most damaging anion because it migrates under

coating film. Chloride containing solution has a high osmotic pressure contributing to

moisture penetration, loss of adhesion and blistering. The source of chloride contamination

could be from environment around metallic surface, corrosion products and pits. Alblas and

Londen [15] reviewed the literature concerning the effect of chloride contamination on the

corrosion of coated steel surfaces. Appleman [16], Helvig [17], Weldon [18] and Flores [19]

showed various correlations between level of chloride and premature coating failures. These

investigators apply the contaminant (chloride) in known quantities to the steel surface and

apply the coating shortly thereafter. Niel and Whitehurst [20] used chloride contaminations

that remained in the micropits after sand blasting of steel surface for studying FBE coating

performance. They found that in presence of pitted surface, chloride contamination could

cause serious loss of performance in FBE coatings in hot cathodic disbonding and hot water

tests. For underground coatings and other immersion coatings in critical applications, a

maximum chloride level of 2 g/cm2was suggested [21].

1.4 Polyurethane as I nternal Coating for Water Transmission

Moisture curing polyurethane based coatings has long been used for construction and

rehabilitation of steel structures providing economical reliable protection. These coatings with

proven, long-term field applications can be applied over both abrasive- blasted and power tool

cleaned steel. They are quick to dry and cure, provide good adhesion and endurance, they do

not embrittle with age and retain their color and gloss. Polyurethane has a long chain polymer

structure with a number of building blocks including a backbone resin or polyol (A) a di-

isocyanate (B) and a curing agent, usually a diol or diamine. The polyol component usually

contains pigments. A coating is formed when the two components are combined; a rapid and

exothermic chemical polymerization reaction takes place.

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O

R-NCO + R-OH = R- N- C - OR

HB A

Isocyanate Polyol Urethane

The exothermic nature of this chemical reaction enables the coatings to be applied at almost

any ambient temperature. The chemical resistance of such coatings is directly related to the

degree of cross-linking of polymer. A highly cross-linked system generally results in good

chemical and corrosion resistance. The desirable attributes for internal lining is that the

material should be solvent free with good mechanical properties, e.g., abrasion resistance,

tensile strength, elasticity and adhesion and good resistance to water. Polyurethane polymers

based on different resins, e.g., polyester, polyether, etc. generally fulfil the requirements

although the selection of appropriate polymer depends upon particular service environment.

For example, a polyester based polyurethane will generally not offer as good a long term

performance in water as a polyether based material. Polyurethane coating material Aqualine-

600A has been used for internal coating applications [22]. It meets the British regulations for

use with cold potable water and for hot water (60 oC). During long-term contact with water, it

is imperative for polyurethane coating to undergo hydrolysis causing thickening and even

gelation of the material. Water is normally miscible with polyols and there is no apparent

reaction of water with polyol component while the water is absorbed. When the water

contaminated polyol component meets with the Isocyanate component, the following reaction

occurs:

O

2 ( R NCO) + H2O = > R-HN C HN R + CO2

Isocyanate Urea

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CO2 is evolved from the reaction generating bubbles in the coating during cure. If there is

significant bubbling then the physical and chemical properties will be diminished.

Solvent free polyurethane sometimes called multicomponent liquid urethane or high buildelastomeric urethanes have been commercially available for more than 30 years. These

coatings have gained wide acceptance for at least 15 years for their resistance to corrosion,

impact, and abrasion, and for their thermal insulation properties. In general, solvent free

polyurethanes offers the advantages of speed of application under almost all environmental

conditions, rapid cure and return to service time, long-life maintenance free periods and a

reasonable life-cycle cost per liter [23]. Solvent free polyurethanes have proven performance

on pipelines, structural steel work and steel structures.

In recent years, a new generation of solvent free polyurethane materials have been developed

which offer high strength and have elongation at breaking points [24]. This combination of

properties allows the materials to stretch over a crack without rupturing. The results of

immersion tests on solvent free polyurethane at ambient and high temperatures indicate a 20

years life expectancy at ambient temperature and a reduction in tensile strength of only about

30% over a two years period. The solvent free polyurethane confirms to the most stringentpotable water regulation 25 section (1) paragraph (a) administered by the Drinking Water

Incorporate of the U.K. Department of the Environment [22].

1.5 Electrochemical Impedance Spectroscopy (EI S) As Appl ied to Coatings

The most common methods used to analyze the degradation of coated metal surface are

potential/time, DC resistance, polarization curve, polarization resistance, galvanic current,dynamic relaxation and AC impedance at fixed and wide range frequency. Several reviews

are published on electrochemical methods for coated metal evaluation [25-27]. The

potential/time method is time consuming while in other DC methods some DC potential has to

be applied which can disturb the equilibrium at the coating/metal interface. While using these

methods, the highly resistive nature of the coating and ohmic drop can cause severe distortions

on polarization curves resulting in the underestimation of corrosion rates. However, in AC

impedance tests, a small AC signal is applied which may not cause disturbance to the system(5-10 mv peak to peak). A corroding system can be expressed in terms of an electric circuit

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network consisting of various elements like resistors, capacitors and inductors, which can be

determined by analyzing the response received upon applying the AC signal. Thus AC

impedance technique becomes a basic tool for characterization/evaluation of coated metal

surfaces, inhibitors and any corroding system.

Electrochemical Impedance Spectroscopy (EIS) has found widespread application in coating

technology. The availability of modern instrumentation to obtain impedance data as well as

computer program to interpret the results has made the technique popular [28]. EIS is very

suited to the study of polymeric coated metals. From experimental data it is possible to

establish relationship of different physico-chemical parameters with the values of the

corresponding components of the equivalent electric circuit and obtain trend towardsdegradation, water absorption, porosity and corrosion rate. The latter can be evaluated as a

function of natural or artificial degradation phenomenon including mechanical deformation

[29]. Considering the determination of water absorption in coating, EIS measures the flow of

electric current through a coating film. A good barrier allows very little current flow, heavy

current flow, on the other hand, indicates a poor barrier, which means salt and water

permeated the coating and set up conditions for corrosion. In a study [30] concerning with

behavior of polyurethane coating in a 3% NaCl aqueous solution, the data analysis was carriedout using a simple Ru(RcCc) equivalent circuit, where Ru, Rc and Ccare electrolyte resistance,

ohmic resistance and capacitance of the coating, respectively. The coating capacitance, Cc,

which would be accurately determined by EIS, was used for the evaluation of the barrier

properties of the coatings. Analysis of the results shows that Cc values, which depend on

coating formation and thickness increase with exposure time indicating progressive absorption

of water by the coating. Generally, the primer/intermediate/top coat systems were found to be

particularly effective barrier against water and ion penetration as indicated by their lowcapacitance variation after prolonged exposure to the test solution. Epoxy model coatings [31]

were investigated while immersed in a 3% NaCl solution using EIS during first stage of the

exposure where water uptake is the main process and long-term exposure when the corrosion

starts. The results of the impedance measurement on the water uptake of the coatings showed

that the entering water not only affects the dielectric properties but also yields swelling of the

coating polymer. Impedance measurement during the long-term immersion showed that the

start of the corrosion process under high impedance barrier type coatings can be detected bythe changes of the dielectric properties of the coating. Kellner [32] carried out EIS studies on

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polyethylene, coal tar enamel and fusion bonded epoxy (FBE) to compare the extent of water

penetration into these coatings. Mansfield et al. [33] performed EIS tests for coated sheet

(polybutadiene) and aluminum alloys in 0.5 N NaCl solution with different pretreatment

procedures. Based upon this analysis, ranking of different pretreatment procedures was carriedout. During the degradation of marine paints on steel, the primary controlling factor in the life

of the paint was the amount of water uptake while ionic concentration was a secondary

controlling factor [34]. For the optimization of automotive electro-deposited coatings,

container interior coatings and industrial maintenance coating, EIS data were used to predict

corrosion protection, film porosity, solution absorption into the coatings and film

delamination properties [35]. Variables such as resin contents, cross link densities, cure

temperatures and solvent types and contents were evaluated for the various types of coating. Ingeneral, EIS data correlated well with conventional exposure test results such as salt fog, cycle

scale corrosion and delamination test. The impedance spectra permits a rather rapid (15-75

min per sample) assessment of coating film characteristic even when no visually observable

changes have occurred. EIS provides a technique to optimize coatings while reducing the time

of coating evaluation and gives insight into chemical and physical properties of the coatings.

Titz et al. [36] characterized the protection of coatings through EIS and determinedquantitatively the local defects within the coating and delamination effects at the substrate

coating interface. EIS method has been applied successfully to evaluate the degradation of

organic coating on stainless steel (SS) with a macroscopic line defect [37]. The delamination

propagated in the direction normal to the macroscopic defect during the corrosion test, and a

thin electrolyte layer was formed under the delaminated coatings. EIS data are interpreted in

terms of a model in which the equivalent circuit of SS/coating/solution interfaces are

composed of a parallel of the circuits for a macroscopic defective part and for a delaminationpart. The detection and mapping of chemical heterogeneities or physical defects in organic

coatings [38] have been carried out using local electrochemical impedance spectroscopy

method (LEIS). Coating failure initiates as a local event at defects which can result from

chemical heterogeneities in the resin or physical defects such as bubbles, under film deposits

or pin holes. The study helped in identifying the source of failure (i.e. coating chemistry,

methods of application and cure schedule) and providing an insight into the mechanism of

degradation.

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While considering the selection of organic coating for pipelines some common defects which

are characteristic of these types of coating are to be taken into account. These defects include

blistering, early rusting, anodic undermining, filiform corrosion, cathodic delamination and

loss of adhesion.

1.6 Blistering

Blistering is one of the first signs of the breakdown in the protective nature of the coating. The

blisters are local regions where the coating has lost adherence from the substrate and where

water may accumulate and corrosion may begin. Under different circumstances, blister

formation can follow different mechanism [39].

Sometimes water absorption leads to swelling of the coating and when this occurs locally for

any reason, blisters may form and water may accumulate at the interface [40]. Potential

gradients developed due to galvanic coupling may cause electroendosmosis, leading to a

blister. There are reported cases of blistering of internal epoxy coating in product water

transmission lines [1].

The osmotic mechanism is probably the most common mechanism by which blisters form

[41]. The driving force for osmotic blistering is the presence of soluble salt at the

coating/substrate interface. As water penetrates the coating to the interface, a concentrated

solution is developed with sufficient osmotic force to drive water from the coating surface to

the interface and a blister is formed.

1.7 Ear ly Rusting

This term is applied to a measles-like rusting that occurs after the coating has dried to the

touch. It only occurs after the coated metal is exposed to high moisture conditions [42]. The

three conditions, which lead to early rusting, are: (i) a thin latex coating (< 40 m), (ii) a cool

substrate temperature, and (iii) high moisture conditions. Thus, early rusting is a consequence

of moist conditions occurring before the latex coating has dried sufficiently.

1.8 Anodic Undermin ing

Anodic undermining represents that class of corrosion reactions underneath an organic coating

in which the major separation process is the anodic corrosion reaction. An outstanding

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example is the dissolution of the thin coating between the organic coating and the steel

substrate in a food container. In each case, the cathodic reaction may involve a component in

the foodstuff or a defect in the tin coating, exposing iron, which then serves as the cathode.

The tin is selectively dissolved and the coating separates from the metal and loses itsprotective character. Aluminum is particularly susceptible to anodic undermining [43].

1.9 F il if orm Corr osion

Filiform corrosion is a type of attack in which the corrosion process manifests itself as thread

like filaments. It represents a specialized form of anodic undermining. It generally occurs in

humid environments and is most common under organic coatings on steel, aluminum,

magnesium and zinc. In some cases, filiform corrosion will develop on uncoated steels onwhich small amounts of contaminating salts have been accidentally deposited.

The threads which form in filiform corrosion exhibit a wide variety of appearance from

nodular shapes such as those on aluminum to the very fine, sharply-defined threads observed

on steel [44]. Corrosion products appeared in the form of thread like filaments in the inner

walls of liquid applied epoxy coated water transmission pipe lines, presumably indicate a

filiform corrosion attack [1].

1.10 Cathodic Delamination

One of the undesirable consequences of cathodic protection is that the coating adjoining the

defect may separate from the substrate metal. This loss of adhesion is known as the "Cathodic

Delamination". It is generally believed [45, 46] that the major driving force for cathodic

delamination in corrosion processes is the presence of air in the cathodic reaction.

H2O + O2+ 2e = 2OH-

When an applied potential is used, the important reaction may be:

2H+ + 2e- = H2

Studies indicate that the pH beneath the organic coating where the cathodic reaction occurs ishighly alkaline [47] as the cathodic equation indicates. The hydroxyl ions generated appear to

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have major destructive influence on the organic coating/substrate bond. The strong alkaline

environment may attack the oxide at the interface or may attack the polymer. Attack of the

oxide hasbeen observed and there is clear evidence that carboxylated species are present at

the interfaceas aresult of hydroxyl ion attack of the polymer [48]. The mechanism of accessof water and oxygen is not well established. Water and oxygen reach the reaction site largely

by diffusion through the coating [49], however, it appears unlikely to eliminate completely

these constituents by diffusion through the defect zone of the coating [50]. Another

mechanism involves electron transfer to the polymer functional groups along the coating

electrolyte interface during cathodic delamination of the polymer coating [51].

2. OBJECTIVES

The following are the project objectives on which different tasks are based.

(i) To investigate the influence of chloride ion, pH, temperature and pressure on the

corrosion resistance behavior of fusion bonded epoxy (FBE), polyethylene (PE) and

polyurethane (PU) coatings in product water of desalination plants.

(ii) To investigate the mechanism of adhesion loss of coated metals in hot water test.

(iii) To study the protective behavior of above-mentioned coatings in a corrosion test loop.(iv) To determine the ability of alkali metal ions to migrate through various coatings under

a potential gradient and correlate this ability of alkali ions with the cathodic

delamination resistance of different coatings.

(v) To determine whether the cathodic delamination is due to the attack of hydroxide ion

on polymer or on metal oxide at the coating/substrate interface.

(vi) Evaluation of anti-corrosion behavior of the above mentioned coatings by computer

controlled AC impedance measurements.(vii) Comparison of performance of all three coatings and evaluation their suitability for

water transmission systems by conducting short duration or accelerated tests.

3. PROJECT DESIGN

Following are the outlines of the different tasks, which have been completed for achieving the

objectives of the project.

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Task 1 - Literature Survey

Literature survey covers the important research work carried out in field of protective

behavior of organic coatings particularly FBE, PE and PU during the last 15 years.

Task 2 - Establishment of Facilities

Experimental facilities were attained to carry out the tests under different tasks. This

includes fabrication of corrosion test loop and cathodic disbondment test assembly,

acquisition of adhesion tester, holiday detector and coating thickness gauge. Some of the

tests such as autoclave tests were carried out by the outside agencies. The coating material

specimens were acquired from different coating facilities inside and outside the Kingdom.

Figures 1-9show photographs of coated panels received and the equipment used during

the testing.

Task 3 - Mechanical Testing

It comprised of the following tests:

(a) Adhesion (b) Bending (c) Cathodic Disbondment.

Task 4 - Wet Tests

It consisted of salt spray or salt fog test, close circuit loop and autoclave tests.

Task 5 - Impedance Studies

It consisted of AC impedance tests.

Task 6 - Data Analysis and Report Preparation

4. EXPERIMENTAL

4.1 Coating

Three types of organic coatings namely, Fusion Bonded Epoxy (FBE) Scotchkote-206N,

Polyurethane (PU) Aqualine-600A, PU-Irathane-155 and 3-Layer Polyethylene (PE) were

employed for the studies(Figure1).

4.1.1 Fusion Bonded Epoxy (FBE)

FBE coated panels specimens of Scotchkote-206 N were obtained from Al-Qahtani Pipe

Terminal (AQPT) of Dammam of the following specifications:

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4.1.3.1 Aqualine-600A

Color: Gray

Thickness & coupon size: Size Coating Thickness Quantity

(mm) (mils) (Nos.)

100x 50 ~35-40 50

200x 200 ~40-55 50

200x 25 ~20-30 25

Pipes: Two internally coated pipes of 68 mm diameter and

500 mm long.

4.1.3.2 Irathane-155

Type: Polyurethane (PU)

Name: Irathane 155 with Primer

Color: Yellow

Thickness & coupon size:

Size Coating Thickness Quantity

(mm) (mils) (Nos.)

100x 50 ~35-40 50

200x 200 ~30-50 50

200x 25 ~40-50 25

Pipes : Two internally coated pipes of 68 mm diameter and

500 mm long.

4.2 Equipment

Following instruments have been used for carrying out the experimental work for this project.

(i) Salt spray cabinet

(ii) Holiday Detector; with Calibration Meter- model AP-W, Tinker and Rasor.

(iii) Coating Thickness Meter, Elcometer Model 345 and Posi Tector-2000.

(iv) Adhesion Meter from DYNA Proceq, Zurich, Switzerland.

(v) Cathodic Disbondment Testing Assembly It was fabricated in the Corrosion

Research Lab. from the parts acquired through Thyseer Al-Sheikh Corp.. Al-Khobar.

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(vi) A.C Impedance Unit Solarton 1250B Frequency Response Analyzer with blank

front panel and 1287 Electrochemical interface.

(vii) Close circuit corrosion test loop.

5. EXPERIMENTAL METHODOLOGY

The work on the project was started with effect from November 15, 1998. In the following

sections the salient information regarding the experimental work carried out under different

tasks.

5.1 Mechanical Testing

5.1.1 Adhesion Test

Adhesion tests on coated steel samples were carried out under the following conditions:

Sample : Coated with FBE, Irathane-155 and Aqualine-600A

Temperature : Room temperature (25C)

Technique : ASTM D4541 85 (Re-approved 1989)

Pull-Off adhesion test and/or crosscut methods were employed to determine the adhesive

strength of the coatings. Adhesion tester consists of dollies made of aluminum, which were

glued perpendicular onto the coated surface of the samples. After the curing of adhesive (glue)

testing apparatus (Section 5.2) was attached to the loading fixture(Figures 2-3)and aligned to

apply the tension normal to the test surface. The force applied to the loading fixture is then

gradually increased and monitored until either plug of coating material is detached or a

specified value is reached. The relative stress applied to each coating can be calculated as

follows:

where

X : Greatest mean pull-off stress applied during the pull off strength achieved at failure (psi)

F : Highest force applied to the test surface (pounds)

d : Equivalent diameter of the original surface area stressed (inches)

2

d

F4X

=

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In crosscut adhesion test, a crosscut was made with the help of a utility knife on the coated

surface deep to the metal substrate. At the crosscut the blade of the knife was inserted under

the coating and with a levering action force was applied to chip off the coating. The chipped

off area was observed under microscope (magnification. x 40) to see the extent of removal ofthe coating from the substrate.

5.1.2 Flexibility Test

Flexibility or bending test provides information on the ability of coatings applied to pipe to

resist cracking, disbonding, or other mechanical damage as a result of bending. This test has

also been application as a quality control method when variations in coating application or

material formulation would affect bending performance.

Mandrel Bend Machine (Figure 4) was used to test the steel specimens coated with FBE,

Irathane-155 and Aqualine-600A at room temperature. The main objective of the bending test

is to determine the strength of the coating under bending condition. Prior to bending, the

specimens were inspected visually for any visible defect followed by holiday test. The FBE

coated samples were tested by pulse type detector set at 2500 50 Volts while Irathane-155

and Aqualine-600A were tested using a wet sponge set at 67.5 Volts. The thickness of the

specimens was also measured before the test. The specimens were then clamped in the holder

and bent flat-wise at 60oC over a thick shoe, bending was accomplished in approx. 30

seconds. The specimens were again inspected by holiday detector to confirm any cracking in

the coating after bending.

The Mandrel Ben Machine was programmed to carry out the flexibility test by increasing the

mandrel radius step by step until the coating stops failing. The smallest available mandrel shoe

was of 87 mm radius. The percent strain was calculated as given below:

Where:

t = Effective thickness of the specimens (DFT + Metal)

r = Radius of the mandrel shoe.

DFT = Dry Film Thickness

%( )

Straint

r t=

+100

2

1983


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The percent strain is directly proportional to the effective thickness t of the specimen.

5.1.3 Cathodic Disbondment Test

This test provides accelerated adhesion assessment and determines resistance of the coating to

cathodic potential and current flow. Coated steel samples of dimension 200 x 200 mm were

used for the tests. In the middle of the coated specimen a hole of 6 mm dia. (PE) or 3.2 mm

dia. (FBE and PU) was drilled through the coating to expose the substrate. A 200 mm long

plastic pipe of 100 mm diameter was glued on to the specimen with the holiday at the center

of the tubing. A cathodic disbondment test cell was assembled with a DC power supply,

platinum wire as anode, high resistance volt/amp meter and a calomel reference electrode as

shown inFigure 5. The DC power supply was designed and fabricated at the research and

development center by the instrumentation section. The advantage in using this power supply

was that it keeps the applied potential constant irrespective of current flowing through the cell.

All the four test specimens glued with the plastic pipe were kept on a hot plate and 900 ml

solution of 3% NaCl was poured in each plastic pipe(Figure 5).The temperature of the hot

plate was raised to maintain the temperature of the NaCl solution at 40oC.

The negative lead of the power supply was connected to the coated plate and positive lead to

platinum anode. After 7 days, the electrolyte was drained out and the test cell was immediately

dismantled. Coated plate was cooled down to room temperature. The blade of a hard utility

knife was inserted under the coating near the holiday edge and using a levering action, coating

was chipped off. This action was continued till it became impossible to flake off the coating.

Radius of the disbonded area from the holiday edge was measured along seven angles and

average was obtained.

The disbondment tests were carried out under the following conditions:

Samples : FBE (Green), 3-Layer PE (Black), Irathane-155 (Yellow) and Aqualine-

600A (Gray)

Temp. : (a) Room temperature (25C). (b) 40oC

Duration : 7 days at 40o

C and 4 weeks at 25C.

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Test Method : CAN/CSA-2245.20 M92 Canadian.

5.2 Wet Test

5.2.1 Salt Spray Test

Salt spray tests were carried out in a salt spray fog chamber following ASTM B117 90. A

photograph of the equipment is shown in Figure 6. The coupons were exposed for time

periods varying from 25 to 100 days.

During salt spray tests, the development of corrosion on some abraded area was studied. In

one set of samples, scratch lines (scribes) were made through one corner of the samples to the

diagonally opposite corner of the sample, i.e. X shaped. One side of the coupons wasscribed while the other side was left unscribed. The specimens, without the scribe mark, were

weighed before starting the salt spray test.

In the salt spray chamber the specimens were placed meeting the following conditions:

(i) All the specimens were supported parallel to the principal direction of horizontal flow

of fog.

(ii) Specimen holder was made of plastic and, therefore, specimens were not in contact

with each other or worth any metallic material.

(iii) A 5% solution of sodium chloride was atomized by compressed air in the chamber.

(iv) The temperature of the chamber was kept at 38oC (100oF).

Specimens were exposed under above-mentioned conditions for 25, 50, 75 and 100 days,

respectively. After the required exposure period, the samples were examined as per ASTM

D1645-71a (Re-approved 1984). This method provides a means of evaluating and comparing

basic corrosion performance of substrate, pretreatment, or coating system, or combination

thereof, after exposure to corrosive environment. The specimens were carefully removed from

the holder and gently washed in clean running water, to remove salt deposits from their

surfaces, and then immediately dried. Exposed surface at the scribes was cleaned with brush to

remove all the rust. Mean creepage from the scribe and failed area was measured and rated as

per ASTM D1654-71a (Table 5). Similarly, measurements were also carried out for the

blisters appeared on scribed and unscribed sides.

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5.2.2 Close Circuit Loop Test

The close circuit loop was fabricated in the corrosion laboratory. It has a reservoir of 200

liters water capacity for internal circulation, plastic (HDPE) pipes (60 mm diam) witharrangement of fixing coupons internally in preinstalled coupon holders. It has provisions of

adjusting pressure, flow rate and temperature.

Specimens of FBE, Aqualine-600A and Irathane-155 were fixed in coupon holders and

installed in an indigenously designed and fabricated close circuit loop (Figure 7). The

experiments were carried out under the following conditions.

Temperature : 40oC

Medium : Distilled water

pH : 7.3

Duration : 4 Weeks

Flow Rate : 60 GPM

5.2. 3 Autoclave Test

The autoclave test was carried out at Al-Qahtani Pipe Coating Terminal (AQPCT), Al-

Dammam under the supervision of SWCC-RDC staff (Figure 8).The test was carried out on

an AQPCT autoclave at 1500 psi, 40C in distilled water for 48 hours. The specimens were

half immersed in the test solution during the test. The thickness of coating was measured

before and after each test using a electromagnetic thickness gauge Posi-Tector 2000 at 6

different places (3 in aqueous and 3 in vapor phase) on the specimen. After completion of the

test the samples were assessed visually for swelling and blistering. The pull-off adhesion test

was also carried out on each phase i.e. vapor and aqueous.

The test were conducted on samples a, b, c under following conditions:

i. Samples

(a) Scotchkote-206N (Green) 3 No.

(b) Irathane-155 (Yellow) 3 No.

(c) Aqualine-600A (Gray) 3 No.

ii. Test conditions

Sample size: 100 x 25 mm

Pressure: 1500 psi

Temperature: 40o

CAtmosphere: Nitrogen gas

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Test medium: Distilled water

pH: ~7.3

Duration: 48 hours

5.3 Impedance Studies

The AC Impedance tests were carried out on FBE, Polyethylene, Irathane-155 and Aqualine-

600A coated specimens. The main objectives of the AC Impedance Measurements were to

evaluate quantitatively the water uptake by the coatings and non-destructive determination of

cathodic disbondment. On the basis of this information the performance of coating was

evaluated. The measurements were carried out on Solarton AC Impedance System, which is

consisted of 1250B frequency response analyzer with blank front panel and 1287

electrochemical interface unit(Figure 9). The samples and test conditions for AC Impedance

studies were:

Sample : Steel coated with FBE, polyethylene, Irathane-155 and Aqualine-600A

Medium : 3% NaCl

Temperature : Room temperature (25C)

Duration : 6 months.

6. RESULTS AND DISCUSSION

Coated panels of four different type coatings(Figure 1)were obtained from different supplies.

The details about the supplies and samples are given in section 5.1. It is to be noted that,

before carrying out any test, all the samples were checked visually and by holiday detector

including coating thickness measurements. The holiday detection method has been discussed

in detail in section 5.1.2.

6.1 Adhesion Test

Adhesion test was performed on FBE, PUAqualine-600A and PU-Irathane-155 as mentioned

in section 6.1.1. In all the tests the dolly was detached at the coating/dolly interface. This

confirms that the bonding between the metal substrate and coating was more than the coating

and dolly (Figures 10-12). The adhesion test results obtained are shown in Table 3. The

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results were not consistent i.e. a large difference among the data was observed. The maximum

adhesion strength between coating and dolly for FBE, Aqualine-600A and Irathane-155 was

345, 451 and 270 psi, respectively. The lower adhesion strength value of 270 psi for Irathane-

155 shows that the bonding strength of adhesive was lowest and highest with Aqualine-600A.Adhesion test was also carried out on samples used for autoclave test at AQPC facility. Here

again the strength of glue and coating was not enough to pull-off the coatings. Maximum

adhesion strength of glue used to fix the dollies to coatings was around 500 psi.

6.2 F lexibil ity Test

The samples of FBE, PU Aqualine-600A and Irathane-155 were tested as explained in

section 6.1.2. After bending the samples were examined visually followed by holiday test at

the bend site. No defect was found either visually or by holiday tester on any of the samples

tested(Figures 13-15).This confirms that FBE, 600A and 155 can sustain up to 2.41, 3.06 and

3.33 percent strain respectively (Table 2).

6.3 Cathodic Di sbondment Tests (CDT)

CDT test was carried out on all the four types of coatings i.e. FBE, PE, PU Aqualine-600A

and Irathane-155 at 232 C and 402 C. The details about the CDT test has been explained

earlier in section 6.1.3. An increase in pH value from 4.5 at the start of the test to 8.5-9.0 at

the end of all tests was recorded. Radial Disbondment (RD) results obtained from the CDT at

40C are given in Table 3. The fusion bonded epoxy coated samples showed the lowest

average RD value of 2.0 mm. While the PU coated 600A and 155 have the high average RD

values of 17.0 and 14.9 mm, respectively (Figures 16-19).The 3 layer PE coating has slightly

higher average RD value than FBE (3.16). On the basis of average RD results at 40C, the

four types of coatings can be arranged in the following ascending order:

FBE > 3-Layer PE > Irathane 155 > Aqualine-600A

At room temperature (25C), FBE, 3-Layer PE and Aqualine-600A showed almost negligible

average RD(Table 4).However, the Irathane-155 has very high RD value of 30 mm (Figures

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20-22). The performance of these coatings at 25C can be arranged in the following

descending order:

FBE 3-Layer PE Aqualine-600A > Irathane 155

Under both the test conditions no deposits on or underneath the coated surface were found.

However, the coated area exposed during the CDT test for Aqualine-600A and Irathane-155

were swelled and sticky. This shows that due to increase in pH these coating react with salt

and/ or absorb water from the test solution. A change in color on the area exposed for CDT of

Aqualine-600A and Irathane-155 samples can be seen in Figures 18-19 and 21-22,

respectively.

6.4 Salt Spray Tests

Specimens with and without scribe exposed to the salt fog were evaluated with respect to

mean creepage (from scribe) and blistering.Figures 23-30show photographs of the coating

after 25, 50, 75 and 100 days exposures to salt spray. Table 6 summarizes the salt spray

results for FBE, Aqualine-600A, Irathane-155 and 3-Layer PE coatings.

FBE coating (green) shows little creepage (0.09 mm) after 25 days of exposure but it is

increased considerably (2.06 mm) after 100 days exposure although no blistering in the

coating was found. Irathane-155 shows high creepage of 0.48, 1.51, 1.92 and 2.12 mm after

25, 50, 75 and 100 days of exposure, respectively but no blistering was observed even after

100 days of exposure. Surprisingly, Aqualine-600A has relatively low creepage (0.13 after 25

days and 1.53 after 100 days) but invariably shows blistering on scribed and unscribed sides

after 50, 75 and 100 days of exposure(Tables 7 and 8).The failure rating at the scribe and for

FBE and Irathane-155 was 6 while for 3-Layer PE and Aqualine-600A is 7 (Table 6).This

shows that, the Aqualine-600A and 3-Layer PE have better performance than FBE and

Irathane-155 at the scribe after 100 days of exposure in salt spray test. The mean creepage

value for Aqualine-600A and 3-Layer PE coatings is almost similar. Figure 25 shows

Aqualine-600A samples exposed for 50 days in the salt spray chamber with scribe (Left) and

without scribe (Right). The scribed samples show a number of blisters where as unscribed

samples are devoid of any blister. It is interesting to note that, a decrease in number of pits

was found from 50 to 100 days of exposure in salt spray chamber (Tables 7 and 8). The

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maximum number of blisters was found on the scribed side (Figures 27-30). 3-layer

polyethylene shows 0.08 and 1.66 mm creepage after 25 and 100 days of exposure

respectively in salt spray chamber but no blistering was observed.

6.5 Close Cir cui t Loop Test

Coupons of FBE, Aqualine-600A and Irathane-155 were exposed to distilled water in the

close circuit loop at 40C for 1 month under flowing condition (Flow rate 60 GPM). All the

samples were intact and no remarkable change in the physical condition of the coating was

observed.

6.6 Au toclave Test

The autoclave tests were carried out in order to know the behavior of coatings under high

pressure and temperature. The test duration was 48 hours and the temperature was fixed to

40C. The pressure of the test vessel was kept at 1500 psi. After the test samples were

examined for color, blistering, loss in adhesion strength and thickness. These tests were

carried out at AQPCT, Dammam. Figures 31-33 show the samples after autoclave test.

Tables 9 and 10 present the thickness of Scotchkote-206N (FBE) coating in vapor and

aqueous phases respectively. A slight increase in thickness can be seen in both phases.

Similarly Aqualine-600A coating shows an average increase of 1-2 mil in coating thickness in

aqueous phase. While a slight decrease in thickness in vapor phase was observed (Tables 11

and 12). Contrary to Aqualine-600A, the Irathane-155 coating which showed a reverse

behavior. An increase in the average coating thickness in vapor phase and a decrease in

aqueous phase (Tables 13and 14). This shows that coating has absorbed moisture from the

vapors and resulted in increase in coating thickness. While a decrease in coating thickness and

appearance of texture on the coating surface exposed to aqueous phase confirms the

dissolution of coating in the test solution. Aqualine-600A and FBE coatings do not show any

loss of color in autoclave test. While carrying out Pull-Off adhesion test on the panels of FBE

and Aqualine-600A after the autoclave test, again failure (at 500 psi) of dolly and coating was

observed (Tables 15 and 16).A slight discoloration and texture appearance in both the phases

was found on the Irathane-155 panels(Figure 34).Appearance of textured surface can be seen

in Figure 35. The dolly could not be fixed properly for adhesion test on either vapor or

aqueous phases exposed part of the panel.

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On coating stability consideration, the results of autoclave tests show opposite behavior of two

urethane coatings viz. Irathane 155 and Aqualine 600 A. Irethane shows an increase in the

average coating thickness in the vapor phase and a decrease in aqueous phase (both at 40oC

and 1500 psi) whereas a reverse behavior has been observed in Aqualine 600A and FBE

coatings. The peculiar behavior of Irethane could be attributed to an exothermic disbondment

reaction, which is not favorable in the vapor phase because of the enormous amount of heat

energy required to generate and sustain water vapors in the vapor phase at a high pressure of

1500 psi and a relatively low temperature of 40oC. The heat content of vapor phase might be

further enhanced by inevitable condensation of some of the vapors. In contrast, the heat

contents of aqueous phase are expected to be lower and more favorable in energy content to an

highly exothermic disbonding reaction. This peculiar behavior of Irathane 155 is in

conformity with the results of the cathodic disbondment studies of the two-urathane coatings.

The results indicate that Irathane deteriorated more severely at room temperature (25OC) than

at higher temperature (40OC). This curious behavior points out to an exothermic reaction,

which is suppressed at higher temperature, yet favored at low temperature. In Aqualine 600 A

and FBE coatings, the disbonding reaction in the coating seems to be endothermic reaction

thereby showing the stability of the coatings in aqueous solution.

On practical considerations pertinent to the application of organic materials as internal

coatings in water transmission lines, it must be emphasized that vapor forming conditions do

not exist in flowing water under high pressure (60 bar). The results of vapor phase are,

therefore, only relevant to shut down conditions or to external coatings.

6.7 A.C Impedance Test

Bode plots for FBE, Aqualine-600A, Irathane-155 and 3-Layer PE samples exposed to 3%

NaCl solution at room temperature (25C) after 6 months of exposure are shown inFigures

36-39. In fact after 6 months of exposure, only slight change in impedance value was found.

This could be due to surface adsorption of moisture. In Nyquist plots a straight line was

observed instead of a semicircle. This confirms that no corrosion process was started even

after 6 months of exposure.

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1. The results of adhesion tests carried out on FBE, PU 600 A and 155 show that the

bonding between the metal substrate and the coating was more than the coating and

dolly. The maximum adhesive strength was for Aqualine-600 A and minimum for

Irathane-155.

2. The flexibility test (bending test) carried out on FBE and PU 600 A and 155 shows no

defect or presence of holidays at the bending site. Irathane-155 coating can sustain up

to 3.33% strain.

3. On the basis of radial disbondment measurements from cathodic disbondment tests,

the decreasing performance of the coatings can be represented as:

FBE > 3-Layer PE > Aqualine-600 > Irathane-155

4. During cathodic disbondment tests, Aqualine 600 and Irathane-155 were found

swelled and sticky.

5. The results from salt fog tests show following behavior for different coatings.

(a) In scribed samples, the creepage increases with increasing exposure time:

25 days test : from 0.09 mm (FBE) to 0.48 mm (Irathane 155).100 days tests : from 1.53 mm (Aqualine 600 A) to 2.12 mm (Irathane 155).

(b) Whilst FBE, Irathane-155 and 3-Layer PE show no blistering after 100 days,

Aqualine-600 shows blistering on scribed and unscribed surfaces.

6. The pull off adhesion tests carried out on coated samples after autoclave tests show

that the adhesive strength of FBE, 3-Layer PE and PU 600-A and 155 coatings is

greater than 500 psi.

7. The results of the autoclave tests indicate that FBE and Aqualine-600A coatings show

very small variations in thickness in vapor phase and a definite increase in aqueous

phase. However, Irathane-155 shows a clear increase in thickness in vapor phase and a

decrease in thickness in aqueous phase indicating the dissolution of coating in test

solution.

8. Aqualine-600A and FBE coatings do not show any loss of color in autoclave tests.

7. CONCLUSIONS

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9. AC impedance tests carried out on all three coatings in 3% NaCl at room temperature

(25oC) show only slight change in impedance due to surface adsorption of moisture.

However, no corrosion process appears to be initiated after 6 months of exposure.

10. Close circuit loop tests results of 1-month exposure in distilled water indicate no

marked change in the color and texture of the coating. There was no perceptible

change in weight.

8. RECOMMENDATIONS

1. Out of the 4 organic coatings, viz. Scotchkote-206 N (FBE); Aqualine-600A (PU),

Irathane-155 (PU) and 3-Layer PE tested, only FBE coating appears to have

formidable properties. FBE has good mechanical properties, low water permeation, no

chemical degradation and good corrosion resistance. Moreover, FBE shows small

increase in radial disbondment under applied potential (1.5 volts Vs SCE) thus

indicating its stability towards cathodic disbondment. This combination of properties

provide FBE as a suitable choice for internal and external lining material for steel

pipes in water transmission systems.

2. Considering the application of FBE as internal coating in water transmission system,

the effect of chlorinated water on FBE is not well documented. It is therefore,

recommended to carry out studies related to the influence of chlorinated water on FBE

coatings.

3. Polyurethane 600A and 155 have reasonably good mechanical properties though, but

show degradation during cathodic disbondment and poor performance in autoclave

tests and therefore, do not appear to be suitable for internal lining. However, new

generation of solvent free polyurethane which showed promising properties as internal

coating can be considered for detailed studies in future research projects.

4. 3-Layer polyethylene showed good resistance to water and chloride permeation. Such

a material can be considered for external coating on steel pipes exposed to marine

atmosphere and/or in contact with high chloride low resistivity soil (Subkha).

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Table 1. Pull-off adhesion test results measured by DYNA adhesion tester with 50

mm dolly

Adhesive Strength (psi)S. No. Coating Type

#1 #2 #3 Average*

1. Scotchkote-206N

(FBE) Green

150 210 345 277

2. Aqualine-600A Gray 375 120 451 413

3. Irathane-155 Yellow 225 75 270 247

* Average of two comparable values

Table 2. Calculated Average Percent Strain of the specimens under test

S.No. Coating Type Thickness t (mm) % Strain

1. Scotchkote-206N (FBE)

Green

4.3 2.41

2. Aqualine 600A PU

Gray

5.5 3.06

3. Irathane-155 PU

Yellow

6.0 3.33

Thickness t: DFT + MetalPU: Polyurethane

DFT: Dry Film Thickness

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Table 3. Measured radial disbandment after the Cathodic Disbondment test carried out

at 40C in 3% NaCl solution for seven days. The applied voltage was 1.5against Saturated Calomel Electrode (SCE).

S.No. Coating Type Sample # Average

DFT(mils)

Radial

Disbondment(mm)

Average

Disbondment(mm)

1. Scotchkote-206N Green A

B

C

23.0

24.4

27.7

1.7

2.2

2.0

2.0

2. Aqualine-600A Gray A

B

C

54.4

35.1

36.9

13.5

16.5

21.0

17.0

3. Irathane-155 Yellow A

B

C

33.7

49.9

28.4

15.0

12.7

16.9

14.9

4. 3-Layer PE Black A

B

C

4.5

4.5

4.5

2.5

4.0

3.0

3.2

DFT : Dry Film Thickness

Table 4. Measured radial disbondment after the Cathodic Disbondment test carried out

at 25C in 3% NaCl solution for 4 weeks. The applied voltage was 1.5 againstSaturated Calomel Electrode (SCE).

S.No. Coating Type Radial Disbondment (mm)

1. Scotchkote-206N Green Negligible

2. Aqualine-600A Gray Negligible

3. Irathane-155 Yellow 30.00

4. Polyethylene 3 Layer- Black Negligible

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Table 5. Rating of failure at scribed and unscribed area [ASTM D1654 71a]

Mean Creepage from scribe (mm) UnscribedS.No.

Millimeters Rating Number % Area Failed Rating Number

1. Over 0 10 No Failure 10

2. Over 0.0 0.5 9 0 1 9

3. Over 0.5 1.0 8 2 3 8

4. Over 1.0 2.0 7 4 6 7

5. Over 2.0 3.0 6 7 10 6

6. Over 3.0 5.0 5 11 20 5

7. Over 5.0 7.0 4 21 30 4

8. Over 7.0 10.0 3 31 40 3

9. Over 10.0 13.0 2 41 55 2

10. Over 13.0 16.0 1 56 - 75 1

11. Over 16.0 0 Above 75 0

Table 6. Salt Spray Test Results: Mean Creepage from Scribe (mm)

Coating Exposure (days) Rating Visual Examination

Remarks

25 50 75 100

Scotchkote-206N

(Green)

0.09 1.27 1.57 2.06 6 No blistering

Aqualine 600 A(Gray)

0.13 0.21 1.13 1.53 7 Blistering observedafter 50 days.

Irathane 155

(Yellow)

0.48 1.51 1.92 2.12 6 No blistering

Polyethylene

(Black)

0.08 0.23 1.27 1.66 7 No blistering

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Table 9. Thickness (mils) of Scotchkote-206N (FBE) - Green color coatings measured at

3 different locations on 3 specimens exposed to vapor phase in autoclave test

carried out at 1500 psi at 40C for 48 hours in distilled water.

S.No. Sample # Location Before Test After Test Remarks

1. 1

Average

1

2

3

21.1

20.9

20.5

20.83

20.9

20.1

20.4

20.46

- 0.36

2. 2

Average

1

2

3

20.3

20.2

20.3

20.26

20.9

21.6

20.3

20.93

+ 0.67

3. 3

Average

1

2

3

20.8

21.4

21.6

21.26

21.4

21.9

21.7

21.66

+ 0.39

Table 10. Thickness (mils) of Scotchkote-206N (FBE) - Green color coatings measured at

3 different locations on 3 specimens exposed to aqueous phase in autoclave test

carried out at 1500 psi at 40C for 48 hours in distilled water.


1. 1

Average

1

2

3

20.9

20.3

20.5

20.56

21.3

22.6

21.9

21.93

+ 1.36

2. 2

Average

1

2

3

21.0

21.7

21.521.40

21.0

20.5

21.220.9

+ 0.50

3. 3

Average

1

2

3

21.5

21.8

20.9

21.40

21.7

21.8

21.5

21.66

+ 0.26

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Table 11. Thickness (mils) of Polyurethane Aqualine-600A - Gray color coatings measured

at 3 different locations on 3 specimens in vapor phase in autoclave test carried

out at 1500 psi at 40C for 48 hours in distilled water.


1. 1

Average

1

2

3

28.6

24.9

26.2

26.56

29.4

28.7

29.6

29.23

+ 2.67

2. 2

Average

1

2

3

23.0

22.2

18.5

21.23

21.9

23.2

17.0

20.70

- 0.53

3. 3

Average

1

2

3

18.8

21.2

25.2

21.73

18.5

20.4

25.8

21.56

- 0.16

Table 12. Thickness (mils) of Polyurethane Aqualine-600A - Gray color coatings measured

at 3 different locations on 3 specimens exposed to aqueous phase in autoclave

test carried out at 1500 psi at 40C for 48 hours in distilled water.


1. 1

Average

1

2

3

24.48

33.5

30.6

29.63

33.3

35.2

30.8

33.10

+ 3.46

2 2

Average

1

2

3

13.6

13.2

18.3

15.03

13.7

13.9

20.5

16.03

+ 1.00

3. 3

Average

1

2

3

22.9

27.8

26.1

25.60

24.6

28.8

27.2

26.86

+ 1.26

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Table 13. Thickness (mils) of Polyurethane Irathane155 - Yellow color coatings measured

at 3 different locations on 3 specimens in vapor phase in autoclave test carried

out at 1500 psi at 40C for 48 hours in distilled water.


1. 1

Average

1

2

3

51.9

46.5

44.6

47.66

60.2

59.3

54.6

58.03

+ 10.36

2. 2

Average

1

2

3

48.3

45.0

42.3

45.20

62.5

57.6

55.3

58.46

+ 13.26

3. 3

Average

1

2

3

39.2

38.8

41.1

39.70

48.3

48.7

48.3

48.43

+ 8.73

Table 14. Thickness (mils) of Polyurethane Irathane155 - Yellow color coatings measured

at 3 different locations on 3 specimens exposed to Aqueous Phase in autoclave

test carried out at 1500 psi at 40C for 48 hours in distilled water.


1. 1

Average

1

2

3

43.2

41.5

41.6

42.10

41.2

41.0

38.9

40.36

- 1.73

2. 2

Average

1

2

3

41.3

42.8

41.7

41.93

40.8

40.3

39.7

40.26

- 1.66

3. 3

Average

1

2

3

45.1

48.7

46.3

46.70

38.3

39.0

41.8

39.70

- 7.00

2000


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Table 15. Physical appearance and adhesion test results of the Scotchkote-206N (FBE)

Green color coatings after autoclave test exposure. The maximum adhesion

strength of glue used to fix the dollies to the coatings was 500 psi

Adhesion TestS.No. Sample # Physical Appearance

Gas Phase Aqueous Phase

1. 1 No Blistering or Swelling Glue Failure Glue Failure



Table 16. Physical appearance and adhesion test results of the Polyurethane Aqualine-

600A - Gray color coatings after autoclave test exposure. The maximum

adhesion strength of glue used to fix the dollies to the coatings was 500 psi

Adhesion TestS.No. Sample # Physical Appearance


1. 1 No Blistering or Swelling.A light texture in the

aqueous phase.

Glue Failure Glue Failure

2. 2 No Blistering or Swelling.

A light texture in the

aqueous phase.


3. 3 No Blistering or Swelling.

A light texture in the

aqueous phase.


2001


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Table 17. Physical appearance and adhesion test results of the Polyurethane Irathane155 - Yellow coatings after autoclave test exposure.

Adhesion TestSample # Physical Appearance


1 Discoloration and swelling on

the gas phase. Both phases

have heavy textured

appearance

Dolly could not be

fixed due to surface

roughness. It could be

easily removed byapplying little force by

hand.

Dolly could not be



easily removed byapplying little force

by hand.

2 Discoloration and swelling on

the gas phase. Both phases

have heavy textured

appearance

Dolly could not be



easily removed by

applying little force by

hand.

Dolly could not be



easily removed by

applying little force

by hand.

3 Discoloration and swelling onthe gas phase. Both phases

have heavy textured

appearance

Dolly could not befixed due to surface


easily removed by

applying little force by

hand.

Dolly could not befixed due to surface


easily removed by

applying little force

by hand.

2002


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Figure 1. Photograph showing the coated panels received, [A] for Cathodic

Disbondment Test [B] for Autoclave and Bend (Flexibility) Test and [C]

for Salt Fog Test. Yellow: Irathane-155 (PU), Gray: Aqualine-600A (PU),

Black: 3-Layer Polyethylene (PE) and Green: Fusion Bonded Epoxy

(FBE).

Figure 2. Photograph showing the Adhesion Testing Equipment

2003


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Figure 3. Schematic of Pull-Off Adhesion Tester

Figure 4. Photograph showing Bend Test equipment used for bend test.

2004


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Figure 5. Photograph showing the Cathodic Disbondment Testing Equipment

Figure 6. Photograph showing the Salt Spray Testing Equipment

2005


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Figure 7. Photograph showing the close circuit test loop

Figure 8. Photograph showing the Autoclave used during the study

2006


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Figure 9. Photograph showing AC Impedance system used during the

study

Figure 10. Photograph showing Scotchkote-206N(FBE)

coupons used for Pull-OFF Adhesion Test

2007


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Figure 11. Photograph showing Aqualine-600A (PU) coupons used

for Pull Off Adhesion Test

Figure 12. Photographs showing Irathane-155 (PU) coupons used

for Pull Off Adhesion Test

2008


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Figure 13. Photograph showing Scotchkote-206N (FBE) panels after

flexibility test

Figure 14. Photograph showing Aqualine-600A panels after

flexibility test

Figure 15. Photograph showing Scotchkote-206N (FBE) panels after

flexibility test

2009


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Figure 16. Photograph showing the Scotchkote-206N(FBE) panel tested

Cathodic Disbondment test in 3% NaCl solution at 40oC for

7 days

Figure 17. Photograph showing the 3-Layer Polyethylene (PE) panel tested

Cathodic Disbondment test in 3% NaCl solution at 40oC for

7 days

2010


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Figure 18. Photograph showing the Aqualine 600 A panel tested

Cathodic Disbondment test in 3% NaCl solution at 40oC

for 7 days

Figure 19. Photograph showing the Irathane-155 panel tested Cathodic

Disbondment test in 3% NaCl solution at 40oC for 7 days

2011


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Figure 20. Photograph showing the Scotchkote-206N (FBE) panel tested

Cathodic Disbondment test in 3% NaCl solution at room

temperature for 4 weeks

Figure 21. Photograph showing the Aqualine-600 A panel tested Cathodic

Disbondment test in 3% NaCl solution at room temperature

for 4 weeks

2012


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Figure 22. Photograph showing the Irathane-155 panel tested Cathodic

Disbondment test in 3% NaCl solution at room temperature

for 4 weeks

Figure 23. Photograph showing coupons taken out after 25 days of

exposure in Salt Fog Chamber

2013


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Figure 24. Photograph showing coupons taken out after 50 days of exposure

in Salt Fog Chamber

Figure 25. Photograph showing Aqualine-600A coupons exposed in salt spray

chamber for 50 days. Large numbers of blisters can be seen (left)

on the scribed samples while absence of blisters on unscribed samples

(right)

2014


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Figure 26. Photograph showing coupons taken out after 75 days of exposure

in Salt Fog Chamber

Figure 27. Photograph showing Aqualine-600A coupons taken out after 75 days

exposure in Salt Fog Chamber. Some blisters marked with black

dashes can be seen.

2015


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Figure 28. Reverse side of the same as in Fig. 27. The blisters are marked

with bluish dash marks

Figure 29. Photograph showing coupons taken out after 100 days of

of exposure in Salt Fog Chamber

2016


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Figure 30. Photograph Showing Aqualine-600A coupons taken out after 100 days

of exposure in Salt Fog Chamber. Some blisters marked with red

arrows can be seen

Figure 31. Photograph showing Scotchkote-206N(FBE) panels exposed in

distilled water at 40oC for 48 hours in autoclave test

2017


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Figure 32. Photograph showing Aqualine-600A panels exposed in distilled

water at 40oC for 48 hours in autoclave test

Figure 33. Photograph showing Irathane-155 panels exposed in distilled

water at 40oC for 48 hours in autoclave test

2018


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Vapor Side

Aqueous Side

Figure 34. Close-up views of the each coated panel after autoclave

test exposure showing both vapor and aqueous phases

Vapor Side Aqueous Side

Figure 35. Close-up views of Irathane-155 panel after autoclave test

exposure showing both vapor and aqueous phases. Loss in

surface texture in the aqueous phase can be seen

2019


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2020


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2021


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2022


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Figure 39A. Nyquist plots for 3-Layer Polyethylene (Black) exposed in

3% NaCl solution for 6 months

Figure 39B. Bode plots for 3-Layer Polyethylene (black) exposed in 3%

NaCl solution for 6 months

2023


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Documents

Corrosion Protection Evaluation of Some Organic Coatings Incorrosion Protection Evaluation