coating selection.pdf

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4thPipeline Technology Conference 2009

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Designing a method for selecting the most appropriate external

pipeline protective coating

Ali Reza Moeini, Ali Ehsan Nazarbeygi

Presenter: Ali Reza Moeini

Research Institute of Petroleum Industry

National Iranian Oil Company, Iran

AbstractSelection of protective pipeline coatings has always been a challenging subject.The appropriate coating is the one with high performance, high durability, low

monitoring and maintenance costs, easy application method and also the onethat is cost effective and health friendly.

The objective of this article is to present a method which helps with selectingthe most appropriate coating through running a qualitative as well as aquantitative comparison between different types of external pipeline coatingsconsidering the technical and financial priorities of the user. To design thismethod, we have applied the QFD (Quality Function Deployment), which is aknown process. This method is indeed remarkable since it gives user theopportunity of applying new data regarding to users own experiences andrecords as well as the opportunity of determining whether the technical

concerns are of more importance or the financial concerns.

Keywords: pipeline protective coating; quality function deployment; externalcoating; coating selection.

1. IntroductionTransmission of oil, gas, water and other fluids by means of steel pipelines isone of the safest and most economical methods. But metal pipes suffer fromcorrosion across the whole surface if they are exposed to air and moisturewithout protection; therefore to minimize the probability of corrosive attacks andhence the formation of cracks and holes which may lead to serious damages oreven explosion, the pipe surface must be isolated from oxygen and moisture.Applying appropriate coatings along with cathodic protection system is apractical way to avoid corrosion and since the coating costs are approximately4% of the total costs of pipeline construction, it would be an economical way toprevent failures to occure. It should be attended that application of the selectedcoating must be followed by regulated control and inspections in order tocomplete the protection process and minimize the in-service repair costs.

To design the method, we have applied the QFD process, in which bothtechnical and economical concerns are taken into account. On the other hand, it

is necessary to define related technical criteria. These technical criteria are


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taken from reliable international standards that are drawn up by experts andspecialized institutes and have been the reference for technical evaluations ofcoatings field performance for years.

2. Theory of the Method

2.1. Standard CriteriaAlthough assessing and comparing various coatings with each other is possibleif only the experimental procedures applied for testing them are the same (or atleast the results of the different procedures of a special test method areconvertible to a single measure), coatings are being assessed by differentexperimental procedures from different standards. In table (1), we havecompared the standard criteria of eight frequently used pipeline protectivecoatings in Iran. As it is seen, no uniform measure exists for assessing thesecoatings and lack of such uniform and identical measure is the main challenge.

For instance, the methods for testing adhesion of polyurethane and three-layerpolyethylene (3LPE) coatings are completely different from the method used fortesting the adhesion of coal tar based enamel and hence comparing theadhesion of these coatings would not be correct.

2.2. Comparison between the CoatingsTo compare the coatings, standard measures must be normalized for eachcharacteristic. This normalization has been done regarding to field experiencesand investigations of our working group. It should be attended that each groupor organization can restablish this method and attribute other ratings toproperties according to their own experiences and records and then use themethod.

2.3. Description of the MethodAs it is illustrated in table (2), by means of QFD method, requirements of acoating are first divided into three main categories: performance, applicationparameters and hygenic concerns. Then each of these categories branches outto the related properties, which have the greatest influence and share. Forexample, the performance of coatings is divided into four groups: stability anddegredation resistance, mechanical resistance, chemical resistance, andcathodic protection concerns. Application parameters and hygenic concerns are

also divided into their related properties.

To quantify the importance of each property, a number from 1 to 10 is attributedto each property, where 1 indicates the lowest importance and 10 the highest.These numbers, which are located in the third column of table (2), are calledImportance Weight (IW). In the rest of the columns of table (2), specificnumbers (1 or 10 or 100) called as Importance Number (IN) are applied toshow the importance level of coating characteristics related to the coatingproperties. Number 100 shows the highest level of importance and number 1shows the lowest.


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Equation (1) illustrates a logical and quantitative relation between the coatingproperties and the coating characteristics; it gives the score for eachcharacteristic, which is consequently converted to a relative percentage calledas Relative Importance (RI) using equation (2).

]3[ log10

1

iiIN

i

j IWScore =

(1)

IW=Importance WeightIN=Importance Number

Relative Importancej 10016

1

=

=j

j

j

Score

Score (2)

In the next step, as it is shown in table (3), to establish a quantitative relationbetween the performance of each coating and the coating characteristics, anumber between 1(the worst) and 10(the best) is attributed to each coating forthe related characteristic; this is called Performance Number. Through thecalculated relative importance and also the performance number, the AbsoluteWeight (AW) of each coating is determined, using equation (3):

=

=16

1j

KAW Performance Numberj, forK=1,,9 (3)

AW: Absolute Weight

RI: Relative Importance

So, according to the attributed performance numbers, as it is shown in table (3),liquid epoxy gets the highest and bitumen enamel gets the lowest absoluteweight from the technical point of view.

As it was mentioned previously, each user can restablish this method andattribute other ratings to parameters in tables (2) and (3) according to their ownexperiences and records and obviousely the results will be different from thoseobtained here.

In the last step, through equation (4), the economical concerns are taken intoaccount and the final score of each coating is calculated by means ofcoefficients of technical and financial concerns (X and Y respectively):

Final score=(X)(T)+(Y)(F) , X+Y=1 (4)

T (Technical score)and F (Financial score)are calculated using equations (5)and (6) as follows:

100)],...,(/[ 91 = AWAWMaxAWT K (5)

100]/[ = coatingtheofpricecoatingcheapesttheofpriceF (6)


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Prices of the various coatings in Iran are shown in table (4). Regarding to theprice fluctuations (prices of coatings and transportation) during different periods,the total cost must be determined by the user at the time he wants to use the

method.

At the end, when the final scores, according to the given data by user, arecalculated, the coating with the highest score would be the most appropriateone for the case.

3. Developing a SoftwareTo facilitate the process, this method can be developed as computer software,which enables the user to perform more easily and precisely. In addition,several options can also be considered when designing the software; theseoptions may ask about: maximum operating temperature, type of transmitted

fluid, pipeline substrate, pipeline pressure, and size of the pipes. So it would bepossible for the user to enter the required project data and let the software torun the process according to the specifications established for each coating andmake the coating selection automatically.

3.1. Maximum operating temperature: since different types of coatings havedifferent service temperatures, this software asks about the required maximumoperating temperature and doesnt count those coatings that have loweroperating temperatures than the specified amount.

3.2. Type of the fluid:using some coatings is not advised when the transmittedfluid is a hydrocarbon liquid and this has been taken into account whendesigning the software. For instance the software omits the bituminous coatingswhen the fluid is one of the hydrocarbon liquids.

3.3. Pipeline substrate:the pipeline substrate (whether it is in a harsh, rocky orforestial area or not) is so important for laying a pipeline network. For examplein harsh areas, some coatings- if selected by the software- must be applied withhigher thickness. We have inserted limitations for bitumen and polymer modifiedbituminous enamel without PP topcoat for forestial areas where there is rootpenetration and bacterial attacks; the user can insert other limitations for other

substrates.

3.4. Pipeline pressure: although there are not pressure limitations for coatingselection, the software is capable of considering limitations if necessary.

3.5. Size of the pipes: it is also possible to insert limitations for the size of thepipes if necessary.


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4. ExampleTo explain how the method works, an example is presented. Consider two gaspipelines with the below-mentioned specifications:

Case (1) Case (2)Length 120 Km 10 KmOperating Temperature 40C 25CSize 42 in. 20 in.Pressure 1050 psi 200 psiSubstrate Harsh Normal

By using the data in table (2), (which can be changed by the user), the relativeimportance of each characteristic is calculated. Then, through table (3), theabsolute weight (AW) is calculated; it is also possible for the user to change thedata in table (3). In the next step, the user must choose the desired values for

technical and economical coefficients X and Y in equation (4) considering thedemands, circumstances and the budget. Since in the first case, the pipeline ispassing through a harsh area, the pipes are heavy, the pressure andtemperature is high, so it is essential to put more emphasis on the technicalissues comparing to the conditions of the second case. Therefore the user canattribute X=0.7 and Y=0.3 for the first case and X=0.3 and Y=0.7 for the secondcase. The calculated final score of each coating is shown in table (5). For thefirst case, where the technical issues are of more concern, the polyurethanecoating would be the best selection and for the second case, where the financialissues are of more concern, the bitumen enamel coating would be the bestselection.


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Table 1: Standard criteria for various coatings

ElecResis

ElongationFlexibilityIndentationResistance

CathodicDisbondment

ImpactResistance

Pull offAdhesion

CoatingCharacteristic

CoatingMaterial

@2310

7

ISO 527> 10%

@23 & 0C:No cracksdisbond orpinehole

@23C


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Table2: Relationship between properties and characteristics of coaCoating Characteristics

SoilStressResistan

ce

ShieldingPotential

CathodicDisbondm

ent

@Low&HighTemp.

FlexibilityorBend

WaterAbsorption/Water

VaporTransmition

HotWaterSoak

SpecificElectrical

Resistance

ThermalCycle&Aging

Resistanc/

StabilitorDeradation

Indentation/Penetration

ImpactResistance/Hardness

Adhesion/Peel/Pu

lloff

SurfacePreparation

ImportanceWeight

Coating PropertiesRequirem

ents

101010010100100101001001010010010Stability & DegradationResistance

10-10100100100-100100100119Mechanical Resistance

--111010-100101115Chemical Resistance

101001001100100100100111001009Cathodic Protection ConcernsPerformane

1010101-10--10101001004Sensitivity to SurfacePreparation & ApplicationConditions (speed, equipmentrequirements,..)

101010010010101001001010100107Maintenance & Repair

-1-100---10100100--8Storage & Handling

101110111111001001006Inspectability

Application

Parameters

-----1-----105Environmental Concerns

-----------104Health & Safety ConcernsHygenic

30158284282294311180390306284338323IWScore i

IN

ij

=log

10

1

3

7.43.876.966.917.217.624.419.547.56.968.287.9210016

1

=

=j

j

j

Score

ScoreRI


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Table3: Relationship between performance and properti

SoilStressResista

nce

ShieldingPotential

Cathodicdisbondment@low&

highTemp.

Flexibility/Ben

d

Waterabsorption/WaterVaper

transmition

Hotwatersoak

SpecificElectricalResistance

Thermalcycle/Aging/S

tabilityor

degradationResistance

Indentation/Penetration

ImpactResistance/Hardness

Adhesion/peel/pulloff

SurfacePrepatation

Coating

Characteristic

Coating Material

997677788593Poly Urethane97.9357.14

9996886885102Liquid Epoxy10050

686467655669Coal Tar Enamel83.0280

748766768972Three Layer Poly Olefine85.9350

997687679382Fusion Bonded Epoxy94.4640

475833643868Polymer Modified

BiumenEnamel

72.0957.14

555854654868Polymer Modified Biumen

Enamel with PP topcoat

79.9450

222946644658Tape Coating67.4557.14

474533542448Bitumen Enamel61.12100


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Table 4: Prices of various types of coatings in Iran

Cost

Rial/m2

Coating Material

140000Poly Urethane

160000Liquid Epoxy

100000Coal Tar Enamel

160000Three Layer Polyethylene

200000Fusion Bonded Epoxy

140000Polymer Modified Bitumen Enamal

160000Polymer Modified Bitumen Enamal with PP topcoat

140000Tape

80000Biumen Enamel

Table 5: Calculated final scores of coatings for two different cases

Case1 Case2Coating

Score(1)

Rating(1)

Score(2)

Rating(2)

Polyurethane 85.7 1 69.4 3

Liquid Epoxy 85 2 65 4

Coal Tar Enamel 82 3 81 2

3LPE 75.15 5 60.8 6

FBE 78 4 56.3 9

Polymer Modified Bituminous Enamel 67.6 8 61.6 5

Polymer Modified Bituminous Enamel + PPLayer

70.96 7 59 8

Tape 64.36 9 60.2 7

Bitumen Enamel 72.78 6 88.3 1


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References[1]. S.W.Guan, Corrosion Protection by Coatings for Water and WastewaterPipelines, W&W Pipe Coatings, 2001

[2]. S.Papvinasam, R.W.Revie, Coatings for Pipelines, CANMET MaterialsTechnology Laboratory, Canada, 2000[3]. E.W.Kelechka, Coatings for Corrosion Protection, Colorado School ofMines, 2004[4]. G.Koh, M.Bronger, N.Thompson, Corrosion Cost and Prevention Strategiesin the United States, Technical Report, Technologies Laboratories and NACEInternational, Houston TX, 2001[5]. N.I.G.C. Standards, IGS[6]. EN 12068, External Organic Coatings for the Corrosion Protection ofBuried or Immersed Steel Pipelines Used in Conjunction with CathodicProtection Tapes and Shrinkable Materials

[7]. ISO 21809, External Coatings for Buried or Submerged Pipelines Used inpipeline Transportation Systems[8]. J.R.Hauser, D.Clausing, The House of Quality, Harvard Business Review,1998[9]. Y.Akao, S.Mizuno, QFD: The Customer Driven Approach to QualityPlanning and Deployment, Asian Productivity Organization, 1994[10]. J.Terninko, Step by Step QFD: Customer Driven Product Design,St.Luice Press, 1997

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