3layerPE coating.doc

7/29/2019 3layerPE coating.doc

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HEAT APPLIED POLYETHYLENE PRE-FORMED

MULTIPLE LAYERED COATING SYSTEMS........

A TOTAL SOLUTION

Samuel Thomas Francisco Trespalacios Quijano


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ABSTRACT

This paper addresses the current State-Of-The-Art Polyethylene Pre-formed plant

coating solutions for the corrosion protection of Steel pipes for the Oil, Gas and

water industries. The technology of Polyethylene Multiple Layered coating systems

will be reviewed relative to the design of the coating and the fabrication of the

coating on the pipe; plus practical experience in pipeline design and performance

behavior. Two State-Of-The-Art coating systems will be reviewed and discussed

showing proven performance as a long term corrosion protection system on a

global basis. Finally, this paper will present unique high performance girth weld

coating systems, which works in conjunction with the mainline primary coating

systems to provide a total coating solution.

INTRODUCTION

Two new polyethylene based coatings have been developed for corrosion

protection of buried pipelines. The coatings are designed to be applied in most

existing coating plants using a new spray applied primer and a multifunctional

polyethylene laminated. The laminated is applied in the solid state to the

preheated, primed pipe and fused immediately by residual heat in the pipe. The

results are monolithic coatings with no mastic like components.

The Multi-Layer Coating system is an advance protection system for oil & gas

pipelines, utilizing three layers of high technology polymeric materials that form an

impermeable barrier to moisture, oxygen and other corrosion causing agents. The

system is composed of three engineered layers that, when heated, fuse into a

tough and durable, yet flexible coating that exhibits important performance

characteristics such as:

Low cathodic protection consumption.


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High soil stress resistance.

Impermeability to oxygen and moisture.

High shear resistance.

Flexibility & durability for rugged handling ( in plant and in the field ).

This coating system is shown schematically in Figure 1. The polyethylene

component is preformed in an extremely efficient and productive plastics

converting factory and delivered to the coating plant in rolls that are easily handled

and stored. The liquid primer can be applied with a conventional and portable

sprayer. With a reasonable source of pipe heating, the spray unit already

mentioned and roll let off stands, virtually any fixed or portable pipe coating plant

can apply this new coating system.

The 3-Layer coatings generally have a fusion bonded epoxy primer and a two

layer polyethylene based material extruded over it. The two layers consists of a

thin layer of modified polyethylene for the adhesion to the epoxy primer and a

thicker working layer of polyethylene on the outside. This combination utilizes the

strengths of each type of material. The epoxy advantage of good adhesion to steel

and good cathodic disbonding characteristics are combined with the water barrier

and good mechanical properties of polyethylene. The combination has better

adhesion, cathodic disbonding resistance, hydrolytic stability and impact strength

than either coating used by it self.

The mayor drawback of these 3-Layer coating is that they require application in a

fusion bonded coating plant to which has been added expensive plastic extrusion

equipment. The temperatures required for epoxy fusion are high and the plastic

extrusion rates are low, both of which limit the coating rates that can be achieved.

The new coating overcomes these limitations without sacrificing the excellent

performance of the 3-Layer system. This coating system is shown schematically

in Figure 2. The polyethylene component is preformed in an extremely efficient and


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productive plastics converting factory and delivered to the coating plant in rolls that

are easily handled and stored. The liquid epoxy primer can be applied with a

conventional and portable plural component sprayer rather than a fixed

electrostatic flocking installation. With a reasonable source of pipe heating, the

spray unit already mentioned and roll let off stands, virtually any fixed or portable

pipe coating plant can apply this new coating system.

APPLICATION

The Multi-Layer coating system consists of three layers: A synthetic thermoplastic

elastomer primer blended with heat activated polymeric resins, dissolved in an

organic solvent system, with SCC (Stress Corrosion Cracking) inhibitor that helps

prevent the brittle fracture associated with SCC (Stress Corrosion Cracking). The

elastomer layer is specially designed for use in a hot applied coating system. It

consists of a synthetic cross linked elastomer adhesive laminated to a polyolefin

based polymeric alloyed backing. The polyolefin layer consists of a polyolefinc

based polymer alloy designed for the hot applied coating system. It is formulated to

chemically and mechanically fuse to the elastomer layer as well as itself to form a

totally fused, holiday free coating system.

The 3-Layer consists of four elements: A thermosetting liquid epoxy primer, a

functionalized polyolefin adhesive layer, a polyethylene outer layer for mechanical

protection, and a unique polyolefin cap layer to promote total fusion of the system.

The epoxy primer and the polyolefin laminate that comprise the coating system are

produced under controlled conditions in the factory. The polyolefin laminate is

manufactured under conditions that insure the component layers are inseparable. It

is then supplied in easily handled rolls in the appropriate with and thickness for the

pipe size and customer requirements. The laminate outer layer is spirally applied to

the primed surface in half lap fashion so that the final thickness is twice that of the

applied sheet. More than one laminate outer layer is applied when the customer


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thickness requirements would not be met by a double thickness of a sheet flexible

enough to be applied in the solid state.

Both coating systems, the Multi Layer and the three layer are specifically

designed for plant application using a minimum of equipment and labor in a

continues operation. The basic application process consists on the following steps:

1. Cleaning the pipe to remove surface contaminants.

2. Preheating the pipe to the appropriate preheat temperature.

3. Shot blasting the pipe.

4. Heating application.

5. Application of the primer layer (Multi Layer) or liquid epoxy primer layer (3

Layer).

6. Application of the elastomer layer (Multi Layer) or after inspection of the pipe for

surface irregularities, application of the Outer Layer laminate (3 Layer).

7. Polyolefin Layer (Multi Layer).

8. Water quenching of the coated pipe.

These application steps are schematically summarized in Figure 3 & 4.

1. Preparation of the pipe surface.

Coating performance, regardless of the type of coating system selected, is

dependent on the cleanliness of the pipe surface. The coating must come in

contact with the metal surface itself to insure maximum protection. The pipe

surface must be clean, dry and free of oil, dust and loose rust before it is heated to

desired temperature. Shot blasting should produce an anchor pattern of 1.5 3

mils ( 37 75 microns ) which further promotes adhesion of the coating.

2. Preheating the pipe.

All moisture must be expelled from the pipe surface prior to the application of the

coating system. This could require pre-heating the steel prior to blast cleaning. The


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steel surface shall be warmed above the dew point temperature for a sufficient

period of time as to expel all moisture on the pipe.

3. Shot blasting the pipe.

Before the pipe enter the furnace, it is abrasive cleaned to a SSPC-SP6 or NACE

TM-01-70 #3 or Swedish Standard SA 2/2.5 TM01-75 #3. The surface anchor

pattern profile must be between 1.5 mils (38 microns) and 3.0 mils (76 microns).

4. Heat application.

The pipe is heated using a radiant heat furnace or flame impingement furnace,

either electric or gas fired. Induction furnaces can be used where they are already

in place but this is not the least expensive option for outfitting a new application

site. The temperature of the pipe surface should be in the range of 200-230 F (95-

110 C) for Multi Layer and 300-325 F (150-163 C) for 3 Layer for 50 mil (1.27

mm) final thickness of coating. For a 100 mil (2.54 mm) thick coating the

recommended pipe temperature is 225-250 F (107-121 C) for Multi Layer and

325-350 F (163-177 C) for 3 Layer. The temperature of the heated shot blasted

pipe should be accurately monitored with a contact pyrometer or temperature-

indicating crayon. An infrared digital pyrometer is preferred to monitor pipe

temperature after priming and after wrapping. An infrared pyrometer could be used

to monitor the bare shot blasted pipe if necessary, but only if emissivity is

frequently calibrated using a contact pyrometer. The pipe temperature is critical to

ensure complete fusion of the coating layers and therefore its accurate

measurement and control is necessary.

5. Application of the primer.

The primer for the Multi Layer is applied using commercial spray equipment. For

the 3 Layer, the liquid epoxy primer is applied using commercially available fixed

ratio plural component spray equipment. The two components of the liquid epoxy

primer are mixed in a 1:1 ratio. Typical equipment settings are: Fluid pressure of

20-30 psi (1.5-2.0 bar); line pressure of 80 psi (5.5 bar); and a tip size of 0.046 in


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(1.17 mm). Pressure pot and atomizing air pressure should be adjusted to obtain a

finely atomized spray. The recommended primer thickness is 2 mils (50 microns)

for the Multi layer and 4 mils (100 microns) for the 3 Layer. Adequate ventilation

must be provided to be sure the operators are not exposed to overspray.

6. Elastomer layer (Multi Layer) or Polyethylene Layer (3 Layer) application.

The elastomer layer (Multi Layer) is spirally wrapped with not less than (19.1

mm) overlap. The Polyethylene layer is the outer layer of the 3 Layer preformed

system, it is spirally wrapped in a half lap manner (at 50% overlap). This layer is

supplied in roll form of suitable width and thickness for the pipe to be coated. It is

spirally wrapped on the pipe under tension using a mechanical coating apparatus

equipped with a constant tension breaking system. The apparatus ensures that a

uniform tension is achieved through a series of pressure rollers. The uniform

tension facilitates good contact between the primer and the coating. Tension is

determined by a measurement of the with of the applied film. The correct tension is

reached when the width has decreased by 1-2%. A pressure roller is applied

against the pipe surface at a point of outer layer application in order to eliminate air

bubbles and facilitate good contact between layers. Since the outer layer is applied

to a partially cured surface (adhesive for the Multi Layer and epoxy for the 3

Layer), chemical links are formed at the (adhesive/adhesive in the Multi Layer or

epoxy/adhesive in the 3 Layer) interface by reactions between adhesive (Multi

Layer) and epoxy (3 Layer) groups and the reactive functionalities of the elastomer

(Multi Layer) and the polyolefin layer (3 Layer). The hot pipe surface also facilitates

interlayer fusion creating a completely fused coating system.

7. Polyolefin layer (Multi Layer).

Simultaneous with the elastomer layer, the polyolefin layer shall be spirally applied

directly over the elastomer layer and positioned such that there is no thermal

distortion or damage to either the elastomer layer or the polyolefin layers. A tight,

wrinkle-free layer shall be maintained throughout the application. The polyolefin

layer should be applied with dispensing equipment equipped with a constant


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tension brake system. An additional rolling spreader bar is recommended, just

prior to the application of the polyolefin layer onto the coated pipe surface to

produce a smooth coating.

The overlap of the polyolefin layer shall not be applied directly on to the overlap of

the elastomer layer. The overlaps of each layer shall not coincide with each other.

The minimum overlap separation is 25% of the roll with. The correct tension is

reached when the width has decreased by 1-2%. A pressure roller is applied

against the pipe surface at a point of outer layer application in order to eliminate air

bubbles and facilitate good contact between layers.

8. Quenching.

The coated pipe is then progressively cooled by cold water spray over a distance

of 20 feet to avoid damage to the outer coating surface during subsequent pipe

handling. Computer spreadsheets templates have been developed which enable

the coater to predict quenching requirements as a function of pipe size, coating

speed, and coating thickness.

9. Quality Control.

To insure high quality and precise coating application, several quality control

measures should be taken. First, the coating rolls and primer are manufactured at

the state of the art facility using modern techniques of production to achieve total

quality and zero defects. Incoming raw materials and finished products are tested

under strict quality assurance guidelines to ensure a consistent and uniform

coating system. The finished roll and primer is shipped to the applicator for final

application on the pipe.

During the coating application, key parameters are monitored. These include pipe

preheat temperature, temperature of the primer, coating temperature and line

speeds. Only coated pipe that has a record of the correct parameters during

application is released. The combination of total quality manufacturing standards


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and parametric release at the point of application assures the quality of the pipe

coating.

LABORTATORY EVALUATION

Extensive testing in the laboratory was performed using a battery of standard

pipeline coating evaluation tests in the USA and abroad. All samples used were

obtained from commercial production runs at qualified applicators facilities. At

least one of these facilities was a portable plant, which was easily and quickly

modified to apply the new system. The test results are averages of at least three

samples and are typical of the performance of multi layer or 3 layer systems in

these tests. Tests of shear strength, thermal and hydrolytic stability were modified

tests which are described in previous publications. The shear test is similar to the

Aramco Alyeska shear test and a test protocol from Russia. The results are given

bellow in Table 1 for the 50 mil (1.27 mm) coating considering the two layers of 25

mil outer wrap.

Peel forces are high even at elevated temperatures and after thermal aging at

100C for 2,000 hours. Peel forces after aging in 95 C water for 300 hours are

higher in the 3 Layer than would be the case for bare epoxy not coated with

polyethylene. More important than peel force, from a coating functionality point of

view is the shear strength of the coating. The shear strength will determine the

tendency of a coating to slide across the pipe surface under the action of soil

moving across the pipe. These sliding of the pipe coating could result in wrinkling

and coating failure. The shear strength is measured by a technique that determines

the rate of movement under the influence of a normal force and a shear force. The

rate of movement is so low in both 3 Layer and Multi layer, that no shear

movement at all could be detected even after 48 hours of testing. These extremely

low rates of shear movement assure that no soil stress effects will be seen by the

coating after burial even at elevated temperatures.


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Impact strength is chiefly a function of coating thickness and it is given in units of

average energy that causes a detectable holiday at about 12 kV. For 50 mil

(1.27mm) system, the impact strength is 76 in-lb. Or 8.6 J. this is more than

sufficient to resist damage from the normal mechanical stress of handling and

transportation. The penetration resistance is high because of the absence of an

elastomeric adhesive which cold flow under the influence of steady pressure. This

allows the coating to withstand the localized pressure of contact with rocks after

burial. The tensile strength of the high molecular weight polyethylene is higher than

conventional polyethylenes. The coated pipe can be bent to grater than API

specification for steel pipe without producing a holiday or damaging the coating in

any way. The water vapor transmission rate is very low as is typical of this class of

polyethylenes.

The dielectric strength and resistivity values are typical of polyethylene. The

dielectric strength is a function of the coating thickness and is high per unit coating

thickness for this coating due to the fact that an elastomeric adhesive, with a lower

dielectric strength is absent. The cathodic disbonding resistance is excellent and

better on the 3 Layer due to the effect of the epoxy primer and the polyethylene

acting together. The epoxy has excellent interface adhesion with steel, and the

polyethylene is an excellent barrier to water penetration to the epoxy layer.

Results for the 100 mil (2.54mm) 3 Layer coating system consisting of 4 layers of

outer wrap are given in Table 2.

Test protocols for the 100 mil (2.54mm) 3 Layer coating system were taken from

the DIN standard (DIN 30 670) in common use in Europe and other parts of the

world for 3 Layer coatings. This was done because it is common in European

countries to use a larger coating thickness for the same size pipe than is commonly

used in the USA. Differences in the angle of peel and the rated peel resulted in

different values for the peel forces, although the same excellent aging results were

obtained. Since the shear strength depends on the shear adhesion at the


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steel/coating interface, these values were independent of sample coating

thickness.

PATCH AND REPAIR AND GIRTH WELDS

There is always a possibility that damage could occur to the coating during

handling and transportation. The toughness and thickness of the polyolefin layer in

the new systems and its shear resistance should make these areas small an

infrequent compared to some plant coatings. However some areas damaged by

handling will be unavoidable and they must be repaired, incurring a significant

labor commitment. The damaged areas of this new coatings can be repaired in the

field with the help of a patched and repair kit which consists of a roll of polyolefin

laminated, primer for the Multi Layer and liquid epoxy primer for the 3 Layer

provided in a twin pack. Some kind of heat source (torch, propane gas burner or

specially designed machinery) is required for the repair process. The process

consists of first cleaning the damaged area to remove any dirt and other foreign

bodies with a power wire brush, for example. If the primer or epoxy primer in the 3

Layer is intact, then a piece of polyolefin laminated is cut from the roll sufficient to

cover the damaged area. The adhesive side of the laminate is heated with a torch

at low flame. As The adhesive layer becomes tacky it is adhered to the pipe

surface over the damaged area and compressed wind a hand held pressure roller.

The covered area is carefully heated with the torch and at the same time is

compressed with the pressure roller to ensure the patch is completely fused. The

surface is then left to cool to the ambient temperature. If the primer or epoxy primer

is compromised by the handling damaged, it can be first repaired using primer or

the applicator packs described in the girth weld coating procedure in the following

paragraph.

A similar procedure may be followed for the coating of girth welds in the field. In

these case, the primer for the 3 Layer may be mixed in small packets that allow

the A and B components of the liquid epoxy primer system to be mixed without a


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separate contained. The primer or epoxy primer is then squeezed onto the cleaned

pipe surface and spread with a brush. A length of the polyolefin laminated is then

applied in a cigarette wrap fashion and held in place with several turns of fiber

glass backed tape. As for the repair process, a propane torch can be used to heat

the coating until the fiber gall tape turns brown, a process which can take about 2

to 3 minutes. The coating is now fused to the primer or epoxy primer and to itself at

its overlap. Also, the overlap of the polyolefin laminated is fused to the upper

surface of the line pipe coating. In this way, the girth weld coating has the same

anti-corrosion quality as the coating used on the rest of the pipe.

CONCLUSIONS

1. Two new heat applied plant coating have been developed, the 3 Layer, with

similar adhesive, mechanical and electrical properties as the commonly used 3

Layer epoxy/polyethylene coating systems and the Multi Layer.

2. The new coating systems are supplied from the manufacturer in roll form with

the proper thickness and width for the pipe size to be coated. The application

process is simple, requiring only a primer spray unit, a roll gods let-off stand

and a preheat temperature of about 230 F (110 C) for the Multi Layer or

350F (177 C).

3. Similar materials and process are used for field repair and for the coating of

girth welds.

REFERENCES

1. Kellner, J. D., J. M. Serra, Recent Developments in Polymer Pipeline

Coatings, Corrosion91, National Association of Corrosion Engineers, 1991,

Paper # 355.

2. Plolyken/VNIIST Methods of Adhesive Compound Tests for Shear Resistance

by V. K. Skubin, S.A., Rijov and I.G. Kitina, Moskow, 1989.

3. ASTM, American Association for Testing Materials, 100 Barr Harbor Drive,

West Conshohocken, Pennsylvania, 19428.


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4. Aramco Materials Specification No. 09-AMSS-96 Alyeska Shear Rate

Determination.

5. CSA, Canadian Standards Association, 178 Rexdale Boulevard, Rexdale,

Toronto, Ontario, Canada M9W 1R3.

6. DIN, Deutsches Institut fur Normung e. V. (German Institute for

Standardization), Berlin, Germany.


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Table 1 - 50 mil

Adhesion Properties 3 Multi

Property Test Method English Metric English Metric

Peel Force @ 20C ASTM D 1000 62 lb./in 108 N/cm 50 lb./in 8.9 Kg/cmPeel Force @ 50C ASTM D 1000 41 lb./in 71 N/cm

Shear Strength Kendall < 10-9 m/seg < 10-9 m/seg < 10-7 M/sec < 10-7 M/sec

@ 85C

Thermal Stability

200 hours Kendall 38.7 lb./cm 67.7 N/cm

Hydrolytic Stability

300 hours Kendall 14 lb./in 25 N/cm

Mechanical Properties 3 Multi

Impact @ 20C DIN 30670 76 in-lb. 8.6 J 44.1 in-lb. 5.0 J

Penetration @ 25C ASTM G 17 5.5.mils 0.14 mm 7.8 mils 0.2 mm

Tensile Strength ASTM D 1000 129 lb./in 23 Kg/cmElongation ASTM D 1000 > 200 % > 200 %

Bend Strength CSA Z 245 2.5 DPL 2.5 DPL

Water Vapor ASTM F 1249 0.01 1.15 0.03 0.5

Transmision Rate 95C, 100% RH g/100in2/day g/m2/ day g/100in2/day g/m2/day

Electrical Properties 3 Multi

Volume resistivity ASTM D 257 6.65 x 10-14 1.7 x 10-15 6 x 10-15 6 x 10-15

ohm-in ohm-cm Ohms-cm Ohms-cm

Dielectric Strength ASTM Dm 1000 42.8 KV 42.8 KV 45 Kv 45 KV

Cathodic Disbonding

48 hours @ 65C CSA Z 245 .1 in radius 3mm radius .25 in 7.0 mm


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Table 2 - 100

Adhesion Properties

Proprty Test Method English Metric

Peel Force @ 20C DIN 30670 47 lb./in 83 N/cm

Peel Force @ 50C DIN 30670 29 lb./in 50 N/cm

Shear Strength@ 85C Kendall < 10-9 M/sec < 10-9 M/sec

Thermal Stability

2,000 hours Kendall 38.7 lb./in 67.7 N/cm

Mecanical Properties

Impact @ 20C DIN 30670 153 in-lb. 17.3 J

Penetration @ 25C DIN 30670 6.3 mils .16mm

Penetration @ 50C DIN 30670 8.7 mils .22mm

Tensile Strength DIN 30670 313 lb./in 56 Kg/cm

Elongation DIN 30670 > 200 % > 200 %

Bend Strength CSA Z 245 2.5 DPL 2.5 DPL

Water Vapor ASTM F 1249 0.005 0.08

Transmission Rate 95C, 100 % RH g/100in2/day g/m2/day

Electrical Properties

Volume Resistivity ASTM D 257 6.65 x 10-14 1.7 x 10-15

Ohm-in Ohm-cm

Dielectric Strength ASTM D 1000 85 KV 85 KV

Polyolefin


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1. Schematic representation of the construction of the new hot applied, Multi Layer

plant coating.

2. Schematic representation of the construction of the new hot applied, 3 Layer

plant coating.

WaterQuench

PrimingStation

EpoxyPrimer

ModifiedPolyolefin

Adhesive

High MolecularWeightPoyethylene

ModifiedPolyolefinOuterLayer

Three Layer IntegratedOuterwrap

PrimerElastomer

ShotBlast


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3. Illustration of a typical setup for application of new, multi layer hot applied plant

coating.

4. Illustration of a typical setup for application of new, 3 layer hot applied plant

coating.

PolyolefinApplicator

ElastomerApplicator

PreheatOven

WaterQuench

PrimingStation

OuterwrapApplicator

ShotBlast

PreheatOven

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3layerPE coating.doc