CA1318263C

CA1318263C - Coated pipes

Info

Publication number: CA1318263C
Application number: CA 590363
Authority: CA
Inventors: Walter R. Lunt
Original assignee: Marathon Oil Co
Current assignee: Marathon Oil Co
Priority date: 1988-03-04
Filing date: 1989-02-07
Publication date: 1993-05-25
Anticipated expiration: 2010-05-25
Also published as: NL8920232A; WO1989008220A1; GB2215427A; GB2215427B; GB8805225D0

Abstract

Docket 880006 000 ABSTRACT
COATED PIPES
A coated pipe 4 having a first coating layer 5 comprising a thermally stable polyurethane elastomer, and a second coating layer 2 comprising a matrix of polyurethane elastomer having dispersed therein a plurality of discrete hollow units 3.

Description

~ 3 ~ Docket 880006 000 DESCRIPTIC)N
COATED PIPES
BACKGROUND OF THE INVENTIQN
T0chnical Field:
05 This invantion relates to coated pipes, a process for their preparatisn, and pipelines incorporating them.
Background Informatiorl:
It has been proposed to provide a pipe having a thermally-insulating coating by enclosing insulating sections of ~oamQd polyurathane within an enveioping matrix of abrasion-resistant and corrosion-resistant elastomer such as polychloroprene. This coating is effective for use on pipelines which are subject to very low temperatures and a corrosive environment. However, they are not generally suitable in applications where they might be subjected to high temperatures and pressurss. For example, in deep water applications, the foam insulation would be vulnerable to water penetration.
It has also been proposed to apply one or more layers of continuous non-foamed plastics or rubber material to a pipeline. This provides exceilent protection for tha pipeline against corrosion and mechanical damage, but the heat insulation properties of the non-foamed material are considerably inferior to those of a foamed coating. In very cold environments such as offshore in deep water, good heat insulation is oft0n essential.
European Patent Application 0188340 describes pipelines having a thermally-insulating coating comprising a continuous matrix of a water-impermeable material having dispers~d therein a plurality of discrete hollow units, said units being thermally condu~ive to a lesser degree than the water-imp~rmeable material. A corrosion-resistant layer may be present between the pipeline and the thermally-insulating coating, which layer may bs of a rubber product such as polychloroprene.
In some applications, a pipeline may be re~uired to carry fluids at very high temperatures. For example, oil from some off-shor@ fields may be at temperaturas as high as about 120C. The coating materials used in the hitherto proposed insulated pipelines havs not been capable of simultaneously withstanding high temperatures (e.g. over about 75C) and pressures typically encountered in deep water applications.

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- 2 - Docket 880006 000 SUMMARY OF THE INVENTION:
We have now found it possible to provide a coating for pipes having good thermal insulation properties while at the same time being capable of withstanding tha high pressures encountered in deep water offshore 05 applications and tha effects of the pip~ carrying materials at high temperatures, e.g. over about 75C.
Thus in one aspect, the invention providQ~ a coated pipc having a ~irst coatin~ layer comprising a thermally stable polyurethane elastomer, and a second coating layer comprising a matrix of polyurethans elastomer havin~
10 dispersed therein a plurality of discrete hollow units.
In a fu~her aspect, the invention provides a process for the preparation of a coated pipe which comprises forming a ~irst coating layer of thermally stable polyurethane elastomer on a pipe and subsequently forming a second coating layer on the pipe, said second coating layer comprising a matrix of 15 polyurethane elastomer having dispersed therein a pl~lraiity of discrete hollow units.
IEF DESCRIPTION OF THE DRAWINGS:
Figure 1 is a sectional front view of a pipe in accordance with the present invention; and Figure 2 is a part sectional side view of the pipe of Figure 1.
DESCRIPTION OF PREFERREG EIYIBODIMENTS:
Th~ term "thermally stable" is used herein to indicate that the polyurethane elastomer of the first layer is resistant to thermal degradation when the pipe is used to carry materials at relatively high temperatures e.g.
above about 75C and preferably up to about 11 0C or even 1 20C.
The polyurethane 01astomers of the first and second coatin~ layers may be the same or different. Preferably the elastomers will be of similar composition to optimiz0 cornpatibility and thus adhesion between the layers.
However, the thermal stability of the material for the second layer, i.e. ths polyurethan~ matrix and discreta hollow uni~s therein, is not usually critical since this layer is not in direct contac~ with tha pipe.
The poiyurethane elastomers used in the first and second layers are resilient and this allows flexing of ~he pipe when being laid as a pipeline.
Polyurethane is also abrasion-resistant.
The first polyurethane layer ~enerally acts as a corrosion-resistant layer between the pipe and the thermally-insulating second layer. This first 3 Docket 880006 000 layer is praferably con~inuous for maximum resistance to penetration. Thus, sven if ths second thermally-insulating coatin~ is damaged the pipeline is protec~ed from corrosion. The fir~ layer, being thermally stable, also serves to protect the second layer from the effects of heat from the pipe contents.
05 The discrete hollow units dispersed in the poiyurethan0 matrix or the second layer may be for example wallsd spheres containing a heat-insulating liquid, a gas (including mixtures of gases such as air and mixtures of air with other gases~ or a vacuum. Gas-filled microspheres are especially suitabie, and their walls may be for example sf glass or plastics material suoh 10 as polyvinylidene chloride. A number of such units can ~hen be mixed ~,vith the polyurethane so that they becoma dispersed therein.
The units are preferably introduced in~o the polyurethane by being present in one or more components of a mix which reacts to ~orm ~he polyurethane, i.e. the units may be dispersed in an isocyanate and/or polyol 15 component.
The material forming the units may be of the same as or different from the polyurethane of the matrix, although genarally it will be differsnt.
The discrete hollow units may range in size from a few microns to 200 microns in the case of microspheres; the pa~icular units selected will depend 20 on the type and use of the pipeline. Preferably, however, the units will be microspheres of polyvinylidene chloride or glass containing gas.
The hollow units serve to reduce the thermal conductivity of the polyurethane acting as tha matrix in the second layer. In this way, the second layer is provid~d with good thermal insulation properties. In addition, the 25 presence of the hollow units substantially reduces the material costs for thecoating, sinca tha amount of relatively expensive polyurethane required to give a coating of desired insulation properties can bs reduced. The units may be included in th0 polyurethane matrix in an arnoun~ selected to suit the required properties of the pipeline and praferably reduce the thermal 30 conductivity of the polyurethane matrix material by up to about 60%. For example when a polyurethane matrix material is used having a thermal conductivity constant of 0.19W.m~1.K~1 the units may be dispersed through it in sufficien~ amount to reduce the thermal conductivity constant of the second layerto around 0.12W.m~1.K~1.
The thickness of the first coating layer will generally be chosen to ensure that, in use, the temperature drop across the layer is such that the second layer is not adversely affected by heat from the pipe~s contents.
When the pipe is carrying oil at up to aùout 110C, W2 have found that the , 4 Docket 880006 000 thickness of the first ~ayer is conveniantly about ~ to 15 mm, preferably about 10 mm.
The thickness of the second layer will be dictated by ambient conditions and the insulating requirements of the pipeline, but generaliy for 05 subsea use a thickness of 20 to 80 mrn, and about 30-40 mm is preferrad In order to aid adhesion of the nrst layer to the pipo, we haYa found it convenient to apply a primcr material to ~he pipe before the first l~yer is formed. The primer conveniently comprises a conventional two compon~nt solventl@ss polyol-based polyur~thans rcsin. The use of a polyurethana lo resin for the primer leads to good compatibility with the polyurethane ~lastomer of the first layer.
Ths process of the invention may conveniently be effected as follows.
The uncoated pipe, which may be of th0 duplex or stainless steel type (although other materials, e.g. carbon steel, may be used), is first cleaned and prepared, for example by steam, solvent and/or shot blasting cleaning.
The primer, if desired, may then b~ applied, e.g. by spraying or brushing.
YVithin a relativ~ly short period, usually 30 to ~0 minutes, ths primed pipe is placed in a mould for application of the first layer. Since the pipe is often ralatively flexible, it is usually supported in the mould to ensure a uniform thickness of the layer along the length of the pipe. The pipe may be conveniently supported using spacer rings of cured polyurathane material.
The polyurethane first layer is then formed on the pipe by injecting uncured polyurethan~ into the mould and keeping it there until curing takes place.
The second layer may then ~e applied by placing the first coated pipe in a second mould and again, if necessary and/or desired, supporting it theroin with suitable spacars. The uncured polyurethane matrix matarial with hollow units dispersed therein, may then be injectod into the mould and subse~uently cured. Tha finished coated pipe may then be removed from ths mould.
To form a pipeline, pips lengths may be joined together according to conventional techniques, e.g. by welding. Th~ welded joints may be preferably covered with one or more layers of polyurethans elastomer to yi~ld a substantially continuous coa~ing on the pipeline. Most conveniently the Joints can b~ covered with a singla layer of the elastomer used for the first layer of the pipe.
Ernbodiments of the present invention will now be described, by way of non-limiting example, with referenc~ to the accompanying drawings.

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5 Docket 880006 000 EXAMPLE
R~rring to Figures 1 and 2 of the drawings, a pipe coating 1 includes a heat-insulating resilient second layer 2, which is approximately 3~ mm thick, in the form of a body of polyurethane providing a matrix which has 05 disp~rsed throughout it a plurality of polyvinyliden~ chloride-walled hollow microspheras 3 containing gas. The microspheres 3 range in size from 10 to 100 rnicrons. The second coating 2 surrounds a duplex pipe 4 which is conveniently 150 mm in diameter thickness provided with a first coating layer 5 of polyurethane. The first layer 5 is approximately 10 mm thick.
The pipes can be used to form a pipeline having a length of up ~o, for example, 20 km or more and can bo of any external diamet~r. The pipeline may extend from an offshore wellhead (no~ shown) at which the oil temperatura is about 110C, and the oil flowing in the pipelinc rnust be kept warm for processing reasons.
The polyurethane elastomer for the first coating layer 5 is preferably derived from a solventless polyurethane elastomer composition, e.g. it may be derived from a solventlass polyether base with an appropriate isocyanat0 to give an injection mouldable polyurethane elastomer with good hydrolysis resistance and capable of withstanding temperatures up to 120C. An example of such an elastomer composition is Hyperlast 285~/407 available from Macpherson Polymers Limited of Stockport, Lancashire, England. The polyurethane ~lastomer is capabl~ of providing a tough coating which is highly chemical and temperature resistant and impervious to moisture and sea water. It is also resistant to abrasion and has high tear and tensile strength, as well as being highly resistant to ozone attack and flex cracking. It is resistant to oils, waxes and gases and most aliphatic hydrocarbons.
The polyurethane component of the second layer 2 may be the same as or diffarent to th~ polyurcthane of the first layer 5. The insulation prop~rties of the polyurethane are conveniently substantially modified by incorporating gas-filled microspheres 3 of polyvirlylidene chloride. The large numb~r of gas-filled microspheres 3 in th~ coating 1 thus gives the pipeline a good degree of thermal insulation and also provides a degree of abrasion resis~ance ~or the coating. The walls o~ the microspheres 3 prevent water from penetrating through interconnecting bubbles in the coating, as can happen in the case of foamed polyurethane in which air bubbles rather than walled microspheres provide ~he insula~ion.

~31~

- 6 - Docket 880006 000 A particularly pref~rred polyurethane composition for forming the elastsm~ric malrix o~ th~ second layer is Hyperlast 2851/512 also available from Macpherson Polymars Limited.
Tha pipeline of this ambodiment can be manufactursd as follows. The 05 pipe 4 is first cleaned, o,g. by steam claanin~ andlor shot blasting, and a primer is applied. The primer may be a conventional two component solventless polyurethano primer such as, for example, Hyperlast 2874/016 available from Macpherson Polymers Limited.
The primed pipe 4 is then placad in a mould usually within 30 to 90 1Q ~ ~ninutes o)Sapplying the primer, and ths polyurethane composition of the first A l~yer s ifl injected into the mould around tha prirned pipe 4. The polyurathane is then allowed to cure, forming tha first layer 5. As indicated above, the polyurethane composition is derived from isocyanate and polyol components, and prior to their introduction into thc mould they ar~
15 maintained apart in separate holdin~ tanks. Th~ isocyanate and polyol components are fed separately to a mixing and dispensing machine in which they are intimately mixed and fed in con~inuous manner into the mould. The isocyanate and polyol react in the mould to form the polyurethan0 elastomer.
When the first elastomeric laysr has been formed, the intermediate 20 coated pip9 iS transfsrr~d to a second mould and the polyurethane composition of the second layer having the microspheres 3 dispersed ~herein is inject~d into th0 mould around th~ pipo. As for the first lay~r polyurethane composition, the polyurethane for the s~cond layer may be formed from isocyanate and polyol components separately stored and mixed immediately 25 prior to injection in the mould. The microspheres 3 may be presen~ in either of the starting isocyanat~ and polyol components, or indeed in both. The microspheres ars, however, usually present in the polyol component only.
Whsn th~ second polyurethane layer has cured in the mould, ~he pipe can be removed therefrom. As indicated above, pipes according to the 30 invention can be joined together to forrn pipelines which ar~ particularly suitable for carrying oil at high temperatures (e.g. up to about 110C or 120C) in deep water offshore applications. The use of a thermally stable first layer helps to prevent thermal degradation of the pipe coating, while the use of microspheres in the second layer provides good thermal insulation 35 and aids in reducing material costs.
Modifications and irnprovaments may be made without departing ~rom the scope of the invention.

Claims

1. A coated pipe comprising a first coating layer comprising a thermally stable polyurethane elastomer, and a second coating layer comprising a matrix of polyurethane elastomer having dispersed therein a plurality of discrete hollow units.

2. A coated pipe according to claim 1 wherein the polyurethane elastomers of the first and second layers are the same,

3, A coated pipe according to claim 1 wherein the polyurethane elastomers of the first and second layers are different.

4. A coated pipe according to claim 1 wherein the hollow units are gas-filled microspheres,

5, A coated pipe according to claim 4 wherein the gas-filled microspheres are gas-containing polyvinylidene chloride beads.

6. A coated pipe according to claim 1 wherein the first layer has a thickness of from 5 to 15 mm.

7. A coated pipe according to claim 1 wherein the second layer has a thickness of 20 to 80 mm.

8, A coated pipe according to claim 1 wherein a primer has been applied to the pipe.

9. A process for the preparation of a coated pipe comprising forming a first coating layer of thermally stable polyurethane elastomer on a pipe and subsequently forming a second coating layer on the pipe, said second coating layer comprising a matrix of polyurethane elastomer having dispersed therein a plurality of discrete hollow units.

10. A process according to claim 9 wherein the layers are formed by injection moulding.

11. A process according to claim 9 wherein a primer is applied to the pipe before forming the first layer.