COATED METAL PIPE JOINTS

FIELD OF INVENTION

The present invention relates to coated metal pipe joints and methods of forming coated metal pipe joints. In particular it relates to composite materials for forming bonds between a coating that is applied as a liquid and a polymer coated pipe element, methods of forming coated metal pipe joints and uses of said composite material.

BACKGROUND OF THE INVENTION

Polymer coated pipes are well-known in the field of transmission and distribution of liquids and gases. The pipes are typically metal pipes, for example steel. Typical polymers used for coatings include polyolefins . The polymer coating to pipes commonly comprises three elements; an inner layer of epoxy based material applied to the suitably prepared outer surface of the pipe, an outer layer of polymer (e.g. polyolefin) based material, and a thin intermediate layer which forms a bond between the other two layers. The intermediate layer is necessary because the bond between the other two layers would otherwise be unacceptably weak. The complete system is commonly known as 'Three Layer Polyolefin' (TPO) and is commonly used for the corrosion protection of pipe externals .

Typical polyolefins used include Polyethylene and

Polypropylene. Polyethylene based coatings are selected for pipe service temperatures up to 80 ⁰ C and Polypropylene based

coatings are selected for pipe service temperatures up to 140 ⁰ C.

Individual elements of TPO coated pipe are aligned longitudinally and the ends circumferentially welded together to form a pipeline. To facilitate the welding and jointing of the pipe the coating adjacent to the weld area is substantially removed prior to welding. This area is known as the "cutback" and typically extends around the full circumference of the pipe some 150 mm either side of the weld. The edge of the TPO adjacent to the "cutback" may be chamfered. The inner layer of Epoxy based material may extend beyond the chamfer to form a "toe" . Alternatively, the pipe may be supplied in such form.

The contiguous pipe elements so formed are protected, e.g. by Three Layer Polyolefin, along the major portion of the pipe element. However, in the area of the "cutback" the coating is discontinuous and the application of additional protection to this area is required. It is essential that the coating selected for the protection of the area of the cutback is mutually compatible with the coating. In principle, Three Layer Polyolefin itself could be used for the protection of the welded joints. However, the complex nature of the equipment required to execute such a joint, and other constraints, limits the practicality of this approach .

Alternatively, 'Multi Component Liquid Applied Coatings' can be used. Multi component liquid applied coatings are conveniently used for corrosion protection on steel pipe. As the name suggests these coatings are applied in liquid

form and may subsequently be cured, hardened or otherwise treated in order to form the final protective coating. Such coatings are well known and include epoxies, urethanes, and hybrid systems.

However, these coatings exhibit very poor adhesion to the outer polymer layer of polymer coatings such as Three Layer Polyolefin. In addition, polymers, such as polyolefins typically have a low energy surface; they are not readily wetted and liquids that are applied to their surface tend to bead and run under the influence of gravity. These factors can lead to variations in the thickness of the applied coating and poor coating adhesion which adversely affects or negates the effectiveness of the corrosion protection system.

One method of overcoming this problem is by roughening the surface of the polymer to provide a mechanical key. This is usually attempted by abrasive blasting. A disadvantage of this method is that the abrasive blasting is time consuming and expensive and the degree of roughening is not easily controlled. The bond that results is purely mechanical in nature and consequently is mechanically weak.

Another method of overcoming this problem is to adhere an intermediate layer of material onto the polymer and subsequently apply the multi component liquid applied coating onto said intermediate layer such that a bond is formed at the interface of the polymer coating and the intermediate layer and also at the interface of the intermediate layer and the multi component liquid applied coating. This method is essentially the subject of United

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States Patent 6065781 (Method and apparatus for protecting the weld area of polyolefin coated pipe US Patent Issued on May 23, 2000, assignee Power Lone Star Inc, Houston, TX) wherein an adhesive mastic is preferred as the intermediate layer .

This method has the following disadvantages. The thickness of the liquid applied to the mastic is not easily controlled. The bond strength between the liquid coating and the adhesive mastic and consequently the effectiveness can vary considerably as the bond is mainly chemical in nature. Prior to application of the liquid applied coating, the surface of the adhesive mastic is also susceptible to contamination from moisture, dust, and dirt.

It will be seen that a need exists for an improved method of achieving and maintaining a bond to the polymer coating.

SUMMARY OF THE INVENTION

The present invention relates to the development of a 'composite material, comprising an adhesive layer and a wicking layer to form and maintain an effective bond between the polymer coating of a polymer coated pipe and a further coating layer which is subsequently applied to the polymer coating, for example at a joint, in liquid form.

The composite material is thus in laminate form, comprising a layer of wicking material, for example a fibrous material which is laminated directly or indirectly to an adhesive, such as a pressure sensitive adhesive which may be self adhesive, which is adapted to bond to the polymer coating of

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the polymer coated pipe . It is intended that the wicking effect is such that any subsequently applied multi-component liquid applied coating is drawn into wicking material by capillary action.

The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect described and the individual features thereof may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous . It will be recognised that features described in the context of one aspect may be combined with other aspects where appropriate .

Accordingly, in a first aspect, the present invention provides a metal pipe joint comprising a polymer coated pipe element comprising on its outer surface a composite material, said material comprising a layer comprising an adhesive and a layer comprising a wicking material, said adhesive compound layer contacting said polymer coating.

The coating may comprise multiple layers, for example an inner epoxy based layer, and intermediate layer and an outer polymer layer. The polymer may be a polyolefin. The coating may therefore be a 'three layer polyolefin ¹ . The polymer may for example be polyethylene or polypropylene (each examples of polyolefins) .

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In a preferred embodiment, the adhesive of the composite material may be a self adhesive compound. The adhesive may be a pressure sensitive adhesive. It may for example comprise a polymer modified bitumen, or a butyl rubber mastic or hot melt adhesive.

In a further preferred embodiment the weight of the adhesive layer may be between about lOOgsm to about 2000gsm, or between about 500gsm to about 700gsm.

The wicking layer of the composite material may comprise any suitable material, for example a foam, a sponge, or fibres. If the wicking layer comprises fibres, said fibres may be arranged as: a tissue, a fleece, a roving, a woven construction, a stitch-bonded construction, a needle punched construction, a felt, a knitted construction, a bonded fibre construction, or a spun laced construction. More than one type of fibre arrangement may be present, for example, combinations of the above identified fibre arrangements are contemplated.

Wicking materials comprising fibres may be advantageously used since they have a suitable wicking action, are mechanically strong, easy to obtain and to prepare in a composite material.

In some preferred embodiments different types of fibre are possible, for example synthetic fibre (such as polyester, rayon, acrylic, or nylon), natural fibre, glass fibre or a combination thereof.

In preferred embodiments the weight of the wicking layer is between about 30gsm to about 50OgSm, or between about 75gsm to 150gsm.

In some preferred embodiments the composite material is formed from a continuous sheet. It may alternatively be formed from separate sheets. The composite material may be formed prior to application to the coated pipe element or may be formed from separate layers at the point of application to the coated pipe element .

Preformed composite materials are preferred since these are more conveniently and more rapidly applied. Furthermore, the physical dimensions of the composite materials are more easily controlled if the composite materials are preformed. As a consequence, a thinner, and thus more economical, adhesive layer may advantageously be used.

In preferred embodiments the composite material extends around the full circumference of the pipe. This ensures that any subsequently applied liquid coating is evenly and consistently distributed.

In preferred embodiments the composite material does not contact the metal pipe. It is normally only necessary for the composite material to contact the polymer coating of the coated pipe element since adequate adhesion of any subsequently applied liquid coating to the (typically metal) pipe itself is normally achieved without the need for the use of the composite. However, if desired, the composite may also be applied to the (typically metal) pipe itself.

The composite may be pre- formed such that it is applied as a single, multi- laminate entity.

In particularly preferred embodiments the pipe joint comprises a further protective layer. The further protective layer is typically applied as a liquid (i.e. it is a subsequently applied, liquid applied coating) and typically comprises a multi-component liquid applied coating. Suitable multi-component liquid applied coatings include those that comprise an epoxy based material.

Preferred pipe joints may also comprise an additional outer protective layer. The additional outer protective layer may comprise fibrous material. Suitable fibrous materials include non-woven polyester or glass fibre. The additional outer protective layer may be introduced into the wet film of any liquid applied coating. Such an additional outer protective layer has the advantage of mechanically reinforcing the coating and protecting it from contamination or physical damage.

In particularly preferred embodiments the joint is between two polymer coated pipe elements. For example, this will often be the case when a pipeline is formed from separate elements joined longitudinally. However it is also envisaged that the joint may be between a polymer coated pipe element and a different element, such as a valve, pump terminal or other element or device. In particularly preferred embodiments wherein the joint is between two polymer coated pipe elements, each polymer coated pipe element may comprise on its respective outer surface a composite material as defined above.

In some embodiments the joint is a welded joint. In some embodiments the pipe is a steel pipe.

in another aspect the present invention also provides a method for forming a coated pipe joint comprising applying to the exposed coating of the polymer coated pipe element a composite material, the composite material being as defined above .

In preferred embodiments the method further comprises applying a further protective layer to the joint, wherein the further protective layer is as defined above. In some preferred embodiments the method further comprises applying an additional outer protective layer, wherein the additional outer protective layer is as defined above.

In preferred embodiments the method is between two polymer coated pipe elements. The composite material may be applied to the adjacent ends of each polymer coated pipe element.

The joint may be a welded joint. The pipe may be a steel pipe.

In the most preferred embodiments the join is made to the coated pipe element before the composite material is applied. However, in other preferred embodiments the join is made to the coated pipe element after the composite material is applied.

In another aspect the present invention also provides use of a composite material comprising a layer comprising an adhesive and a layer comprising a wicking material in the

coating of a joint between a polyolefin coated pipe element and another element.

The skilled person would recognise that the discussion above relating to different types of composite materials, components of said composite materials, weights, liquid applied coatings, further outer protective layers, pipe elements etc applies mutatis mu.ta.ndis to each aspect of the invention .

BRIEF DESCRIPTION OF THE FIGURES

Fig 1. Shows a joint between two polymer (in this case polyolefin) coated pipe elements, prior to the addition of a further protective coating according to the present invention.

A - Weld bead B - Metal pipe

D - Fusion bonded epoxy based material (shop coated) E - Intermediate adhesive layer (shop coated) F - Polyolefin layer (shop coated)

Fig 2. Shows a transverse section through a pipe wall, including a joint between two polymer (in this case polyolefin) coated pipe elements, following the addition of a further protective coating according to the present invention.

A - Weld bead

B - Metal pipe C - Liquid applied coating

D - Fusion bonded epoxy based material (shop coated)

E - Intermediate adhesive layer (shop coated)

F - Polyolefin layer (shop coated) G - Pressure sensitive adhesive H - Wicking material

Fig 3. Shows a composite material according to the present invention, comprising a wicking layer, in the form of a fibrous layer laminated directly to an adhesive layer.

Fig 4. Shows a composite material according to the present invention, comprising a wicking layer in the form of a fibrous layer laminated directly to an adhesive layer. The fibrous layer being penetrated by and saturated with a multi-component liquid applied coating.

DETAILED DESCRIPTION

Composite sheet

The invention relates to a composite sheet (also referred to herein as a composite) wherein a layer comprising an adhesive is bonded, directly or indirectly, to a layer comprising a wicking material. Suitable methods for forming such a composite sheet are well known in the art and include, but are not limited to: - adhesive lamination and hot melt processing.

It is envisaged that the composite will generally be preformed and applied to the pipe element once the adhesive layer and wicking layer have already been combined into a composite material.

Any suitable adhesive may be used in the adhesive layer. These include pressure sensitive adhesives and self

adhesives. The adhesive may for example comprise a polymer modified bitumen, or a butyl rubber mastic. The adhesive must function to maintain a good adhesion between the composite material and the polymer coating of the coated pipe element .

The layer comprising the wicking material may comprise any suitable material. Such a layer may comprise for example a foam, a sponge or fibres. If the wicking layer comprises fibres, these may comprise for example fibres arranged as: - a tissue, a fleece, a roving, a woven construction, a stitch-bonded construction, a needle punched construction, a felt, a knitted construction, a bonded fibre construction, or a spun laced construction. Combinations of different fibre arrangements are also possible.

The fibres may comprise a synthetic fibre, for example polyester, rayon, acrylic, nylon, or combinations thereof or a natural fibre. The fibres may alternatively be comprise glass fibre. Combinations of the different types of fibres are possible, for example combinations of synthetic fibre and natural fibre, natural fibre and glass fibre, synthetic fibre and glass fibre, or combinations of synthetic, natural and glass fibre.

The essential characteristic is that under conditions of use the layer comprising the wicking material has a "wicking effect" which draws and anchors any subsequently applied liquid coating into close proximity to the adhesive layer. In this way the joint will be well protected since a layer of coating liquid of uniform and reproducible thickness will result as determined by the characteristics of the composite

material, specifically the wicking layer. Thus where the wicking layer is applied to a coated pipe element, for example to the outer polymer coating, a consistent coating may now be achieved.

Method

The proximate ends of the polymer coating on either side of the joint (such as a welded joint) may each separately (where present) be prepared in the following manner. In addition to the procedures described below, preparation of the joint may also comprise washing (for example with water) , and/or abrasive cleaning, in particular of the pipe.

If the coating of the coated pipe element is a three layer polyolefin coating, this may be removed adjacent to the join. This is generally done before the join is completed. Where the polymer coating is a three layer polyolefin it may be desirable to leave a chamfered edge and/or a protruding ' toe ' of epoxy based material . This can improve the bond between the adhesive layer of the composite and the coating of the coated pipe element, by providing a suitable surface for contact between the two (i.e. one that is suitably broad and flat for adequate mechanical adhesion) . Alternatively, the pipe element may have already be supplied in such form prior to joining. It is not essential that the edge be chamfered, or that an epoxy toe be present. However, the presence of these features in the preparation of the polymer coating may facilitate the subsequent steps .

The polymer coating of the pipe element being thus prepared, the composite material may then be applied to the pipe in such a position that the composite extends substantially

around the full outer circumference of the pipe. Generally, speaking, the polymer coating of the pipe element will be prepared, and the composite material applied, after the join has been made. It is technically possible to prepare the polymer coating and apply the composite material prior to the join being made, though this is not usually preferred.

The width of the composite (dimension parallel to the major axis of the pipe) and the position of the composite (relative to the major axis of the pipe) is selected to ensure that the composite extends onto the outer surface of the polymer coating of the coated pipe element, and also extends to the chamfered area (if present) . The composite may also extends onto the "toe" of the epoxy based material (if present) . The composite may extend onto the uncoated area of the pipe surface if desired.

However, it is not usually necessary for the composite to extend onto the uncoated (e.g. bare metal) area of the pipe outer surface, since the subsequently applied multi- component liquid applied coating may bond satisfactorily to the bare (i.e. uncoated) portion of the pipe. If such bonding between the bare pipe and the subsequently applied multi-component liquid applied coating would be unsatisfactory, the composite may be additionally applied to the bare portion of the pipe, prior to application of the multi-component liquid applied coating.

The composite so applied may then be overpainted with a liquid applied coating (such as an epoxy based coating) .

The thickness of the liquid applied coating is controlled by the absorption property of the wicking material of the

composite. The liquid applied coating extends onto the suitably prepared outer surface of the pipe, for example the bare uncoated portion adjacent to the joint, if the composite is only applied to the polymer coating of the coated pipe element. A continuous film is thereby formed which encapsulates the joint. This film may be substantially, or entirely continuous. The aim is generally to entirely encapsulate the joint to thereby provide protection (e.g. protection from corrosion) .

The liquid applied coating may be mechanically reinforced by the introduction into the wet film of an additional fibrous material comprising a non woven polyester or glass fibre.

If necessary the wet film thus applied (with or without mechanical reinforcement) may be further treated. Further treatment may be necessary for example to cure, harden or otherwise mature the liquid applied coating into its final form. The nature of any further treatment and the necessity of it will be largely determined by the type of liquid applied coating that is used. The skilled person would be entirely familiar with the necessary further treatments associated with each type of coating.

ADVANTAGES

Compositions, methods and uses according to the present invention have inter alia the following advantages:

The problem of achieving consistently reliable adhesion strength to conventional adhesive mastics and consequently to the polyolefin coated pipe surface is overcome. The

wicking effect of the liquid coating into the fibrous backing laminated to the pressure sensitive adhesive provides a mechanical interlock, in addition to the chemical bond, which ensures that the optimum bond strength can now be achieved.

Unlike previous methods a minimum controlled thickness of the liquid coating can now be achieved.

Specialised or dedicated equipment is not required.

The wicking layer mechanically reinforces the composite which allows for a thinner and more economical adhesive layer .

PREFERRED EMBODIMENT

Wicking Layer

Preferably the wicking layer comprises fibres said fibres comprising a non woven polyester or glass fibre. A wicking layer with the following properties is preferred: -

i. Weight per unit area 30-500 gsm. ii. More preferably 75-150 gsm.

Adhesive Layer

It is preferred that the adhesive layer comprises a self adhesive material comprising a polymer modified bitumen or a butyl rubber mastic. Both types of material are well known in the art. For example Densoclad ^® Adhesive Compounds and

Denso ^® Butyl Adhesive compounds supplied by Winn & Coales

(Denso) Ltd. An adhesive layer with the following properties is preferred: -

i. Weight per unit area 100 to 2000 gsm. ii. More preferably, weight per unit area 500 to 700 gsm.

EXAMPLES

Example 1 Composite material

Composite materials were prepared according to methods known in the prior art as discussed above.

An extruded layer of mastic with a weight per unit area of 0.6 Kg m ^~2 and thickness of 0.6 mm was laminated to a wicking layer comprising a polyester fleece with a weight per unit area of 0.09 Kg m ^"2 .

Example 2 Method of coating a joint

A 300mm diameter three layer polyethylene coated carbon steel pipe joint was butt welded to a similar pipe element.

The resultant field joint was prepared and protected in the following manner.

The exposed steel surface was water washed and abrasively cleaned to Sa 2 % (ISO 8501-1) and a surface profile in the range Rz 75μm to lOOμm was obtained.

A circumferential wrap of the composite material obtained in Example 1 was applied to the three layer polyethylene coating adjacent to the prepared steel surface.

A two pack epoxy coating was applied to the prepared steel surface and the adjacent composite. A woven glass reinforcement fabric was spirally wound into the wet coating such that the woven glass reinforcement fabric was saturated with the epoxy coating. The coating was allowed to cure to a Shore "D" hardness of 80.

In this way, a uniform, durable waterproof pipe coating was obtained.