Method of Applying Heat Activatable Covering The present application relates to methods of applying a heat activatable covering to a substrate coated with a heat sensitive coating. More especially, but not exclusively, the invention relates to application of a heat activatable and shrinkable sleeve in circumstances in which the installation procedure requires preheating of a tubular article to a temperature greater than the melting or softening point of its coating, or of any of the components thereof, in the case in which the coating is a multi- component system. For example, the coating may comprise an inner or secondary adhesive layer and an outer polyolefin coating.

By way of example, recently, polypropylene pipe coatings, usually termed mainline coatings, have been developed for use in providing a protective coating on pipelines used for conveying products at high temperature, for example at greater than 100°C.

Specialized materials and techniques have become available for applying heat shrinkable polypropylene sleeves on the joint area between two welded pipe sections.

However, the application of the heat shrinkable sleeve or other covering may require heating the substrate such as the metal pipe to a temperature that is in excess of the melting or softening point of the outer polypropylene coating or of an underlying adhesive material coating, and it has been found that this risks impairment of the mainline polypropylene coating.

Method of applying a heat activatable covering to an area of a substrate article coated with a heat sensitive coating having a melting point or a softening temperature lower than an activation temperature for said covering, said method including the step of maintaining said covering in contact with said area including a portion of said heat

sensitive coating while said portion of said coating is at least said activation temperature, and further including the step of heating said portion to at least at said activation temperature while said coating has a heat resistant mold structure applied thereon, at least adjacent said portion.

This method can be used particularly advantageously where the procedure of installation of a sleeve or other covering applies a temperature in excess of the heat sensitive coating's melting point or softening temperature.

It has been found that, in such cases, there may be a tendency for the main line coating to become damaged, corrugated or wrinkled outwardly from the sleeve or other covering. Corrugation or wrinkling of the coating is particularly undesirable, since it can render the coated article susceptible to failure. For example, it may make the coating more liable to failure as a result of soil stress in service.

In the method of the present invention, the mold structures allow the sleeve or other covering to be applied successfully, even where extreme temperatures are applied in excess of the melting point or softening temperature of the coating without impairing the uniformity, continuity or profile of the mainline coating.

In a further aspect, the invention provides a method of applying a heat shrinkable sleeve to a joint area between two tubular articles, wherein said articles outwardly from said joint area are coated with a heat sensitive coating and adjacent said area are bare of said coating, comprising: applying a heat resistant spacer structure to bear on a region of each coating outwardly from said joint area; applying said sleeve; initially heating and partially heat shrinking said sleeve; removing the spacer structure; and further heating and shrinking said sleeve; wherein each spacer comprises a base portion

having an inner side for bearing on said region of the coating, an intermediate bridge portion offset outwardly from said inner side whereby said intermediate portion is spaced outwardly from said coating, and an end portion offset inwardly from said base portion for bearing on said bear oven.

This procedure is again particularly advantageous when, in the course of the sleeve application, the substrate is raised to a temperature in excess of the melting point or softening temperature of the coating or of any component of the coating. The spacers allow gases to escape from the region between the inner side of the sleeve and the outer side of the substrate as the sleeve shrinks, while avoiding deformation of the coating, since the intermediate portion of the spacer is spaced away from and does not impinge on or apply pressure on the heated coating. The base portion may bear indirectly on the outer region, for example through mold structure applied in accordance with the first aspect of the invention.

The invention will now be more fully described by way of example only with reference to the accompanying drawing.

Figure 1 is a side elevation, partially in section, showing a weld joint area and mold structures as employed in a first form of method in accordance with the invention.

Figure 2 is a partially perspective view of the weld joint area of Fig. 1, showing the application of spacer structures.

Figure 3 is a perspective view of the joint area of Fig. 2, showing a succeeding stage wherein a sleeve has been applied on the joint area.

Figure 4 is a partially perspective view of the joint area of Fig. 3 having an induction heater coil applied

thereover.

Figure 5 is a side elevational view, partially in section, of the joint area of Fig. 4 after removal of the induction heater, wherein the left half of the Figure shows heat shrinking of the sleeve with the spacer and mold structures in place. The right half of the Figure taken from a position rotated with respect to the viewpoint of the left hand half, shows the heat shrink sleeve in the area of the closure strip after the mold and spacer structures have been removed.

Figure 6 is a side elevational view, partially in section, showing mold structures as employed in a second form of the method of the invention.

Figure 7 is a side elevational view, partially in section showing the completed joints.

With reference to the accompanying drawings, Fig. 1 shows pipe sections 11 and 12 welded together at a weld joint 13. Outwardly from the joint 13, each pipe section 11 and 12 has a polyolefin, for example polypropylene pipe mainline coating 14 and 16 thereon. The coatings 14 and 16 may be of the multi-component type, and may comprise a outer polypropylene coating on an inner polypropylene adhesive coating, the latter being applied directly on the metal pipe. Preferably, as seen in Fig. 1, the ends of the coating 14 or 16 adjacent the weld joint area are chamfered, as indicated by reference numerals 17 and 18, respectively.

The end portions 19 and 21 of the pipe are bare of the coating 14 and 16, in order to allow the weld 13 to be accomplished. It is desired to apply a heat shrinkable sleeve protecting the bare portions 19 and 21 and the weld 13 and rendering them resistant to corrosion.

Preferably, before applying the sleeve, a curable primer composition, for example a mixed two part epoxy primer, is applied on the portions 19 and 21. The epoxy coating is then preferably force cured by application of heat to the primer coating, for example by application of a propane torch flame in order to heat the primer to a temperature that ensures the primer is cured before the remaining stages of the installation procedure. The cured epoxy coating provides improved corrosion resistance and a key to promote adherence of the subsequently applied sleeve components.

A heat resistant mold structure is applied on each coating 14 and 16 axially outwardly from the joint area.

The mold structures 22 and 23 are spaced apart generally symmetrically with respect to the weld 13 a distance slightly greater than the length of the sleeve 24 to be applied to the joint area, so that, as best seen in Figs. 3 and 5, the inner ends of the mold structures 22 and 23 are spaced slightly longitudinally outwardly from the ends of the sleeve 24.

Preferably, the inner sides of the mold structures 22 and 23 provide a cylindrical inner surface that conforms closely to the outer cylindrical surface of each mainline coating 14 and 16.

The mold structures 22 and 23 are preferably of sufficient width to extend longitudinally outwardly over the entire portion of the coating 14 and 16 that, in the installation procedure, is exposed to potentially deleterious temperature. Typically, the molds 22 and 23 may have a width, measured in the longitudinal direction of the pipe of about 5 to 30 cm, more typically about 15 cm.

Before applying the sleeve 24, a pair of heat- resistant spacer members 26 and 27 may be applied to the joint area to provide a channel allowing gases to escape

from underneath the sleeve as it shrinks.

As best seen in Figs. 2 and 5, each spacer member 26 and 27 is preferably of a generally rectangular or bar like-shape and comprises a relatively thick base portion 28 that bears on the coating 14 or 16 outwardly from the ends of the sleeve 24. In the example illustrated, the portion 28 bears indirectly on the coating 14 and 16 and engages on the outer side of the mold structure 22 or 23. Each spacer structure 26 and 27 includes an intermediate bridge portion 29 that has its inner side off-set outwardly from the inner side of the base portion 28, so that its inner side is spaced radially outwardly from the mainline coatings 14 and 16, as seen in Fig. 5, and an end portion 31 that curves radially inwardly toward an end surface 32 that rests on the portions 19 and 21 of the pipes that are bare of the coating 14 and 16.

If desired, the spacer members 26 and 27 may be located against displacement by taping their base portions 28 to the outer sides of the mold structures 22 and 23 with a heat resistant adhesive tape. Preferably, the spacers are applied centrally of the uppermost side of the pipe sections 11 and 12 (i. e. at the 12 o'clock position visualising the pipe cross section as a clock face).

A heat shrinkable sleeve 24 is applied over the assembly, as seen in Fig. 3. The sleeve may be a wrap- around sleeve the ends 33 and 34 of which are overlapped, as seen in Fig. 3, and may include an integral closure strip or, as shown in Fig. 3, may have a separate closure strip 36 applied. Alternatively, the sleeve 24 may be a cylindrical sleeve that is slid over an accessible end of one of the pipe sections 11 and 12 usually before the weld 13 is accomplished.

Such cylindrical sleeves, wrap-around sleeves and closure sheets are well known to those skilled in the art,

and need not be described in detail herein. Sleeves and closure sheets are described, for example, in Steele et al U. S. Patent 5,411,777, Steele et al U. S. Patent 5,175,032 and in Tailor U. S. Patent 4,472,468, the disclosures of all of which are incorporated by reference herein.

Usually, the sleeve 24 comprises an outer backing comprising a heat shrinkable cross-linked polyolefin, for example polypropylene, having on a side that is applied inwardly toward the joint area a functional coating, such as a heat-activatable mastic, sealant or adhesive.

In the case in which the sleeve 24 is a wrap-around sleeve, the overlapped ends 33 and 34 and closure sheet 36 are fusion bonded together, for example by heating to weld them together with a propane torch flame. Further heating, for example with a propane torch flame is then preferably applied to the sleeve, whether a wraparound or pre-formed cylindrical sleeve, to at least partially shrink the sleeve onto the assembly of the pipe sections and the spacers 26 and 27, so that most of the inner side of the sleeve is shrunk down in tight conformity with the bare portions 19 and 21 and into intimate contact with the adjacent portions of the coatings 14 and 16, as seen in the left hand half of Fig. 5.

In order to fully activate the sleeve 24 or the functional coating thereon, and cause it to bond effectively to the joint area, it is desired to heat the coatings 14 and 16 and the substrate, namely the steel pipe, to an elevated temperature. Such elevated temperature will usually be at least an activation temperature for the sleeve 24 or its functional coating.

For example, such activation temperature may be a temperature at which the functional coating will wet and bond to the coatings 14 and 16 and will wet and bond to the substrate. Problems arise when such elevated temperature is in excess of the melting or softening point of the

coating 14 or 16, or of at least one of its components.

The coating 14 or 16 may comprise, two or more layers.

For example it may comprise an outer crystalline coating, and an inner or secondary amorphous adhesive layer between the outer layer and the substrate. The coating may or may not comprise a layer such as cured resin, e. g., epoxy resin, between the substrate and the adhesive layer. It has been found that raising the temperature of the coating 14 or 16 above either the softening point of the adhesive material or the melting point of the polyolefin material renders the coating susceptible to undesired deformation, for example as evidenced by wrinkling, corrugation, and the like undesired deformation.

As will be understood by those skilled in the art, the term"melting point"applies normally to crystalline polymers that have a discrete crystalline melting point, such as can be determined, for example by differential scanning calorimetry measurement. Many materials, such as, for example, many non-crystalline amorphous materials such as many adhesives, do not have a discrete melting point.

In such a case, the temperature at which the material softens and becomes susceptible to undesired deformation can be defined in terms of the softening temperature of the material. By reference to melting point and softening temperature herein is meant melting point as determined by differential scanning calorimetry (DSC) measurement and the VICAT softening temperature, respectively.

In the first aspect of the invention, such undesired deformation is avoided by employing the heat resistant mold structures 22 and 23 that retain the original configuration, profile and continuity of the coatings 14 and 16 during the stage of heating the coatings to the activation temperature. Usually, such heating is effected by heating the substrate.

While various procedures for heating the metal substrate to the required temperatures are contemplated, in the preferred form, induction heating is employed.

Referring to Fig. 4, this shows an induction heating coil 37 that is slid along the pipeline and positioned over the joint area. The induction coil 37 is energized using a current strength and a duration of energization sufficient to heat the metal pipe substrate to a desired temperature at which the coatings 14 and 16 and the substrate are heated such that the sleeve 24 or a component thereof, such as a functional coating on the inner side of the sleeve, bonds adequately to the bare portion 19 and 21, to the weld joint 13, and to the adjacent portions of the coatings 14 and 16.

In the preferred form, during the induction heating step, the metal of the pipes 11 and 12 is heated, in the heated area, to a desired temperature substantially uniformly throughout the entire wall thickness of the pipe.

This is achieved using relatively low frequency induction heating, for example less than about 10 KHz, more typically about 0.5 to 6 KHz and more preferably about 1 to 3 KHz.

The thorough heating of the pipe wall ensures that the joint area and the components of the joint remain adequately hot until the joint is completed. Typically, for example, in the case of bonding of a polypropylene backed sleeve 24 to polypropylene coverings 14 and 16, in the area underlying a center region of the induction coil 37, the metal of the pipe wall is raised throughout its entire thickness to a temperature of approximately 180 to 220°C, more typically about 200°C. It may be noted that a typical melting point of an outer polypropylene coating 14 or 16 may be about 160°C, while a softening temperature of an inner adhesive layer of coating 14 or 16 may be about 150°C. During the induction heating, a temperature gradient is established wherein the temperature of the substrate diminishes outwardly from the center region of the induction coil. The coatings 14 and 16, in the region

overlapped by the sleeve and slightly outwardly beyond the edges of the sleeve are heated to a temperature in excess of the activation temperature for the sleeve 24, e. g. about 165°C. However the area of the coatings 14 and 16 that is heated to above the melting point or softening temperature of the coatings 14 and 16, or of any component thereof, does not extend outwardly beyond the mold structures 22 and 23.

Following the desired induction heating, the coil is deenergized and removed from the joint area'e. g. is slid along the pipe. At this point, it may be desired to visually inspect the sleeve 24 to make sure that it is in full contact with the steel at the joint area, and that there are no cracks or holes in the backing of the sleeve 24. The spacers 26 and 27 are then carefully removed.

During the heating of the joint area before and during the induction heating stage, the spacers 26 and 27 provide channels allowing air or other gases to exit from the space between the sleeve 24 and the external surfaces of the portions 19 and 21, so that no gas bubbles remain trapped within the sleeve.

After removal of the spacers 26 and 27, the entire sleeve 24 may be heated for example with a propane torch flame in order to completely shrink the sleeve 24 and ensure that-there is good contact between pipe sections 11 and 12 including the coatings 14 and 16 and the portions of the sleeve 24 that were adjacent the spacers 26 and 27. At this point, the mold structures may normally be removed.

Pressure may then if desired be applied to the exterior of the sleeve 24 while the sleeve 24 is still hot and soft in order to ensure intimate contact between the sleeve 24 or its components and the underlying portions of the pipe sections 11,12 and the weld 13. Such pressure may be applied with a hand roller rolled circumferentially

around the central portion of the joint area and subsequently longitudinally outwardly therefrom, and longitudinally along the closure strip 36, if present.

Desirably, at the completion of the operation, adhesive material or other functional coating material on the inner side of the sleeve 24 will be visible as having oozed out beyond the end portions of all longitudinal end edges of the sleeve 24 and having wetted the adjacent surface of the coatings 14 and 16.

The completed joint is as shown in the right hand half of Fig. 5 with the sleeve 24 and its components shrunk down onto and bonding to the pipe sections 11 and 12 including the coatings 14 and 16.

Turning now in more detail to the mold structures 22 and 23, the mold structures may desirably be formed of any preferably flame and heat resistant material that will serve to confine the coatings 14 and 16 and preserve their as-manufactured mainline form when the substrate is heated above the melting point or softening temperature referred to above, and that can be removed from the pipe or other tubular article after the coatings 14 and 16 have cooled.

Further, where induction heating is employed, the mold structure should be electrically insulating or non- conductive and substantially non-responsive to induction fields. In one preferred form, the molds 22 and 23 comprise silicone rubber tapes or bands that are wound tightly around the coatings 14 and 16. The rubber tapes or bands may contain a mesh or fibrous reinforcement, for example, a glass fiber mesh reinforcement, in order to improve their resistance to tearing. The silicone rubber tapes or bands may be provided with a fastening system such as a conventional adhesive tape fastening, with a plastic buckle or with a hook and loop (e. g. VELCRO trademark) fastener system in order to retain an outer end of the silicone rubber tape or band so that the tape or band is held tightly wound around the exterior of the coatings 14

and 16. It is found, however, that with the silicone rubber tapes or bands, a fastening system is often not required, since the silicone rubber material has a high coefficient of friction and the end tends to engage tightly on an outer side of the remainder of the winding. Other materials may of course be used in place of the silicone rubber material, for example glass fiber-reinforced polyamide or aramid (KEVLAR trademark) fiber reinforced high temperature plastics. Since it is desired that the mold structure should not bond to the coatings 14 and 16, and be easily separable from the coatings 14 and 16 after cooling, if necessary the inner surfaces of the mold structure material may be coated or lined with a high temperature resistant release coating or lining, for example of polytetrafluoroethylene (TEFLON trademark).

Further, instead of using the mold structures formed by a strip-like material around the coatings 14 and 16, it is contemplated that each mold structure may comprise hinging clam-shell like members, molded for example from epoxy resin, that in use may be applied around the coatings 14 and 16 and the hinged halves retained in a cylindrically closed position. After completion of the operation the halves are unfastened, and pivoted to an open position in which they can be removed from the tubular articles.

With regard to the spacers 26 and 27, as will be appreciated these serve to space a portion of the sleeve 24 away from the outer surfaces of the pipe sections 11 and 12, allowing gases to escape, and are designed to space the bridge portions 29 away from such surfaces and avoid applying pressure on the coatings 14 and 16 while the substrate is above the softening temperature or melting pointy referred to above. In this way, the coatings 14 and 16 are not deformed inwardly as a result of such pressure.

The spacers 26 and 27 may be formed of any material that will not adhere to the portions with which it is in contact and which will retain its structural integrity at

the temperatures to which it is subjected. Where induction heating is employed, as in the example described above the spacers should be of a material that is non-responsive to induction fields, for example is electrically insulative.

Preferably, for example, the spacers may be formed of polytetrafluoroethylene (TEFLON trademark).

It is contemplated that the spacers may be employed with procedures similar to those described above in detail with reference to Figs. 1 to 5 but modified in that the substrate is not heated to a temperature greater than the melting point or softening temperature referred to above outwardly from the ends of the sleeve 24. In such case, the base portions 28 of the spacers may engage directly on the relatively unheated outer regions of the coatings 14 and 16. In the preferred form, however, the spacers 26 and 27 are used with and applied on the outer sides of the mold structure 22 and 23 as described in detail above.

Referring to Fig. 6, in a modified form of the present method, instead applying the mold structures 22 and 23 slightly outwardly from the ends of the sleeve 24, the mold structures 22 and 23 are applied adjacent the chamfered ends 17 and 18 of the coating. The induction coil 37 is then brought into position and the assembly is induction heated in the absence of the sleeve. As before, the area of the coatings 14 and 16 that is heated to above the activation temperature for the sleeve 24 extends outwardly slightly beyond the position that the ends of the subsequently applied sleeve 24 will occupy. The portions of the coatings 14 and 16 that are heated to above their melting point or softening temperature do not extend outwardly beyond the outer ends of the mold structures 22 and 23. Once the desired temperatures have been reached, the induction coil 37 is deenergized and removed from the joint area.

Because of the relatively high heat capacity of the

metal substrate, once the substrate, namely the metal pipe, is heated throughout its wall thickness, the substrate, as well as the portions of the coatings 14 and 16 that are desired to be heated above the activation temperature, remain at the desired temperatures for a period sufficient to allow the remaining steps of the installation procedure to be accomplished. The mold structures 22 and 23 may be removed at this point. If desired, in order to eliminate risk of undesired deformation of the coatings, the mold structures 22 and 23 may be re-applied as shown in Fig. 7 at positions corresponding to those used for the mold structures 22 and 23 in the procedure of Figs. 1 to 5, namely slightly outwardly from the ends of the sleeve 24.

The sleeve 24 is applied and is heat shrunk down onto the joint area, as seen in Fig. 7, into intimate contact with the substrate and with the coatings 14 and 16, and pressure may be applied, for example with a hand roller, to complete the installation, as described above in connection with Figs. 1 to 5.

It has been found that the procedure described above with reference to Figs. 6 and 7 tends to result in significantly less or no entrapment of gas underneath the sleeve 24, and, usually, the use of spacers such as the spacers 26 and 27 applied as described above, is not necessary unless the procedure is applied to large diameter pipes for example in excess of about 450 mm (18 inches) in outside diameter.

While the above detailed description has referred to application of sleeves, the principles of the above described methods may be employed in application of other heat activated coverings, for example patches. The procedure of either Figs. 1 to 5 or of Figs. 6 and 7 may be employed. In the former case, as will be appreciated, the patch and the mold structures are applied with the mold structures placed slightly outwardly from the edges of the

patch, followed by heating, for example induction heating, to rise the underlying portion of the coating to above the activation temperature. In the latter case the substrate and coating may be preheated with mold structure applied on the coating. The mold structure is then removed and the patch applied to the coating while the latter remains at a temperature above the patch's activation temperature.

While, in the above description, reference has been made to the mainline coatings 14 and 16 and the sleeve 24 or other covering comprising polypropylene, it will be appreciated that the technique described above can be employed with coatings and sleeves or other coverings formed from other materials, for example other polyolefins.

Further, while in the preferred example described above induction heating is used to heat the substrate and a torch flame is used to heat the sleeve 24 or other covering, other heating arrangements can of course be employed, for example conventional ovens.