CA2045749C - Novel tape coating - Google Patents

Abstract

A tape wrap system adapted for protecting tubular articles comprising an innerwrap covering the surface of the article to be protected and an outerwrap placed over said innerwrap, said innerwrap comprising an impact-resistance polyolefin layer carrying an adhesive layer on its inner surface and a layer comprising an heat fusible material on its outer surface, or a single layer comprising a blend of an impact resistant moiety and a heat fusible moiety carrying an adhesive layer on its inner surface, said outerwrap comprising an impact-resistant polyolefin layer having an heat fusible layer on both surfaces or the inner surface thereof, or a singular layer comprising a blend of an impact resistant moiety and a heat fusible moiety; said tape wrap system fusing said innerwrap and outerwrap together when heated and thereafter cooled.

Description

Title: NOVEL TAPE COATING
Baclsaround of the Invention The present invention relates in general to protective coatings of tubular objects and specifically to protective coatings of pipes, and even more particularly to inground pipes.
The art is replete with protective pipeline coatings which provide varying degrees of resistance to impact, mechanical penetration, storage, indentation, abrasion, soil stresses and cathodic disbondment. Four major categories of protective pipeline coating are presently employed by the pipeline industry. They are:
(1) Hot Applied coal-tar enamel and asphalt mastics in relatively thick layers (100 mils) and commonly reinforced on the outside with glass or asbestos sheets. While such coatings are reported to represent over half of the plant-applied coatings in the United States, the hazards presented by their use foretell a decreasing popularity of this category. Further, the products show poor impact resistance, poor resistance to mechanical penetration, poor abrasion resistance, poor stability to soil stress conditions, and are only deemed fair in regard to indentation resistance, pipe bending, cathodic disbonding and resistance to hydrocarbon solvents.

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(2) Extrusion coatings of a thermoplastic resin: (typically 40 mils). In practice, polyethylene has virtually a monopoly in this area. The technique may involve a seamless tubular extrusion over the pipe or a flat die sheet extrusion wrapped over the pipe.
In most cases, the polymer is appli~d to a first-applied mastic layer (e. g. bituminous). These coatings show improved properties in regard to those mentioned above for the Hot-Applied enamel and coal tar coatings except insofar as resistance to hydrocarbon solvents.

(3) Fusion-bonded coatings - A thermoplastic powder is electrostatically applied to hot pipe where it "melts", adheres to the metal and fuses to itself. Only three basic materials have been widely used--polyethylene, vinyl and epoxy powders with only the latter enjoying commercial success in the United States.
Chemically,~these are, generally, bis-phenol A polymers with epoxy end groups.
The epoxies require a thermal curing to the thermoset form and usually a catalyst is used in the system (e.g. amines, acids, boron halides, etc.). Often times a liquid epoxy primer is used prior to the powder coating. Typically epoxy coatings have been 12-14 mils in thickness to provide at least acceptable resistance to cathodic disbonding, although in M.D. Simpson's paper "External Protection of Steel Pipes Using Epoxy Powder Coatings"
(contribution SI) presented at the Second International Conference on the Internal and External Protection of Pipes (in England Sept.
1977) he states (page X2) I
(' n ~, 204~'~~9 ~'Bitumen coal tar and polyethylene are required to be fed relatively thick, but epoxy powder coatings g i v a a x c a 11 a n t protection with only 3 mm of coatings."
Apparently and obviously "3 mm" should be -0.3 MM-(12 mils) nevertheless, this value (i.e. 0.3 MM) still represents a relatively thick coating and its attendant disadvantages, e.g.
brittleness and lack of flexibility and stresses at the pipe-epoxy interface.
In order to effect a satisfactory epoxy coating which would have satisfactory resistance to impact, mechanical penetration, indentation, abrasion, soil stresses, and cathodic disbondment it has been accepted that about a 12-14 mil thickness coating is required, which is very costly to produce.

(4) Tape Coating Systems (typically 20-80 mils thick) This method entails spirally wrapping a corrosion protective tape around a rubber based primer coating, referred to in the art as the innerwrap, followed by applying a second plastic outerwrap tape in a similar fashion as the innerwrap.
Many improvements on this tape coating system involving an inner and an outerwrap, have been advanced all of which have at their essence the primary task of promoting a tight bond thereby creating a coating which insulates the pipe from degradative external forces.
Accordingly, some tapes comprise polyethylene backings with a pressure-sensitive adhesives, or primer-activated adhesive coating thereon. The properties exhibited by these pipe coatings .~
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are similar to those of extrusion coated pipe coatings.
U. S. Patent No. 4, 213, 486 issued to Samour et al. and assigned to the present assignee, discloses a polyethylene outerwrap carrying a means for effecting bonding to the innerwrap epoxy layer wherein the means may be a hot melt adhesive or a pressure-sensitive adhesive.
U.S. Patent No. 3,874,418 issued to Hielema and assigned to the present assignee discloses:
"A method of coating a pipe and a pipe coated thereby, said method comprising the steps of progressively spirally winding a corrosion protective adhesive coated plastic tape onto the outer surface of the pipe with a spiral overlap, covering the coated pipe by progressively winding a film thereon with a predetermined overlap, and, as the film is wound onto the coated pipe, introducing and distributing under pressure a hot melted adhesive into intimate contact with the surface of the marginal portion of the trailing edge of the film and the surfaces of the overlapped portion along the leading edge thereof and of the portion of the tape immediately adjacent the leading edge of the film."
Still a further advancement in the art of tape coat systems is disclosed in U.S. Patent No. 4,806,400 issued to Sancaktar and assigned to the present assignee, wherein the improvement consists of tapering the opposed edges of the tape to enhance a tighter closure by being less subject to soil stress.

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While all the aforementioned tape coat systems provide for successful protective coatings, they still comprise separate layers. Accordingly, the task of the present invention can be described as being directed to improving the present tape pipewrap systems against degradative external forces by providing for a continuous and seamless protective tape coating system.
Brief Description of the Invention In accordance with the present invention, the aforementioned task is solved in a simple and elegant manner by heat fusing a polymeric outerwrap to a polymeric innerwrap tape coating, by incorporating a heat fusible material into said inner and outer wrap, which when heated and cooled forms a completely closed protective tape coating.
According to one aspect of the present invention there is provided a tape wrap system adapted for protecting tubular articles comprising an innerwrap covering the surface of the article to be protected and an outerwrap placed over said innerwrap, said innerwrap comprising a blend of an impact resistant moiety and a heat fusible moiety carrying on adhesive layer on its inner surface, said outerwrap comprising blend of an impact resistant moiety and a heat fusible moiety, said tape wrap system fusing said innerwrap and outerwrap together when heated and thereafter cooled.
According to a further aspect of the present invention there is provided a process for externally protecting a pipe which comprises the steps of:
(ay cleaning said pipe;

(b) applying primer to said pipe;
(c) wrapping said pipe with a protective coating of a tape wrap system as defined above;
(d) heating said pipe from about 225°F to about 325°F to fuse adjacent surfaces of the heat-fusible moieties; thereafter (e) cooling said pipe.
Detailed Description of the Invention As mentioned previously, the present invention relates in general to protective coatings of tubular objects and specifically to protective tape coatings for inground pipes.
The novel coating system of this invention comprises a polymeric innerwrap and a polymeric outerwrap. The polymeric innerwrap yields an A/B/C
or AB/C layered construction wherein the A layer consists essentially of a heat fusible material from about 0.5 to about 10.0 mils thick; preferred heat fusible materials are 5a 244~'~~9 ethylene vinyl acetate having a melting point below the application temperature, ethyl methyl acrylate, and low density polyethylene, ethylene vinyl acetate being particularly preferred. The 8 layer consists essentially of an impact resistant polyolefin material, preferably polyethylene, and most preferably a mixture of low and high density polyethylene from about 5.0 to about 30.0 mils thfckt and the C layer consists essentially of an adhesive, preferably a thermosetting adhesive from about 2.0 to about 20.0 mils thick..
Exemplary thermosetting adhesives are thermosetting rubber-based adhesives such as butyl rubber, natural rubber and styrene butadiene, butyl rubber and styrene butadiene, as wall as Kratons.
In still a further embodiment the innerwrap comprises a single layer ranging from about 5 to about 30 mils in thickness and having an A B blend corresponding to the aforementioned description.
The novel outerwrap comprises an A/B/A or an A/B layer construction corresponding to the aforementioned description wherein the A layer is from about 0.5 to about 10.0 mils thick, the B layer is from about 5.0 to about 30.0 mils thick, and the A
layer is from about 0.5 to about 10.0 mils thick. In still a further embodiment the outerwrap comprises a single layer ranging from about 15 to about 30 mils in thickness and having an A B blend corresponding to the aforementioned description.
The manufacture of such coatings is well known in the art comprising such well known processes as calendering, extrusion and coextrusion, and as such comprises no part of the present invention. Notably, both the inner and the outerwrap may contain . ""~-....
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additional ingredients performing specific desired functions. As illustrations of such additives mention may be made of fillers such as carbon black, zinc oxide, clays, chalk, whitings, calcium silicate, barium sulfate and the like in order to reduce the cost, increase the specific gravity, and/or to raise~the viscosity;
plasticizers and softeners such as mineral oil, lanolin, etc.;
antioxidants, e.g. aromatic amine antioxidants, substituted phenols, hydroquinone (p-dihydroxybenzenej, etc.: curing agents such as sulfur, organic peroxides and the like; accelerators:
sequesting agents; biocides such as bactericides, etc.
The general process of producing a tape coating system comprising the novel invention includes well known plant tape coating methods. The pipe may be first preheated to approximately 200°F and then prepared by any of the conventional ways known in the art such as by shot or grit blasting. Primer is then applied to the pipe by way of well known processes such as spraying or brushing. Next, the pipe is coated with the A/B/C or AB/C
innerwrap by progressively spirally winding said tape onto the outer surface of the pipe thereby maintaining a marginal overlap.
Notably, the innerwrap is applied in such a way that layer C is placed on the pipe while layer A or the AB blend layer is on the outer surface. Outerwrap A/B/A, A/B or single layer blend A B is then applied to cover the coated pipe by progressively winding said tape onto the innerwrap coated pipe with a predetermined overlap.
Next, flame or oven heat is applied to the coated pipe to attain a tape temperature ranging from about 225°F to about 325°F.
Lastly, ... _ 204740 the pipe is cooled by any of the known methods, exemplary of which is water cooling.
The present invention has particular application to small pipe segment patching. However, this application requires minor modifications in the aforementioned general process. First, the outerwrap must be crosslinked prior to pipe application.
Crosslinking may be accomplished by any of the well known methods such as chemical, radiation, etc. Second, the inner and/or outerwrap is preferably applied by enveloping the pipe segment in the wraps) as opposed to spirally winding although spirally winding is not excluded; and overlapping the longitudinal edges of said wrap(s).
Third, the area to be fused may be protected with a heat resistant sheet prior to applying heat to prevent tape coating dimensional distortion. Said sheet comprises a composition able to resist the heat and flame of a torch for a time sufficient to allow the underlying outerwrap and innerwrap to malt and fuse to each other and to the pipe. Materials which have been found suitable are polyamide film (i.e. "Kapton", trademark of Dupont) and aluminum foil. Other materials which could be used are Kevlar fabric, fiberglass fabric, laminate of fiberglass fabric with aluminum foil, flame resistant cotton, etc. Fiberglass fabric is particularly preferred. Last, flame or oven heat is applied to the coated pipe to attain a tape temperature ranging from about 225°F
to about 3 2 5°F .
In accordance with this novel process, the outerwrap is 2~4~'~~~
completely heat fused to the innerwrap thereby forming a uniform, . continuous, and completely closed protective coating which fully protects against external degradative forces. More specifically, the ethylene vinyl acetate components namely layers A or the A
moiety in blend AB are heat fused, thereby creating a tight bond between the inner and outerwrap so ws to achieve essentially a one layer seamless coating. Said seamless coating is highly advantageous in that no openings are present which when subjected to externai forces create potential portals of entry for pips corrosion factors. In sum, the present invention provides for a completely closed internal pipewrap environment which advantageously maintains pipe integrity.
Additionally, the present invention is particularly useful for wrapping pipe segments, such as in j oining the exposed ends of pipe segments before ground implantation. Notably, during pipe production pipes are cut into particular length to make transportation possible. Pipe coatings are either applied in the plant or in the field. If they are applied in plant the ends are left exposed. Thus before ground implantation the adjoining pipe ends need to be joined and coated. The present invention offers a particularly advantageous joint coating.
The following examples show by way of illustration and not limitation the novel characteristics of the present invention.
xamplg (Innerwrap) Layer Ingredients) Thickness (mils) A Ethylene Vinyl Acetate 4 (softening point* 59°C) B 64% Low Density Polyethylene 11 32% High Density Polyethylene 2.5% Black Concentrate 1.0% Antioxidant/Low Density *as determined by the American Society for Testing and Material D-1525.

r ~ .~ 204~'~49 ~amnle ~ (Outerwrap) Layer Ingredient($) Thickness (mils) A 96% Ethylene Vinyl Acetate 3 (softening point 67°C) 4% White Concentrate B 66-96% High Density Polyethylene 19 0-30% Low Density Polyethylene 4% White Concentrate A 96% Ethylene Vinyl Acetate 2.5 mils 4% White Concentrate Coatings prepared by the previously mentioned process and in accordance with example I and II were subjected to Cathodic Disbondment, Impact, and Soil Stress Testing. Prior art tapes comprising an outerwrap with a polyethylene backing and a pressure-sensitive adhesive coated thereon and an innerwrap consisting of polyethylene, prepared in the aforementioned process but omitting both the heating and cooling steps, were used as controls.
The following data illustrates the advantageous characteristics of the novel invention and consequently the longevity and integrity of a pipe coated with the novel invention.
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Cathodic Disbondment (measured after 30 days) System Temperature Cathodic Disbondment (°F) (inches squared) Test Sample 140 2.44 Control 140 6.00 Test 70 0.75 Control 70 0.6-0.75 Impact (administered and measured in accordance with ASTM G-14 guidelines) Test Sample 60 in/lb Control 45 in/lb Soil Stress at 90°F

(Disclosed in U.S. Patent No. 4,483,197 issued to Jordan Kellner) Test Sample . No peel back of outerwrap Control Outerwrap peeled back These test results demonstrate the advantageous characteristics and hence resistance to external degradative forces. Specifically, cathodic disbondment is more than 50%
decreased at 140°F, which is particularly advantageous given the implantation of pipes in hot temperature regions. The results of impact testing will show an advantage over the control yet the most important soil stress testing shows a highly significant improvement, no peeling of the outerwrap at 90°F. Resistance to soil stress is highly significant since pipeline tape deterioration, corrosion, is mostly caused by soil stress imparted on the inground pipe.
Example III is illustrative of a single layer blend outerwrap.
Example III

20~~'~~9 Ingredient A - Ethylene vinyl acetate copolymer 35 (softening point 59°C) B - Low density polyethylene blend 59 White concentrate 5 Antioxidant 1 By way of recapitulation, heat fusing polymeric outerwrap tape to a polymeric innerwrap tape by incorporating an heat fusible moiety in both wraps, advantageously prolongs the integrity and hence longevity of inground pipes.
Since certain changes may be made without departing from the scope of the invention herein described, it is intended that all matter contained in the foregoing description, including the examples, shall be taken as illustrative and not in a limiting sense.

Claims (20)

1. A tape wrap system adapted for protecting tubular articles comprising an innerwrap covering the surface of the article to be protected and an outerwrap placed over said innerwrap, said innerwrap comprising a blend of an impact resistant moiety and a heat fusible moiety carrying an adhesive layer on its inner surface, said outerwrap comprising blend of an impact resistant moiety and a heat fusible moiety, said tape wrap system fusing said innerwrap and outerwrap together when heated and thereafter cooled.

2, The protective tape coating described in claim 1, wherein said innerwrap comprises a first layer which comprises an AB blend wherein A is selected from ethylene vinyl acetate, ethyl methyl methacrylate and low density polyethylene, and B is selected from polyethylene and mixtures of low and high density polyethylene, and a second layer C which consists essentially of an adhesive.

3, The protective tape coating of claim 1, wherein the heat fusible moiety is ethylene vinyl acetate.

4. The protective coating of claim 3, wherein the impact resistant moiety is polyethylene.

5. The protective tape coating of claim 4, wherein the polyethylene is a mixture of high and low density polyethylene.

6. The protective tape coating of claim 1, wherein the heat fusible moiety is ethyl vinyl acetate.

7. The protective tape coating of claim 1, wherein the blend layer is crosslinked.

8. The protective tape coating of claim 1, wherein the impact resistant moiety is polyethylene.

9. The protective tape coating of claim 8, wherein the polyethylene is a mixture of low and high density polyethylene.

10. The protective tape coating of claim 1 having a total thickness from 10 to 200 mils.

11. A tape coated article comprising a pipe having thereon a protective tape coating as defined in claim 1.

12. A process for externally protecting a pipe which comprises the steps of:
(a) cleaning said pipe;

(b) applying primer to said pipe;
(c) wrapping said pipe with a protective coating of a tape wrap system as according to claim 1.
(d) heating said pipe from 225°F to 325°F to fuse adjacent surfaces of the heat-fusible moieties; thereafter (e) cooling said pipe.

13. The process as described in claim 12, further comprising the step of crosslinking said blend layer prior to wrapping said pipe.

14. The process as described in claim 12, wherein the pipe is first preheated.

15. The process as described in claim 12, wherein wrapping comprises first spirally wrapping said innerwrap while maintaining a marginal overlap and second spirally wrapping said outerwrap layer over said innerwrap layer while maintaining a marginal overlap.

16. The process as described in claim 12, wherein wrapping comprises first spirally wrapping said inner wrap while maintaining a marginal overlap and second wrappping said outerwrap around the surface of a portion of said pipe and overlapping the longitudinal edges of said outerwrap and applying heat to fuse said outerwrap to said innerwrap.

17 17. The process as described in claim 12, wherein wrapping comprises first wrapping said innerwrap around the surface of a portion of said pipe and overlapping the longitudinal edges of said innerwrap, and second wrapping said outerwrap around the surface of a portion of said pipe and overlapping the longitudinal edges of said outerwrap and applying heat to fuse said outerwrap to said innerwrap.

18. The process as described in claim 12, wherein the tape wrap system is crosslinked before wrapping onto said pipe.

19. The process as described in claim 18, wherein a heat resistant film is applied to the outerwrap prior to heat fusing to prevent dimensional distortion.

20. The process as described in claim 19, wherein the heat resistant film consists of fiberglass.