AU8821382A

AU8821382A - Elastic cover for pressurized couplings

Info

Publication number: AU8821382A
Application number: AU88213/82A
Authority: AU
Inventors: R.H. Keith
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1981-08-17
Filing date: 1982-07-12
Publication date: 1983-03-08
Also published as: JPS58501303A; WO1983000779A1; ZA825931B; EP0087435A1

Description

Description ELASTIC COVER FOR PRESSURIZED COUPLINGS

This invention relates to an elastic tubular cover member for covering joints or splices on pressurized members such as pressurized cable splices, the union between two pipes, or welded pipe joints. The cover member of this invention will provide corrosion-preventing protection as well as prevent leaks occurring below a predetermined pressure. This invention provides an improvement over commercially available elastically shrinkable cover members which are constructed to be shrunk down or relaxed to form a closely conforming protective covering on splices and joints. Prior protective cover members are disclosed in U.S. patent No. 3,515,798, issued June 2, 1970, and assigned to the assignee of this application. This patent disclosed a cover member of highly stretched elastic material supported on a core which was helically grooved along its entire length such that the core could be progressively withdrawn from within the elastic tube to allow the same to shrink back onto and closely conform to the member disposed within the core. This patent also describes earlier examples of coverings used for sleeves and as protectors for splices. The present invention provides an improvement in that the elastically shrinkable tubular cover member is folded inward at least at one end to form a seal at the folded end such that pressure building within the cover member is trapped by the sealing character of the cover member and expands the cover between the ends until such time as the strength of the cover member is reached, causing a rupture of the cover, rather than migrating along under the cover to the end thereof.

The present invention provides an improved elastic cover for pressurized couplings or splices and comprises an elastic tubular cover member having at least one end of the member folded inward of the member with the entire member supported in a highly stretched condition on a hollow core member. The core member comprises a rigid cylindrical core of tough flexible polymeric ribbon material which is spirally wound and tacked or bonded to form a substantially rigid closed helix such that upon pulling one end of the ribbon it can be unwound and progressively removed from within the elastic member. The present invention will be more fully described with reference to the accompanying drawing wherein:

Figure 1 is a plan view of an elastic cover constructed in accordance ,with the present invention being positioned over a cable splice with parts thereof being shown in section to show interior parts; and

Figure 2 is a sectional view of the ribbon forming the core.

The present invention provides an improved rubbery or elastically shrinkable tubular cover member 0 supported in radially expanded or stretched condition on a removable core, with one or both ends of the cover member folded inward of the ends to define an improved pressure- retaining cover member for joints on pressurized conduits, i.e. pipes, cables, tubes, etc. 5 The illustration shows the cover member of the present invention being positioned over two cable ends 5 over one which the cover and core was placed prior to the two cable ends being suitably spliced. The cables 5 would typically be cables with air pressure applied within the " cables at 0.083 megapascals (12 pounds per square inch) to prevent corrosion of the conductor 6 or conductors.

The cover assembly comprises an elastic cylin¬ drical tube 8 which is folded inward at each end by 12.7-76.2 mm (one-half to three inches) as illustrated by 5 the cuffs or folds 9, and is radially extended to a stretched condition and is supported on a hollow cylindrical core 10. The cover member may be formed of compounded synthetic rubbers or other elastomers, examples include neoprene, silicone elastomers or ethylene propylene co- polymers. By the term compounded is meant normal conven- 5 tional operations in which ingredients are added to provide the required processing behavior and physical properties of the elastomeric device. Processing could entail open mill or internal mixing, extrusion, steam autoclave or continuous vulcanization or molding tech- 10 niques. In keeping with conventional preparation of such elastomeric materials, typical process aids, process oils, coupling agents, and vulcanizing agents (if necessary) are included in the compounded elastomeric component. Typically the elastic cover is expanded to 15 afford a stretch ratio of 1 to 1.2 up to 1 to 4. For these reasons the rubbers should be compounded as known in the art to increase cut and tear resistance, and have a minimum of permanent set. Permanent set is a measure of the elastic memory of a cured elastomer. Excellent 20 elastic memory will typically allow for coverage of a broad range of cable or workpiece diameters with a minimum number of sizes of pre-stretched articles. For adequate sealability and optimum product versatility, the permanent set should not exceed about 30 per cent. To ascertain 5 permanent set, a sample is subjected to a preselected strain at a specified temperature for a period of ^"time, and released, whereupon the distance (diameter, length, etc.) that is unrecovered can be measured. The conditions herein involve stretching the specimen 100 percent for 22 30. hours at 100°C, following which the samples are allowed to equilibrate for one hour at room temperature. The samples are then released, and after a 30 minute recovery period, are measured.

The core 10 is formed of a tough polymeric 5 material such as tough flexible cellulose acetate butyrate, polyvinyl chloride polymer material, or polypropylene. The core is formed by spirally wrapping an extruded ribbon 13 having stepped edges as shown in Figure 2. Upon wrapping the ribbon it is fused or tacked at spaced points along the edges to form a rigid core for supporting the stretched covers 8. The core 10 is removed from the cover member by pulling on the free end of the ribbon, disposed within the core and extending from one end, with sufficient force to separate the ribbon such that the core may be unwound as illustrated, leaving the cover tightly affixed to the ends of the connected cables ' ^■*-^* 5. The material and the manner in which the ribbon is fused determines the separation forces required but, the core must maintain its integrity to prevent premature collapse of the structure.

The ribbon 13 may have various widths and thick¬ 5 nesses to provide cores of varying inside diameter. Examples of the same are given in the table below.

Wid th Thickness Inside Diameter mm ( in . ) mm ( in . ) mm ( in. )

5. 9 .232 . 040 .46-1.07 11.7-27.2 0 5 5..99 . 223322 . 005500 1.30-1.72 33.0-43.7

9. 1 . 360 .060 1.50-2.40 38.1-61.0

9 .1 . 360 . 075 2.60-4.50 66.0-114.3

15. 7 . 618 . 090 3.87-5.00 98.3-127.0

Illustrations of the elastic covers 8 in the relaxed state

25 are

Inside Diameter Wall Thickness

(in. ) mm (in. ) mm

.14 3.6 .16 4.1

.19 4.8 .12 3.0

.24 6.1 .15 3.8

.30 7.6 .24 6.1

.32 8.1 .16 4.1

.37 9.4 .14 3.6

.42 10.7 .17 4.3

.50 12.7 .18 4.6

.60 15.2 .18 4.6

.84 21.3 .18 4.6

.96 24.4 .18 4.6

1.20 30.5 .22 5.6

1.50 38.1 .22 5.6

As the cover 8 is placed onto the cable ends a seal is formed between the cable ends such that air pressure may be maintained between the cable ends without the use of adhesive sealants or clamping bands placed around the outside of the cover 8.

Seals formed in this manner on unsealed unadhered galvanized pipe have proved to successfully maintain air or grease pressures in the range of 0.055-0.083 megapascals (8 to 12 psi). As presently formulated, covers folded according to the present invention can withstand pressures up to a bursting point of 0.255 megapascals (37 psi) without the use of retaining clips or clamps. This sealing results since the internal pressure moving along the cover from the spliced point toward the end of the cover reaches the inwardly folded end 9, and then follows a path along the cover between the fold and the end of the cover. The pressure between the fold and the cover then increases the seal by pressing the folded end more tightly to the tube and overcoming the tendency to expand the end of the cover. This expanding tendency is responsible for a catastrophic loss of pressure at 0.040 to 0.055 megapascals (6 to 8 psi)

OMPI for prior art cover members.

A test example of the sealing effectiveness of an elastic cover 8 was made by placing over a hole in the surface of a 19.1 mm (three quarter inch) nominal galvanized pipe, approximately 26.7 mm (1.05 inches) in outside diameter, an elastic cover corresponding to the sleeve used on a 8412-12 PST sleeve available from Minnesota Mining and Manufacturing Company, of St. Paul, Minnesota which has a relaxed inside diameter of 20.3 mm (0.80 inch), a wall thickness of 4.6 mm (0.18 inches) and a relaxed length of 304.8 mm (12 inches). The sleeve was folded inward between 25.4 mm (1 inch) and 38.1 mm (1 and one-half inches) at each end and then stretched initially onto a core having an inside diameter of 53.8 mm (2.12 inches). The cover 8 maintained a pressure of 0.124 megapascals (18 pounds per square inch) gauge on a sustained dead end test. The cover was then subjected to higher pressure and ruptured at between 0.248 and 0.262 megapascals (36 and 38 pounds per square inch). There are uses for covers which utilize the folded pressure-retaining cuff or fold at only one end and the other end has no fold but is adapted to be secured by a suitable external clamp such as the normal hose clamp. That being so, the product may be made with the cover member 8 folded inwardly at only one end and disposed on the core 10.

To apply the cover 8 over a joint between two tubular members, the core 10 is first slipped over one of the members and then the desired splice or union is formed between the two. The core is then slid back to a position over the splice and the end of the ribbon 13 of the core 10 is pulled through the core to unwind the core, allowing the cover to relax to a position tightly affixed to the cable. Having described the present invention it should be appreciated that cores other than cylindrical cores may be utilized, including tubular structures of nonuniform cross-section.

Claims

1. An elastic cover assembly for pressurized couplings or splices comprising an elastic tubular cover member supported in a radially stretched condition on a hollow core member comprising a tough flexible material formed as a substantially rigid tube which can be collapsed and removed, characterized by the feature that one end of the cover member is folded inward to define an internal portion lying against inner surface of the cover member.

2. An elastic cover according to claim 1 wherein said core member is a spirally wound polymeric ribbon having inner locked edges.

3. An elastic cover according to claim 1 characterized by the feature that ends of said cover member are folded inward to form a cuff at each end.

4. An elastic cover assembly according to claim 1, 2, or 3 characterized by the feature that said core member is cylindrical and has an inside diameter between 11.7 mm and 127.0 mm.

5. The assembly of any preceeding claim characterized by the feature that said core member is formed of a ribbon of cellulose acetate butyrate, polyvinyl chloride polymer, or polypropylene.

6. An elastic cover according to any preceeding claim characterized by the feature that the. entire cover member is supported on said core member.

OMPI