GB1578125A

GB1578125A - Sample line tube

Info

Publication number: GB1578125A
Application number: GB8901/76A
Authority: GB
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1976-03-05
Filing date: 1976-03-05
Publication date: 1980-11-05

Description

(54) " SAMPLE LINE TUBE" (71) We, RAYCHEM CORPORATION, a corporation organised according to the laws of the State of California, United States of America, of 300 Constitution Drive, Menlo Park, California 94025, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to tubing, especially tubing suitable for conveying fluids, either liquid or gaseous, whilst maintaining the temperature of the conveyed fluids sub stantially constant.

Such tubing is, for example, used in the chemical processing and petroleum refining industries for conveying samples of fluids from process lines or reaction vessels to sampling instruments such as chromatrographs, spectrometers and pressure or temperature sensors. It is necessary that the fluid samples taken should be maintained at a relatively elevated temperature in order to keep the viscosity of the fluid as low as possible and also, in the case of gases, to ensure that condensation does not occur.

Typically such tubing comprises a relatively flexible tubular line member made, for example, from stainless steel, which is provided with electrical heating wires which are disposed in engagement with the tubular line member, typically by laying them parallel or by wrapping them helically about the line member. Such an arrangement can also be used as protection against freezing.

The assembly formed by the tubular line member and its associated heating element(s) is provided with insulation and a protective covering, as described, for example, in U.S.

Patent No. 3,355,572. The composite tubing member thus produced has proved satisfactory in many applications, but the insulation used until now has not been entirely satisfactory and, furthermore, the heating clements used have not, in all cases, been able to meet the requirements of certa in specific applications.

The present invention provides a composite tubing member comprising: (a) a tubular line member (b) heating means disposed externally of said line member; and (c) insulation comprising at least two layers, each of which comprises foam material and, preferably, rcinfolciilg material.

At least two layers within the insulatioii ale preferably in helically counter-wrappctl relationship, i.e. so that one layer is wrapped in a sense opposite to that of Illc otller, the present invention being basel, itiler er alia, on our observation that especially suitable insulation for sampling line tubes can be obtained by helically counter-wrapping at least two layers of foam material.

Such a helically counter-wrapped configuration ensures that the insulation remains tighl and free of leakage paths.

In some cases it may not be necessary or desirable to provide separate reinforcing material. For example, certain insulation materials, e.g. polypropylene foam, have sufficient structural integrity to be used without additional reinforcement.

However, each layer will preferably comprise both a low density foam material and reinforcing material so as to include both thermally insulating and reinforcing materials and the arrangement will be such as to prevent the thermally insulating low density foam material from being crushed by overwrapped reinforcing material. Thus the insulation preferably comprises at least two layers each of which is formed from a thermally insulating low density foam material and a reinforcing material, the arrangement of the foam and reinforcing materials in the layers and the arrangement of the layers being such that each section of the insulation comprises both foam material and reinforcing material in over-wrapped relationship. Such an arrangement can readily be obtained by helically counterwrapping the layers, especially if each layer contains the foam material and the reinforcing material in side-by-side relationship.

However, other arrangements may be used to take advantage of this aspect of the present invention In one preferred form of the present invention the layers of the insulation are formed by helically wrapping a laminated tape comprising a width of low density foam material and a width of high density foam material. A further layer of laminated tape is then wrapped helically in the opposite direction about the article so formed to produce a final tubular insulating member, the low density foam material supplying the necessary thermal insulation and the high density material providing the necessary structural integrity.

Of course, each layer of such insulation could be formed by wrapping two separate tapes rather than a single laminated tape.

The foam material is typically a polyurethane although other materials, e.g. polyethylene, polypropylene or rubber, may be employed.

By " low density material " there is herein meant material having a density of not more than 4lbs/cubic foot and by "high density material" there is herein meant material having a density of not less than 6lbs/cubic foot. Preferably the density of the low density material lies in the range of from 1 to 2lbs/cubic foot and the density of the high density material lies in the range of from 6 to 101bs/cubic foot.

In another preferred embodiment of the present invention the reinforcing materiil comprises plastics rope or tubing, for example, polypropylene or nylon rcpe which is helically wrapped together with the low density foam material. Thus in this embodiment each layer can be formed by first helically wrapping low density tape and then, in the same sense, helically wrapping the polypropylene rope. It may be advantageous, in other cases, to wrap the low density foam material and the rope simultaneously in side-by-side relationship.

It will be appreciated, that although two layers will in general be sufficient to meet the insulation requirements, in some applications it may be appropriate to use three or more layers, especially where flexibility of the composite tubing member is relatively unimportant. In such cases, each adjacent pair of layers will preferably be in helicallycounter-wrapped relationship.

The insulation produced by wrapping the various layers may be finally covered by an outer sheath of plastics material, e.g. polyvinyl chloride or polyethylene, and it will be appreciated that other materials may be included within the insulation of the line member for specific purposes, for example it may be appropriate to add a braid material, for example fibreglass braid or tape, to provide high temperature thermal insulation.

The heating means may comprise, for example, one or more electrical heating wires wrapped helically about the tubular line member and, advantageously, held in position by binder strands made from nylon fibre or tape material. Alternatively, one or more of the heating wires may be arranged to run parallel to the longitudinal axis of the tubular line member. However, in the preferred forms of the present invention the heating element comprises a self-regulating heating strip which increases its electrical resistance as the temperature increases and which is preferably provided with its own mechanical protection. An especially suitable self heating strip which may be wrapped helically around the tubular line member or which may be run parallel to the longitudinal axis of the line member is that sold commercially under the name "Autotrace" (Registered Trade Mark) by Chemelex Inc., a subsidiary of Raychem Corporation, and which is described, for example, in British Patents Nos. 1,449,261, 1,449262 and 1,456,047 the disclosures of which are incorporated herein by this reference.

However, other heating means may be used in the present invention, including for example non-electrical heating means, e.g.

a thin pipe through which steam or another heating fluid is passed.

The thickness of the low density foam material and the reinforcing material will vary according to the application but, in general, the thickness of the material used in each layer will lie in the range of from 1/8 inch to 3/8 inch giving a total thickness of at least 1/4 inch.

It will be appreciated that the insulation used in the present invention can easily be applied to the line member and its associated heating means. However, in some cases, it may be advantageous to form a prefabricated two-layered insulation mem- ber into which the line member may be pushed or drawn to form the final composite article.

Various embodiments according to the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a first form of com posite tubular article in accordance with the present invention Figure 2 shows a second form of com posite tubular article in accordance will the present invention Figure 3 is a cross-section taken along the line 3-3 of Figure l; and Figure 4 shows part of a heating clement suitable for use in the present invention.

Referring now to the drawings, in Figure l there is illustrated a composite sampling line 1 comprising a tubular line member 2 made, for example, from stainless steel or a plastics material such as polytetrafluoroethylene or nylon, provided witll an electrical heating element 3 secured in position with relation to the tubular line member 2 by tape 4 so that it occupies a position substantially parallel to the longitudinal axis of the tubular line member 2. In accordance with the present invention the assembly of the line member 2 and the heating element 3 is insulaled by first wrapping a laminated tape 5 comprising a width 6 of low density polyurethane foam and a second, narrower, width '7 of high density polyurethane foam, about the assembly and then wrapping a similar tape 8 over the wrapping 5 but in an opposite sense. The insulation so obtained is finally protected by means of an outer plastics sheath 9.

Turning now to Figure 2 there is shown a somewhat similar assembly Il in which the tubular line member 12 is provide(l with a helically wound electrical heating element 13 held in position by tape 14. The assembly so produced is insulated by means of a helically wrapped tape 15 of low density polyurethane foam reinforced by several windings 16 of polypropylene rope which has been helically wrapped about the layer 15 in the same sense. A second layer of the same construction is then wrapped in the opposite sense over the first layer. Once again the insulation is finally protected by means of an outer plastics sheath 17.

Finally, in Figure 4 there is shown Ilic end of a heating element suitable for use in the present invention. This comprises two spaced apart parallel electrodes 21 all(l 22 embedded in a carbon-filled polymeric composition and protected by an insulating layer 23 and a metal braid 24 (in some cases the metal braid may be omitted). Such a heating element is described, for example, in aforementioned British Patents Nos.

1.449,261, 1,449,262 and 1,456,047, and is especially suitable for use in the present invention.

Whilst the present invention has been described with specific reference to tubular sampling line members it will be appreciated that it is also applicable to other fields and.

equally, it will be appreciated that the word " tubular as used herein does not limit Tulle invention to hollow right cylindrical mem- bers, but it is intended to cover members of irregular and/or varying cross-section as well as members having one or more branches, such as Y-shaped, T-shaped and X-shaped members.

Further modifications and variations falling within the scope of the present invention will be apparent to those skilled in the art.

WHAT WE CLAIM IS: 1. A composite tubing member comprising: (zi) a tubular line member (b) heating means disposed internally or externally of said line member; and (c) insulation comprising at least two layers, each of which comprises foam material.

2. A composite tubing member as claimed in Claim 1, wherein at least two layers ol the insulation are arranged in helically counter-wrapped relationship.

3. A composite tubing member as claimetl in claims I or 2, wherein the foam material is a thermally insulating low density foam material.

4. A composite tubing member as claimed in claim 3, wherein the density of the foam material is from 1 to 2 lbs/cubic foot.

5. A composite tubing member as claimed in any one of Claims 1 to 4, wherein each layer of the insulation also comprises a reinforcing material.

6. A composite tubing member as claimed in any one of claims 1 to 5, wherein the insulation comprises at least two layers, each of which is formed from a thermally insulating low density foam material and a reinforcing material, the arrangement of the foam material and the reinforcing material in each layer and the arrangement of the layers being such that each longitudinal section of the insulation comprises both foam material and reinforcing material in over-wrapped relationship.

7. A composite tubing member as claimed in claims 5 or 6, wherein the reinforcing material is high density foam material.

8. A composite tubing member as claimed in claim 7, wherein the density of the foam material is from 6 to 10 lbs/cubic foot.

9. A composite tubing member as claimed in claims 7 or 8, wherein at least one layer of the insulation is made from a laminated tape comprising a width of low density foam material and a width of high density foam material.

10. A composite tubing member as claimed in any one of claims 5 to 9, wherein at least one layer of the insulation comprises plastics rope or tubing as reinforcing material.

11. A composite tubing member as claimed in claim 10, wherein the plastics material is polypropylene or nylon.

12. A composite tubing member as claimed in any one of claims 5 to 11, wherein at least one layer of the insulation is made from a strip of foam material and a strip on reinforcing material.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. line 1 comprising a tubular line member 2 made, for example, from stainless steel or a plastics material such as polytetrafluoroethylene or nylon, provided witll an electrical heating element 3 secured in position with relation to the tubular line member 2 by tape 4 so that it occupies a position substantially parallel to the longitudinal axis of the tubular line member 2. In accordance with the present invention the assembly of the line member 2 and the heating element 3 is insulaled by first wrapping a laminated tape 5 comprising a width 6 of low density polyurethane foam and a second, narrower, width '7 of high density polyurethane foam, about the assembly and then wrapping a similar tape 8 over the wrapping 5 but in an opposite sense. The insulation so obtained is finally protected by means of an outer plastics sheath 9. Turning now to Figure 2 there is shown a somewhat similar assembly Il in which the tubular line member 12 is provide(l with a helically wound electrical heating element 13 held in position by tape 14. The assembly so produced is insulated by means of a helically wrapped tape 15 of low density polyurethane foam reinforced by several windings 16 of polypropylene rope which has been helically wrapped about the layer 15 in the same sense. A second layer of the same construction is then wrapped in the opposite sense over the first layer. Once again the insulation is finally protected by means of an outer plastics sheath 17. Finally, in Figure 4 there is shown Ilic end of a heating element suitable for use in the present invention. This comprises two spaced apart parallel electrodes 21 all(l 22 embedded in a carbon-filled polymeric composition and protected by an insulating layer 23 and a metal braid 24 (in some cases the metal braid may be omitted). Such a heating element is described, for example, in aforementioned British Patents Nos. 1.449,261, 1,449,262 and 1,456,047, and is especially suitable for use in the present invention. Whilst the present invention has been described with specific reference to tubular sampling line members it will be appreciated that it is also applicable to other fields and. equally, it will be appreciated that the word " tubular as used herein does not limit Tulle invention to hollow right cylindrical mem- bers, but it is intended to cover members of irregular and/or varying cross-section as well as members having one or more branches, such as Y-shaped, T-shaped and X-shaped members. Further modifications and variations falling within the scope of the present invention will be apparent to those skilled in the art. WHAT WE CLAIM IS:

1. A composite tubing member comprising: (zi) a tubular line member (b) heating means disposed internally or externally of said line member; and (c) insulation comprising at least two layers, each of which comprises foam material.

13. A composite tubing member as claimed

in claim 12, wherein the strip of foam material and the strip of reinforcing material are arranged in side-by-side relationship.

14. A composite tubing member as claimed in claim 12, wherein the strip of foam material and the strip of reinforcing material ale arranged in over-wrapped relationship.

15. A composite tubing member as claimed in any one of claims 1 to 14, wherein a polyurethane is used as the foam material in at least one layer of the insulation.

16. A composite tubing member as claimed in any one of claims 1 to 14, wherein polypropylene is used as the foam material in at least one layer of the insulation.

17. A composite tubing member as claimed in any one of claims 1 to 14, wherein polyethylene or a rubber is used as the foam material in at least one layer of the insulation.

18. A composite tubing member as claimed in any one of claims 1 to 17, wherein the thickness of each layer of the insulation is in the range of from 1/8 to 3/8 inch.

19. A composite tubing member as claimed in any one of claims 1 to 18, wherein the insulation comprises an outer plastics sheath.

20. A composite tubing member as claimed in any one of claims 1 to 19, wherein the insulation is provided with a layer of a braid material to provide high temperature insulation.

21. A composite tubing member as claimed in any one of claims 1 to 20, wherein the heating means comprises a self-regulating heating strip which increases its electrical resistance as the temperature increases.

22. A composite tubing member as claimed in claim 1, substantially as described herein with reference to, and as illustrated in, the accompanying drawings.