CA1224018A - Method of establishing sealed pipe lengths of plastic pipes by joining of pipe elements, particularly district heating pipe lengths - Google Patents

Abstract

A B S T R A C T :

By the construction of pipe lines having an outer, sealed mantle tube of plastics and being made of joined, prefabricated pipe elements, particularly heat insulated pipe elements, various types of sealing problems occur in local surface areas of the plastic tubes. According to the invention it is proposed to overcome these problems by drilling out the said local areas into conical holes, which are thereafter closed entirely sealingly by means of complementarily conical stoppers, which are welded into the holes by a welding technique resulting in a surface-to-surface welding between the stoppers and the hole surfaces.

Description

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The present invention relates to a method of establish-ing pipe leng-ths of plastic pipes by joining of prefabricated pipe elements, preferably heat insulated pipe elements having an outer mantle pipe of plastics, whereby by said ~oining it is desirable to utilize or provide such holes therein, which are later on closed in a fully sealed manner.

By the establishing of district heating pipe systems by means of prefabricated insulated pipe elements it is customary that the pipe elements are provided with one or two interior con-ductor pipes, which endwise protrude from a surrounding insula-tion material and from the ends of an outer mantle pipe sur-rounded the insulation material, and that the pipe elements are ~oined by welding together the respective conductor pipe ends and thereafter mounting an outer connector tube between the mantle pipe ends at the joint, whereafter the space inside the connector tube is filled with an insulating foam material produced by pour-ing a foaming liquid down through a hole in an upper wall portion of the connector tube. Upon the foaming of the liquid the hole is to be closed absolutely tightly, such that intrusion of exter-- nal moisture will be excluded for many years. The connector tube may consist of metal, but usually it is sufficient or desirable that it consists of plastics, and in such cases the connector tubes will constitute plastic pipe pieces which are to be joined to other plastic pipes, viz. the mantle pipes. As described below, by such joining of plastic pipes the desire as to provi-sion and sealed closing of holes therein may have purposes other than enabling the introduction of a foam material; the basic problem will be the same, however, viz. that an existing or a provided hole in a wall portion of a plastic pipe is to be closed in an entirely sealed manner.

On this background the present invention provides a method of ensuring a really sealed closing of a hole in the wall of a plastic plpe. For this purpose a stopper has been used, which by passive or active clamping in or in-to the hole has been 3, ~

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able to close the hole, but according to the invention it is desirable to effect the closing by a real welding ln of a stop-per, because any better closing is hardly achievable when the welding is effectable in a really efficient manner. Thus, it is decisive for the invention that the closing of the hole shall take place by welding in of a stopper, which in practice, there-fore, should consist of a weldable plastics material.

Now, parts of plastics may be welded together by vari-ous welding methods, e.g. by the welding in of a plastic strip lnthe joint area between the parts to be ~oined, and beforehand the invention is restricted to the use of a special and particularly effective welding method, viz. a so-called mirror welding, whereby the surfaces to be joined are formed or machined to fit each other exactly and are heated prior to or during the joining in such a manner that by the ~oining the surfaces will be sub-jected to a welding together without the use of extra welding material, the joint hereby being extended all along the adjoining surfaces as a whole and not only being active in a border area.
Thereof, such as achieved by the welding in of a ~oining strip from the accessible side of the joint.

According to the invention care is taken that the hole in the wall of the plastic pipe appears as or is cut as a hole having an outwardly conically diverging wall shape, while a plas-kic stopper for closing the hole shows a correspondingly conical outer wall, and that immediately before or by the lnsertion of the stopper into the hole , \ - 2 -~z~

a welding heating of the relevant surface or surfaces ls effectual.
Preferably this heating is effected by means ol a spec:Lal mirror welding hollow body tool, which is conica~ both on its in-terior and exterior side, and which is used, in a heated condition, to heat both the hole wall surEace and the outer stopper surface. Alternatively, a fullY usable surface heating is achievable by sending an electric current through one or more heatingwires which are located on or embedded in the relevantsurface if desired with the use of a special stopper preparell accordingly.
Above it has been mentioned as an example that ~ile hol~ in question-is used for -the filling in of a frall1lng liquid, but in the discussed-connection there will b~1 other important fields of application of the inventlon.
Thus, in case of welded joints oE plastic pipes the method may be used for enabling a welding control,the~.
hole then being provided across a welding seam and thereafter being closed upon inspection of the seam cross section. The hole may be provi~ed in -two s-tages,~irst by taking out a cylindrical bore probe for inspection and then by machining the hole conical prior to the clos:lng thereo~.
Ano-ther important application of the method according to the invention relates to the provision of a complete seal:Lng o~ such a small pipe wall area which would otherwise be diEficult to seal- This may be actual where a longitudinal welding seam in a~welded-in connector skirt meets wi-th the ajoining round going welding seams, or where a roundgoing welding is effected by means of a welding strip member, which may show a sealing problem adjacent its own intermeeting ends. Ins-tead oE seeking to fully weld together the ma-terial portions at such difficult welding areas it may be considerably easier just to drill out the relevant areas and close the ?.,i resulting holes by a welding operation according to the inven tion.

The present invention will be further described wlth reference to the accompanying drawings, in which:-Fig. 1 is a perspective view of a pipe ~oint;

Fig. 2 is a perspective view of one embodiment of the present inventiOn;

Fig.s 3 and 4 are associated sec-tional views illustrat-ing the mounting of a stopper by mirror welding;

Fig.s 5, 6 and 7 are corresponding sectlonal views of modified systems;

Fig. 8 is a perspective view of an alternative pipe joint; and Fig.s 9-11 are views of another pipe joint.

In Fig. 1 is shown a conventional joint between two district heating pipes 2 having endwise projecting inner conduc-tor pipes generally designated by the reference numeral 4, whlchare welded together as a first stage o-f the joining operation.
The pipe ends 4 pro;ect from an insulation material 6 which is surrounded by an outer mantle tube 8 of a plastic material. Then a mantle connector tube 10 of a plastic material is pushed over the -Joint from a prelocated position about one of the mantle tube ends and the connector tube 10 is shrunk to be endwise tightened about the ends of the mantle tubes 8. Thereafter a foaming liquid is poured through an upper hole 12 in the connector tube 10, and the hole 12 is closed by a stopper 14 when the space inside the connector tube has become filled with foam.

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According to the invention the closing of the hole is effected by machi.ning the hole wall lnto a conical shape and by using a correspondingly conical stopper 14 of a plastic material which is prepared by surface heating for insertion welding into the hole 12.

A preferred heating method is illustrated in Fig.s 2 and 3. Use is made of a conical tube body 16 consisting - 4a -

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of iron or another material which is well suited to give ofE heat energy, upon being heated, from its surfaces to the outside oE the correspondingly conical stopper bod~
14 when the latter as shown in Fig. 3 is placed inside the tube body 16 and to the edge surface of the hole 12 by insertion of the tube body therein, respec-tively.
Preferably the hole 12 -s provided by conical drilling or cutting such that i-ts edge surface will in advance show the same conicity as the tube body 16, although smaller deviations in this respect may be corrected Eor by way of forcing the heated tube body 16 into the hole 12. The tube body may be heated to a well defined temperature in a suitably adapted heating apparatus ~not shown~, which is placed ne~r the mounting site, and in practice it is possible -to achieve a high quality welding when the tube body 16, wi-th the use of the handle 1~ as shown in Fig. 2, is rapidly moved from the heating apparatus to the position shown in Fig. 3, in which the inserted stopper 1~ is forced more or less firmly against the tube surface, cand when the parts are separated after a short, predetermined time interval and -the stopper 14 is immediately thereafter forced into the hole 12 as illustrated in Fig. 4. I -the relevant parts are prepared with smooth and regular surfaces it will be possible by this mirror welding technique to produce a first class welding under fully acceptable temperature and pressure conditions of the plastic material.
It may be sufficient to effect a heating of only one oE the surfaces to be ~oined When the sto~per 14 is somewhat longer than the thiclcness of the material around the hole 12, then the diameter tolerances oE the various parts ~ill not be critical because of their conical shape.
It will oE course be possible to use welding tools corresponding to the tube body 16 directly provided or connected with heatlng means, which ensures , .
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a well defined temperature of the tool in its position as shown in Fig. 3.

In Fig. 5 is shown an embodiment, in which the s-topper 14 is provided with a built-in electrical hea-ting wire 20 extend-ing through windings down along the outer stopper surface immedi-ately ad~acent or inside the surface and having outer connector wires 22, which are connectable to a current source for electri-cal heating to the outside of the stopper prior to or during the insertion of the stopper into the hole 12. In such a case sur-face- or rnirror welding may be achieved without the use of any special mirror welding tool.

In the arrangement shown in Fig.s 6 and 7 a conical intermediate ring member 24 made of a plastic material is used and is provided with a heating wire in a similar manner as the stopper in Fig. 5. It will be understood that this member 24 may, in a well controlled manner, be caused to become heated even to initial melting prior to or during the insertion of the stop-per 14, whereby the ring body 2~ will constitute a lasting weld-ing tool in the ~oint (Fig. 7).

Fig. 8 shows that a connector tube consists of a sheet member 26, which has, by any suitable welding technique, been welded in between the ends of the mantle tubes 8, flush therewith along annular welds 28, e.g. according to our ~uropean Patent Application No. 80201208.8 published June 24, 1981. Normally such a flush welding in will require an additional longitudinal weldlng of at least one butt seam 30. At those places where the butt seam 30 abuts the side of the annular welds 28 problems may exist with respect to the attainment of a completely sealed weld-ing, and according to thQ invention these problems may be over-come in an easy manner by drilling out the relevant local areas to form holes 12 as shown in dotted lines, whereafter these holes are closed by welding in s-toppers as described above.

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In Fig . 9 is shown a pipe j oint, in which the - 6a -~L~Z4~8 abutting plastic tube ends are welded together by means of a separate welding strip 32, wh'ch is laid around the joining area 34 and is welded to the outer surfaces of the opposed mantle tube ends. The welding strip 32 will present its own joint 36, Fig. 10, and with usual welding techniques for the annular welding of the strip 32 this joint will not automatically be welded, i.e. the possibility of a leak will exist.
According to the invention, however, this undesirable possibility will be easily avoidable by machining or drilling out the joint area 36 to form a hole 12 as shown in dotted lines, whereafter this hole is effectively closed by means of a stopper 14 as shown in Fig. 11 and in accordance with the technique according to the invention. It will be unimportant that the welding strip is located on the outside of the mantle tube ends, since according to Fig. 11 a full welding contact will exist between the stopper 14 and the adjacent surfaces of both the mantle tubes and the opposed ends of the strip 32 when these ends are formed by the through-going drilling of the hole 12 (Fig. 1~).
The term l'welding" as used throughout this specification should not necessarily designate a heat welding, since it will be within the scope of the invention to make/use of other welding methods, e.g.
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cold welding or~ by means of suitable binding agents and suitable application methods therefore.

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of establishing sealed pipe lengths of plastic pipes by joining prefabricated pipe elements having an outer plastic tube in which on join-ing the plastic tubes holes are provided therein which are thereafter sealingly closed, the improvement in which each of said holes is provided by drilling or cutting an out-wardly conically opening hole in the wall of the plastic tube and the hole thus provided is closed by means of a corresponding conical stopper of plastics, the conical outside of which is heated or treated for sealed welding to the hole wall by insertion of the stopper into the hole.

2. A method according to claim 1, in which the outside of the stopper is heated by means of a conical welding mirror immediately prior to insertion of the stop-per.

3. A method according to claim 2, in which a conical hollow body is used as the welding mirror, the interior surface of which is used for heating the outside of the stopper while its exterior surface is used to simul-taneously heat the wall of the conical hole.

4. A method according to claim 1, in which the heating of at least one of the surfaces to be joined is effected by sending an electric current through one or more heating wires locked on one of said surfaces or embedded therein, such that the wire is welded in in a lasting manner by the insertion of the stopper.

5. In a method of joining plastic pipes by welding, whereby juxtaposed ends of the plastic pipes are welded together along a peripheral annular welding zone presenting a discontinu-ous meeting area between continuous or uniform welding zone por-tion extending to both sides of said meeting area, the method comprising the steps of drilling or cutting in the material of the pipe, in situ, an outwardly conical opening substantially covering the meeting area so as to expose effectively welded weld seam cross sections on a side of the opening, and closing the opening by a conical stopper of a plastic material by heating a conical outer portion thereof and forcing the conical stopper into the opening to thereby endwise seal each of said effectively welded weld seams individually as well as mutually.

6. A method according to claim 5, in which said dis-continuous melting area is represented by an area in which opposed ends of a welding strip laid around the joining area are located next to each other.

7. A method according to claim 6, in which the conical opening is drilled or cut through opposed welding strip ends such that these ends will thereafter present part-frusto conical sur-faces with the conical opening as sharing generators with the conical opening in the pipe material.

8. In a method of establishing a heat insulated, sealed pipe length of prefabricated pipe elements including at least one interior conductor pipe having a surrounding heat insu-lation and an outer mantle tube of plastic material, whereby the juxtaposed ends of the conductor pipe or pipes projecting from the corresponding ends of the mantle tubes are joined by welding, whereafter the adjacent ends of the mantle tube are intercon-nected by an axially split connector tube of a plastic, the opposed ends of which are welded along respective annular welding zones, to ends of the mantle tubes, while also the axial split of the connector tube is closed by welding along the axial welding zone, the opposed ends of which are located close to respective portions of the annular welding zones, in a meeting area therewith, the method compri-sing the steps of drilling or cutting in the pipe material, in situ, an outwardly conical opening substantially covering the meeting area so as to expose effectively welded seam cross sections on a side of the opening, and closing the opening by a conical stopper of a plastic material by heating a conical outer portion thereof and forcing the conical stop-per into the opening to thereby endwise seal each of said effectively welded weld seams individually as well as mutually.

9. A method of establishing sealed pipe lengths of plastic pipes by joining prefabricated heat insulated pipe elements including at least one interior conductor pipe having a surrounding heat insulation and an outer mantle tube of plastic material, the method comprising the steps of welding juxtaposed outer mantle tubes so as to join the same to-gether, said welding being effected along discontinuous weld-ing seam areas so as to provide for at least one unwelded seam area, drilling or cutting, in situ, an outwardly conical opening in a meeting area of the discontinuous welding seam so as to expose effectively welded weld seam cross sections on a side of the opening, and closing the opening by a conical stopper of a plastic material by heating a conical outer por-tion thereof and forcing the conical stopper into the open-ing.

10. A method according to claim 9, wherein the weld-ing seams are butt seams between adjacent wall portions of the outer mantle tube.

11. A method according to claim 9, wherein the welding seams are located at an outer surface of the outer mantle tube, between said outer surface and an outer welding strip means as welded to the outer surface, and wherein the concial stopper welded in the hole is also welded to edge surfaces of the welding strip means created by the hole dril-ling or cutting.