DE3140695A1 - Method for laying pipelines for hot media - Google Patents

Abstract

In a method for laying pipelines, which are pretensioned by electrical heating of the inner pipe and in which the forward and return line are laid parallel to one another, the inner pipes of the forward and return line are electrically conductively connected to one another at the ends. A voltage is applied to the ends of the inner pipes which are remote from the connection point and, in the event of non-uniform expansion of the forward and return line, a parallel conductor is connected to the line having the greater expansion at the flow inlet or outlet end.

Description

Procedure for laying pipelines for hot media

The invention relates to a method for laying pipelines for hot media, preferably from a metal inner tube carrying the medium made of steel, an outer tube made of plastic, preferably polyethylene and one between the inner pipe and the outer pipe consists of a layer of thermal insulation material, which creates a force-fit connection between the inner and outer pipe, preferably made of in situ foamed plastic based on polyurethane or polyisocyanurate, in which the individual pipe sections are connected to one another, and the laid Pipeline elongated by heating the inner pipe using electrical energy and is fixed in the elongated state, and in which a supply and a return line laid parallel to each other.

In a known method (DE-OS 27 07 799) the tubes are on-a Heated temperature, which is approximately the middle temperature between the laying temperature and the operating temperature of the pipeline corresponds to At this temperature the pipes, for example in a Trench are laid with Earth covered. Both at the later operating temperature and when it cools down the mechanical that then occur in the pipeline remain at the ground temperature Stresses sufficiently far below the yield point of the metal of the inner pipe. The inner pipe can be heated up, for example, by means of heated water, the disadvantage of this method is that large amounts of water are required, which have to be heated up as a heat transfer medium. Furthermore, the attachment and removal of connections for the water cycle is quite complex. It seems more advantageous therefore, to make the heating of the inner tube by electrical energy.

The invention is based on the object of the method of the opening paragraph mentioned type to the effect that this is carried out in an economical manner can be and that it is ensured that both flow and return line expand evenly.

This object is achieved in that the inner tubes of the front and Return line are electrically conductively connected to each other at the end that on a voltage is applied to the ends of the inner tubes facing away from the connection point and that in the event of an uneven expansion of the supply and return lines the line with the larger extension has an impact conductor on the current supplying or discharging The end is closed. The main advantage of the invention is to be seen in that the flow and return lines of a pipeline run simultaneously from one end starting to be heated and that with an uneven expansion as a result of uneven resistances these can be adapted to one another. The mentioned resistance differences arise, for example, from dimensional tolerances and fluctuations in the specific Resistance of the line pipe here. Because of the resistance difference the current heat developed in the individual pipe sections is different, what has an effect in different temperatures, which are also reflected in longer constant heating does not balance completely within the pipeline. The sizes of the temperature-related Expansion differences within a pipe string are within the scope of the safety factor tolerable, the total elongation of the Strar .- = - s should, however, correspond to the theoretical value An accumulation of negative resistance deviations in the supply line with simultaneous accumulation of positive resistance deviations in the return line leads to an overall higher temperature of the return line and thus to a higher elongation. The parallel conductor is used here in a particularly simple manner Compensation for such deviations.

A multi-core copper conductor is particularly advantageous as a parallel conductor used, the individual wires of which are electrically isolated from each other. To this In this way, a finely graded correction is possible by adding a or more wires are connected. The invention is based on the in the figure schematically illustrated embodiment explained in more detail The figure shows a District heating line, which consists of a flow line 1 and a return line 2 Both the flow line 1 and the return line 2 are made up of a large number of pipe lengths constructed, which consists of a metallic inner tube 3, preferably made of steel, a concentrically arranged outer jacket 4- made of polyethylene and one between the inner pipe 3 and the outer jacket 4 are made of a layer of polyurethane foam the individual conduit pipe are made by, for example a steel pipe of approx. 12 m length is arranged concentrically to a polyethylene pipe and fills foamable polyurethane into the annular space. By foaming in In situ, the polyurethane foam sticks to both the steel pipe and the polyethylene pipe, so that a force-fit connection between the steel pipe and the polyethylene pipe will be produced. To form the pipeline section shown 1 and 2 are "e inner tubes 3 are welded together and the connection point is known per se Way insulated. The laying of the pipelines 1 and 2 is done in advance suspiciously in a ditch.

After completion of the pipeline strands 1 and 2, the inner pipes 3 at one end, as shown at 5, electrically connected to each other and on their ends facing away from the connection point 5 are connected to a power generator 6. Sn longitudinal direction of the feed line 1 or

of the return line 2, a five-wire line 7 is laid and connected to the ends of the inner tubes 3 facing away from the power generator 6. Will the power generator 6 is now turned on, a current flows through the inner tube 3 of the flow line 1 via the connection point 5 and the inner tube 3 of the return line 2 back to the power generator 6.

Due to the resistance of the inner tubes 3, they heat up and expand from. In the expanded state, the trench is filled with earth and the power generator 6, the connection 5 and the line 7 removed. By frictional engagement with the ground flow and return lines 1 and 2 remain in the pretensioned state.

Due to different resistances in the inner tube 3 of the flow line 1 or the return line 2, the lines can expand differently 1 and 2 are coming. Around to compensate for this difference in resistance, is attached to the strand with the greater resistance, d-oho the greater extension one or several wires of the line 7, in the figure this is the return line 2, connected in parallel.

A partial current now flows through the wire or wires of the line 7th

Typical operating data for this process using the example of a DN pipeline 150 are: Pipe type: Outer diameter: Wall thickness: 4.0 + 0.45 / -0.35 mm Pipe length: 300 m flow + 300 m return Laying temperature: Operating temperature: 130 OC Pre-tensioning temperature: (1300 + 10 °) / 2 = 70 0C warming umo. 60 k specific elongation: 12. 10 ~ 6k 6k -n 1 stretch: 300 m. 60 k. 12. 10 k 0.216 m resistance per m: at ° C R # 0.08. 10 - 3 @ / m at 70 ° C: R # 0.11. 10-3 # / m total resistance: at 70 ° C: 600 m. 0.11 . 10-3 / m = 0.066 # Maximum heating voltage tVDE): 42 V Heating current strength: 42 V; 0.066 = 636 A heating output per m: 45 W / m By the example for filamentous Line 7 allows a finely graduated correction to be made by the line Depending on the requirements, one or more wires can be connected.

If one of the free wires at the front end is successively connected to a voltmeter against the connecting lines of the flow line and return line, the partial voltages in the flow Uvl and return UR1 can be measured. From this and from the heating current I, which can also be measured, the outputs in the flow PV and return PR can be calculated: PVl = Uvl 1 P Rl = URl II If P 6 PRl, the different expansion to be expected must be corrected. There are also the resistances from Vorlauf and rewind are known, based on the assumption that P2 = PR2, the desired changed partial voltage can be calculated: UR2 = U UV2 [v The resistance of the parallel-connected line RL is calculated as follows: The meter resistance of the Skhuntleitung results with the and the cross-section of the shunt line Carrying out the calculation for the above example with the stipulation that an expansion deviation of 10% is to be compensated (PR1 = 1.1. PVl) leads to a 2 cross-section of the shunt line AL = 18 mm. By using a cable of 4 mm each, a fine adjustment is possible.

The inventive method can be used in the same way for Use piping systems in which one or more metal pipes inside a metal pipe are arranged (steel jacket pipe method). Essential here is, however, that the inner tube or the inner tubes are electrically insulated from the outer tube are relocated.

Blank page

Claims (2)

P a t e n t a n s p r ü c h e 1. Procedure for laying pipelines for hot media, preferably from a metal inner tube carrying the medium made of steel, an outer tube made of plastic, preferably made of polyethylene, and one between the inner pipe and the outer pipe consists of a layer of thermal insulation material, which creates a non-positive connection between the inner and outer pipe, preferably made of in situ foamed plastic based on polyurethane or polyisocyanurate, connected to each other at the individual pipe section, and the laid pipe elongated by means of heating the inner tube by electrical energy and in the elongated State is fixed and in which a supply and a return line are parallel are laid to each other, characterized in that the inner tubes of the front and Return line are electrically conductively connected to each other at the end that on a voltage is applied to the ends of the inner tubes facing away from the connection point and that with an uneven expansion of the front and back conduit Connect a parallel conductor to the line with the larger extension at the power supply or - outgoing end is connected. 2. The method according to claim 1, characterized in that as a parallel conductor a multi-core copper conductor is used, the individual cores against each other are electrically isolated.