To preserve the energy efficiency of the pipeline in polyurethane foam insulation, it is important to correctly isolate the pipe joint. The most effective reliable way to seal the joints is a heat shrinkable sleeve (thermal coupling), made of the same material as the shell of the heating main. Our company manufactures thermocouples from heat-stabilized low-pressure and high-density polyethylene, manufactured according to GOST 16338. Coupling length – 500 mm, 600 mm, 700 mm and 1300 mm, diameter – from 110 to 1400 mm, all sizes are manufactured. The product has a certificate of conformity and test protocol for compliance with the requirements of GOST 30732-2006, EN-489-2003 and SP-41-105-2002 for the number of cycles equal to 1000.

The joint is a structure consisting of a one-piece polyethylene sleeve of increased diameter, seated during heat treatment to the diameter of the PE of the pipe shell. The coupling is welded to the shell using hot melt, and thus the joint is sealed and connected to the PE pipe. To create a heat-insulating layer, thoroughly mixed and metered PPU components are poured into the joint cavity between the coupling and the steel pipe.

The main errors in the installation of thermo coupling:

    Before welding butt joints of the pipeline in PU foam insulation, it is necessary to put a sleeve on the pipes. If the joints have already been brewed, and they have forgotten to put on the couplings, as an option, they use split couplings, which are welded with a manual extruder.
It is forbidden to remove the protective film, which protects the thermo coupling from UV exposure, prior to the isolation of the joint. Otherwise, in hot sunny weather, the clutch will heat up and its spontaneous shrinkage will occur.

Cooking surface.
Before proceeding with the installation of a thermal coupling, it is necessary to clean the surface of the polyethylene pipe shell from dirt so that the coupling can be moved along a clean surface. Then use a gas torch to dry the metal pipe and the ends of the insulation from moisture. In the presence of wet polyurethane foam in the insulating layer of the pipeline, the wet layer is removed around the entire circumference of the pipe.

We mount the conductors of the ODK system.
First, at the junction, it is necessary to fix the wires of the operational remote control system (UEC) with the help of racks and tape tape and clean them with sandpaper to a metallic sheen. Then insert the wires into the coupling so that their ends extend from opposite sides, and apply tension so that the conductors along the entire length of the joint deviate from their axis by no more than 5 mm. Compress the middle part of the coupling. Trim excess wires from the edge of the coupling at a distance of 2-10 mm. At the edges of the coupling to apply a neutral flux, and then solder the wires. As a result, the solder should evenly cover both the coupling and the wires.

Couplings on the joint!
Unpack and clean the thermal coupling on the center of the joint and mark its edges on the pipe shell with a marker. Use a coarse-grained emery tape to clean the edges of the coupling from the inside (to a depth of 100-150 mm) and the surface of the pipe shells on both sides from the mark to the edge of the surface. Wipe cleaned areas with a cloth moistened with solvent to remove the stripping products. Move the coupling 450-500 mm away from the joint, without subjecting the treated surface to contamination. Cut 2 strips from the hot melt adhesive glue, corresponding along the joint diameter L = 3.14D + 4 mm, where D is the diameter of the polyethylene sheath, L is the length of the hot melt adhesive strip. Then the flame of the gas burner to heat the surface of the pipe in the place of installation of hot melt to 80-100ºС. Control of heating is carried out with a piece of hot melt glue in several places (it should melt), but with obligatory control of the lower and side surfaces. The installation of hot melt glue is carried out according to Fig.1.


Fig. one

Before installing a strip of hot melt glue on the polyethylene sheath with a small force, it must be heated from the inside before melting. After that, push the coupling in such a way that its inner surface does not touch the hot melt adhesive. While heating both ends of the coupling uniformly on each side, to shrink it. It is prohibited to overheat the clutch, since overheating is accompanied by the appearance of a glossy bluish gloss on the clutch surface, and this, in turn, leads to a loss of the strength characteristics of polyethylene in the overheated area. Shrinkage is considered complete if there is no gap between the sleeve and the shell over the entire circumference of the coupling at a distance of 200 mm from the edge, and the molten glue protrudes from under the edges of the seated coupling.

Joint fill

Before starting to fill the joint, it is necessary to check the tightness of the joint by pressing the air with an overpressure of 0.5 bar. To do this, in the upper part of the coupling 10 cm from the center, you need to drill a hole with a diameter of 25 mm for small diameters of the shell (up to 315 mm) and 15 cm for large diameters. Install a pressure test device with a pressure gauge into this hole and produce air pressure in the butt of the compressor with 0.5 bar. Then around the perimeter of the edges of the coupling in excess to apply a soap solution. The joint underwent pressure testing if there are no bubbles along the edges of the coupling. Next, you need to drill another hole symmetrically to the first and begin to mix the components to fill. The temperature of the component immediately before mixing should be strictly 18-24 ° C. When mixing components for pouring joints up to 315 mm, it is necessary: Pour the contents of the isocyanate container into the container with the polyol, wrap the lid and vigorously shake the container for 20-30 seconds to mix the components. If the diameter of the joints is 400 mm or more, then it is necessary to pour into the container for mixing first the contents of the container with polyol, then the container with isocyanate and mix until a homogeneous mass for 20-30 seconds using an electric drill with a special mixing nozzle at the maximum possible speed. Pour a homogeneous mixture of components into the joint and install plugs to vent air into the holes. After curing of the foam, remove the plugs, clean the holes and process with a conical cutter. Not earlier than 30 minutes after the end of pouring, brew the holes in PE with stoppers.

All work on the insulation of butt joints should be carried out by specialists. It must be remembered that with strict observance of the technology for the construction of pipelines in PUF-insulation and a well-performed installation, the thermo-coupling heating main will serve at least 30 years without accidents and leaks, with high heat-resistant performance and significant savings in maintenance money during operation.

2. Instructions for use of the Component packaged for filling joints of all sizes.

Polyurethane (foam) is a ready-to-use product that is neglected.

By mixing the two components

A polyol bottle is transparent PET.

Used case-plastic matt packaging,
For blending, polyol (transparent PET bottle) must be carefully poured into fertilizer (plastic matt container). Hermetically close the lid and continuously shake for 20-30 seconds. During thorough mixing, a reaction occurs when mixing the two components. It turns PENA (polyurethane).

Then pour the finished product (polyurethane) into the technological opening of the heat shrinkable sleeve.

The temperature of the mixed components should be 18-24

CAUTION! Avoid direct contact of the component with unprotected skin. In case of contact with eyes, rinse with plenty of water and seek medical attention immediately.