Assembly
Before starting the installation of a Hart-pipe system, it is necessary to carry out the physical inspection of the route with a precise delineation of the fracture points, as well as an inspection of the trench and the prepared sand bed, which must be free of hard, sharp, and coarse particles (sand fraction 1-8mm). Mounting pads lacking sharp edges are placed onto the prepared, levelled, compacted, and properly inclined bed with the thickness of 100 mm. The bottom of the trench is deepened by approx. 100 mm at the point where pipes connect to complete the joint. The tubes are placed in the trench so that after they are welded in the alarm system, the wires are axially connected (tin to tin, copper to copper wire). Pipes may only be welded by a welder who has the appropriate qualification certificate for welding work. The assembly work also includes adjustment, i.e. cutting off and, if necessary, adjusting the finishing piece. The pipe must be aligned on the axis in all directions.
The piping along the line is laid out according to a layout scheme where each component of the line is accurately identified. The method and symbolism of the markings, including the size of the anchors, are evident from the legend appended to the layout scheme. The dilatation of the bonded system (up to +130 °C) is carried out by means of compensating pads made of flexible moulded rubber or other elastic material, which capture the dilatation axial forces in bends. When installing a pre-insulated system, preheating must be carried out before the actual backfilling.
After the welding work is finished, anchors are constructed. Anchors must be set into the rising ground. The bottom of the foundation joint at the anchor is deepened so that the horizontal axis of the system in cross-section is at the centre of the block. In case of a multi-pipe distribution system (e.g. central heating and domestic hot water) or if an anchor is not placed on some of the pipes, the axial movement of the pipe must not be restricted at its location - this can be achieved by wrapping the pipe with cardboard, which enables the lengthwise dilatation of the pipe through the body of the anchor even after the anchor is concreted in. The directional routing of the pipe in front of the compensator is also handled this way. The compensator is fitted into the piping line in accordance with the layout scheme. Increased attention should be paid to the direction of its dilatation - this is shown on the compensator casing in the shape of an arrow, which must be oriented in the direction determined by the layout scheme.
Pressure tests can be started no sooner than 10 days after the completion of the concreting of the anchors and compensator guides. After successful completion of the pressure tests, the joints can be assembled.
For proper operation of the system, it is very important to thoroughly compact the pipe backfill material to at least 150 mm above the top of the pipe. Each pipe is covered with a green warning foil with a minimum 50 mm overlap across the diameter of the pipe on each side. With underground pipelines, it is essential that the pre-insulated piping system is backfilled as soon as possible. It may remain uncovered only for the time necessary for assembly. The effects of UV radiation cause significant dilatation of the HDPE sheath, in turn threatening to tear it away from the PUR foam, which can result in system failure.
Installation of watertight joints on the line of pre-insulated piping is carried out after a defectoscopy and pressure testing of the piping has been performed by trained installers. It is necessary to follow the prescribed procedure of joint installation and the procedure for the alarm system wiring. Perfect cleaning, degreasing, and drying of the joint area is important. Particular attention should be paid to drying out the joint area during rainy weather and in the summer months when dew can be present in the early mornings due to a temperature drop.