The pre-insulated (geothermal) pipe is a light pre-insulated pipe that is very easy to join and install, minimizes energy loss and reduces costs in the future. It is used especially for retrofitting in new buildings. It is insulated by using high-energy foam. Thus, its efficiency also increases. Insulated pipes are widely used in district heating systems and hot water supply processes. Pre-insulated pipes generally consist of 3 basic parts. These 3 parts are a steel pipe called a service pipe, a heat insulation layer and an outer casing. The purpose of heat-insulated pipes is to maintain the heat of the transported material inside.
The quality of pre-insulated pipes is very high. It is also very comfortable to use. Pipes with the latest technology are produced in accordance with TS EN 253, TS EN 448, TS EN 12201-2 + A1 international standards. In heat-insulated pipes, polyurethane foam is used to provide insulation between the carrier pipe and the sheath pipe. Polyurethane material absorbs thermal expansion tensions and also transfers the friction between the soil and the outer casing to the carrier pipe. In heat-insulated pipes with this feature, there is no need for a compensator, which is a separate part. Since the heat-insulated pipe consists of different materials, it belongs to the composite pipe group.
The inner part of the pre-insulated pipes is the carrier pipe, the second layer is polyurethane foam and the last and 3rd layer is a protector made of high-density polyethylene (HDPE).
The thermal conductivity of the foam, which is a thermal insulation material, is approximately 0.024-0.033 W/(m-K), λ 50. According to the European standards EN 253:2019 & EN 15698-1:2019, thermally insulated pipes should be prepared to withstand a constant temperature of 120 °C (248 °F) for 30 years. Insulated pipes are commonly installed from pipes of 6 meters (20 ft), 12 meters (39 ft) or 16 meters (52 ft) in length. They are also commonly buried to a soil depth of 0.6-1.2 meters (2 ft 0 in).
Pre-insulated pipes, also called geothermal pipes, are produced in three layers. These layers consist of carrier pipe in the inner part, insulating material polyurethane layer (PUR) as the 2nd layer and the outermost layer consists of Polyethylene (PE) pipe as a protective sheath. If we explain these layers;
The material in the carrier pipe can vary according to the usage temperatures. In the inner layer, Polypropylene Random (PPR) pipe is used if the usage temperature is at or below 70 °C, and steel pipe is used if the usage temperature is at or below 140 °C. In standard production, the carrier pipe material is steel. Steel pipe, ERW (longitudinally welded) P235TR1 and P235TR2 grades, SAW (spiral welded steel pipe) pipe and seamless pipes are in P235GH quality.
Some of the carrier pipe materials are as follows:
Thermal insulation is provided by using polyurethane. Polyurethane rigid (solid) foam consists of a mixture of polyol and isocyanate components in a certain ratio. The components are injected under pressure.
The polyurethane foam material used as insulation material in pre-insulated pipes is purchased from manufacturers that comply with EN 253 standards. It has a cell structure that does not absorb water. It has a heat conduction coefficient [(50°) <0.026 W/(mK)] which provides heat saving. The heat conduction coefficient remains constant throughout the insulation life (min. 30 years).
According to TS EN 253 standard, the foam core density of polyurethane insulation material is a minimum 60 kg/m3 and holistic density ≥80 kg/m3. Compression resistance strength≥0,3 N/mm2 and axial shear strength ≥ 0,12 N/mm2. The shear strength of the insulating material along the perimeter is ≥0,20 N/mm2. Polyurethane can be continuously processed from the temperature of the fluid to be transported through the pipe up to 120 ˚C up to 140 ˚C.
Heat loss in polyurethane insulation is very low. The operating cost does not change during the insulation process. The insulation material, which is simple to install, saves time and reduces labor costs. Labor errors are thus minimized. Since it is applied by being buried in the soil, there is no need for a gallery.
Connection extension parts (compensators) are either not used or minimally used according to underground laying and spreading methods. Heat bridges do not occur in the applications on the cantilever in the inner zone of the gallery where the bearings are applied on the outer zone casing.
In the outermost region, there is an extruded polyethylene sheath pipe with a roughened inner surface that protects the insulation material from external factors and chemicals. Casing pipes are manufactured with HDPE (High-Density Polyethylene) 100 raw material, which is 100% original, high-density polyethylene in accordance with TS EN 253- TS EN 12201-2 +A1 norms. It stands out with its high resistance to abrasion and resistance to impacts. HDPE is obtained from petrol. It is much more solid than different polyethylenes, heavier and harder than strong and low-density polyethylenes. HDPE is lighter than water.
The sheath pipe used as a casing has the characteristics of UV-doped, black, high-density polyethylene, density > 940 kg/m3. High-density seamless polyethylene pipes in terms of size and properties are produced in accordance with TSE EN 253 standard. With the corona application, the sheath is attached to the pipe and does not separate, and the continuous connection is protected with PUR solid (rigid) foam. Tensile resistance provides assurance up to -50 degrees.
Pre-insulated pipes are prepared as one piece in the factory of the production company. PPR pipe as the main carrier pipe is produced in extrusion lines, which is a plastic forming system used for forming. Production is continued by placing it into the mass production system. Leakage sensor wires are placed on the PPr pipe consisting of random copolymer polypropylene material with axing parts. Polyethylene (PE) pipe is passed over the parts placed after the axing process. In the part between the inner transport pipe and the threaded casing, the mouth areas are closed for printing polyurethane material.
There are holes on the pipe for pressing pur. The polyol and isocyanate liquids forming PUR are mixed with the machine and pressed with a special dosing pump. The 2 reacting liquids swell and expand. Thanks to the foam pores filling the space between the steel pipe and the sheath pipe, it acquires a structure that does not conduct heat. After the solidification of PUR, bur production is completed. Steel pipe can be used instead of PPR pipe. If a steel pipe is to be used, the same processes are performed on the steel pipe supplied by another manufacturer. The outermost sheath pipe, which must be resistant to the pressure created by the polyurethane material, must have dimensions to meet the standards. For this reason, production must comply with TS EN 253 norms.
The product is produced manually without the need for a pipe intermediate unit (fitting). The carrier pipe in the inner layer is produced by injection or confection method and placed inside the product. If steel is used as the carrier pipe, epoxy paint, which is a paint formed by adding barite, titanium, color pigments, and surface agents into the resin obtained from a chemical substance, can be applied on the outer surface and, if desired, on the inner surface of the steel pipe after the mechanical cleaning process.
Geothermal pipes consisting of steel or PPR pipe, polyurethane foam, and polyethylene sheath are manufactured as a whole. The production, transport, and installation of geothermal(heat-insulated) pipes is a process that must be followed meticulously. It is necessary to pay attention to protection in all of these processes. During the evacuation and unloading of the pipes, the workers performing the process should not step on the pipes and should not put weight on them. When lifting during unloading, the steel pipe should be held by the steel pipe assembly or the transport hooks should be attached to the steel pipe.
If the necessary care is not taken, there is a risk of damage to the pipes by falling or crashing. Heat-insulated pipes should be unloaded in a dry and unshaded area. The stock period of the pipes should not exceed 6 months. As far as possible, the pipes should not be stacked on top of each other during stacking, and if they must be stacked, the number of rows should be very small. In order to prevent damage to polyethylene pipes, wedges can be placed between steel pipes.
The installation of heat-insulated geothermal pipes should be carried out by an expert team with the help of joining sets, elbows, T-pipes and reducers. It is important that the assembly materials to be used and the pipe to be the same in order to adapt to each other. Joining materials to be used in assembly are as follows:
Special diameter prepared pipe with holes having two plugs similar to a sleeve
The required amount of polyurethane compound
Two heat shrinkable tapes
Pre-insulated, geothermal pipes can benefit the projects you want to implement. With technological developments moving to a new stage every day, pre-insulated pipes have started to be used in ship projects. This approach can be used in the construction of new ships as well as in the renewal of already-used lines. The use of pre-insulated pipes can be a good solution for the elimination of adverse conditions caused by salt water reaching due to waves, high winds, excessive rain, heat and human traffic.
Pre-insulated pipes have also found their use in the ship industry. As in every field where it is used, it has many usage advantages in the ship industry. For example;
Pre-insulated pipes, also known as geothermal pipes, package pipes or pre-insulated pipes in the sector, have an insulation life of 30 years at a continuous operating temperature at 120 ° C, 50 years at a continuous operating temperature at 115 ° C and more than 50 years at temperatures below 115 ° C when they are made of TS EN 253 norms.
Pre-insulated geothermal pipes can be used for transports with fluid temperatures up to 140°C.
If the fluid temperature is above 140°C, the thermal insulation pipe is used by making a rockwool-PUR combination.
Heat-insulated pipes made of steel can be used to transport steam.
Heat-insulated pipes that prevent heat transfer from inside to outside and from outside to inside can also be used in cold fluid transport. Cold fluids are delivered to the consumers in need with pre-insulated pipes without heating.
In pre-insulated pipe systems, compensators, which are a tool that prevents dimensional change and eliminates the problems caused by heat-related expansion and contraction in the pipeline, are not used. Because in pre-insulated pipes, expansion and elongation of the pipe in the inner region are absorbed by soil friction forces, compensators are not required.
Since no compensator is used in pre-insulated pipes, soil friction forces are utilized to pull in the pipe elongation. For this to happen, polyurethane foam must react chemically with both steel and polyethylene and bond. This is exactly where the corona process is performed to establish the bond between polyurethane and polyethylene. Compensators must be used in applications without corona.
Since pre-insulated, geothermal pipes are laid by burying under the ground, the process is carried out without opening a gallery. In case of gallery opening, pipe elongation should be emphasised.