Pre-Insulated Pipes

What is a pre-insulated (geothermal) pipe?

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).

What is the structure of pre-insulated (geothermal) pipes?

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;

Carrier Pipe (Inner layer)

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:

Rigid (Solid) Polyurethane (PUR) Insulation

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.

Sheath Pipes:

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.

Production of pre-insulated (geothermal) package pipes

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.

Features of pre-insulated package pipes

  • Heat-insulated (geothermal) pipes are manufactured as fabricated.
  • They are home and non-domestic district heating pipes in accordance with TS EN 253 norms.
  • They maintain the temperature/coldness of the fluid transported through pre-insulated pipes.
  • It can be applied both in geothermal water heating and in central heat plants.
  • Heat-insulated pipes consist of carrier pipe, polyurethane foam (heat insulation material) and sheath pipe.      
  • As carrier pipe; welded pipe (ERW), spiral welded steel pipe (SAW), seamed or seamless steel pipe, stainless steel pipe, copper pipe, high-density polyethylene pipe (HDPE100), PPR, PPR-C, GRP (glass fiber reinforced polyester pipe) and glass fiber reinforced epoxy pipe (CTE) are used.

Application areas of pre-insulated (geothermal) pipes

  • Geothermal heating and cooling systems
  • In central heating systems
  • In a gallery or underground pipe systems
  • Fire lines
  • In industrial plants
  • Greenhouse applications
  • In oil lines and gas transmission systems
  • Hotels and tourism applications
  • Military installations
  • Ship and marine vessel installations
  • In mass housing structures
  • It can also be used in various cooling systems.

How are geothermal pipes protected?

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.

How to install pre-insulated 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

Advantages of using pre-insulated geothermal pipes

  • Heat loss during the transport of the fluid is at a very low level.
  • Easy to use, transport and installation is simple.
  • Resistant against corrosion.
  • It can last continuously at a temperature of 120 °C for over 50 years. .
  • Thanks to its heat conduction coefficient and polyurethane foam, heat loss is very low compared to other classical systems.
  • No leakage due to the use of high density (HDPE) sheath pipe.
  • Reinforced concrete, duct, gallery, gallery, support operations that cause the cost to increase are not performed.
  • Laying time of heat insulated pipes is less than other classical systems.
  • Insulation thickness is equal in every region.
  • Pipes and connection fittings are manufactured in accordance with TS EN 253, TS EN 448, TS EN 12201-2 + A1 standards and these dimensions are tested and controlled in the laboratory.
  • Thermal insulation pipes are meticulously and safely protected and transported from manufacturing to installation.
  • Underground and above ground moisture does not affect the insulation material.
  • The insulation period against external damaging effects is at least 30 years.
  • In the application, corona treatment is performed and thanks to this, a chemical bond is established between the polyurethane foam and the sheath pipe. Thus, the elongation of the carrier pipe is prevented from damaging the insulation by acting as a single piece in thermal expansion.
  • With the help of the structure applied as a single piece, soil creep forces and steel pipe elongation are prevented.
  • Polyurethane, the insulation material, conforms to EN 253 standard. 
  • It is designed for fluid transport at 140°C temperature.  
  • There is no need to use compensator.
  • Sliding sheath system can be used to prevent leakage at the joints and to protect the insulation. Thanks to the sliding sheath system used at the joints, leakage at the joints and deterioration of the insulation are eliminated.
  • Since the heat insulated pipe is completely made and prepared in the factory, problems such as poor quality and prolonged assembly time caused by construction site conditions are not encountered. 
  • Problems that may occur with water filling of the channel are not seen. 
  • It has international certificates (GEF)
  • Thermally insulated geothermal pipe can be used for transporting waste heat generated in district heating, geothermal energy systems and cogeneration applications.

The use and advantages of pre-isolation geothermal pipes in the shipbuilding industry

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;

  • It withstands temperatures ranging from -200°C to +315°C.
  • No energy losses.
  • It is made in a way not to be damaged by chemical substances.
  • It has high resistance against ultra-viola rays.
  • It has corrosion-resistant carrier pipes due to the use of high-density polyethylene (HDPE) sheath pipes.
  • It is manufactured and constructed in a simple, easy and serial way.
  • Repair and maintenance costs are low.
  • Service life is quite long.

What is the lifetime of pre-insulated geothermal pipes?

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.

Things to consider when using heat-insulated pipes

  • During the installation of the heat-insulated pipe, care should be taken to ensure that the cable drawn into the PUR pipe is not adversely affected. Solid workmanship should be exhibited when the cable ends are joined together.
  • Polyethylene tapes may shrink at the pipe joints. In order to prevent gaps in this part, the heating process must be carried out properly. If this is not taken into consideration and gaps remain, PUR can be damaged by getting wet. Even the structure of PUR may deteriorate.
  • Sparks may occur when welding the steel pipe in the inner layer. If no safety device is placed in between, PUR may be affected by sparks.
  • The part of the PUR that is open to the atmosphere must be closed when the stock is made. If the part of the PUR open to the atmosphere is not closed, it may be adversely affected by rain and humid air.
  • When filling the duct, the pipe perimeter, including the bottom of the pipe, should be filled in such a way that there is no gap. Layer compression can be done. If the filling is not done well and there is a gap, the friction force will remain low and the pipe will extend more.
  • Polyurethane foam should be placed well between the carrier and the sheath pipe and at the same time it should adhere very well to both the carrier pipe and the sheath pipe. In cases where the PUR does not adhere well, the effect of soil friction force preventing elongation will disappear.
  • Having a synchronized plant is important for the success of the process. If the manufacturer has only a foam pressing machine, this will not be sufficient for him. In the absence of a synchronized unit, the polyurethane foam will remain inside if the void cannot be expelled while swelling. This situation damages the insulation. Even collapses may occur with the soil load.


How many centigrade temperatures can pre-insulated geothermal pipes be used for fluids up to?

Pre-insulated geothermal pipes can be used for transports with fluid temperatures up to 140°C.

Can pre-insulated pipes be used at temperatures above 140°C?

If the fluid temperature is above 140°C, the thermal insulation pipe is used by making a rockwool-PUR combination.

Can pipes be used for steam transport?

Heat-insulated pipes made of steel can be used to transport steam.

Can pre-insulated pipes be used for cold water transport?

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.

Is compensator used in pre-insulated pipes?

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.

What is corona treatment in heat-insulated pipes?

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.

Is a gallery opened when laying pre-insulated geothermal pipes?

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.

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