| Insulated pipes (called also preinsulated pipes) are | | | | for district heating in European Union is regulated by |
| widely used for district heating and hot water supply | | | | the standard EN253. According to EN253:2003, pipes |
| in Europe. They consist of a steel pipe, an insulating | | | | must be produced to work at constant temperature |
| layer and an outer casing. The main purpose of such | | | | of 130 C for 30 years, keeping heat conductivity |
| pipes is to maintain the temperature of the fluid in | | | | less than or equal to =0,033 W/mK. There are three |
| the pipes. A common application is the hot water | | | | insulation thickness levels. Insulated pipelines are |
| from district heating plants. Most commonly used are | | | | usually assembled from pipes of 6 m, 12 m or 16 m |
| single insulated pipes, but more recently in Europe it is | | | | in length, laid underground in depth 0.41.0 m. Efficient |
| becoming popular to use two pipes insulated within | | | | working life of district heating pipelines networks is |
| the same casing. The insulating material usually used is | | | | estimated as 2530 years, after which they need to |
| polyurethane foam or similar, with a coefficient of | | | | be replaced with new pipes. Four major producers of |
| thermal conductivity k=0.033-0.024 W/mK (thermal | | | | preinsulated pipes in Europe are located in Denmark |
| conductivity). Outer casing is usually high density | | | | and Sweden. |
| polyethylene (HDPE). Production of preinsulated pipes | | | | |