Glossary of terms

Preinsulated pipe

A preinsulated pipe is a factory-bonded assembly of three layers: a steel service (carrier) pipe, rigid polyurethane (PUR) foam insulation and an outer high-density polyethylene (HDPE) casing. It is used in district-heating networks laid directly in the ground. On a longitudinal profile it is described by two diameters — the carrier (DN) and the casing (Da), e.g. “DN100/200” — and a leak-detection alarm system is embedded in its insulation. Key design aspects are fixed points, thermal-expansion compensation (self-compensation or expansion joints) and the insulation series, which sets the casing diameter and therefore the trench width.