Welding methods
Socket fusion: small diameters with sockets and mandrels
Bead welding with hand or machine tools for pipes from Ø20 to around Ø125. The classic method for geothermal probes and installations.
See all welding methods in the overview
The principle of socket fusion
In socket fusion, the pipe's outer surface is heated on a heated mandrel and the fitting's inner socket is heated on the same tool. Both parts are pushed together and held steady while the melts fuse and form a bead.
The method is typically used for PE and PP pipes from Ø20 to around Ø125: geothermal probes and probe bends, installation pipework in buildings and branch saddles.
The working sequence
The pipe is cut square and deburred. Mark the insertion depth on the pipe so it is not pushed too far into the socket, which would form an internal bead that restricts flow.
Heat the mandrel and socket to the recommended temperature (around 260 degrees Celsius for PE) before fitting pipe and fitting. Push them together steadily all the way, keep them still during cooling, and clean the tools after use.
Hand tools or machine?
For the smallest diameters, hand tools are used (a welding iron with interchangeable mandrels and sockets). For larger diameters and repetitive work there are portable socket fusion machines that keep temperature and time more consistent.
For branch saddles on mains, saddle clamps and fusion outlets (colloquially "hole welding") are used, where a special fitting is welded directly onto the pipe with electrofusion or heated tool equipment.
| Dimension | PN16 / SDR 11: e | Heating | Afkøling fastholdt | Samlet afkøling før belastning | PN10 / SDR 17: e |
|---|---|---|---|---|---|
| d20 | 2,0 mm | 5 s | 6 s | 2 min | approx. 1.5 mm |
| d25 | 2,3 mm | 7 s | 10 s | 2 min | approx. 1.5 mm |
| d32 | 3,0 mm | 8 s | 10 s | 4 min | ca. 2,0 mm |
| d40 | 3,7 mm | 12 s | 20 s | 4 min | ca. 2,4 mm |
| d50 | 4,6 mm | 18 s | 20 s | 4 min | ca. 3,0 mm |
| d63 | 5,8 mm | 24 s | 30 s | 6 min | ca. 3,8 mm |
| d75 | 6,8 mm | 30 s | 30 s | 6 min | ca. 4,5 mm |
| d90 | 8,2 mm | 40 s | 40 s | 6 min | ca. 5,4 mm |
| d110 | 10,0 mm | 50 s | 50 s | 8 min | ca. 6,6 mm |
| d125 | 11,4 mm | 60 s | 60 s | 8 min | ca. 7,4 mm |
Afkøling fastholdt = den tid rør og fitting skal holdes stille i værktøjet. Samlet afkøling = tid før samlingen må belastes, flyttes eller trykprøves. Omstillingen fra værktøj til samling skal ske inden for ca. 8-10 s. Ved lavere omgivelsestemperatur, træk eller tyndere væg end tabellen viser, følges fittingproducentens tabel.
Håndværktøj eller maskine?
Til de mindste diametre bruges håndværktøj (svejsejern med udskiftelige dorne og muffer). Til større diametre og gentagne opgaver findes der bærbare muffesvejsemaskiner, som holder temperatur og tid mere konstant.
Til anboringer på hovedledninger bruges anboringsbøjler og svejsehuller (på folkemunne kogehulssvejsning), hvor en specialfitting svejses direkte på røret med elektro- eller varmelementværktøj.
Checklist: start-up and inspection
PE, PP and PVDF in small diameters. Spigot and socket on the same tool.
Before startup
- Spigot and socket fit the dimension and are clean and free from burnt-on material.
- The tool temperature has been checked with an external gauge.
- The pipe is cut square and deburred, and the insertion depth is marked.
- Fitting and pipe are of the same material and class.
First joint (test)
- The test joint shows a uniform bead all the way round.
- Pipe and fitting are aligned relative to each other, without misalignment.
- No internal bead restricting the flow.
At each joint
- The heating time complies with the table for dimension and PN class.
- The changeover takes place within approx. 8-10 s, and the components are inserted smoothly all the way.
- The joint is held still during the specified cooling time.
After the joint
- The seam has been visually inspected all the way round.
- The tool has been cleaned while the residues are warm.
- The joint is documented with dimension, date and operator.