Re-rounding tools: restore the round shape of squeezed PE pipes

What does a re-rounding tool do?

Re-rounding tools – in English rerounding or re-rounding – press a squeezed or otherwise deformed PE pipe back into its circular cross-section. Clamping and squeeze-off flatten the pipe, and although PE has material memory, the pipe does not always fully recover on its own: severe squeezing, long squeeze duration or heat can leave permanent ovality.

An oval pipe provides poor conditions for further work: wall thickness varies around the circumference, the pipe does not fit properly in the butt fusion machine clamps, and welding or installing a fitting on a deformed section leads to incorrect tolerances. The re-rounding tool evenly compresses the pipe back into a circular shape until the ovality is within the limit specified by the pipe and welding instructions.

How to use the tool

The tool – typically a re-rounding clamp or rounding shell – is positioned over the squeeze zone and then tightened evenly until the pipe is round again. Always follow the tool manufacturer's instructions for tightening and dwell time, and verify the result by measuring the transverse and longitudinal dimensions of the pipe (ovality) around the squeeze zone.

The sequence is important: first release the squeeze-off tool, then perform re-rounding. If welding is to be carried out nearby afterwards, scrape off the oxide layer as with any other PE welding – and always outside the squeeze zone itself, which must not be welded on or fitted with a fitting.

When is re-rounding necessary?

Use re-rounding tools after every squeeze-off or squeeze-off where the pipe continues in the system: before new welding, before installing a fitting, or before re-clamping the pipe. For temporary squeeze-offs where a coupler is not welded over the squeeze point afterwards, mark previously squeezed pipes with special tape ("Squeeze off applied") so clearly that no one will weld or squeeze the same location later.

Squeeze locations are easily forgotten: the pipe looks normal again, even though the material in the zone is damaged. The marking is therefore a safety precaution, not a formality.

Standards and guidelines

DVGW GW 332 describes post-treatment and inspection in connection with squeeze-off of PE80 and PE100 pipelines, and DS/EN 12132 describes the principles of squeeze-off. There is no generic standard for re-rounding tools across manufacturers: the tool's diameter range, SDR approval and application are specified in the manufacturer's instructions.

The basic rule is the same as for squeeze-off tools: the tool must match the pipe diameter and SDR rating, and the instructions for the specific pipe never yield to rules of thumb.

Hvorfor bukke plast?

PE er sejt og kan formes med varme i stedet for at samles af mange fittinger. Mindre fittinger betyder færre samlinger, mindre tryktab og færre fejloplevelser. Typiske opgaver er sondebøjler til geotermiske anlæg, kurve omkring knaster og specialkonstruktioner.

Værktøj til bukning

Til jævnlig formgivning findes bukkeværktøj og skabeloner, der sikrer ens resultater. Til enkelte opgaver kan varmluftpistol, sand og en skabelon komme langt.

Bukseradius og varme

Som tommelfingerregel bør bukseradius ved koldbukning ikke være mindre end cirka 20 gange rørets diameter. Med varme kan man bukke strammere, men materialet skal varmes jævnt og ikke overophedes.

Til stramme kurve fyldes røret ofte med sand eller bruges indre støttestikker, så røret ikke klapper under bukningen. Varm området jævnt med varmluft eller bukkeværktøj, og lad røret køle i formen, før det belastes.