Welding PP-R: times and pipe length
Times are for a clean 260 °C iron. On a cold set add a second or two of heating, never of joining.
How long to hold it on the iron
Heating is counted from the moment both parts are fully on the nozzles, not from when you touched them. Under time the weld is cold and lets go under pressure; over time the melt collapses inward and closes the bore, which nobody sees until the tap runs thin.
Joining is one straight push, no turning. Twisting a socket joint on the way in tears the melt and leaves a spiral channel through the weld.
| Ø | Heating, s | Hold, s | Before pressure, min | Socket depth, mm | Mark at, mm |
|---|---|---|---|---|---|
| d16 | 5 | 4 | 2 | 13,3 | 12,3 |
| d20 | 5 | 4 | 2 | 14,5 | 13,5 |
| d25 | 7 | 4 | 2 | 16,0 | 15,0 |
| d32 | 8 | 6 | 4 | 18,1 | 17,1 |
| d40 | 12 | 6 | 4 | 20,5 | 19,5 |
| d50 | 18 | 6 | 4 | 23,5 | 22,5 |
| d63 | 24 | 8 | 6 | 27,4 | 26,4 |
The last column is where to draw the mark: socket depth minus a millimetre, so the pipe stops just short of the bottom and the displaced melt has somewhere to go instead of the bore.
The piece is always longer than the gap
The pipe disappears into a socket at each end, so a 500 mm clear gap between two fitting faces takes a piece longer than 500 mm — by two socket depths. On d25 that is 30 mm, on d32 it is 34, and a run of ten joints cut short by that much ends a hand's width away from where it was drawn.
The calculator does the arithmetic in both directions: the length to cut, and the mark to draw on the pipe before the iron is even hot.
If you measured between axes
Nobody measures between fitting faces on a wall — they measure between corners, that is between the axes of two elbows. Each elbow eats its own arm from that number, and the arms differ by diameter: d20 gives 25.5 mm, d32 gives 34.2.
Set what you measured from and to in the second panel and the arms come off by themselves. The numbers are the real ones from serial fittings, the same table that draws the parts in the builder.
| Ø | 90° elbow, mm | 45° elbow, mm | Tee, run, mm | Tee, branch, mm |
|---|---|---|---|---|
| d16 | 22,0 | 17,5 | 22,0 | 23,0 |
| d20 | 25,5 | 19,5 | 25,5 | 25,5 |
| d25 | 29,0 | 22,0 | 29,5 | 31,4 |
| d32 | 34,2 | 25,5 | 35,5 | 35,0 |
| d40 | 41,5 | 30,0 | 41,5 | 41,5 |
| d50 | 48,5 | 34,5 | 49,5 | 49,0 |
| d63 | 59,2 | 44,5 | 60,0 | 60,0 |
A tee on the run is symmetrical, so half its length is taken; on the branch the arm is measured from the run axis to the socket face.
What actually ruins the joint
Four things, in order of how often they happen. A dirty or scored nozzle coating — the melt sticks and tears away with the pipe. Heating with the iron still climbing to temperature, which looks the same and welds nothing. A wet or dusty pipe end, since fusion needs a clean surface and no wiping happens after the heat. And loading the joint before it has cooled, which pulls the weld apart while it is still soft.
None of them show on the outside. A PP-R joint either holds for thirty years or fails within a week, and it is these four that decide which.
Common questions
How many seconds do you weld 25 mm polypropylene?
Seven seconds on the iron, four seconds held still after joining, two minutes before it takes pressure — with the iron at 260 °C. The full row by diameter is in the table above.
What temperature is polypropylene welded at?
260 °C at the nozzle. Higher scorches the surface and the joint goes brittle; lower looks identical and welds nothing. Give a cold iron a full ten minutes after the light goes out before the first joint — the first two are the ones that fail.
How far does the pipe go into the fitting?
As deep as the socket, less about a millimetre: 14.5 mm on d20, 16 mm on d25, 18.1 mm on d32. Mark that depth on the pipe before heating — once it is on the nozzle there is no time to judge it by eye.
How do I measure a pipe between two elbows?
Measure between the corners — between the elbow axes — and let the tool take off both arms and add both socket depths. Doing it the other way, by eye, is where the extra trip to the shop comes from.
When can I turn the water on?
Two minutes per joint for small diameters, four from d32 up, six on d63 — and that is the minimum before pressure, not before you touch it. Leave a freshly welded run alone until the whole thing is cold; testing it warm is what turns a good weld into a weeping one.