PP-R pipe is sized by its outside diameter in millimeters: 20, 25, 32, 40, 50, 63, 75, 90 and 110 mm are the standard commercial sizes for water systems inside buildings. The second coordinate of the size is the pressure class PN (PN10, PN16, PN20 and PN25), which states the allowable pressure in bar with water at 20 °C projected over 50 years of service. A "25 mm PN16" PP-R pipe therefore measures 25.0 mm outside diameter with a 3.5 mm minimum wall, and its trade equivalent is 3/4 inch.
The selection verdict: for cold water use PN10, or PN16 where the network sees high pressure or frequent water hammer; for domestic hot water use PN20 (SDR 6), because the allowable pressure of PP-R drops to less than half between 20 °C and 70 °C. TECTUL supplies PN16 socket-fusion polypropylene pipe and matching fusion fittings such as the socket-fusion polypropylene elbow. The tables below are referenced to ISO 15874 and to manufacturer dimension tables.
PP-R is polypropylene random copolymer (type 3), a thermoplastic for conveying cold and hot pressurized water in building installations. The complete system — pipes, fittings and their fitness as a system — is standardized by the ISO 15874 series; the current edition is 2013, and the pipes part (ISO 15874-2:2013) carries amendments Amd 1:2018 and Amd 2:2022. Unlike PVC, PP-R is not joined with solvent cement or threads: pipe and fitting are fused together by heat fusion at 260 °C, forming a monolithic joint of the same material with no adhesives or sealing elements.
In PP-R the nominal size is the actual outside diameter of the pipe, in millimeters. This is the opposite of NPS-designated steel or PVC, where "1/2 inch" is a name rather than a physical dimension. The inch equivalence of PP-R is therefore commercial only: it helps order material and compare against existing networks, not interchange fittings. An NPT threaded fitting connects to a PP-R system only through metal-insert adapters.
| Outside diameter (mm) | Trade equivalent (inches) | Inside diameter at PN16 (mm) |
|---|---|---|
| 20 | 1/2 | 14.4 |
| 25 | 3/4 | 18.0 |
| 32 | 1 | 23.2 |
| 40 | 1 1/4 | 29.0 |
| 50 | 1 1/2 | 36.2 |
| 63 | 2 | 45.8 |
| 75 | 2 1/2 | 54.4 |
| 90 | 3 | 65.4 |
| 110 | 4 | 79.8 |
The inside diameter depends on the pressure class: the higher the PN, the thicker the wall and the smaller the bore. A 20 mm PN20 pipe leaves a 13.2 mm bore, versus 16.2 mm for the same diameter in PN10. Since hot water requires PN20, long runs sometimes justify moving up one diameter to keep the design velocity.
PN is the nominal pressure: the bar the pipe withstands with water at 20 °C over 50 years of service. SDR (Standard Dimension Ratio) is the ratio of outside diameter to wall thickness (SDR = d/e), and the ISO 4065 pipe series S relates to it by SDR = 2S + 1: the lower the SDR or S, the thicker the wall and the higher the pressure. ISO 15874-2:2013 classifies pipes by S series and application class (service temperature), not by PN; the PN designation comes from the DIN 8077 system and remains the commercial way to order the material in Colombia.
| Trade class | SDR | S series | Typical service |
|---|---|---|---|
| PN10 | 11 | S5 | Cold water at 20 °C |
| PN16 | 7.4 | S3.2 | Cold water at high pressure; hot water at low pressure |
| PN20 | 6 | S2.5 | Domestic hot water |
| PN25 | 5 (solid) or fiberglass composite | S2 | Hot water and heating with higher demands |
Minimum wall thickness (e min, in mm) per manufacturer dimension tables conforming to EN ISO 15874 and DIN 8077, built on the ISO 4065 metric series:
| Outside diameter (mm) | PN10 — SDR 11 (mm) | PN16 — SDR 7.4 (mm) | PN20 — SDR 6 (mm) |
|---|---|---|---|
| 20 | 1.9 | 2.8 | 3.4 |
| 25 | 2.3 | 3.5 | 4.2 |
| 32 | 2.9 | 4.4 | 5.4 |
| 40 | 3.7 | 5.5 | 6.7 |
| 50 | 4.6 | 6.9 | 8.3 |
| 63 | 5.8 | 8.6 | 10.5 |
| 75 | 6.8 | 10.3 | 12.5 |
| 90 | 8.2 | 12.3 | 15.0 |
| 110 | 10.0 | 15.1 | 18.3 |
Class PN25 is not in the table because manufacturers build it two ways: as solid SDR 5 pipe (S2 series) or as composite pipe with an intermediate fiberglass layer over SDR 6 geometry. Before computing PN25 inside diameters, check the specific manufacturer's datasheet.
PP-R loses mechanical strength as water temperature rises, in a continuous and predictable way. The material regression curves, translated into manufacturer tables with a 1.5 service coefficient and a 50-year life, show the drop:
| Water temperature | PN10 — SDR 11 (bar) | PN16 — SDR 7.4 (bar) | PN20 — SDR 6 (bar) |
|---|---|---|---|
| 20 °C | 12.8 | 20.4 | 25.8 |
| 60 °C | 6.4 | 10.3 | 12.9 |
| 70 °C | 4.3 | 6.8 | 8.5 |
The practical reading: at 70 °C a PN10 pipe is down to about 4 bar allowable, below the pressure of many building networks, which is why it is not used for hot water. PN20 keeps about 8.5 bar at 70 °C over 50 years, sufficient for domestic hot water. ISO 15874-1:2013 formalizes this with application classes by service temperature (class 1: hot water at 60 °C; class 2: hot water at 70 °C; classes 4 and 5: heating). Also account for thermal expansion: long hot-water runs are compensated with flexible arms, expansion loops or a socket-fusion polypropylene compensation pipe.
The standard PP-R joint up to 63-75 mm is socket fusion: the heated tool with sockets melts the pipe outside and the fitting inside simultaneously at 260 ± 10 °C, per DVS 2207-11. Heating time depends on diameter — on the order of 5 s at 20 mm and close to 50 s at 110 mm; the exact values per diameter, the insertion depths and the cooling times are tabulated in DVS 2207-11 and in the tool manual, and must be followed without improvising. Do not twist the pipe while inserting it into the fitting. From 63-75 mm a bench machine is recommended, and larger diameters use butt fusion.
To execute the joint, TECTUL offers the digital socket-fusion welder for PP-R, whose heater adjusts between 240 and 300 °C with a digital indicator to set the working point, along with system fittings such as the socket-fusion polypropylene coupling.
Pressure PVC joins with solvent cement and is limited to cold water; CPVC handles hot water up to 82 °C (180 °F) in systems conforming to ASTM D2846, also cement-joined; PP-R covers cold and hot water with a monolithic fused joint and no adhesives. Quick criterion: to extend an existing cold-water PVC network, stay with PVC; for a new hot-water network with crews equipped with a fusion welder, use PP-R PN20; CPVC is the cemented alternative for hot water. Schedules, RDE and PVC types are detailed in the guide types of PVC, and the general material overview in types of industrial piping.
3/4 inch as a trade equivalence. The actual outside diameter is 25.0 mm: the inch label only names the size and does not allow coupling fittings from other dimensional systems.
Nominal pressure of 20 bar with water at 20 °C projected over 50 years of service. Geometrically it corresponds to SDR 6 (S2.5 series): on the 20 mm pipe the minimum wall is 3.4 mm.
PN20 (SDR 6) as the general rule for domestic hot water; for permanent recirculation or heating, fiberglass PN20 pipe or PN25 according to the ISO 15874-1 application class.
Not as a design practice: at 70 °C its 50-year allowable pressure is around 4.3 bar and the margin against pressure and temperature peaks disappears. For hot water, the starting class is PN20.
Always order PP-R with two data points: outside diameter in millimeters and PN class, and buy pipe and fittings from the same fusion system. In a typical dwelling the distribution runs in 25 or 32 mm with 20 mm branches; cold water in PN10 or PN16 and the entire hot-water line in PN20. Make sure the installer has a temperature-controlled fusion welder and applies the DVS 2207-11 times. TECTUL stocks the PN16 PP-R pipe, the fusion fittings and the digital fusion welder to build the complete network.
