Strong as steel yet protected against rust, the galvanized threaded pipe is the benchmark for water, compressed-air and low-pressure steam lines. This guide gathers every dimension from EN 10241 / ISO 7-1, explains the hot-dip galvanizing process and helps you select the right diameter and length.
Home Invasion range: from ¼″ (DN 8) to 4″ (DN 100)
- ¼″ (DN 8): 50 – 300 mm
- ⅜″ (DN 10): 50 – 500 mm
- ½″ (DN 15) → 4″ (DN 100): 40/50 mm → 2 000 mm
1. How the pipe is galvanized
After cutting and threading, each pipe is :
- Degreased and pickled (mild acid)
- Fluxed in a chloride bath to activate the surface
- Dipped into molten zinc at 450 °C: steel and zinc form an 85 µm Fe-Zn alloy layer (≈ 400 g/m²)
- Leveled with an air knife for even thickness
This sacrificial layer corrodes first — providing cathodic protection. In dry indoor air (ISO 12944 C1-C3) service life exceeds 25 years.
2. What EN 10241 requires
2.1 Minimum wall thicknesses
| DN | Inch | OD (mm) | s min (mm) | ID min (mm) |
|---|---|---|---|---|
| 8 | ¼″ | 13.5 | 2.3 | 8.9 |
| 10 | ⅜″ | 17.2 | 2.3 | 12.6 |
| 15 | ½″ | 21.3 | 2.6 | 16.1 |
| 20 | ¾″ | 26.9 | 2.6 | 21.7 |
| 25 | 1″ | 33.7 | 3.2 | 27.3 |
| 32 | 1¼″ | 42.4 | 3.2 | 36.0 |
| 40 | 1½″ | 48.3 | 3.2 | 41.9 |
| 50 | 2″ | 60.3 | 3.6 | 53.1 |
| 65 | 2½″ | 76.1 | 3.6 | 68.9 |
| 80 | 3″ | 88.9 | 4.0 | 80.9 |
| 100 | 4″ | 114.3 | 4.0 | 106.3 |
These walls qualify every size for PN 50 (50 bar at 20 °C).
2.2 Length tolerances
- L ≤ 300 mm : −0 / +2 mm
- 300 < L ≤ 2 000 mm : −0 / +3 mm
2.3 BSP T tapered thread
Male R (1 : 16 – 55°) into female Rp (parallel). Seal flank-to-flank with hemp + paste or 0.2 mm PTFE; tighten ¼–½ spanner turn.
2.4 Thread length & effective engagement
Add 75 % of L2 on each end to get the “face-to-face” length.
| DN | Inch | L₂ (mm) | ≈ Engaged (mm) |
|---|---|---|---|
| 8 | ¼″ | 10.4 | 8 |
| 10 | ⅜″ | 10.9 | 8 |
| 15 | ½″ | 12.7 | 9 |
| 20 | ¾″ | 13.6 | 10 |
| 25 | 1″ | 17.1 | 13 |
| 32 | 1¼″ | 22.4 | 17 |
| 40 | 1½″ | 22.4 | 17 |
| 50 | 2″ | 26.7 | 20 |
| 65 | 2½″ | 31.8 | 24 |
| 80 | 3″ | 36.5 | 27 |
| 100 | 4″ | 41.1 | 31 |
3. Diameters & available lengths
Factory-cut and fully threaded — install straight out of the box.
| DN | Inch | OD | Lengths (mm) |
|---|---|---|---|
| 8 | ¼″ | 13.5 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 |
| 10 | ⅜″ | 17.2 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 |
| 15 | ½″ | 21.3 | 40 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 20 | ¾″ | 26.9 | 40 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 25 | 1″ | 33.7 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 32 | 1¼″ | 42.4 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 40 | 1½″ | 48.3 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 50 | 2″ | 60.3 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 65 | 2½″ | 76.1 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 80 | 3″ | 88.9 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
| 100 | 4″ | 114.3 | 50 | 60 | 80 | 100 | 120 | 150 | 180 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1 000 | 1 500 | 2 000 |
Summary: DN 8 ≤ 300 mm • DN 10 ≤ 500 mm • DN 15 to DN 100 ≤ 2 000 mm.
View all available lengths
4. Sizing safely
4.1 Three key parameters
| Criterion | Good practice | Formula / cue |
|---|---|---|
| Flow rate | Velocity ≤ 3 m/s (water) • ≤ 10 m/s (air) | v = Q / (π·D²/4) |
| Pressure drop | ≤ 2 kPa/m (water) • ≤ 10 % pup (air) | Δp ≈ 0.23·Q²/D⁵ |
| Working pressure | PN 50 across the range | Steel S195T + smin |
⚡ Cold water DN 15 → 35 L/min over 10 m • air 8 bar DN 25 → 1 000 L/min.
4.2 Length: one piece or assembly?
≤ 2 000 mm: one factory pipe — fewer joints, fewer leaks.
> 2 000 mm: join two pipes with an Rp coupling; add a mid-support (DN 100 × 2 m ≈ 30 kg).
5. Installation step by step
Careful installation assures tightness and long life.
| Step | Action | Detail |
|---|---|---|
| 1 | Clean | Degrease threads, remove chips. |
| 2 | Seal | Hemp + paste or PTFE 0.2 mm (2-3 threads). |
| 3 | Tighten | ¼–½ turn after hand snug (DN 15 ≈ 45 N·m → DN 50 ≈ 160 N·m). |
| 4 | Test | Hydro test 1.5 × working pressure; no seepage after 5 min. |
6. Frequently asked questions
- Can I paint a galvanized pipe?
- Yes: degrease, lightly sand, epoxy primer, top coat.
- Maximum operating temperature?
- 120 °C continuous (hemp/paste limit).
- Potable-water safe?
- Zinc ≥ 55 µm, ACS compliant; flush before service.
- Nominal pressure rating?
- 50 bar at 20 °C, factory tested.
- Length tolerance?
- −0 / +2 mm ≤ 300 mm • −0 / +3 mm > 300 mm.
- Lengths by diameter?
-
- ¼″ (DN 8): 50–300 mm
- ⅜″ (DN 10): 50–500 mm
- ½″ (DN 15): 40–2 000 mm
- ¾″ (DN 20): 40–2 000 mm
- 1″ (DN 25): 50–2 000 mm
- 1¼″ (DN 32): 50–2 000 mm
- 1½″ (DN 40): 50–2 000 mm
- 2″ (DN 50): 50–2 000 mm
- 2½″ (DN 65): 50–2 000 mm
- 3″ (DN 80): 50–2 000 mm
- 4″ (DN 100): 50–2 000 mm
- Difference BSP T / BSP P / NPT?
- BSP T tapered 55° • BSP P parallel 55° • NPT tapered 60°.
- Are 30 mm short nipples available?
- Yes, DN 10 to DN 25 on request.
- How to calculate the span between two elbows?
- Pipe length + 75 % of L₂ each side (≈ 10 mm for DN 20).
- Can I weld a galvanized pipe?
- Possible but messy – Zn fumes; threading is safer.