Piping
Jacketed pipe calculator
In short
A jacketed pipe is a core pipe held centred inside a jacket pipe by spacers. Radial gap g = (De − 2 Te − dc) / 2, spacer height h = g − clearance; the calculation also gives the spacer sections, the annulus volume V = π/4 (Die² − dc²) × L and the gaps in the elbows.
Calculation
Example calculated with the tool’s default values.
Inputs
- Core pipe (process)
- DN50 · 60.3 × 2.9 mm
- Jacket pipe
- DN80 · 88.9 × 3.2 mm
- Section length
- 6000 mm
- Spacers per section
- 3 at 120°
- Max spacing between sections
- 3000 mm
- Spacer to jacket clearance
- 1.5 mm
- Elbows (core 1.5 D, jacket 1 D)
- EN 10253-2 (3D / 2D)
- Material
- Carbon steel
- In service
- Core and jacket full of water
Results
- Core to jacket radial gap
- 11.1 mm
Worked example
Every value in this section belongs to the example, calculated with the tool’s default values.
Other results of the example
- Spacer height
- 9.6 mm
- Spacer sections
- 2
- Spacers in total
- 6
- Actual spacing
- 3000 mm
- Spacer pitch around the core
- 63.1 mm
- Jacket (annulus) volume
- 14.9 L
- Core volume
- 14.0 L
- Weight per metre in service
- 15.69 kg/m
- Section weight in service
- 94.1 kg
- Core elbow radius
- 76 mm
- Jacket elbow radius
- 76 mm
- Elbow: gap at the back
- 11.1 mm
- Elbow: gap at the belly
- 11.1 mm
- The core takes the jacket pressure from outside: check its wall for external pressure (ASME VIII-1 UG-28 or EN 13480-3).
- Spacer pitch is set by the project specification; do not fit any inside the elbows.
Step-by-step calculation
Radial gap
g = (De − 2 Te − dc) / 2
(88.9 − 6.4 − 60.3) / 2 = 11.1 mm
Spacer height
h = g − jeu
11.1 − 1.5 = 9.6 mm
Sections
n = ⌈L / p⌉; actual pitch = L / n; 1st at L / 2n
n = ⌈6000 / 3000⌉ = 2 ; 3000 mm
Annulus volume
V = π/4 (Die² − dc²) × L
2.490 L/m × 6.000 m = 14.9 L
Weight per metre
tubes (EN 10220) + eau
10.87 + 4.82 = 15.69 kg/m
Gaps in the elbow
dos = (Re + Die/2) − (Rc + dc/2) ; ventre = (Rc − dc/2) − (Re − Die/2)
11.1 mm ; 11.1 mm
Spacer section positions (from the end)
| Section | Position (mm) |
|---|---|
| 1 | 1500 |
| 2 | 4500 |
How to use it
- Pick the core (process) pipe and the jacket pipe, then the section length.
- Pick the spacers per section (3 at 120° or 4 at 90°), the max spacing between sections from the project specification and the spacer to jacket clearance.
- Pick the elbows (EN 10253-2, ASME B16.9 or no elbow), the material (carbon steel, stainless 304L or 316L, duplex 2205, aluminium, copper) and the service.
- Read the core to jacket radial gap.
Frequently asked questions
How do I size a jacketed pipe?
The radial gap between core and jacket is g = (De − 2 Te − dc) / 2, with De and Te the jacket outside diameter and wall, dc the core diameter. The spacer is h = g − clearance. Example: 60.3 × 2.9 core in an 88.9 × 3.2 jacket: (88.9 − 6.4 − 60.3) / 2 = 11.1 mm gap, spacers of 11.1 − 1.5 = 9.6 mm.
Where do the spacers go in jacketed pipework?
On a section of length L with a max spacing p: n = ⌈L / p⌉ sections, the first at L / 2n from the end, then every L / n. For 6000 mm and a 3000 mm spacing: 2 sections, at 1500 and 4500 mm, so 6 spacers at 120°. Sources give guides every 3 m with a 1.5 mm clearance (Fluor India, ISFT 2016) and a 2 to 5.5 m interval depending on DN (Piping World). No spacers inside the elbows.
Which jacketed pipe fittings for the elbows?
Common practice: long radius core elbow (1.5 D), short radius jacket elbow (1 D), same bend centre. Gap at the back = (Re + Die/2) − (Rc + dc/2), at the belly = (Rc − dc/2) − (Re − Die/2). In the EN 10253-2 example, both elbows have a 76 mm radius and the back and belly gaps are 11.1 mm.
How much does a jacketed pipe weigh?
Pipe weight per metre is π (D − T) T × ρ: the EN 10220 formula M = (D − T) T × 0.02466 for steel at 7 850 kg/m³, with the density of the chosen material (carbon steel, stainless 304L or 316L…). The water in service is added. Carbon steel example, core and jacket full of water: 10.87 + 4.82 = 15.69 kg/m; jacket volume 14.9 L.
Limits
Indicative results. The core takes the jacket pressure from outside: check its wall for external pressure (ASME VIII-1 UG-28 or EN 13480-3), not calculated here. Spacer pitch is set by the project specification. Elbows come from the EN 10253-2 or ASME B16.9 tables: a size missing from the tables has no elbow.
Sources
- Piping World : tuyauteries à double enveloppe : Entretoises à 120°, intervalle 2 à 5,5 m selon le DN ; coudes cœur 1,5 D / enveloppe 1 D ; pression extérieure sur le cœur (consulté le 09/11/2026) (link)
- Vinoth, Vivek, Siva Kumar (Fluor India), ISFT 2016, ID 2016-ISFT-259 : § 3.3.2 : guides de centrage tous les 3 m selon le projet, jeu de 1,5 mm entre guide et enveloppe (link)
- Masse linéique des tubes : EN 10220:2002, § 5 (M = (D − T) T × 0,02466 pour 7 850 kg/m³)
- EN 10253-2:2021+A1:2026 (raccords à souder bout à bout) : Coudes 2D/3D (rayon R), tés égaux (F), réductions (L) ; tableaux Zickwolff, consultés le 08/11/2026 (link)