Pipe and hanger arrangement is the backbone of a sprinkler system. FM Global DS 2-0 covers pipe material, diameter, velocity, hanger spacing and seismic detailing.
Pipe Materials
- Schedule 40 black steel: the standard, with no hazard class limitation
- Schedule 10/30 thin-wall: lighter applications, where FM Approved
- Galvanised steel: external and dry pipe use, but with internal corrosion risk (see DS 2-1)
- CPVC: permitted only in defined light hazard areas such as hotel rooms, hospital wards and offices
- Copper: small diameters and sensitive applications
Diameter and Velocity Limits
- Branch line maximum velocity around 4.6 m/s
- Cross main maximum velocity around 6.1 m/s
- Riser maximum velocity around 6.1 m/s
- Sizing is by hydraulic calculation; schedule sizing is only permitted in limited cases
Hanger Spacing
| Pipe size | Maximum spacing |
|---|---|
| DN25–50 | 3.7 m |
| DN65–100 | 4.6 m |
| DN150 and above | 4.9 m |
| Sprinkler drop | One additional hanger within 600 mm |
Joint Types
- Threaded: DN50 and below, smaller systems
- Welded: larger diameters, permanent
- Grooved couplings: fast to install and demountable, where FM Approved
- Flanged: valve and pump connections
Seismic Bracing (with DS 2-8)
- Sway bracing, both lateral and longitudinal, for DN65 and larger pipe
- Brace angle typically between 30 and 60 degrees
- FM Approved anchors and clamps
- A full bracing package in high seismic zones
Quick Checklist
- Pipe material suits the hazard class
- Velocity limits respected on branches and mains
- Hanger spacing correct for the pipe size
- Joint type appropriate, with grooved preferred for speed
- Seismic bracing coordinated with DS 2-8
Frequently Asked Questions
Where is CPVC pipe accepted in a sprinkler system?
CPVC is accepted only in defined light hazard areas such as hotel rooms, hospital wards and offices, and only where the product is listed for the application. It is not accepted in storage, industrial or high hazard areas, and exposure and temperature limitations must be respected.
Why are pipe velocity limits imposed?
High velocity increases friction loss disproportionately, causes noise and accelerates erosion at fittings and valves. Keeping branch lines below roughly 4.6 m/s and mains below 6.1 m/s keeps the hydraulic calculation realistic and protects the pipework over the life of the system.
How is hanger spacing determined?
Spacing follows pipe diameter, with larger pipe permitted greater spans - roughly 3.7 m for DN25 to 50, 4.6 m for DN65 to 100 and 4.9 m above DN150. An additional hanger is required close to each sprinkler drop so the head is not supported by the branch line alone.
What pipe should be used on a dry system?
Galvanised steel is common on dry and external installations, but it carries a real internal corrosion risk because residual moisture and air remain in the pipework. FM Global DS 2-1 addresses this, and nitrogen supply or careful drainage detailing is increasingly used to extend pipe life.
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Download MEP Calc on the App StoreFM Global Property Loss Prevention Data Sheets DS 2-0 (Installation Guidelines for Automatic Sprinklers), DS 2-89 (pipe friction) and DS 2-8 (earthquake protection).