Sprinkler Pipe Material Comparison: Steel, Galvanised, Copper, CPVC and Stainless

Choosing sprinkler pipe is not only a price question: the material sets the permitted hazard class, the friction coefficient and the corrosion picture twenty years from now.

Comparison table

Criterion	Black steel	Galvanised steel	Copper	CPVC	Stainless
Permitted hazard classes	All	All	Wet only; LH, OH1–OH3	Limited (light load, low temperature)	All
Hazen-Williams C (EN 12845 Table 22)	120	120	140	Not in EN (NFPA: listed plastic 150)	140
Dry / alternate systems	Permitted but corrosion prone	Preferred	Not suitable	Not suitable	Suitable
Jointing	Welded, threaded, grooved	Threaded, grooved	Brazed, mechanical	Solvent weld	Welded, grooved
Site welding below DN50	Prohibited (except automatic machine)	Prohibited (except automatic machine)	—	—	Prohibited (except automatic machine)
Corrosion resistance	Low	Moderate (internal surface open to MIC)	High	Very high	Very high
Fire resistance	High	High	Moderate	Low (melts)	High
Cost	Lowest	Low	High	Moderate	Highest
Typical use	Standard installations	Dry, alternate, pre-action	Offices, hotels; downstream of steel	Residential, low hazard	Marine, chemical, food

The C values are from EN 12845 Table 22. NFPA 13-2025 Table 28.2.4.8.1 gives different values: black and galvanised steel 120 on wet systems and 100 on dry and pre-action systems (120 where nitrogen, vacuum or a vapour corrosion inhibitor is used); copper, brass and stainless 150; listed plastic 150. The copper limits come from EN 12845 17.1.9, the galvanised preference for dry and alternate systems from 17.1.2, and the DN50 welding rule from 17.1.3.

Wall thickness: the detail that quietly changes the calculation

EN 12845 17.1.2 defines two minimum wall thicknesses. Steel pipe up to DN150 that is threaded, cut-grooved or otherwise machined must meet ISO 65; pipe whose ends are formed without significantly reducing the wall, such as roll-grooved or weld-prepared pipe, must meet ISO 4200 range D. Where mechanical joints are used, the wall thickness must also follow the manufacturer's recommendations. Thicker wall gives an internal diameter 1.5 to 2.5 mm smaller at the same DN, and the Hazen-Williams friction loss rises noticeably. The hydraulic calculation uses the actual mean internal diameter, not the nominal size, taken from the manufacturer's certificate.

Galvanising: a two-sided solution

External galvanising (buried, outdoors) is protective. Internal galvanising presents a double picture: it slows oxygen corrosion but can provide nutrients for microbiologically influenced corrosion (MIC). EN 12845 17.1.2 prefers galvanised steel on dry, alternate and pre-action installations, because those systems hold humid air (an alternate system holds water through the summer and air through the winter) and the corrosion risk is far above a wet system. Where uncoated black steel is chosen, endoscopic corrosion monitoring every two years is recommended.

The three limits on copper

1. Only on wet pipe systems (EN 12845 17.1.9).
2. Only in the LH, OH1, OH2 and OH3 classes; not in OH4, HHP or HHS.
3. Always downstream of the steel pipe, complying with EN 1057 and joined mechanically or by hard soldering with EN 1254 fittings. Copper-to-steel joints are flanged with stainless steel bolts, and the pipe is not bent on site.

Copper's C=140 advantage is real: at the same internal diameter and flow, the Hazen-Williams friction loss comes out about 25 percent lower than C=120 steel ((120/140)^1.852 ≈ 0.75). But that gain matters on long runs; on a short office branch it does not repay the cost difference.

Hanger and support differences

The material also changes the hanger spacing. EN 12845 17.2.2 requires a maximum of 4 m on steel pipe and 2 m on copper; for pipes over 50 mm those distances can be increased by 50 percent where two independent supports are fixed directly to the structure or a support rated for 50 percent more than the Table 40 load is used. Copper is supported more closely because its modulus of elasticity is lower than steel's, so it deflects more under the same load. Supports for copper pipe get a lining with sufficient electrical resistance to prevent contact corrosion (17.2.1).

Frequently Asked Questions

In which hazard classes can copper pipe be used?

Under EN 12845 17.1.9, only on wet pipe systems and in the LH, OH1, OH2 and OH3 classes. Not in OH4, HHP or HHS. It must always be downstream of the steel pipe and comply with EN 1057.

Why is galvanised pipe preferred on a dry system?

Dry and alternate installations hold humid air and the corrosion risk is far above a wet system. An internal galvanised coating adds life, although it can also provide nutrients for MIC bacteria.

Does the wall thickness change with grooved pipe?

Yes. Under EN 12845 17.1.2, threaded and cut-grooved pipe must meet ISO 65, while roll-grooved and weld-prepared pipe must meet ISO 4200 range D. A thicker wall reduces the internal diameter at the same DN and raises the friction.

Can I weld pipe below DN50 on site?

No. Under EN 12845 17.1.3, pipe and fittings smaller than 50 mm may not be welded on site unless an automatic welding machine is used, and welding, flame cutting, soldering or any other hot work on the installed pipework is prohibited in all cases.

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