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	120	120	140	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	—	—	Prohibited
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

Wall thickness: the detail that quietly changes the calculation

EN 12845 defines two wall thickness classes. Threaded or cut-grooved pipe must meet ISO 65; roll-grooved or weld-prepared pipe must meet ISO 4200 range D. 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 prefers galvanising on dry, alternate and pre-action installations, because those systems hold water through the summer and humid 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.
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 brazing.

Copper's C=140 advantage is real: at the same diameter and flow, the friction loss comes out about 30 percent lower than steel. 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 requires a maximum of 4 m on steel pipe and 2 m on copper; above 50 mm those distances can be increased by 50 percent where two independent supports or a single support rated 50 percent higher is used. Copper is supported more closely because its modulus of elasticity is lower than steel's, so it deflects twice as fast under the same load. An insulating liner goes inside the copper clamp to prevent galvanic corrosion.

Frequently Asked Questions

In which hazard classes can copper pipe be used?

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. 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. Pipe and fittings smaller than 50 mm may not be welded on site unless an automatic welding machine is used, and flame cutting and brazing are prohibited under any circumstances.

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