Three materials, three European standards, three uses that overlap only at the margins. Choosing between black cast iron, galvanized steel, and brass fittings is not a matter of preference — it is a matter of technical compliance. The wrong fitting will either leak within two years or fail an installation inspection. This guide decides by application, backed by the relevant standards, and explains what each material can do in a decorative context.
Three materials, three standards: what drives the choice
The material follows the application, not the other way round. Three European standards govern threaded fittings:
- EN 10242 — fittings in malleable cast iron (black or galvanized). Supersedes DIN 2950 and BS 143/1256. PN25 from -20 to 120 °C, 20 bar at 300 °C.
- EN 10241 — fittings in carbon steel (black or galvanized), machined from tube, grades S195T or S235. DN 6 to DN 150, up to +230 °C.
- EN 1254-4 — threaded fittings in copper alloys (brass). Design life 50 years, hydrostatic test at 1.5× nominal pressure.
All three use the same parallel BSP (ISO 228) or taper BSP (ISO 7) threads: a black cast iron floor flange screws onto a galvanized tube or a brass reducer without changing your wrench. What changes is the permitted application.
Black cast iron: the versatile mechanical framework
Metallurgy: annealed malleable iron, not grey cast iron
Black cast iron fittings are not the brittle grey cast iron you might expect. They are made from malleable cast iron produced by prolonged annealing of white iron: the cementite converts into graphite nodules, which delivers both mechanical strength and ductility. The material handles hemp-sealed joints without cracking and absorbs pipe vibration without fatigue.
Performance under EN 10242: PN25 and real burst pressure
EN 10242 sets 25 bar service pressure between -20 and 120 °C, 20 bar at 300 °C. Design proof pressure: 100 bar for sizes 1/8" to 4" (the core of our range), 64 bar for 5"–6". In documented burst tests, a 1/2" elbow holds up to 550 bar, a 1" flat union to 248 bar. That is a very large safety margin for domestic applications.
Permitted technical applications
Black cast iron (uncoated, anti-oxidation oil finish) is specified for:
- Closed-circuit heating (non-potable water), low-pressure steam, fuel oil, thermal oil.
- Indoor combustible gas — black finish only. The Gas Safety (Installation and Use) Regulations 1998 and BS 6891 exclude galvanized iron from gas pipework (risk of zinc flaking and blocking injectors).
- Dry fire suppression systems.
Prohibited applications
No sanitary use, no drinking water, no domestic hot water circulation, no wash-basin supply. That is what brass is for.
What about decorative use? The Home Invasion DNA
This is where black cast iron comes into its own. Dark, matt, with the characteristic grain of the malleable casting process. The Home Invasion black cast iron range (close-radius elbows, tees, sockets, floor flanges, reducers) covers 1/8" to 4" and is behind the majority of industrial furniture builds: pipe shelving, clothes rails, bar structures, bookcases, balustrades. For a deeper look at the decorative angle, see our guide to cast iron elbows in industrial decoration.
Galvanized steel: the all-round technical workhorse
Metallurgy: S195T, S235 and hot-dip galvanizing
Galvanized fittings and tubes are machined from S195T (Re ≥ 195 MPa, Rm 320–520 MPa, A ≥ 20 %) or S235 grades, then protected by hot-dip galvanizing: immersion in molten zinc deposits a continuous layer of at least 55 µm (≈ 400 g/m²). That coating is what makes the material viable in wet conditions.
Performance: PN25, seamless up to 150 bar
Operating range: -20 °C to +230 °C, nominal pressure PN25. Seamless versions reach up to 150 bar; welded-and-machined versions to 75 bar. On the hydraulic side, flow velocity is limited to 3 m/s for water and 10 m/s for air and gas. Do not install below -10 °C (embrittlement of the zinc layer).
Permitted technical applications
- Non-potable cold water: process water, irrigation, raw water, wet fire suppression.
- Workshop compressed air: the traditional first choice.
- Outdoor use: pergolas, protected buried networks, construction sites.
- Low-pressure heating in closed circuits.
Prohibited applications — three hard stops
- Domestic hot water (DHW) circulation. Zinc becomes unstable above 60 °C (polarity inversion, dissolution). HSE L8 (Legionella: The Control of Legionella Bacteria in Water Systems) and BS EN 806 require DHW storage systems to maintain temperatures that place the 55–60 °C corridor permanently under stress for galvanized steel. The consequence: galvanized steel has effectively disappeared from new DHW installations in favour of copper, 316L stainless, or multilayer pipe. Note for reference: the original French regulatory basis is arrêté du 30 novembre 2005 (FR source).
- Combustible gas: internal zinc flaking is the risk; galvanized steel is prohibited by the Gas Safety (Installation and Use) Regulations 1998 and BS 6891.
- Copper upstream in the flow direction: copper ions deposit on the downstream zinc surface and create a micro-cell that perforates the pipe within months. This is addressed by BS EN 806 and BS 6700 (water supply in domestic buildings). The fix: a brass fitting as an electrochemical buffer, splitting the potential difference into two manageable steps.
What about decorative use?
Galvanized steel has a place in decorative projects with its own distinct logic: a lighter, rawer "workshop" aesthetic. It works in explicitly industrial builds rather than premium furniture. It is also a practical choice in humid environments (open-plan kitchen, ventilated rooms, covered outdoor) where bare black cast iron would rust. Full comparison in our black vs galvanized pipe guide and the galvanized threaded pipe EN 10241 guide.
Brass: the material for sanitary and gas applications
Metallurgy: CW617N and the shift to lead-free brass
The established technical brass is CW617N (CuZn40Pb2, standard EN 12165): copper 57–59 %, lead 1.6–2.5 %, zinc approximately 40 %, density 8.4 kg/dm³. Lead acts as a chip-breaker during machining but migrates into drinking water by leaching. Directive (EU) 2020/2184 (Annex I Part B) lowers the maximum lead concentration at the tap to 5 µg/l from January 12, 2036 (versus 10 µg/l until that date).
The 4MS initiative (Germany, France, the Netherlands, the United Kingdom) provided the technical basis for the publication in April 2024 of the European Positive List of metallic materials in contact with drinking water (Implementing Decisions EU 2024/367 and Delegated Regulation EU 2024/370). CW617N remains admitted, but only for limited contact surfaces (valve bodies, fittings). Main distribution pipework without internal lining is shifting towards lead-free brass grades such as CW724R (CuZn21Si3P, marketed as Ecobrass), which are inherently resistant to dezincification (DZR).
Permitted applications
Brass fittings are the standard choice wherever the application involves:
- Drinking water — cold and hot domestic supply (WRAS-approved alloy).
- Domestic gas (butane, propane, natural gas) — permitted under the Gas Safety (Installation and Use) Regulations 1998 and BS 6891.
- Heating: water heater connections, stop valves, air vents, manifolds.
- The role of galvanic buffer when joining copper to galvanized steel.
Performance under EN 1254-4
EN 1254-4 sets a rigorous test protocol: hydrostatic test at 1.5× service pressure for 15 min, pneumatic test at 5±0.5 bar for micro-porosity, thermal cycling < 1 min, dezincification validation (EN 1254-20). Thread coaxiality ±2°, target design life 50 years.
What about decorative use? Brass as accent, not structure
Brass does not carry the structure (shelves, rails, pipe bookcases): its geometry is designed for technical jointing, not furniture framing. But it plays a clear decorative accent role in the Home Invasion range — warm, contrasted, in dialogue with cast iron. You find it on:
- Brass furniture knobs and handles (raw, polished, chrome, or cast iron + brass mix).
- Cast iron and brass handwheel toilet roll holders and brass tap-head coat hooks.
- Tap-head bookends, red or black handwheels on brass nipples.
The decorative items collection brings together these pieces where brass adds the detail that warms up a cast iron structure. The brass fittings themselves remain dedicated to their primary technical use.
Quick decision table
| Application | Black cast iron | Galvanized steel | Brass |
|---|---|---|---|
| Decoration / DIY furniture | Yes — reference framework | Possible — workshop aesthetic | Accent — knobs, handwheels, holders |
| Drinking water (cold + DHW) | No | No — degrades above 60 °C | Yes — WRAS-approved alloy |
| Non-potable cold water / process | No | Yes | Yes |
| Indoor domestic gas | Yes — black only | No — prohibited by Gas Safety Regs / BS 6891 | Yes |
| Workshop compressed air | Possible | Yes — reference material | Possible |
| Outdoor / damp conditions | No — rusts | Yes — hot-dip galvanized | Yes |
| Low-pressure heating (closed circuit) | Yes | Yes | Yes |
| Copper ↔ galvanized steel transition | — | — | Yes — mandatory buffer |
| Project | Recommended material | Why |
|---|---|---|
| Industrial shelf, bar, clothes rail, pipe bookcase | Black cast iron | Raw aesthetic, ductility under torque, full range 1/2"–1¼" |
| Workshop compressed air network | Galvanized steel | PN25, unaffected by humidity, max flow 10 m/s for air |
| Water supply, water heater connection, sanitary valve | Brass (WRAS-approved) | Only compliant material under Directive EU 2020/2184, 50-year design life per EN 1254-4 |
| Domestic gas connection (after meter, low pressure) | Black cast iron or brass | Gas Safety Regs / BS 6891 — galvanized prohibited (internal flaking) |
| Covered outdoor structure (canopy, pergola) | Galvanized steel | Hot-dip zinc ≥ 55 µm, atmospheric corrosion resistance |
| Industrial furniture in an open-plan kitchen | Lacquered black cast iron or painted galvanized | Protection against condensation, finish maintained |
| Mixed project: cast iron towel rail + brass water supply | Both, kept separate | No shared fluid contact; both materials coexist without risk |
Combining all three: galvanic pairs and sealing
Black cast iron and galvanized steel: fully compatible
Same EN 10242 standard, identical BSP threads, identical geometry. A black cast iron floor flange screws directly onto a galvanized tube without any special precaution. A common DIY configuration: galvanized tube where moisture resistance matters, black cast iron fittings for the aesthetic.
Copper ↔ galvanized steel: never without a brass buffer
BS EN 806 and BS 6700 are unambiguous: do not install a copper component upstream of a galvanized network in the direction of flow. Copper ions deposit downstream on the zinc surface, create a micro-cell, and perforate the pipe within months. The solution: a brass fitting as an electrochemical buffer, which splits the potential difference into two manageable steps.
Thread sealing: 2026 summary
- Water, heating, compressed air: PTFE tape, jointing compound, or hemp + compound. Standard methods remain fully valid. See our threaded fitting assembly guide.
- Combustible gas: the Gas Safety (Installation and Use) Regulations 1998 and BS 6891 prohibit hemp and PTFE tape on gas threads. Only permitted: anaerobic resins to EN 751-1 and non-hardening compounds to EN 751-2, approved by Gas Safe Register. Note: the original FR regulatory basis is arrêté du 23 février 2018 (FR source, Certigaz certification). A Gas Safe inspection will flag a hemp-sealed gas joint as a defect — no gas supply until rectified.
For dimensioning, the dimension calculator and the assembly simulator give thread engagement values. Diameter cross-references are in our DN / mm / inches table.
Practical cases
Industrial shelf for a living room
Black cast iron, 1/2" or 3/4" depending on the load. Floor flanges at the wall, tees at the top, elbows at the ends, threaded black steel tubes between the levels. Hemp seal or jointing compound — no sanitary considerations at all. Head straight to the black cast iron range.
Workshop compressed air network
Galvanized steel, without question. PN25, zinc coating that holds in an unheated workshop, maximum flow rate 10 m/s for air. Elbows, tees, sockets, pre-cut galvanized tubes. The Home Invasion galvanized range covers everything.
Water supply or water heater connection
WRAS-approved brass is mandatory. Check for a WRAS approval mark on every fitting in direct contact with mains water.
Gas connection (after meter, low pressure)
Black cast iron or brass. Never galvanized (Gas Safety Regs / BS 6891). No hemp, no PTFE: anaerobic resin to EN 751-1, Gas Safe Register approved. Any new domestic gas installation must be commissioned and signed off by a Gas Safe registered engineer.
Mixed project: cast iron towel rail + brass water supply
Both materials, no interaction. The black cast iron towel rail (lacquered) is fixed to the wall with no contact with the fluid circuit. The tap supply remains in brass. Each material in its place, zero galvanic coupling in the pipework.
FAQ
Can black cast iron fittings be used for drinking water?
No. Black malleable iron is not WRAS-approved, the anti-oxidation oil finish is not food-grade, and the heat from a sustained hot water circuit accelerates internal corrosion. For drinking water use brass, copper, or 316L stainless steel.
Why is galvanized steel prohibited for domestic gas?
The Gas Safety (Installation and Use) Regulations 1998 and BS 6891 prohibit it: zinc can flake off inside the tube and migrate to the injectors of combustion appliances, causing a blockage. Only black cast iron, black steel EN 10241, and brass are permitted for domestic gas pipework.
Is CW617N brass still permitted for drinking water?
Yes, subject to conditions. The European Positive List (EUPL) produced by the 4MS initiative (Germany, France, the Netherlands, the United Kingdom) admits CW617N for limited contact surfaces (valve bodies, fittings). From January 12, 2036, the lead limit at the tap drops to 5 µg/l (Directive EU 2020/2184, Annex I Part B), which is accelerating the shift towards lead-free grades such as CW724R (Ecobrass). Always verify the WRAS approval or equivalent marking on the product.
Can black cast iron and brass be mixed in the same assembly?
Yes, and it is common in the Home Invasion range — both on the decorative and technical side. In decoration, several of our decorative items combine a cast iron body with brass accents: cast iron and brass toilet roll holders, cast iron and brass furniture knobs, mixed coat hooks. On the fluid side, BSP threads are compatible and the steel/brass galvanic pair is manageable; simply keep the cast iron (structure) and the brass (WRAS fluid supply) without a shared fluid junction.
Are hemp and PTFE tape still permitted for thread sealing?
For water, heating, and compressed air, yes: hemp plus jointing compound or PTFE tape remain standard methods. For combustible gas, no: the Gas Safety (Installation and Use) Regulations 1998 and BS 6891 prohibit them in favour of anaerobic resins to EN 751-1 and non-hardening compounds to EN 751-2, approved by Gas Safe Register.
Further reading
Each material and each sub-topic covered here has a dedicated guide:
- Black steel vs galvanized pipes — complete guide (EN 10255)
- Cast iron elbows and industrial decoration — buying guide
- Galvanized threaded pipe — EN 10241 / ISO 7-1 guide
- BSPT, BSPP, NPT threads — complete guide
- Steel pipe diameters — DN / mm / inches table
- Which floor flange for decorative plumbing
- How to assemble threaded fittings — technique and torque
Browse the full range of black cast iron fittings, galvanized fittings, and brass fittings on homeinvasion.fr — sizes 1/8" to 4", BSP thread conforming to EN 10226.