EN 12845 Pipe Joining: Steel Welding, Flexible Connectors and Copper

Wall thickness, C-factor and certification rules for welded, grooved, threaded, flexible and copper connections.

At the final installation inspection on a logistics warehouse, the inspector had us strip a DN100 distribution pipe joined with grooved couplings in the OH3 area. The pipe end was not roll-grooved but cut and grooved by hand on site, with wall thickness locally down to 2.8 mm. The standard is unambiguous here: the grooving method and the wall thickness decision are locked together. Opening that one joint meant replacing the whole riser. Pipe joining method is not merely an installation detail; it is a decision that determines both the hydraulic calculation and compliance with the standard.

What the standard says

EN 12845:2015+A1:2019 governs above-ground pipework. Downstream of the control valve, pipe material may be steel, copper (per the copper clause) or other material complying with the specifications valid at the place of use. Galvanised steel is preferred in dry, alternate and pre-action installations. Underground pipework may be cast iron, ductile iron, spun cement, glass-reinforced plastic or high-density polyethylene.

The backbone of the whole clause is the relationship between wall thickness and joining method. Confuse the two and you produce a non-compliant installation.

Steel pipe: wall thickness and end preparation

The key paragraph, summarised:

• For threaded, cut-grooved or machined steel pipe up to DN150, minimum wall thickness to ISO 65 is required — generally the medium (standard weight) series.
• For pipe with end preparation that does not significantly reduce wall thickness — roll-grooved or weld-prepared — wall thickness to ISO 4200 range D is sufficient. That is a lighter series; roll grooving compresses the material rather than cutting it.
• For mechanical joints (grooved couplings), the manufacturer's recommendation is also binding.

The most common site error: buying light-series pipe and cutting grooves in it by hand. That satisfies neither the ISO 65 wall thickness nor the coupling manufacturer's listing. Apply cut grooving to pipe invoiced as "ISO 4200 range D" and you are outside the standard.

Welding — who, how and where

The welding clause draws firm lines:

• Pipe and fittings below DN50 may not be welded on site, with the single exception of automatic welding machines. Joining DN25–DN40 pipe with electrode or TIG welding on site is outside the standard.
• Under no circumstances may flame cutting, brazing or other hot work be carried out in situ. That rule pushes welding into the workshop.
• All welds are continuous; the internal surface must not obstruct flow; and after an opening is formed, deburring and slag removal are mandatory.
• Welders must be qualified to EN ISO 9606-1. The certificate has a validity period, and each welder's certificate date must be in the project file.

Field practice: risers and distribution pipework are welded in the workshop and joined on site with flanges or grooved couplings, while sprinkler connections are almost always threaded (DN15–DN25). That combination satisfies the standard and keeps installation quick.

Grooved couplings

Grooved couplings have become the most common joining method on European sprinkler sites over the last twenty years. EN 12845 does not name a certification class for them directly; instead it constrains mechanical joints through material and wall thickness, and through support spacing. In practice the accepted approvals are UL Listed, FM Approved or LPCB certified couplings and fittings.

Two extra support rules apply to mechanically jointed pipework:

• At least one support within 1 m of every joint.
• At least one support on every length of pipe.

Field error: coupling bolt torque below the manufacturer's figure leaks at the gasket; above it, the lugs crack. Each manufacturer gives its own torque (typically 70–150 N·m by size), and it is worth re-checking every coupling bolt with a torque wrench before the pressure test.

Threaded joints

Threaded pipe is tied to ISO 65 wall thickness. In practice threaded joints are used at DN50 and below; a pipe with a thread cut into it is no longer plain pipe, and wall thickness reduces sharply at the thread root. DN65 and above uses grooved or flanged joints.

Sealing is by PTFE tape or fibrous sealant. Where a thread is cut into galvanised pipe, the standard requires the damaged coating to be painted; otherwise surface rust starts at the thread roots and leaks appear within a few years.

Flexible connectors

The flexible connector rules, in order:

• Use: only where relative movement is expected — movement joints, moving racks.
• Test pressure: tested before installation at four times maximum working pressure or 40 bar, whichever is greater.
• No component that would lose integrity in a fire.
• A permanent pressure-retaining stainless steel or non-ferrous inner tube.
• Not installed fully extended.
• Not used to correct misalignment between distribution pipework and intermediate level sprinkler feeds.

The error we see most often: stretching a flexible connector to seat a head in a movable ceiling. That breaches both the standard and the product warranty. A flexible connector is installed with slack, keeping an S shape while the head moves within the ceiling tile.

Copper pipe — limited but useful

Copper has its own rules:

• Wet systems only.
• Only LH, OH1, OH2 and OH3. Prohibited for HHP, HHS and OH4.
• Always downstream of steel pipework.
• Pipe to EN 1057.
• Joints mechanical or hard soldered, with fittings to EN 1254. Hard soldering only by trained personnel.
• Copper-to-steel transitions flanged, with stainless steel bolts.
• No site bending; galvanic corrosion must be prevented.
• Copper supports must be protected from contact corrosion by a suitably resistive lining.
• Support spacing differs from steel: 4 m for steel against 2 m for copper, increasable by 50 % above DN50 under certain conditions.

The C-factor difference

Friction loss follows Hazen-Williams, with C values:

Pipe type	C value
Cast iron	100
Ductile iron	110
Mild steel / galvanised steel	120
Cement (spun or cement lined)	130
Stainless steel / copper / glass reinforced plastic	140

Because friction loss varies inversely with C to the power 1.85, moving from C = 120 to C = 140 reduces friction loss by roughly 26–30 %. That is the technical case for copper; the drawbacks are cost and a limited scope of use. Calculating for steel and then substituting copper in part of the system is equally wrong; the C value used must be recorded on the calculation output.

CPVC and other plastic pipe

EN 12845 admits plastic pipe under "other material complying with specifications valid at the place of use", without naming CPVC. European practice:

• CPVC is generally used in light hazard installations, in concealed spaces above ceilings.
• Temperature tolerance is around 70–90 °C, so it cannot be used in kitchens or boiler rooms.
• Clearance rules apply from heat sources and certain cable types.
• The product must carry UL, FM or LPCB certification and be calculated with the manufacturer's design guide, which has its own C value (typically around 150).

Using CPVC in ordinary hazard and above, or beneath storage, runs against the spirit of EN 12845 and is usually rejected by inspectors.

Three typical field cases

1. Grooved coupling torque error: hand-tightened bolts leak between 6 and 8 bar during the pressure test. The fix is a second pass with a torque wrench to the manufacturer's figure.
2. Site electrode welding below DN50: a clear breach. The only remedy is to cut it out and convert to threaded joints.
3. Direct threaded copper-to-steel joints: galvanic corrosion produces leaks within two to three years. The standard requires a flanged transition with stainless bolts.

Comparison with NFPA 13

NFPA 13 lists pipe materials in its own table. The differences that matter:

• NFPA 13 requires welder qualification to AWS B2.1; EN 12845 to EN ISO 9606-1. The two are equivalent, but on an international project it must be settled which applies.
• NFPA 13 explicitly recognises listed CPVC in light hazard and certain ordinary hazard areas; EN 12845 does not name plastic, deferring to local specification.
• NFPA 13 uses C = 120 for Schedule 40 steel and C = 150 for listed CPVC; EN 12845 lists C values by material only, without a schedule distinction.
• Grooved couplings are accepted by both, and both require a listed or approved product.

Turkish context

BYKHY references TS EN 12845 for sprinkler installations. In practice about 90 % of Turkish sites use:

• Roll-grooved galvanised steel with UL/FM couplings on risers of DN50 and above,
• Threaded galvanised pipe on distribution and sprinkler connections at DN50 and below,
• Listed flexible connectors at movement joints and in demountable ceilings.

Copper is rare in field practice, because of cost and the prohibition on site bending. At fire service acceptance the first three documents requested are the welder's EN ISO 9606-1 certificate, the coupling UL/FM report and the flexible connector listing. Keep those three in the file and the jointing section passes without difficulty.

The summary

EN 12845 ties three decisions together in pipe jointing: material, wall thickness and joining method. Tie your wall thickness choice to the grooving method, and the grooving method to the coupling manufacturer's recommendation, and calculation and site will agree. Copper is hydraulically advantageous but confined to LH and OH1–3. Flexible connectors exist only for expected relative movement, not as slack. And welding belongs in the workshop — prohibited on site below DN50, and inseparable from a qualified welder above it.

Frequently Asked Questions

Can pipe below DN50 be welded on site?

No, except with an automatic welding machine. Flame cutting, brazing and other hot work in situ are prohibited outright, which pushes welding into the workshop.

What wall thickness applies to grooved pipe?

ISO 65 for cut-grooved, threaded or machined pipe; ISO 4200 range D where the end preparation does not significantly reduce wall thickness, such as roll grooving.

Where can copper pipe be used?

Wet systems only, in LH, OH1, OH2 and OH3, always downstream of steel, with flanged transitions and stainless bolts. Prohibited in OH4, HHP and HHS.

What can a flexible connector not be used for?

Correcting misalignment. It exists only for expected relative movement, must not be installed fully extended, and needs a stainless or non-ferrous pressure-retaining inner tube.

SprinkCalc — Fire Sprinkler Design Across Three Standards

SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.

Download SprinkCalc on the App Store

MEP Calc — 86+ Engineering Calculators

MEP Calc bundles 86+ engineering modules in one iOS app: 21 fire calculations plus heating, cooling, HVAC, plumbing, steam and natural gas.

Download MEP Calc on the App Store