Brass Joining Methods Guide

1. The seven joining methods — overview

2. Soft soldering

Soft solder is the lowest-temperature joining method. The base metal is heated and a tin-based filler is wicked into the joint by capillary action. Common fillers (RoHS-safe lead-free):

• Sn-Cu (97/3, 99/1) — general-purpose plumbing solder, melts ~227°C. The dominant lead-free replacement for legacy Sn-Pb 60/40.
• Sn-Ag-Cu (95.5/4/0.5, "SAC") — electronics standard. Melts ~217°C.
• Sn-Ag (96/4) — slightly higher strength, electronics use.
• Sn-Zn (91/9) — for aluminium-to-brass joints in some HVAC contexts. Reactive flux required.

Joint design for soft solder

• Capillary gap: 0.05–0.15 mm. Too tight → poor flow. Too loose → no capillary action, weak joint.
• Overlap length: minimum 3× tube wall thickness; 5–8× for full strength.
• Cleanliness: deburred, abrasive-cleaned (Scotch-Brite or fine emery), flux-coated before assembly.
• Flux: rosin / mildly activated rosin (RMA) for electronics; zinc-chloride based for plumbing.

3. Brazing

Brazing is the workhorse for permanent, high-strength brass joints. Filler metals are alloyed to melt at 600–900°C — well below the brass parent material melting point (~895°C for CW617N) but high enough to wet the surface and form a metallurgically bonded joint that is typically stronger than the brass itself in a properly designed joint.

Filler-metal standards

• AWS A5.8 / A5.8M — American specification for brazing filler metals
• EN ISO 17672 — European harmonised specification (formerly EN 1044)
• ASTM B260 — Specification for brazing filler metal

BAg silver brazing alloys

BCuP copper-phosphorus alloys (Cu-Cu only)

For copper-to-copper joints — most commonly HVAC refrigerant tubing — the BCuP series is preferred because the phosphorus acts as a self-fluxing agent (no separate flux needed on copper). BCuP must not be used to braze brass-to-brass or brass-to-copper joints because the phosphorus reacts with zinc to form brittle Zn₃P₂ intermetallic and the joint fails.

• BCuP-2 — 93 Cu / 7 P. Liquidus 802°C. Standard refrigerant tube brazing.
• BCuP-5 — 80 Cu / 15 Ag / 5 P. Liquidus 645°C. Lower temp, better ductility, no separate flux.

4. Welding

Welding brass is unusual because zinc vaporises at 907°C — close to brass's melting range — and the resulting fume is both a health hazard and disruptive to the weld pool. For most brass-to-brass fabrication, brazing is preferred. Where welding is required:

• TIG (GTAW) with low-Zn filler — possible on low-Zn brasses (CW724R, alpha brasses with Zn < 30%). Argon shielding, helium addition for heat transfer.
• Oxy-acetylene fusion welding — historical method, mostly obsolete; still used for repair of statues and architectural restoration.
• MIG (GMAW) — bronze-MIG with silicon-bronze filler is the practical industrial method for joining brass-to-steel or brass-to-stainless. Effectively a low-temperature brazing process rather than true welding.

5. Threaded joints

The dominant joining method for brass fittings worldwide. See the Thread Standards Guide for the full reference on BSP / NPT / metric / JIC / SAE / ORFS thread standards.

Sealant choice for threaded joints:

• PTFE tape (1.5–2.5 turns wrapped in the thread direction) — most common, low-pressure plumbing and gas.
• Anaerobic thread sealant (Loctite 567, 577) — fills the helical leak path, cures only inside the joint. Higher-pressure rating than PTFE tape.
• Pipe-dope (organic compound paste) — legacy plumbing method. Less common now.
• Bonded washer (Dowty seal) — for BSP parallel (G) joints: elastomer-on-steel washer compressed at the face. Reusable, very leak-tight.

6. Compression fittings

The classic plumbing method for joining brass to copper tube. The "olive" (ferrule) is compressed onto the tube as the nut is tightened, deforming the olive against the tube and seating it on the fitting body's internal cone. Result: a leak-tight metal seal that holds 100–400 psi depending on size and design.

• Standard olive — symmetric brass ring, ~3–5 mm wide on a 15 mm tube fitting. Deformed against the tube.
• Double-ferrule (e.g. Swagelok-style) — front and back ferrule together provide an interference grip and a separate sealing surface. Higher pressure rating.
• One-time olive rule — once an olive is deformed onto the tube, it cannot be re-used. Always replace the olive when remaking the joint.

7. Press-fit, push-fit and crimp

• Press-fit — a brass or copper fitting with an internal EPDM O-ring is pressed onto the tube using a specialised press tool. The press tool deforms the fitting at two locations, locking it mechanically and sealing on the O-ring. Used for commercial and residential plumbing where install speed matters. EN 1254-7 standard.
• Push-fit — fitting contains an internal collet with stainless-steel teeth. Pushing the tube into the fitting causes the teeth to grip; an internal O-ring seals. Reversible by depressing a release ring. Domestic plumbing.
• Crimp — for PEX pipe to brass fitting: a copper or stainless crimp ring is squeezed over the joint. ASTM F1807 standard.

8. Decision matrix — which method when

Frequently asked questions

9. Sources & references

Last reviewed: June 2026. Joining specifications are periodically revised; for safety-critical work verify against the current published edition of the cited standard.