Soldering + Brazing Reference
Why this matters
Solder + braze joints are the foundation of every copper plumbing, refrigeration, + electrical-connection job. Wrong filler, wrong flux, wrong heat, OR contaminated joint = leak the customer finds in the wall a year later. Field techs solder/braze constantly + need the temperature + filler basics cold. This is the field card.
Soldering vs brazing (the distinction)
Soldering: filler melts below 840°F (450°C). Lower temp, weaker joint, easier work. Plumbing standard.
Brazing: filler melts above 840°F (450°C) but below the base metal melt. Higher temp, stronger joint, refrigerant-rated. HVAC refrigerant line + structural.
Welding: filler + base metal both melt (not covered here).
Common solders + uses
50/50 tin/lead : traditional plumbing solder, NOT for potable water lines (banned 1986 federal). Service work on legacy systems only.
95/5 tin/antimony : lead-free, code-compliant for potable water. Wide temp range. Most common potable water solder.
Sn96 (96% tin / 4% silver) : premium, low-temp, high-strength. Some electrical + critical plumbing.
Lead-free solder paste (for circuit boards): different formulation.
Silver-bearing (Sta-Brite, Stay-Brite) : higher temp solder, near brazing strength. Refrigeration low-side.
Common brazing alloys
Silver braze 56% silver (BAg-7). Best flow + corrosion resistance. Stainless steel + brass + copper-to-steel joints. Flux required.
Copper-to-steel brazing needs silver alloy + flux (phosphorus alloys don't work).
Flux
Water-soluble flux (for tin/lead + lead-free solder): white paste, applied to clean joint, activates at solder melt temp. Wipe clean after.
Self-cleaning flux (Oatey No. 5, Bridgit): general plumbing.
Brazing flux (Stay-Silv, Handy Flux): high-temp; for silver brazing + brass/steel.
No flux required: copper-to-copper brazing with BCuP filler (self-fluxing).
Joint preparation
- Cut pipe square (tubing cutter, not hacksaw)
- Deburr inside + outside (reamer + sandpaper)
- Clean OD of pipe + ID of fitting with emery cloth OR fitting brush to bright copper
- Apply flux thin coat to both surfaces
- Insert pipe to stop, twist 1/4 turn to distribute flux
- Heat OPPOSITE side from filler entry; filler flows TOWARD heat
Heat source
Propane torch: adequate for solder on 1/2" - 1" copper. Slow for larger pipe.
MAPP / MAP-Pro torch: hotter (≈ 2900°F vs propane 1900°F). Faster for solder; marginal for brazing.
Oxy-acetylene : up to 5,500°F. Required for brazing. Bench OR portable.
Air-acetylene (Turbo Torch, Goss): hotter than propane, no oxygen tank. Common HVAC brazing rig.
Heat gun: not enough for solder; some compression fittings only.
Temperature ranges
Solder melt temps:
- 50/50 tin/lead: 361 - 421°F (working temp ~ 450°F)
- 95/5 tin/antimony: 452 - 464°F (working temp ~ 500°F)
- Sn96 (4% silver): 430 - 470°F
Brazing alloys:
- BCuP-5: 1190 - 1480°F
- BCuP-3: 1190 - 1500°F
- BAg-7: 1145 - 1205°F
Sweat joint technique (soldering)
- Heat fitting (not pipe) until flux bubbles
- Touch solder to joint opposite of heat
- Capillary action draws solder around
- Wipe excess with damp rag
- Don't move joint until cool
Visual confirmation: silver ring all the way around joint. Black flux residue = too cold OR oxidized.
Brazing technique (refrigeration)
- Purge line with dry nitrogen 2 - 5 SCFH during heating (prevents oxide scale that contaminates compressor)
- Heat joint with rosebud OR brazing tip
- Both pipes to dull cherry red
- Touch filler to opposite side of joint
- Filler flows toward heat
- Allow to cool naturally (don't quench)
Nitrogen purge: critical for HVAC refrigeration. Without it, copper oxide forms inside, breaks loose, scores the compressor. Mandatory for warranty.
Common solder + braze mistakes
Dirty joint (didn't sand bright copper) = leak. Too much flux (drips inside; corrodes long-term). Wrong solder (lead solder on potable water = code violation + lawsuit). Overheating solder (oxidizes; doesn't flow). Insufficient heat (joint cold; "cold joint" leaks). Moving joint before cool = cracked. Skipping nitrogen on refrigerant lines (compressor failure within months). Wrong flux (no-clean electrical flux on plumbing won't activate). Using propane torch on 3" copper (heat sinks too fast; can't reach temp).
Pipe sizes + heat needed
- 1/2" copper: propane sufficient
- 3/4" copper: propane works (slow), MAPP faster
- 1" copper: MAPP minimum, air-acetylene better
- 1-1/4"+: oxy-acetylene OR air-acetylene
- Brazing 1/2" - 1": air-acetylene minimum
- Brazing 1-1/4"+: oxy-acetylene
Safety
Fire: heat shield + spray bottle nearby. Wet rag for cooling. Watch for combustibles inside walls (heat-shielded blanket).
PPE: safety glasses (always), gloves (heat-resistant), respirator for lead solder OR flux fumes in confined space.
Burns: flux + solder + pipe stay HOT for several minutes after.
Ventilation: brazing produces ozone + metal fume; ventilate.
Cleanup
Wipe joint with damp rag while still warm to remove flux. Cold flux + water = green corrosion on copper. Pressure-test joint per system spec (water, air, OR nitrogen).
Truck stock (HVAC/Plumbing)
Plumbing: 1 lb 95/5 solder, water-soluble flux, brushes, emery cloth, MAPP torch + tip, spray bottle, heat blanket.
HVAC: 1 lb BCuP-5 silver braze, Stay-Silv flux, oxy/acetylene rig OR air-acetylene, nitrogen tank + regulator + purge fitting, emery cloth + brush set.
References
- NSF/ANSI 61 (drinking water system components)
- ASTM B32 (solder metal)
- AWS A5.8 (filler metals for brazing)
- Manufacturer technical data (Oatey, J.W. Harris, Lucas-Milhaupt)
- Manuall internal: Refrigerant Charging, Copper Pipe Sizing