How to weld copper – oxygen-acetylene

Welding Copper Pipe: Oxygen / Acetylene

Safety: Arrange working conditions per OSHA standard practice and rear the proper  protective gear: Long leather gloves without holes, Safety glasses, welding helmet with auto darkening, welding pants and jacket, solid leather boots, respirator, welding table, a bucket of water, and a certified fire extinguisher. All flammables from your non-flammable working surface must be removed. Remove everything except what you need for welding. The welding helmet, shields your skin and eye(careful here) from any sparks; also,  protects against  damaging ultraviolet rays that can burn  your vision. Note: exposed skin will result in a very bad sunburn, so take care. Fully ventilate the area or work outside. Only have the gas welder on ONLY when welding. Tempting:  leave it lit for a moment while you quickly grab something, but, don’t put a lit torch down!  Keep cylinders away from the welding area and fasten in your cart.

Auto Darkening for copper welding

Figure 1 Auto-darkening helmet: welding copper pipe. Don’t fool around, only use the auto-darkening type, your eyes are worth it.

Only weld clean shiny copper. Remove all contaminants….The weld will turn crappy if everything is not newly shiny(wipe condensation from sweating copper pipes, dirt, with isopropyl alcohol, then,  wipe with a dry, clean,  rag).

Use a grinder, emery cloth, wire brushes, to eliminate copper oxide and make everything new looking(shiny). Clamp work securely.

Picking materials: Try to use oxygen-free copper because it  gives off less hazardous fumes.

Picking your welding equipment: Most welders prefer old school: the oxy/acetylene torch set up. Copper is very heat conducive; heat rapidly spreads across the piece. Torch installs enough heat to easily preheat, conversely, a welding machine applies heat into a very small surface area. So, lets talk about oxy  welding.

Welding Copper pipe

Figure 2 Welded copper pipe

Gas equipment set up: Select your head. Use a number 2 or 3, not a cutting head. Be sure to clean the tip free from contaminants before starting. Turn off all valves, both at the torch and the gas cylinders. Slowly turn on the acetylene about a half turn. Pressure should be around 6 psi. Then quickly turn on the oxygen to about 9 psi and light. Did we talk about how important ventilation is ?  The flame will be smoky orange now…increase the oxygen until you get a white and blue flame, the white should be about .4 inches long. Don’t turn on the oxygen too quickly or you’ll flood out the flame. Better to start with a smaller flame and work slowly when beginning.


Test out on scrap metal the same thickness before trying on your final product.

Figure 3 How to weld copper pipe

Start your puddle:. Feed your LEAD FREE silver copper alloy rod into the puddle, again with a small semi-circular motion, then quickly advance the gas tip and rod until complete. Finished result should appear:  a stack of dimes laid aside. The conclusion result is that the two pieces you are welding, and the filler metal all mixes together. Practice with horizontal scrap before attempting vertical joints. The vertical puddle can drip away easily and requires good timing. Always let the copper air cool(not fan assisted) to avoid cracks.

How to Weld Copper Pipe

Figure 4 Welding looks like stack of dimes

Here’s interesting melting point information below. Very hot!

METALs                  Melting points(F)

Copper 1983
Silver, Sterling 1640

How to weld copper with a machine will be in another article. Sweating copper pipe is on the home page.


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