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Why TIG for copper heat exchanger repairs
Copper conducts heat quickly, so a small repair can pull warmth away from the weld before the joint fuses. That makes TIG useful: the operator can place a controlled arc on a narrow area, add filler by hand, and stop quickly. But a TIG welder alone will not make a sound heat-exchanger repair. Clean metal, a well-fitted joint, suitable filler, and enough heat at the workpiece matter just as much.
First confirm the exchanger is copper and identify any brazed joints, coatings, or nearby steel. Drain and thoroughly clean it; trapped water or residue can contaminate the weld or turn to steam. Heat exchangers may also be pressure-bearing components. Follow the manufacturer’s repair limits and applicable pressure-vessel rules, and have a qualified technician inspect and test the repair. If the part is thin, badly corroded, or inaccessible, replacement can be safer and cheaper than welding.
What to look for in a TIG welder
For copper, prioritize stable DC output, a foot pedal or fingertip amperage control, and enough capacity to overcome copper’s heat loss. A compact DC TIG machine in roughly the 200–250 amp class is a reasonable starting point for shop repairs, though the required current depends heavily on thickness, joint shape, and heat sinking. Thin tube can need far less; a thick fitting attached to a large copper mass may need preheating and substantially more heat.
AC/DC capability is not essential for welding copper itself: DC electrode-negative is commonly used. AC/DC machines cost more but are useful if you also weld aluminum. A basic DC TIG machine is the better-value choice when copper and steel are the main jobs. Look for a dependable low-current start, adjustable post-flow, and a duty cycle that suits your workload. A machine rated for 200 amps at a short duty cycle may need frequent cooling breaks.
Compare the main options
| Welder type | Best fit | Trade-off |
|---|---|---|
| DC TIG, about 200–250 A | Copper repairs plus steel and stainless work | Lower cost than AC/DC; no aluminum TIG capability |
| AC/DC TIG, about 200–250 A | Mixed copper and aluminum fabrication | Higher price and more settings to learn |
| Small inverter TIG, under about 160 A | Thin parts and light-duty work | May run short of headroom on thick fittings or heat-sunk joints |
For a dedicated copper repair station, start by comparing 200-amp DC TIG welders. If aluminum work is also on the list, compare AC/DC TIG welders. Check the actual output and duty-cycle chart, input voltage, included torch, and pedal—not just the advertised maximum amperage.
Setup and consumables that matter
Use an argon cylinder and regulator or flowmeter, and set shielding flow according to the torch and cup. A starting range around 15–20 cubic feet per hour is common indoors; drafts can disrupt coverage even at higher flow. Excessive flow can also cause turbulence and draw air into the shield. Use a clean, sharp tungsten and a suitable gas lens and cup for access to the joint. Keep copper filler rod appropriate to the base material and service conditions; do not assume generic filler is suitable for a pressure-containing exchanger.
Clean the joint to bright metal with dedicated abrasives, then remove oil and residue using a compatible cleaner and let it evaporate fully. Contamination causes porosity, unstable arcs, and poor fusion. Fit-up should be close and consistent: gaps make it harder to control the puddle and can burn through thin tube. Copper may benefit from controlled preheating, but the right temperature depends on the assembly and procedure. Avoid guessing with a torch near seals, brazing, or trapped fluid.
Common failure modes
Cold lap or lack of fusion: the bead sits on the surface while the joint remains unfused. Copper’s conductivity can make this happen when heat is not concentrated long enough. Improve fit-up and technique, and use adequate current rather than simply slowing down.
Burn-through: thin tube can collapse or develop a hole when heat builds locally. Use amperage control, short weld segments where the procedure permits, and a heat sink only if it does not pull excessive heat from the joint. Porosity: usually points to dirty metal, a draft, poor gas coverage, or contaminated filler. Stop and correct the cause; adding more filler over porous metal does not fix it.
A practical buying decision
Choose a DC TIG machine with pedal control and roughly 200 amps or more if you expect varied exchanger fittings, repair work, and general metal fabrication. A lower-output inverter can be perfectly adequate for occasional thin-wall work when the material is accessible and the joint does not draw heat away rapidly. Pay the extra for AC/DC only if you will actually weld aluminum or need the added capability for other jobs.
Budget for the complete setup: torch consumables, gas, regulator, filler, cleaning tools, and eye and skin protection. TIG produces intense ultraviolet light; use a properly rated welding helmet, gloves, and protective clothing, and provide ventilation. Before returning a repaired exchanger to service, use the required inspection and leak or pressure test for that equipment. A neat-looking bead is not proof that the repair is safe.