C12200 Tube in Automotive and Heating Systems
Radiators, heater cores, oil coolers and air-conditioning condensers all depend on copper tube that can be formed into dense, thin-walled cores and then joined into a leak-tight assembly. ASTM B111/B111M covers the seamless copper and copper-alloy condenser tube used for this class of heat-transfer product, and UNS C12200 is the grade most often selected for automotive and HVAC duty.
C12200 is deoxidised with 0.015 to 0.040 percent phosphorus, which removes residual oxygen and makes the metal weldable and brazeable. The same addition reduces electrical conductivity to the 70-90 percent IACS band, but for a radiator or heater core that trade is worthwhile: the alloy deep draws beautifully, resists pitting in water and coolant, and maintains its softness through the furnace brazing cycle.
Composition and Mechanical Requirements
| Item | C12200 requirement |
|---|---|
| Copper (Cu), including silver | 99.90 % minimum |
| Phosphorus (P) | 0.015 - 0.040 % |
| Total other elements | 0.05 % maximum |
| Product standard | ASTM B111/B111M, ASME SB111 |
| European designation | Cu-DHP, seamless tube to EN 12451 |
| Typical tube sizes | outside diameter 5 mm to 25 mm, wall 0.4 mm to 1.5 mm |
| Temper | Minimum tensile strength | Minimum yield strength | Typical use |
|---|---|---|---|
| Annealed, O60 | 207 MPa (30 ksi) | - | forming, bending, tube-sheet expansion |
| Light drawn, H55 | 250 MPa | 205 MPa | radiator and condenser tubes |
| Hard drawn, H80 | 310 MPa | 275 MPa | pressure containment, straight runs |
Typical physical data for the grade are a density of 8.90 g/cm³, a melting point of 1083 °C, a coefficient of thermal expansion of 17.7 x 10^-6 per °C over 20-300 °C, thermal conductivity of 290-365 W/(m·K), specific heat of 385 J/(kg·K), modulus of elasticity of 115 GPa and Poisson's ratio of 0.33.
Where the Tube Is Used
Engine cooling radiators, charge-air coolers and exhaust gas recirculation coolers.
Heater cores and cabin heating matrices for cars, trucks and off-highway machines.
Automotive air-conditioning condensers and evaporators.
Hydraulic and transmission oil coolers.
Building heating systems: radiator panels, underfloor heating pipes and solar thermal collectors.
Domestic hot water circuits and storage tanks where corrosion resistance matters.
Corrosion Behaviour in Coolant Service
C12200 gives excellent weathering resistance and very good resistance to a wide range of chemicals. It stands up to non-oxidising mineral and organic acids, alkaline solutions and saline solutions, and it resists pitting when exposed to severe weather and to natural waters. In engine coolant circuits the metal performs well with inhibited glycol coolants, provided the inhibitor package is maintained and chloride levels are kept low.
The practical limits deserve attention. Copper is attacked by oxidising acids, by ammonia and ammonium compounds, and by mercury or lead-bearing contamination. Brazing flux residues are a common cause of early failure in radiators, so cores must be rinsed and dried after joining. Where cooling water is aggressive or high-velocity aerated seawater is involved, tube life should be reviewed against the water chemistry before the bundle is built.
Forming and Joining Practice
Deep drawing and roll forming suit the soft annealed temper; the alloy's excellent deep-drawing characteristics are its main advantage over harder coppers.
Furnace brazing in a controlled atmosphere produces the fin-to-tube bonds in modern cores, and the low oxygen content of the grade avoids hydrogen embrittlement during the cycle.
Soldering and brazing both rate as excellent, gas shielded arc welding rates good, and coated metal arc welding is not recommended.
Annealing is carried out between 250 °C and 650 °C, stress relief between 200 °C and 250 °C, and hot working between 750 °C and 950 °C.
Tube ends should be deburred and cleaned before expansion or brazing; surface oxides and drawing lubricants prevent sound joints.
Inspection Points
Pressure and burst testing of the finished core or tube confirms the design margin, and flattening or expansion tests verify ductility.
Wall thickness and concentricity control both pressure rating and heat transfer, so they are measured on the finished tube.
Eddy-current testing detects cracks, laps and inclusions that could open up under thermal cycling.
Cleanliness limits on residual flux, lubricant and particle contamination should be agreed, because they drive long-term corrosion performance.
FAQ
Q: Why is C12200 preferred over oxygen-free copper for radiators?
The phosphorus addition makes C12200 easier to braze and gives better deep-drawing and pitting behaviour in water. Oxygen-free grades are preferred where maximum conductivity or vacuum cleanliness matters.
Q: What coolant chemistry does the tube tolerate?
Inhibited ethylene glycol and propylene glycol coolants are standard, provided inhibitor levels are maintained. Chlorides, ammonia and oxidising acids should be avoided or held to very low limits.
Q: Can the tube be used in a domestic heating system?
Yes. C12200 is widely used for radiator panels, underfloor heating and solar thermal circuits, where its resistance to pitting in hot water makes it a durable choice.
Q: How does the tube behave during furnace brazing?
The deoxidised chemistry prevents hydrogen embrittlement and internal oxidation, so the tube comes out of the brazing cycle sound and ready for pressure testing without an additional anneal.
Q: Which tempers are supplied for radiator production?
Light drawn H55 is typical for radiator and condenser tubes, annealed O60 for components that are formed after delivery, and hard drawn H80 where the tube must contain higher internal pressure.
Q: What is the biggest field failure risk?
Trapped brazing flux and aggressive water chemistry. Both attack the tube from the inside and are best controlled by proper rinsing after joining and by water treatment during operation.
