Copper is having high thermal and electrical conductivity. It also offers very good corrosion resistance to seawater corrosion, chemicals, and general corrosion. Copper alloys have varied properties compare to copper depending on the chemical composition.
Material delivery Specification:
ASME B16.22, 16.50, ASTM B-42, ASTM B-75, ASTM B-111, ASTM B-152, ASTM B-280, ASTM B-302, ASTM B- 359, ASTM B-543, ASTM B-819
ASME Section IX welding P. No. for copper and copper-base alloys: P31, P32 & P33
Alloys of copper:
- Brass -Copper zinc alloy
- Phosphor bronze- Copper tin alloy
- Aluminum bronze- Copper aluminum alloy
- Silicon bronze- Copper silicon alloy
- Cupronickel- Copper-nickel alloy
Welding consideration for copper welding:
- Copper has high thermal conductivity, approximately 8 times to of steel. This results in very fast heat dissipation in welding.
- The tendency of lack of fusion and insufficient penetration due to high thermal/heat conductivity.
- Chances of porosity due to hydrogen absorbed during welding.
- Risk of hot cracking when welding electrolytic tough pitch copper (C11000 type).
SMAW Welding of copper:
Weld using ECu and ECuSi, ECuSn-A, and ECuSn-C types of welding electrodes.
ECu type welding electrode shall be used when copper is joined for good electrical or thermal conductivity application. E.g. electrical connection or heat sink/ heat transfer weld connection.
ECuSi, ECuSn-A, and ECuSn-C types offer good weldability when good electrical or thermal conductivity is not required, i.e. when need to form joints in pipes or structure. These electrodes offer good penetration & fusion as their thermal conductivity is lower due to alloying. Application for example is copper piping for liquid transfer, copper tank welding, etc.
TIG/ MIG welding of copper:
TIG/ MIG welding is carried out using ERCu, ERCuSi-A, ERCuSn-A, etc.
The applications of these consumables are similar to their equivalent SMAW electrode as explained above.
Pure argon is used as shielding gas for copper welding in TIG & MIG welding. Helium is mixed with argon, which helps to decrease the preheating temperature. TIG welding is useful up to 5 mm thickness. For thickness above 5 mm, MIG welding is preferred.
Preheating of copper for welding:
The loss of heat in the welding joint due to high thermal conductivity requires copper to be preheated before welding. Preheat temperature depends upon:
- Base metal thickness
- Welding process used
- Type of shielding gas
The below graph (Considering the above 3 parameters) is a good guide to deciding the minimum preheat temperature when welding copper:
The below picture shows the effect of shielding gas and preheats temperature on welding penetration in MIG copper welding having identical welding current and travel speed.
Welding Copper to Carbon steel/ Stainless Steel with SMAW, TIG/ MIG
Use ECuSi when welding SMAW welding. ERCuSi-A shall be used for TIG/ MIG welding.
Preheat the copper to 200- 400°C before welding to achieve good fusion & avoid insufficient penetration issues.
Brazing is a versatile method for copper joining. Braze joints are strong and good fatigue resistance.
The main difference between a brazed and soldered joint is the amount of joint overlap or fill necessary to develop the full strength of the joint.
In a brazed joint, full insertion of the tube to the back of the fitting cup is highly recommended; although, complete fill of this joint space thru this entire length is not essential to achieve full joint strength. According to the American Welding Society (AWS), it is recommended that the brazing filler metal penetrate the capillary space at least three times the thickness of the thinnest component being joined, which is usually the tube. This is known in the industry as the AWS 3-T Rule as explained in the below picture.
Brazing Filler wire
BCuP type (SFA 5.8) – Here B stands for Brazing, Cu is the chemical symbol for Copper, and P is the chemical symbol for Phosphorous. Hence, a BCuP brazing alloy is mainly a copper-phosphorous brazing alloy that may contain from 0%-30% Silver (Ag). These brazing filler metals should not be used on ferrous or nickel-based alloys or on copper-nickel alloys containing a nickel content in excess of 10%, as brittle intermetallic compounds are formed at the brazing filler metal–base metal interface.
- BAg type (SFA 5.8) – Here the B stands for Brazing and Ag is the chemical symbol for Silver. While there are other elements found in BAg alloys besides silver, most of BAg alloys may contain silver content of anywhere between 24% and 93%.
The brazing temperatures for these brazing alloys used to joint copper piping mainly (BCuP and BAg alloys see below) are between 1,150°F/621°C and 1,550°F/843°C.
More details for the various brazing rod can be found in ASME Section IIC, SFA 5.8: Specification for Filler Metals for Brazing and Braze Welding.
Steps for brazing
- Clean the surface with the cloth.
- Apply the flux to both surfaces to be brazed. When brazing copper to stainless steel, choose flux capable to etch stainless steel.
- Slip parts together. The tube should be fully inserted into the fitting for a sound brazing joint. Best results are obtained with clearances of 0.03 mm to 0.08 mm [0.001 into 0.003 in].
- Heat the joint in a circular motion to apply uniform heating. Apply the brazing rod. Tighter the joint, the better the joint capillary action.
- Clean the part after it cools.