How to Keep Copper-Nickel Welds From Cracking

As with other metals, copper-nickel welds are at risk of cracking due to contamination.

Copper is often combined with other metals to produce alloys with certain advantages over single-element metals. Copper is often combined with nickel on marine and seawater equipment -- the alloy is resistant to corrosion, giving it a longer lifespan in salty seas than copper alone. Copper-nickel is used as piping and other equipment where salt or water is present, although copper-nickel's use isn't limited to these applications. When welding this alloy it is important that the metal be free of particulates and other contaminants, which can introduce impurities into the metal. These impurities weaken the alloy and can cause cracking.

Things You'll Need

• Organic solvents
• Clean cloths

Instructions

1. Clean the surfaces where copper-nickel welding will take place. This is important for most types of metals to maintain the highest integrity possible in the metal, but copper-nickel welds can be contaminated by the oil from fingerprints and other materials like sulfur, lead and phosphorus. The best way to keep these surfaces clean is to prevent contact between the welding surface and the contaminants. CopperInfo.co.uk recommends using clean cloths to wipe surfaces down with organic solvents that have not been contaminated, then allowing time for the surface to air dry.

2. Brush copper-nickel surfaces with stainless steel brushes to remove corrosion and other contaminants.

3. Avoid stepping onto sheets of metal prior to welding. Even in a clean environment, your shoes likely are carrying contaminants that can weaken the weld and lead to cracking.

4. Keep copper-nickel materials wrapped in their packaging or covered in sheets of plastic to protect them from contaminants. Wait until just prior to use before uncovering the copper-nickel.

5. Keep grease and paint away from the surface of copper-nickel welds. These substances can introduce elements like sulfur, lead and phosphorus that cause the weld strength to be compromised, leading to cracking.

6. Store copper-nickel welds vertically in racks to minimize their ability to collect particulates on their surface.

7. Produce copper-nickel welds using the manual metal arc process, along with flux-coated stick electrodes, when possible. According to Copper Info, this process is widely available for copper-nickel welding and inexpensive. Other alternatives include the gas-shielded tungsten arc, which produces high-quality welds in complicated joints, and the gas-shielded metal arc, which is done quickly and can be tightly controlled.

8. Apply a six-hour heat treatment of the finished weld after fabrication. This treatment involves first heating the weld to 675 degrees Celsius for six hours, then allowing it to air cool. According to Copper.org, this can strengthen the weld against potential cracking.

Tips & Warnings

• Do not use ammonia to clean copper-nickel surfaces. According to Copper.org ammonia increases the corrosion rate in copper alloys.

• Do not transfer grinding discs or stainless steel brushes between copper-nickel and other metal materials, as this can introduce contaminants.

References

• Copper Info; Copper-Nickel Fabrication; 1999
• Copper.org; Experience With Copper Alloy Tubing, Waterboxes and Piping in MSF Desalination Plants; October 1997