Weld Purging Copper Nickel (Cunifer) Pipework

To Understand Weld

Purging & to Obtain Clean Weld Roots

The use of Copper Nickel is still widespread in marine applications, where the corrosion

resistant properties of this alloy are valuable.

Copper Nickel pipework on submarines, other military vessels, oil production platforms and

other ships need many welded joints.

One of the key applications is in water sprinkler systems where the weld quality is as critical

as it might be in any marine application.

Correct weld purging is a key factor in welding Copper Nickel pipework.

Back purge gas type tends to be optional subject to experience.

See further information under 'Tip' 2. 

Welders will generally work to a WPS or Weld Procedure Specification that will specify the

gas for them, but in cases where it isn't specified, the welders can use purge Argon, an

Argon Hydrogen mix or an Argon Helium mix.

Some tips to make welds easier are as follows:

1. Clean the joints and any filler wire thoroughly. First with a mechanical "Scotch" type

product and then a liquid. Cleaning materials such as Acetone or Propanol could be used.

2. If the weld pool is sluggish, leading to a poor looking weld and poor penetration, use an

Argon Hydrogen mixed gas. That will improve the weld appearance, penetration and

wetting action

3. Snip the end of the filler wire if one is used for the root. That avoids transferring oxidised

impurities into the root.

4. A Trailing Shield fitted onto the welding torch provides a superior purge to the tops side of

the root as it is cooling.

5. Ensure at any Tack welds are fully purged. Use Aluminium Tape rings to contain the purge

during tacking and root welding. Tape rings prevent adhesive sticking to the joint area and

possibly transferring to the weld. Contact hft@huntingdonfusion.com for Tape Ring

procedure if needed.

6. Use high quality pipe purging devices to contain the weld purge just a few inches either

side of the weld.

7. Monitor the Oxygen level accurately before and during the weld to maintain about 100

parts per million (ppm) Purge Gas Purity.

8. Proper Weld Purging as part as a qualified Welding Procedure Specification will help to

ensure that there are no particles caused by corrosion to block sprinkler systems that are

used in safety at sea systems.