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Is post weld heat treatment required when welding copper-nickel alloys?

Post weld heat treatment is normally unnecessary.

Are 90-10 and 70-30 copper-nickels susceptible to stress corrosion cracking?

They do not experience chloride or sulphide stress corrosion. They have a high resistance to ammonia stress corrosion compared to other copper alloys and do not require a stress relief anneal for seawater service.

Are 90-10 welding consumables available for welding 90-10 copper-nickel?

They are available but 70-30 copper-nickel consumables are preferred for welding both the 90-10 and 70-30 alloys due to superior deposition characteristics.

Are copper-nickel alloys susceptible to the attachment of marine organisms in seawater?

Copper-nickel alloys can harbour slimes, but the attachment of macro-organisms—such as marine grasses and shellfish—is impaired. If these do become attached under quiet conditions, adherence is poor and they can be easily removed mechanically.

Can copper and copper alloys be hardened by heat treatment?

Some alloys can, including copper-beryllium, copper-chromium and copper-nickel-silicon. Most unalloyed coppers and brasses can only be softened by heating.

Can copper-nickels be brazed?

Yes they can be brazed by all processes. Appropriate silver brazing alloys should be used as phosphorus bearing brazing alloys cause a reaction with nickel to form a brittle phosphide phase.

Can copper-nickels be welded directly to steel?

Yes they can using appropriate 65% nickel-copper consumables to avoid iron dilution effects.

Which copper alloys are currently available for aquaculture and do they have different applications?

Three alloys are currently commercially available: copper-zinc, copper-nickel and copper-silicon.

Copper-zinc is good for flexible mesh containment systems.
Copper-nickel is good for rigid (e.g. welded) mesh.
Copper-silicon is good where rigid mesh is needed, or where panels can have flexible connections.

How much silver is present in nickel silvers?

None, nickel silvers are copper-nickel-zinc alloys which have an attractive colour when polished.

What are the critical pitting and crevice corrosion temperatures for copper-nickels in chloride environments?

Copper-nickels do not behave in the same way as stainless steels do towards corrosion by chlorides and these parameters are not appropriate to them. They do not have a critical temperature limit.

What types of corrosion are copper-nickels sensitive to?

It is important that maximum velocity guidelines are adhered to for piping and heat exchanger/condenser service, as high velocities can cause impingement attack. Exposure to sulphides and ammonia in polluted seawater can lead to pitting or high corrosion rates and it is important to avoid these conditions, particularly during commissioning, start up and standby.

What copper alloy is recommended for condenser tubes cooled by seawater?

90/10 (or 70/30) copper-nickel alloys.