There are two main copper-nickel alloy grades used in marine service which are generally available in most product forms. These are copper base alloys with either 10% or 30% of nickel, and are described as 90-10 and 70-30 copper-nickel respectively. Both alloys contain small but important additions of iron and manganese which have been chosen to provide the best combination of resistance to flowing seawater and overall corrosion resistance.

The 30% nickel alloy is stronger and can withstand higher seawater velocities but, for most applications, the 90-10 alloy provides good service at a lower cost and of the two alloys tends to be the one that is more widely used. Their US and European alloy designations are given in Table 1.

Also worthy of mention is a modified 30%Ni alloy containing 2%Mn and 2% Fe, which is only commercially available as condenser tubing and is being used particularly in the heat rejection section of multistage flash desalination units where higher resistance to impingement corrosion is required.

Although ranges for elements in the chemical compositions vary between standards, grades of the 90-10 and 70-30 alloys suitable for welding generally fall within the limits given in Table 2. Maximum levels are defined for some specific impurities because of their effects on hot ductility, hot workability, and weldability. These elements can also arise from external contamination and therefore precautions are necessary when the alloys are handled during forming and welding. The 2%Mn and 2%Fe grade is produced as seamless tube for expanding into tube sheets so that welding is not necessary. A companion welding product is not available.

The 90-10 and 70-30 alloys, however, are readily welded by most common methods. Consumables of the 70-30 alloy should be used to weld both alloys. For welding copper-nickel to steel, 65% nickel-copper alloy consumables should be used as they can tolerate more iron dilution from the steel than the 70-30 copper-nickel alloy consumables.

Weld consumable specifications and compositions are shown in Table 3. They contain small titanium additions to counteract atmospheric contamination during welding operations.