^ Fig. 8. Pressure testing (credit Inoxyda).
The purpose of this resume is not to deal with all corrosion scenarios but rather to present the main properties of Nickel Aluminium Bronze (NAB) alloys so that their possibilities can be considered early in the design phase of future projects. This family of copper-based alloys is not very well known. Nevertheless, because of their properties, they are a solution worth considering for a number of applications, for even if these alloys are regularly ignored at the expense of titanium, duplex steels, and more generic bronze alloys, they nevertheless provide an excellent solution in many heat exchanger, valve, and pump applications.
The properties of NAB alloys are such that they can even be compared to the capabilities of titanium.
|Specification||Grade||Rm Tensile Strength Mpa||Rp Proof Stress 0.2% MPa||A Elongation %||Hardness HB|
|EN 1982||CuAl10Fe5Ni5 (CC 333 G)||600||250||13||140|
|INOXYDA||I 154 forged||800||500||10||240|
|EN 1982||CuSn10 (CB480K)||250||130||18||70|
Some applications, have additional requirements with regards to:
- Cavitation for pumps.
- Low temperatures for cryogenics.
- Non-magnetic for mine hunter propulsion.
- Non sparking for improved safety on offshore platform.
Much more unusual, but nonetheless interesting, is that the presence of copper and aluminium gives excellent electrical and thermic conductivity capabilities as required for electrical motor cooling applications in sea water environment.
- Sand casting for complex and large size parts (pump casings, impellers, valve bodies…).
- Centrifugal casting (bushings, rings, pressure screws…).
- Continuous castings (billets ready for machining small components or forgings).
And today in connection with the 3D sand printing process, the hassel of creating and storing patterns can be removed, thus creating another advantage for casting technologies.
Controlling the quality of casted components
In addition to commonly required dimensional controls, the quality of casted parts are controlled through a NDT tests such as
- Chemical analysis : spectrometer
- Mechanical properties : tensile test, charpy test, hardness
- Corrosion resistance : salt spray test or micrography,
- Surface defect : dye penetrant test,
- Internal defects : X rays,
- Water tightness : pressure test.
Biocide/biofouling : a property often ignored
Copper is already known for its biocide properties, which in association with nickel, offers excellent biofouling performances. These are found to be interesting for all systems subject to marine organisms since they avoid the application of an additional chemical biofilm to protect infrastructures such as propulsion systems and heat exchangers.
|Casting||Machining||Material cost||Corrosion||Heat treatment||Impregnation|
|Bronze alloys||++||+++||++||++||No||Often needed|
When engineering complex systems different factors have to be taken into account throughout the lifecycle of a product. The end life of a product is not always considered in detail and, again, there are NAB alloys that offer interesting features:
- Reduced downtime due to leakage.
- 100% recycling capabilities as these alloys can be produced from industrial scrap, thus reducing the pressure on world resources.
- Scrap still has an interesting value and can be reused thus increasing ROI even after full equipment has been amortized.
- Guide to Nickel Aluminium Bronze for Engineers, I. Richardson (Copper Development Association).
- Interest in the Use of Cupro Aluminium in Chemical and Allied Industry, (Sulzer Brothers Ltd, Winterthur.
- Aluminium Bronze and their uses. P. Weill Couly, Chief Engineer FFAHR.
- Propriétés Générales du Cuivre, Centre d’Information Cuivre-Laitons-Alliages.
- NAB vs Titanium, Karan Sotoodeh in Valve World, Nov. 2019.