Valves are used on all hydraulic circuits, including sea water and some chemical products which can be corrosive, to shut or regulate the flow. For all the valve components in contact with the liquid, it is important to select the raw material which will ensure operation and tightness during the entire lifecycle. Nickel aluminium bronze alloys, also called NAB alloys or aluminium bronze are a family of copper based alloys including nickel, aluminium and iron enabling to meet the correct corrosion resistance while giving good mechanical characteristics. Aluminium bronze alloys are definitly to be considered in front of titanium and duplex or super duplex alloys as they offer various other advantages.
Valves exist in various configurations (Gate valve, butterfly valves, globe valves, check valves, discharge valves …) for all of which NAB alloys can be used in foundry ( sand casting, centrifugal casting, continuous casting ) or forgings to manufacture various components such as :
Our capabilities enable us to cast any valve components up to 112’’ (DN 2800 ) for an estimated finished machined weight of 8T. Valve castings are usually made according international nickel aluminium bronze standards sur as EN 1982, ASTM B148, BS 1400 but also according more stringent military standards such as Def Stan, Gamm MM11 or MM12, MILSTD. The castings are delivered worldwide as cast, rough or fully machined (with or without hydraulic test and heat treatment). Valves used in shipbuilding or offshore applications regularly have additional requirements such as third party inspections by classification society (Lloyds, Bureau Véritas, DNVGL…) or a specific PED certification.
Nickel Aluminium Bronze alloys are overlooked compared to duplex and super duplex steels, yet they offer interesting properties in corrosive environments. .
Casted Aluminium Bronze is manufactured according to many different international standards ( EN 1982, ASTM B148, Inoxyda proprietary alloys …) and are a combination of copper, aluminium, nickel, iron, manganese which are combined to meet the best compromise between improved mechanical strength, corrosion resistance, weldability and machinability.
These additions produce a unique set of properties (Ref 1) which are useful in valve components :
Some examples of mechanical properties reached by Nickel Aluminium Bronze (NAB) alloys :
For sea water applications the castings can be heat treated at 675°C for six hours to improve the corrosion resistance and for maximum corrosion resistance it is also recommended that aluminium should be less than Al % < (8.2 +Ni /2 )
Other typical valve applications include components in submarines and surface vessels within the Defence Marine sector, firefighting equipment on oil rigs and desalination plants.
Typical properties within these sectors include.
Many design engineers, by lack of data, consider copper based alloys as being low strength. Below chart gives a general comparison between different alloys :
The purpose of pumps is to move liquids, which can sometimes be corrosive as for example sea water or certain chemicals, while turbines are mainly used in electricity generation processes. Choosing the correct material is a critical step to ensure long term service of the pump (for industrial process, cooling or firefighting) or turbine (mostly Kaplan). Aluminium bronze alloys, also called NAB alloys or Nickel Aluminium Bronze, are copper based alloys including Nickel, Aluminium and Iron which gives it both very good corrosion resistance and good mechanical properties, in particular regarding cavitation. Copper based alloys of NAB family should be considered at early design stages in comparison to titanium and duplex or super duplex steels as they offer several advantages among which a good machinability.
Aluminium Bronze alloys are available using various casting processes: sand casting, centrifugal casting or continuous casting for smaller fully machined pump components but also using forging when looking very higher mechanical characteristics thus offering opportunities to manufacture various engineered pump components such as :
Our in house capacities enable us to cast about any pump components up to roughly 4m X 4m and 8t finished machined weight. Casted aluminium bronze components are available according various international standards (EN1982, ASTM B148, BS…) or military (Def Stan, Gamm MM11 or MM12, MILSTD) and can be delivered worldwide in as-cast, rough or final machined stage (including pressure testing, balde sharpening, slotting or balancing). On the side of well known standardised NAB alloys, specific aluminium bronze grades such as Inoxyda 3 Cryo have been developped for very low temperatures.
Bronze alloys are known for friction properties when Aluminium Bronze or Nickel Aluminium Bronze (NAB) alloys are much less known; yet, they offer unique corrosion characteristics as required by pumps, especially in sea water corrosion environments, along with interesting biofouling properties. Those 2 properties make them a preferred solution for all marine related applications (pumps, valves, heat exchangers, propulsion systems).
Aluminium Bronze is a family of alloys including copper, aluminium, nickel and iron ; Each individual component can be adjusted to improve strength, corrosion resistance and/or machinability.
Those combinations allow a unique set of properties (Ref 1) which are usefull in many pump application :
With a main property coming from the protective oxide surface film which has the ability to self- repair, it outstands steel coated applications in the long run.
Optimum corrosion protection is reached when :
Some design engineers, by lack of data often consider copper based alloys of being low strength but again correct selection can lead to high mechanical properties such as with Inoxyda 154 grade.
Very well known to all pump specialist, this results from small water vapour bubbles are formed from the turbulence at low pressure points and these can migrate to high pressure points where they collapse violently on the surface of the component causing eventually erosion at the point of contact. Nickel Aluminium Bronze has excellent resistance to this phenomenon and as such is still the predominant alloy for propellers in shipbuilding industry.
A main requirement for cryogenic pumps is the resistance at low temperatures. Unlike most steels, copper based alloys do not embrittle and have a good dimensional stability at low temperatures down to -190°C . A main issue to be addressed in those applications is the possible presence of oxygen which reduces to scope to bronze alloys; for other application aluminium bronze are regularly used, such as for example the Inoxyda 3 Cryo alloy .
Biofouling can be a serious problem with any systems handling sea water, particularly at elevated temperatures with warm climates.
High copper alloys have considerable resistance to the growth of crustaceans, sea weeds and other marine organismsThe slow dissolution of copper ions inhibits their growth and prevents mass population. The adherence of crustaceans on Nickel alloys and stainless steels can have a massive impact on their corrosion resistance due to crevice corrosion caused by differential aeration associated with these growths.
NAB alloys have 2 main advantages compared to Duplex and Super Duplex alloys :
More detailed technical information available :