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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 :

Valve Bodies
Dics and wedges
Bonnets
Retention ring

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: a reconsideration for casted valve components

Nickel Aluminium Bronze alloys are overlooked compared to duplex and super duplex steels, yet they offer interesting properties in corrosive environments. .

Aluminium Bronze Properties

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 :

High Strength
Density (5 % lighter than steel)
Non sparking (important in some high risk applications)
Low magnetic permeability (of <1.03µ in selected grades)
High Corrosion resistance)
Good cryogenic properties
High resistance to cavitation
High resistance to biofouling (often an ignored property)
A protective oxide surface film which has the ability to self- repair

Some examples of mechanical properties reached by Nickel Aluminium Bronze (NAB) alloys :

Rm
Tensile
Strength
Mpa min
Rp
Proof Stress
0.2%
Mpa min
A
Elongation
% min
Hardness
HBW
min
CuAl9Mn1.5 470 140 25 110
CuAl10Ni3Fe2 500 180 18 100
CuAl10Fe5Ni5 600 250 13 140
CuAl11Fe4Ni4 680 320 5 170

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.

General Corrosion rate 0.05-0.075mm/year
Resistance to crevice corrosion
Impingement resistance Up to 4.3m/sec
Free corrosion potential -0.25V sce
Resistant to stress corrosion cracking
High resistance to cavitation and erosion corrosion
Mechanical Strength

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 :

Pump casings ( split pump, centrifugal, volute)
Impellers (closed, open, fish freindly)
Suction casings or diffusers
Discharge elbows
Riser colums
 
 

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.


Interesting Properties of Nickel Aluminium Bronze (NAB) in Pump Engineering

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).

Interesting properties of Aluminium Bronze for Pumps

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 :

High Strength
Excellent wear and galling resistance
Density (5 % lighter than steel)
Non sparking
Low magnetic permeability (of <1.03µ in selected grades)
High Corrosion resistance
Good stress corrosion properties
Good cryogenic properties
High resistance to cavitation
High resistance to biofouling

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 :

an additional heat treatment at 675°C for six hours is applied
aluminium should be less than Al % < (8.2 +Ni /2 )
Mechanical Strength

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.

Cavitation : an issue in pump design

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.

Cryogenic Pumps : very low temperature requirements

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 : a property often ignored in pumps

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.

Machining & Repairability

NAB alloys have 2 main advantages compared to Duplex and Super Duplex alloys :

Machining of Nickel Aluminium Bronze is easier and more cost effective ,
Nickel Aluminium Bronze can easily be repaired by qualified welders, most of the time using TIG with corresponding feeder material (use of matching welding electrodes is critical to minimise corrosion problems particularly in sea water applications)
Summary

More detailed technical information available :

Guide to Nickel Aluminium Bronze for Engineers (by Ivan Richardson – Metallurgical Consultant), published by the Copper Development Association) is available for download: http://www.inoxyda.co.uk/telechargement.php
EN 1982 – European standard for copper based castings
ASTM/ASME – American standards
  • Aluminium Bronze Heat Exchangers
  • NAB Channels
  • Inoxyda 90 Tubesheet
    (ASTM B 171 C 63000)
  • Inoxyda 53 casted channel
    (ASTM B148 C 95800)
  • Custom Made Aluminium Bronze Tubesheets
  • Floating heat

Sheets

2 alloys in permanent stock
Available stock of 2 mm to 35 mm
Cu Al9 Ni5 Fe4 or Cu Al9 Ni3 Fe2

Bars

2 alloys in permanent stock
Cu Al9 Ni5 Fe4 or Cu Al9 Ni3 Fe2
Round bars of Ø3 to 90
Hexagons bars 7mm to 70 mm

Continuous casting

Permanent stock
Ø100 à Ø415

Forge

Round bars
Flat bars
Other bars
Flanges
etc.