FAQ

What are the working temperatures for CuNi?

The upper working temperature for 90/10 and 70/30 CuNi is normally about 250C.

What are the working pressures for CuNi?

This depends greatly upon the application and type of material supplied. To discuss your particular requirement simply call a CuNi expert today. Call +61 (2) 9734 7730 to speak with a CuNi specialist.

What are the CuNi Standards?

-Offshore CuNi standards?

EEMUA 145 90/10 Copper Nickel Alloy Piping for Offshore Applications Specification: Flanges Composite,PN designed and Solid EEMUA 146 90/10 Copper Nickel Alloy Piping for Offshore Applications Specification: Fittings

-Shipbuilding CuNi standards?

DIN 86037 Loose flanges and welding necks for pipes of Copper Nickel alloys

DIN 86087 Fittings for butt welding into Copper Nickel alloy pipelines - Saddle type connections

DIN 86088 Fittings for butt welding into Copper Nickel alloy pipelines - Tees

DIN 86089 Fittings for butt welding into Copper Nickel alloy pipelines - Concentric reducers

DIN 86090 Fittings for butt welding into Copper Nickel alloy pipelines Elbows

Note: Its possible that some of these standards have recently changed. To be sure simply

call a CuNi expert today. Call +61 (2) 9734 7730 to speak with a CuNi specialist.

What is the Welding Process for CuNi?

Both 90/10 CuNi and 70/30 CuNi alloys are readily welded by skilled welders via the majority of welding techniques. Autogenous welding (which means welding without using a weld consumable) is not recommended due to the risk of weld porosity nor is the oxy-acetylene process practicable.

Copper Nickel alloys can also be joined using appropriate silver-base brazing alloys. Phosphorus-bearing brazing alloys are unsuitable. All processes can be used exceptvacuum brazing due to the high vapour pressure of some brazing alloy constituents. Torch brazing is the most common.

A 70/30 CuNi type welding consumable is preferred for both 90/10 CuNi and 70/30 CuNi alloys. This is because the weld metal is stronger than the 90/10 CuNi, has better deposition characteristics and is at least as corrosion resistant as the base metal. No post weld heat treatment is required for the 90/10 CuNi or 70-30 CuNi alloys.

Where do CuNi alloys sit within the Galvanic Series?

Copper Nickel alloys lie mid-way in the galvanic series and are compatible with other copper alloys. The 70/30 CuNi alloy is slightly more noble than the 90/10 CuNi alloy. Both CuNi alloys are more noble than zinc, aluminum, steel and manganese bronze. Copper Nickels are less noble than passivated stainless steels, nickel alloys and titanium and may suffer higher corrosion rates than normally anticipated if they come into electrical contact with those metals. Careful attention should be given to avoiding un-favorable galvanic area ratios, or suitable insulation to should be provided to prevent galvanic current flow.

Does CuNi have a natural resistance to marine macrofouling?

Copper Nickel has a much higher natural resistance to marine macrofouling than the majority of metals experience. This property can reduce the frequency of cleaning of piping systems and condensers, and it can decrease wave loading and fouling removal costs for platform structures. The biofouling resistance of Copper Nickel tubing allows shipboard condensers to maintain good heat transfer capability for several months between mechanical cleanings without the need for onboard chlorine generators.

Panels from 55 week exposure trials conducted at Langstone Harbour
showing effects of cathodic protection on biofouling resistance
of copper-nickel.

Panels are, left to right, steel, copper-nickel cladding on steel,
copper-nickel panels with aluminium anodes, and, on the far right,
freely exposed copper-nickel.

Why does CuNi have a natural resistance to corrosion and marine macrofouling?

The seawater corrosion resistance offered by Copper Nickel alloys results from the formation of a thin, adherent and protective surface film which forms naturally and quickly upon exposure to clean seawater. The film can be brown, greenish brown or brownish black. The initial film forms fairly quickly over the first couple of days but, depending on the sea water temperature, takes 2-3 months to fully mature. Initial exposure to clean seawater is crucial to the long-term performance of Copper Nickel.

Can you explain Velocity limitations of CuNi alloys in Seawater?

Velocity is the most important single factor influencing design and corrosion in seawater systems. Low general corrosion rates are maintained with Copper Nickel with increasing seawater flow rate due to the resilience of the protective surface film, and the corrosion rates continue as long as the flow velocity for a given geometry does not exceed a critical value called the" breakaway velocity". Above this, shear stresses are sufficiently high to strip off the protective corrosion film causing damage in the form of impingement attack otherwise known as erosion corrosion.Maximum design velocities, therefore, are specified to stop this from occurring.

It should be noted, however, that Copper Nickel has a higher relative resistance to the onset of erosion than copper and aluminium brass. The 70/30 alloy is better than 90/10.

What are the Guidelines for Successful Application of CuNi in Seawater Systems?

To obtain good service from Copper Nickel and take into account the properties they exhibit, several important guidelines emerge. First of all, it is important to use a material that has a carefully controlled composition; so, alloys should be ordered to internationally recognised standards.

Initial Commissioning of a CuNi product

It is often the fitting-out and commissioning period when problems are most likely to commence in relation to the forming of the protective film. The ideal situation whether in a ship or power plant is to recirculate aerated, clean seawater at initial start up for sufficient time to form a good protective film. When formed, this provides a high degree of corrosion protection to subsequent exposure to sulfides.
In situations where it is not possible to use clean seawater, circulating the system initially with fresh water containing ferrous sulfate additive will encourage effective film formation.

Ferrous sulfate treatment has been found to reduce corrosion rates of Copper Nickel in seawater in both polluted and unpolluted conditions

FAQ

Copper Nickel (CuNi) Piping Systems can be installed without welding. There are
fantastic Press Fit Piping Systems that can be used instead of welding.

Guidelines for Shutdown and Standby Conditions?

For shutdown and standby conditions, it is important to avoid deposit build up and long term stagnant conditions which can cause the sea water to putrify. Continuous or intermittent flow or draining down, cleaning and drying are required for long term shut down durations of more than 4 to 5 days.

FAQ

Copper Nickel (CuNi) is used mostly in seawater applications – one such use is on oil rigs and ships

If your company is looking to save money, decrease fouling and minimise welding for your seawater application then you should consider calling a Copper Nickel (CuNI) alloy specialist to discuss how best Copper Nickel alloys can improve your operations.

When should be used CuNi rather than other alternatives?

The corrosion problems experienced in Marine and Salt water systems have been well studied over many years. 
Economic factors have to be considered in selecting materials for these systems and in this context, essentially two types of metal system can be considered, as follows:

  1. A low initial cost system largely based on carbon steel and cast iron which will require considerable maintenance over the life of the plant or ship. Such a system is a reasonable choice in areas where labour costs are low and material is readily available.
  2. A system based mainly on CuNi alloy materials which, if correctly designed and fabricated, will require minimum maintenance and will function reliably.

Rising labour costs in most industries, together with the need for high reliability in capital intensive plant and shipping has produced a trend to CuNi types of alloys. 
Many people desire 20-year trouble-free life but are often unwilling to specify the required material and accept the higher initial costs. It should be noted, however, that various studies of materials in seawater systems have concluded, that systems based on CuNi alloy materials are more economic on a life cycle cost basis.