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The present invention relates to novel nickel-chromium-iron-molybdenum alloys, corresponding products and articles and their uses. The alloys according to the invention allow achieving good mechanical properties combined with a good corrosion resistance in water with high salinity, especially at elevated temperatures. They are thus particularly suited for use in geothermal power plants, e.g. as down-hole-headers.

 

Down-hole-headers in geothermal power plants are required to withstand hot geothermal fluids (e.g. above 100°C) containing high concentrations of chloride ions (e.g. above 100 g/l). These conditions are particularly demanding and often lead to pitting and crevice corrosion. Alloys used for these applications are required to have a sufficient corrosion resistance under these conditions.

 

Up to now titanium based alloys and nickel based alloys are regularly used for constructing such down-hole-headers. These alloys are generally thought to be the only practical and reliable alternative when it comes to this application. However, the use of these alloys is uneconomical. For example, nickel is one of the most costly constituents in corrosion resistant alloys. A59 is an example of an alloy often used. It contains high amounts not only of nickel, but also of molybdenum, which also strongly contributes to the overall cost of the alloy. Moreover, A59 performs considerably worse under reducing conditions than under oxidizing conditions. Austenitic stainless steels, such as 316L, 254SMO or A31 have been proposed as alternatives. Unfortunately these materials are well-known to be prone to crevice corrosion. Even A31 , which is the most highly alloyed steel in this group of materials, is not sufficiently resistant to corrosion in some situations. Hence, it is obvious that * neither the traditional austenitic steels nor the nickel based alloys are fully satisfactory.

 

Corrosion resistant nickel based alloys with lower amounts of nickel than in A59 are proposed in US 5,424,029. However, the alloys disclosed therein still require a relatively high proportion of nickel, rendering them quite costly. In most applications, the costs are a decisive criterion.

 

 

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