Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/053—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 30% but less than 40%

Definitions

• 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.
• 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.
• 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.
• the object of the present invention is to provide alloys combining low material costs and a high corrosion resistance.
• the alloys should have a high wet corrosion resistance in water with high salinity, especially at temperatures above 100°C.
• the alloys should have a good resistance against pitting and crevice corrosion attack.
• Preferred alloys have a good resistance to reducing conditions (as measured e.g. by ASTM G 28 A) and at the same time to pitting corrosion and chloride ion attack (as measured e.g. by ASTM G 28 B).
• Advantageous alloys combine a high corrosion resistance with good mechanical properties, e.g. a high strength. Alloys with such properties are particularly suitable for, but not limited to, down-hole-headers in geothermal power plants operating using hot geothermal fluids containing high chloride concentrations.
• a nickel-chromium-iron-molybdenum alloy comprising 40 to 48 wt% (percent-by-weight) nickel, 30 to 38 wt% chromium, 4 to 12 wt% molybdenum, and iron, wherein the alloy optionally further comprises up to 5 wt% manganese, up to 2 wt% copper and up to 0.6 wt% nitrogen.
• the object of the invention is solved by a nickel-chromium-iron-molybdenum alloy, consisting of 40 to 48 wt% nickel (Ni), 30 to 38 wt% chromium (Cr), 4 to 12 wt% molybdenum (Mo), optionally manganese (Mn), optionally copper (Cu), optionally nitrogen (N), optionally tungsten (W), optionally niobium (Nb), optionally cobalt (Co), optionally carbon (C), optionally tantalum (Ta), optionally titanium (Ti), optionally silicon (Si), and balance iron (Fe) plus impurities.
• a nickel-chromium-iron-molybdenum alloy consisting of 40 to 48 wt% nickel (Ni), 30 to 38 wt% chromium (Cr), 4 to 12 wt% molybdenum (Mo), optionally manganese (Mn), optionally copper (Cu), optionally nitrogen (N), optionally tungsten (W), optional
• the alloys according to the invention provide an economically viable and robust alternative for demanding applications such as contact with hot fluids having a high salinity (e.g. above 100°C, above 100 g/l chloride ions).
• the indicated ranges of nickel, chromium and molybdenum allow balancing these three main alloying elements in order to achieve the desired favourable properties. Outside the ranges of 40 to 48 wt% nickel, 30 to 38 wt% chromium and 4 to 12 wt% molybdenum, at least one of the following properties cannot be expected to be favourable: corrosion resistance, structural properties (e.g. number of phases) and mechanical properties. Additionally, higher amounts of nickel and/or molybdenum would render the alloy uneconomical.
• Manganese and nitrogen may be useful for stabilizing a desired austenite phase.
• Tungsten, niobium, tantalum and titanium may be used for optimizing the mechanical properties.
• Silicon and manganese may improve melting and casting of the alloy.
• Copper and nitrogen may further improve the corrosion resistance of the alloy.
• Carbon may be present either as a side effect or as a deliberate addition. On the one hand carbon affects the corrosion resistance adversely; on the other hand when added in the right amounts carbon improves the mechanical properties. Accordingly it is possible to fine tune the required properties of the alloy according the invention and thus to either add a certain amount of carbon e.g. to improve mechanical strength or to limit it to the minimum amount possible.
• the alloy according to the invention is suitable for use in water with high salinity (also at high temperatures) and in the geothermal, off-shore, chemical, oil and gas industry.
• a preferred alloy according to the inventions consists of 40 to 48 wt% nickel, 30 to 38 wt% chromium, 4 to 12 wt% molybdenum, up to 5 wt% manganese, up to 2 wt% copper, up to 0.6 wt% nitrogen, up to 5 wt% tungsten up to 3 wt% niobium, up to 2 wt% cobalt, up to 0.2 wt% carbon, up to 1 wt% tantalum, up to 1 wt% titanium, up to 1 wt% silicon, and balance iron plus impurities.
• impurities preferably refers to unavoidable impurities, i.e. impurities that result automatically when the alloy is made up of the other components.
• impurities refers to unwanted components.
• impurities does not include any of the following elements: nickel, chromium, molybdenum, manganese, copper, nitrogen, tungsten, niobium, cobalt, carbon, tantalum, titanium, silicon and iron.
• the sum of impurities is at most 0.1 wt%, preferably at most 0.05 wt% and more preferably at most 0.02 wt%. This allows controlling the effect the impurities may have on the properties of the alloy.
• a preferred alloy according to the invention as described above contains at least 2 wt%, preferably at least 4 wt% iron.
• an alloy is preferred that contains one or more of the following: (i) 42 to 48 wt% nickel, (ii) 32 to 38 wt% chromium, (iii) 4 to 11.5 wt% molybdenum, (iv) 0.01 to 5 wt% manganese, (v) 0.1 to 2 wt% copper, (vi) 0.01 to 0.6 wt% nitrogen, (vii) up to 2 wt% tungsten, (viii) up to 1 wt% niobium, (ix) up to 1.8 wt% cobalt, (x) 0.002 to 0.2 wt% carbon, (xi) up to 0.5 wt% tantalum, (xii) up to 0.5 wt% titanium, (xiii) 0.01 to 1 wt% silicon.
• the alloy according the invention accordingly has at least one, several or all of the features described above with reference to points (i) to (xiii), i.e. the amount of one, several or all of the mentioned components is in corresponding ranges.
• an alloy to the invention that contains one or more of the following: (i) 43 to 47 wt% nickel, (ii) 33 to 37 wt% chromium, (iii) 4 to 11 wt% molybdenum, (iv) 0.02 to 2 wt% manganese, (v) 1 to 2 wt% copper, (vi) 0.05 to 0.4 wt% nitrogen, (vii) up to 1 wt% tungsten, (viii) up to 0.2 wt% niobium, (ix) up to 1.5 wt% cobalt, (x) 0.005 to 0.1 I wt% carbon, (xi) up to 0.2 wt% tantalum, (xii) up to 0.2 wt% titanium, (xiii) 0.02 to 0.7 wt% silicon.
• an alloy according to the invention wherein the alloy contains one or more of the following: (i) 43 to 46.5 wt% nickel, (ii) 33.5 to 37 wt% chromium, (iii) 4.5 to 10.5 wt% molybdenum, (iv) 0.05 to 0.5 wt% manganese, (v) 1.5 to 1.8 wt% copper, (vi) 0.1 to 0.3 wt% nitrogen, (vii) up to 0.5 wt% tungsten, (viii) up to 0.05 wt% niobium, (ix) up to 1 wt% cobalt, (x) 0.01 to 0.02 wt% carbon, (xi) up to 0.05 wt% tantalum, (xii) up to 0.05 wt% titanium, (xiii) 0.05 to 0.4 wt% silicon.
• the alloy according to the invention has a PREN value, calculated as wt%Cr + 3.3*wt%Mo + 16*wt%N, of at least 40.
• the PREN (pitting resistance equivalent number) value is a measure for the corrosion resistance of an alloy. Generally, the higher the PREN value, the more resistant the alloy is against corrosion.
• the PREN value of the alloy according to the invention is preferably at least 50, 55, 60, 65 or even 70.
• the alloy according to the invention is austenitic.
• the alloy consists of a single phase.
• the matrix of the alloy may preferably consist of a single phase harbouring precipitates that have a positive influence on the desired properties of the steel.
• an alloy is preferred that is characterized by one or more of the following features (a) to (d) combined with one or more of the following features (e) to (f):
• the alloy accordingly preferably has one, two, three or all of the features listed under points (a) to (d) above and at the same time either or both of the features listed under (e) and (f). These preferred alloys have a combination of a high strength and a high corrosion resistance.
• preferred alloys according to the invention may simply have one or more of the features (a) to (f) as described above.
• Points (e) to (f) refer to corrosion resistance as measured by ASTM G 28 A (reducing conditions: 50% H 2 SO4 + 2.7% Fe 2 (SO 4 ) 3 ) and ASTM G 28 B (pitting corrosion and resistance against chloride attack: 23% H 2 SO 4 + 1.2% HCl +1 % FeCl 3 + 1% CuCl 2 ).
• the R p0.2 proof strength is at least 325 or 350 MPa at 25°C and/or at least 275 or 300 MPa at 150°C, in each case measured according to DIN 10 002-1:2001-12.
• the R m ultimate tensile strength is at least 475 or 500 MPa at 25°C and/or at least 425 or 450 MPa at 150°C, in each case measured according to DIN 10 002-1:2001-12.
• the material loss is at most 0.4, 0.3 or 0.2 mm/year (measured according to ASTM G 28 A) and/or at most 2, 1.5 or 1 mm/year (measured according to ASTM G 28 B).
• the present invention relates to a product comprising an alloy according to the invention.
• Preferred products are selected from the group consisting of powders, granules, sheets, plates, bars, wires, pipes, cast products, wrought products, rolled products, forgings and welding materials (e.g. filler materials).
• the present invention according to another aspect also relates to an article for applications in water with high salinity, comprising an alloy according to the invention.
• the water preferably has a chloride concentration above 100 g/l. Since the alloys according to the invention may withstand water with high salinity, the articles according to the invention are suitable for such applications.
• Preferred articles are selected from the group consisting of down-hole-headers, pipelines, tubes, valves, pumps and housings.
• the present invention relates to the use of an alloy according to the invention, a product according to the invention or an article according to the invention for applications in water with high salinity, preferably with a chloride concentration above 100 g/l.
• the present invention also relates to the use of an alloy according to the invention, a product according to the invention or an article according to the invention for applications in the geothermal, off-shore, chemical, oil and gas industry. Applications at high temperature are preferred.
• Example 1 is a comparative example in which the alloy has a very low molybdenum content.
• Example 14 (alloy A31, comparative example) and example 15 (alloy A59, comparative example) were produced horizontally cast in order to allow comparison.
• the chemical compositions of the castings are listed in Table I, together with the calculated PREN values.
• Table I Chemical analysis Ex. C Cr Ni Mo Fe Cu N Mn Si PREN Melting Casting 1 0.014 34.7 44.3 0.03 Bal. 1.79 0.19 0.43 0.24 38 V CM 2 0.012 35.9 44.9 4.78 Bal. 1.50 0.16 0.46 0.29 54 V CM 3 0.020 35.6 43.4 7.12 Bal. 1.68 0.23 0.35 0.36 63 V CM 4 0.012 35.8 46.3 9.58 Bal.
• the chemical compositions are given in wt%.
• the PREN value is calculated as wt%Cr + 3.3*wt%Mo + 16*wt%N.
• the mechanical properties of the alloy according to the invention are significantly better than those of A31 (Example 14) and with a Mo content in the lower range, comparable to those of A59 (Example 15). With a Mo content in the higher range, the alloy becomes superior to both A31 and A59, especially at elevated temperatures (T>100°C).
• Table III the results from the corrosion tests on the alloys according to the invention of Examples 2 to 4 and 8 to 10 according to ASTM G 28 A (reducing conditions), ASTM G 28 B (pitting corrosion and resistance against Cl - attack) and ASTM A 262 C (oxidizing conditions) are shown.
• Example 1 substantially without Mo suffers from severe material loss as well as from pitting corrosion. As soon Mo in the range according to the invention is added, the corrosion rate is retarded by about a hundredfold. Additional Mo reduces the rate even further and with 9-10 %wt Mo, values close to A59 are reached, but without losing the excellent properties of the alloys according to the invention in reducing acid. In the end the alloy according to the invention allow combining the favourable properties of A31 (corrosion resistance under reducing conditions) and A59 (resistance against pitting corrosion and Cl - induced attack) without suffering from their unfavourable properties.
• the theoretical values have been added in order to allow for a qualitative comparison between the castings and A31 and A59.
• the CPT and CCT values listed are the calculated starting values for the CPT and CCT test according to the ASTM G 48 standard, which standard however only allows testing up to 85 °C.
• the alloys according to the invention have several benefits compared to the two commercial alloys used as benchmark, A31 (Example 14) and A59 (Example 15). They have a good corrosion resistance against both reducing and oxidizing acids and Cl - induced pitting corrosion. Alloy 31 (A31) can resist reducing conditions but has rather poor pitting resistance, while Alloy 59 (A59) has good pitting corrosion resistance but cannot compete with A31 or the alloys according to the invention in reducing solutions.

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• Mechanical Engineering (AREA)
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• 2010
  • 2010-11-19 EP EP10014793A patent/EP2455504A1/fr not_active Withdrawn
• 2011
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