SE527177C2 - Use of an austenitic stainless steel - Google Patents

Abstract

Austenitic alloy with following composition, in weight-percent: Cr 23-30, Ni 25-35, Mo 2.0-6.0, Mn 1.0-6.0, N 0-0.4, C up to 0.05, Si up to 1.0, S up to 0.02, Cu up to 3.0, W 0-6.0, one or more element of Mg, Ce, Ca, B, La, Pr, Zr, Ti, Nd up to 2.0 and balance Fe and normally occurring impurities and additions as wire in oil- and gasextraction, specially reinforcement wire in the application wirelines and which shows a combination of good corrosion resistance and good mechanical properties, especially a tensile strength of at least 310 kpsi at diameters of 1.0 mm and thinner.

Description

25 30 v Q I O no n 527 177 2 The selection of the steel grade is mainly determined by requirements for strength, yield strength, ductility and corrosion properties, especially under the conditions prevailing in an oil or gas source and at temperatures up to 250 ° C.

The use is largely limited by the resistance to fatigue due to repeated use in the oil and gas industry, especially in the use as a slickline or wellbore logging cable and in this application of repeated reeling and transport over a so-called pulleywheel. Furthermore, the possibilities of using the material in this sector are limited by the breaking load of the cable / slickline wire. Today, the breaking load is maximized by using cold-deformed material. The degree of cold deformation is usually optimized with regard to the ductility.

For the manufacture of cables and strings in this application, conventional stainless austenitic steel is mainly used today, e.g. of type A | Sl303, AlSl304 or A | S | 316 according to US-A4 214 693, which by this reference is included in the description or the duplex stainless steel marketed under the trademark FERRINOX 255 according to GB-A-2 354 264, which by this reference is included in the description. The requirements for corrosion resistance where the above-mentioned steels are used are negligible when the string or rope is enclosed by a plastic material such as e.g. polyurethane. Recent developments aim to reduce the self-weight of reinforcing wire as an outer layer.

Corresponding requirements can be set for strip and wire springs, where high demands are placed on strength, fatigue and corrosion properties.

In all cases, the use is limited upwards due to corrosion or load reasons.

In addition, there is a desire for significantly higher strength than current technology allows for a given cold deformation. A strength leading to normal thread dimensions not being surface plasticized or enabling the use of smaller dimensions, i.e. diameters of 1.0 mm and thinner, is desirable. 10 15 20 25 30 o QQI oo oc 527 177 Summary of the invention It is therefore an object of the present invention to provide a stainless steel alloy with an austenitic matrix and at the same time high strength in combination with high ductility and resistance to general corrosion at high temperatures, especially at temperatures up to 250 ° C.

It is a further object of the present invention to provide a stainless steel alloy with a breaking limit of at least 310 kpsi at wire diameters of 1.0 mm or thinner in the well logging cable reinforcement wire application.

It is a further object of the present invention to provide a steel alloy having good corrosion resistance in chloride-containing and high general corrosion environments.

These objects are fulfilled with an alloy according to the present invention, which contains (in% by weight): Cr 23.0-30.0 Ni 25.0-35.0 Mo 2.0-6.0 Mn 1.0-6, 0 N 0-0.4 C up to 0.05 Si up to 1.0 S up to 0.02 Cu up to 3.0 W 0-6.0 one or two elements of Mg, Ce, Ca, B, La, Pr, Zr, Ti, Nd up to 2.0 and the rest Fe together with normally occurring impurities and additives.

Brief description of the cures Figure 1 schematically shows the construction of a wellbore logging cable in cross section, where the reinforcement consists of one or more layers of wire. Figure 2 shows the function of strength versus temperature during hot working for Embodiments X and P of the present invention.

Figure 3 shows the function of strength versus temperature during hot working for Embodiments S and P of the present invention.

Figure 4 shows the breaking point as a function of the area reduction.

Figure 5 shows the load as a function of the length of wire made of the alloy according to the invention.

Figure 6 shows the breaking limit at delivery execution.

Figure 7 shows how much load, including dead weight and bending stress, that wire made of the new alloy compared to wire made of the well-known alloy UNS N08028, can carry as a function of the breaking wheel diameter.

Detailed description of the invention A systematic development work has surprisingly shown that an alloy with an alloy content according to the present invention exhibits these conditions.

The alloy according to the invention therefore contains, in weight percent: Cr 23-30 Ni 25-35 Mo 2.0-6.0 Mn 1-6 N 0-0.4 C up to 0.05 Si up to 1.0 S up to 0.02 Cu up to 3 W 0-6.0 one or fl era of the elements Mg, Ce, Ca, B, La, Pr, Zr, Ti, Nd up to 2.0 and the rest Fe together with normally occurring impurities and additives.

The significance of the alloying elements for the present alloy is as follows: Q 15 Q Q Q Q Q; c 527 177 Iš.-I ° ï "ïï * Nickel A high nickel content homogenises a high-alloy steel by increasing the solubility of Cr and Mo. part consists of the alloying elements chromium and molybdenum.

A disadvantage, however, is that nickel lowers the solubility of nitrogen in the alloy and impairs the hot workability, which entails an upper limit for the amount of nickel alloy. However, the present invention has shown that high nitrogen contents can be permitted at nickel contents as above by balancing the high nickel content against high chromium and manganese contents.

The Ni content of the alloy should therefore be limited to 25-32% by weight, preferably at least 26% by weight / °, most preferably at least 30% by weight or 31% by weight. The upper limit of the Ni content is preferably 34% by weight. Kim (Cr) is a very active element for improving the resistance to various types of corrosion. A high chromium content also means that you get a very good N-solubility in the material. It is therefore desirable to keep the chromium content as high as possible to improve corrosion resistance. For very good values of corrosion resistance, the chromium content should be at least 24.0% by weight, preferably 27.0 -29.0% by weight. However, high levels of Cr increase the risk of intermetallic precipitates, so the chromium content must be limited upwards to a maximum of 30.0% by weight.

Molybdenum In modern corrosion-resistant austenitic steels, a high alloy addition of molybdenum is often made to increase the resistance to corrosion attacks in general.

Unlike chromium, molybdenum increases the corrosion rate. The explanation is the tendency of molybdenum to precipitate, which gives rise to undesirable phases during sensitization. Thus, a high chromium content is chosen in favor of a high molybdenum content, also to obtain an optimal structural stability for the alloy.

Both alloying elements certainly increase the tendency to precipitate, but experiments show that molybdenum does this more than twice as much as chromium. It is possible to reach in the present alloy all or part of the molybdenum with tungsten. Preferably, however, at least 2% by weight of molybdenum should be included in the alloy.

The molybdenum content should therefore be limited to between 2.0 and up to 6.0% by weight, preferably to at least 3.7% by weight, preferably to at least 4.0% by weight. The upper limit of the molybdenum content is 6.0% by weight, preferably 5.5% by weight.

Intermetallic phase precipitation benefits from rising Cr and Mo content, but can be suppressed by alloying N and Ni. The Ni content is mainly limited by the cost aspect and by the fact that it greatly lowers the solubility of N in melt.

The N content is consequently limited by the solubility in the melt as well as in the solid phase when precipitation of Cr nitrides can take place.

To increase the solubility of nitrogen in the melt, the Mn and Cr content can be increased and the Ni content reduced. However, Mo has been considered to give rise to an increased risk of intermetallic phase precipitation, which is why it has been considered necessary to limit this content.

However, higher levels of alloying elements have not only been limited for reasons of structural stability. flfi ß (VV) increases resistance to point and crevice corrosion. However, the alloying of too high levels of tungsten in combination with the high Cr and Mo levels means that the risk of intermetallic precipitates increases. The content of tungsten should therefore be in the range 0 to 6.0% by weight, preferably 0 to 4.0% by weight.

Manganese (Mn) is crucial for the alloy for three reasons. For the finished product, a high strength is sought, which is why the alloy must be deformation hardened during cold working. Both nitrogen and manganese are known to lower an alloy's stacking error energy, which in turn leads to dislocations in the material dissociating and forming Shockley particles. The lower the stacking error energy, the greater the distance between the Shockley particles and the more difficult the translocation of the dislocations becomes, which means that the material has a great tendency to harden to deformation. For these reasons, high levels of manganese and nitrogen are very important for the alloy. A fast deformation hardening is illustrated in the reduction curves presented in Fig. 3, where the alloy according to the invention is compared with the already known steels UNS N08926 and UNS N08028.

Manganese also increases the solubility of nitrogen in the melt, which indicates a relatively high manganese content. The high chromium content alone does not make the solubility sufficient because the nickel content, which lowers the solubility of the nitrogen, has in part been chosen even higher than the chromium content.

A third motive for a manganese content within the range of the present invention is that a yield stress analysis performed at elevated temperature surprisingly demonstrated the manganese improving effect on the hot workability of the alloy. The more high-alloy steels become, the more difficult they are to process and the more important are machining-improving additives, which both simplify and make production cheaper. A manganese addition means a reduction in hardness during hot working, which can be read from the diagram in Fig. 2 which shows the required stress during hot working for variants of the alloy with high and low manganese content, respectively.

The good heat workability of the alloy makes the alloy excellent for the manufacture of pipes, wire and strip, etc. However, manganese has been found to have a weak negative effect on the hot ductility of the alloy, as described by the formula below. However, its strong positive effect as a hardness-reducing alloying element in hot working has been judged to be more important.

Therefore, the manganese content of the alloy should be greater than 2% by weight, preferably 3.0 to 6.0% by weight, most preferably 4.0-6.0% by weight.

Kgl (C) has limited solubility in both ferrite and austenite. The limited solubility involves a risk of precipitation of chromium carbides and therefore the content should not exceed 0.05% by weight, preferably not exceed 0.03% by weight. s (Si) is used as a deoxidizing agent in steelmaking and increases the surface area in manufacturing and welding. However, too high levels of Si lead to the precipitation of undesired intermetallic phase, so the content should be limited to a maximum of 1.0% by weight, preferably a maximum of 0.8% by weight, preferably to 0.5% by weight. 10 15 20 25 30 527 8 Sulfur (S) has a negative effect on corrosion resistance by forming easily soluble solids. In addition, the hot workability deteriorates, which is why the sulfur content is limited to a maximum of 0.02% by weight. gig (N) is like molybdenum a popular alloying element in modern corrosion-resistant austenites to increase the corrosion resistance but also the mechanical strength of an alloy. For the present alloy, it is mainly nitrogen increase in mechanical strength that is used. By nitrogen as well as manganese lowers the stacking error energy of the alloy, a sharp increase in strength is achieved in cold deposition, as mentioned above. The invention also uses nitrogen to increase the mechanical strength of the alloy due to interstitially dissolved atoms which cause stresses in the crystal structure. A high strength is of fundamental importance for intended applications such as sheet metal, pipes, wire and strip, veins, rig wire, wirelines and slicklines. By using a high-strength material, it is possible to obtain the same strength but with less material input and thus lower weight. At the same time, this increases the requirements for the ductility of the material. For springs, its propensity to absorb elastic energy is crucial.

Therefore, the nitrogen content should be 0.20-0.40% by weight, preferably 0.35-0.40% by weight.

The effect of copper on the corrosion properties of austenitic steel is disputed. However, it is considered clear that copper greatly improves the corrosion resistance of sulfuric acid, which is of great importance for the alloys' areas of use. In experiments, copper has also been shown to be an element that is favorable for pipe production, which is why a copper additive is particularly important for materials made for pipe applications. From experience, however, it is known that a high copper content in combination with a high manganese content greatly impairs the hot ductility, so the upper limit for the copper content is determined to be 3.0% by weight. The copper content is preferably at most 1.5% by weight. 10 15 20 527 177 9 At least one of the ductility additives such as Magnesium (Mg), Calcium (Ca), Cerium (Ce), Boron (B), Lanthanum (La), Praseodymium (Pr), Zirconium (Zr), Titanium (Ti) and Neodymium (Nd) should be added at a level of up to 2.0% by weight in order to improve the hot workability. In the following, some embodiments of the alloy according to the invention are described.

These are intended to illustrate the invention, but not to limit it.

Example gel: The following tables show compositions for tested alloys according to the invention and for known alloys which are given for comparative purposes. For the known alloys used as references, in the case where they have been used for testing, the range which defines the composition tested and which is within the standard of the alloy is indicated. Table 1 shows some embodiments of the alloy according to the invention.

Table 1 Charge C Si Mn Cr Ni Mo Cu Cu NA 0.009 0.28 5.04 26.4 30.49 5.78 0.025 0.372 B 0.011 0.27 5.10 26.5 33.70 5.90 0.011 0.380 C 0.008 0.27 4.95 26.7 30.77 5.22 0.011 0.357 E 0.01 0.28 4.73 27.2 30.69 4.47 0.011 0.354 l 0.015 0.22 1.03 27.71 34 .86 3.97 0.500 0.410 J 0.008 0.33 4.99 26.21 33.37 4.86 1.900 0.370 K 0.007 0.28 5.29 26.25 33.83 3.70 0.011 0.390 L 0.012 0.25 5.18 26.36 33.70 5.10 0.940 0.390 M 0.010 0.25 5.04 27.80 35.40 5.47 2.220 0.400 N 0.008 0.26 3.96 28.98 34.68 5.61 2.250 0.380 O 0.008 0.24 5.70 23.57 24.82 5.00 0.013 0.360 P 0.015 0.24 1.07 26.91 30.77 6.41 1.180 0.220 S 0.015 0.22 5.57 26, 11 30.30 6.20 1.150 0.200 T 0.017 0.26 2.97 26.18 30.87 5.86 1.160 0.290 X 0.0147 0.24 1.14 27.72 29.87 3.91 1.480 0.250 10 Example 1 The stress required in hot working the present alloy, at different manganese and molybdenum contents, is shown in Figs. 2 and 3. The negative effect of molybdenum on the required stress is demonstrated by variants X and P in Fig. 2.

The positive effect of manganese on the required voltage is demonstrated by variants S and P in Fig. 3.

Example 2 The significantly better yield strength increase in cold working of the present alloys, variants B, C and E, in comparison with the known UNS N08028 and UNS NO8926 is shown in Figure 4.

The ductility of the material in delivery design was evaluated through industry-typical twisting and winding tests. The twist test is performed by twisting a 20 cm long thread until a fracture occurs, but at least 5 turns. The winding test is performed by winding the wire at least 5 turns around its own axis and then winding up the wire without breakage or cracks. The present invention meets the ductility requirements even with a high-strength delivery design. As shown in Figure 5, the alloy's uptake meets the ductility requirements even at breaking strengths exceeding 310 kpsi.

Example 3 Figure 6 and Figure 7 illustrate essential properties of wire for the application wirelines.

The voltage picture for a wire in wireline applications is mainly composed of three components as shown in Table 2: the dead weight of the wire according to equation (1), the suspended load according to equation (2) and the voltage induced by the different support wheels of the feeding equipment according to equation (3) and the total voltage as the sum of the partial voltages according to equation (4). As can be seen from the terms of the various voltages, described below, a higher yield strength limit allows the use of both smaller feed wheels and a larger applied load per unit area.

Table 2 Load drop Expression for induced voltage (1) Thread weight c1 = pgl / 2; p = density of the material, g = acceleration of gravity, l = free length of the wire in the borehole. (2) Attached load GFF / A; F = suspended load, A = wire area (3) Support wheel ø3 = dE / R; d = wire diameter, E = E module, R = support wheel radius (4) T ° la | o = ol + oz + oz Table 2 shows how much load in addition to dead weight wire made of the alloy according to the invention compared to wire made of the well-known alloy UNS NO8028 can carry as a function of the length of the trees.

The density of the alloys has both been estimated at p = 8,000 kg / m3.

The acceleration of gravity has been approximated to g = 9.8 m / sz.

A long wire, which in the intended application slickline can be up to about 30,000 feet long and has a noticeable dead weight that loads the wire. This dead weight is usually supported by wheels of varying curvature which further give rise to stresses for the wire. The smaller the radius of curvature of the wheel, the higher the bending stress of the wire. At the same time, a smaller wire diameter can withstand heavier bends. Figure 7 shows how much load, including dead weight and bending stress, that wire made of the new alloy compared to wire made of the well-known alloy UNS NO8028, can carry as a function of the breaking wheel diameter.

The modulus of elasticity of the alloys has both been estimated at E = 198 000 MPa 10 15 20 25 30 527 177 12 The calculations for the diagram are made on the condition that the voltage drop is purely linear elastic and the maximum load-bearing load is determined by the material fl surface tension (RpO, 2).

Example 4 The alloy according to the invention surprisingly shows a very high corrosion resistance in an environment relevant to the application wirelines.

The test so far shows surprising results, but at the time of writing is not yet complete. The test is performed in an environment as follows: Saturated NaCl (26 wt%) + 5 wt% MgCl 2 + 5% HgS at 177 ° C and 5000 psi (34.5MPa) for 336 hours.

Claims (2)

Use of an austenitic stainless steel alloy having the following composition, by weight: 23-30 25-35 3.7-5.5 1-6 0.35- 0.40 up to 0.05 up to 1.0 up to 0.02 up to 3.0 0-6.0 one or more of the elements Mg, Ce, Ca, B, La, Pr, Zr, Ti, Nd up to 2.0 and the rest Fe together with normally occurring contaminants such as wire with a diameter of 1.0 mm or thinner in oil and gas extraction. Use of an austenitic stainless steel alloy according to claim 1 as a reinforcing wire in the application wirelines.