Austenitic drill string component with high corrosion resistance, and method for the production thereof

Abstract

Austenitic drill string component having a composition comprising or consisting of the following elements (all specifications in wt.%): carbon (C) 0.05–0.30, silicon (Si) < 0.50, manganese (Mn) 8.50–13.00, phosphorus (P) < 0.05, sulfur (S) < 0.005, chromium (Cr) 18.00–22.50, molybdenum (Mo) 0.50–5.00, nickel (Ni) 0.50–6.00, vanadium (V) < 0.50, tungsten (W) < 3.00, copper (Cu) < 0.50, cobalt (Co) < 0.50, titanium (Ti) < 0.50, aluminum (Al) < 0.50, niobium (Nb) < 0.03, boron (B) < 0.01, nitrogen (N) 0.40–0.80, with the remainder being iron and unavoidable impurities, wherein: formula A [wt.%]: 0.55 ≤ (C + N) ≤ 0.95 and formula B [-]: 0.07 ≤ (C / N) ≤ 0.50, and wherein formula A is in wt.% and formula B is dimensionless.

Description

[0001] International patent application

[0002] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0003] Austenitic drilling stratum component with high corrosion resistance and high strength and methods for its production

[0004] The invention relates to an austenitic drill string component, in particular for use in media with high corrosive attack, and a method for its production.

[0005] Austenitic materials are used in deep drilling technology, particularly in oil and gas fields. In these applications, it is essential to determine the borehole trajectory as precisely as possible. This applies especially to drilling operations that are not exclusively vertical or perpendicular, but also those that involve changes in direction. For this purpose, it is necessary to determine the borehole trajectory as accurately as possible in order to control the drilling accordingly. This is typically achieved by determining the drill head's position using magnetic field probes, which utilize the Earth's magnetic field for measurement. For this purpose, certain components of the drill string are made of non-magnetic alloys. This means that parts of the drill string located in the immediate vicinity of magnetic field probes must have a relative magnetic permeability (PR) < 0.1.

[0006] Such components include, in particular, the so-called heavy bars or MWD (Measurement While Drilling) and LWD (Logging While Drilling) components, which are positioned above the actual drill head and serve, among other things, to house the corresponding measuring electronics. These applications are characterized by having a diameter greater than 80 mm and being free of precipitates right to the center.

[0007] Another requirement for austenitic drill string components is that they must withstand corrosive attack.

[0008] International Patent Application AT 412 727 B discloses a superaustenitic alloy as a drill string component. The corrosion-resistant austenitic steel alloy used here is the subject of an international patent application.

[0009] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO This is an alloy comprising, in particular, high contents of manganese, chromium, molybdenum, and nickel. To achieve high strength, nitrogen is present in contents of 0.35 to 1.05 wt.%, which also contributes to corrosion resistance and is a strong austenite former. However, with increasing nitrogen content, the tendency to form nitrogenous precipitates, especially chromium nitride, also increases. To achieve this high nitrogen solubility, manganese is used in contents of more than 19 to 30 wt.%. This is intended to ensure that pore-free materials can be produced even when solidifying under atmospheric pressure. Furthermore, the manganese is intended to stabilize the austenitic microstructure against the formation of deformation martensite at high degrees of deformation.

[0010] From EP 1 069 202 Al, a paramagnetic, corrosion-resistant, austenitic steel with high yield strength, strength, and toughness is known, which is said to be particularly corrosion-resistant in media with high chloride concentrations, and which contains 0.6 to 1.4 wt.% nitrogen. It also contains 17 to 24 wt.% chromium and manganese.

[0011] From EP 4 279 628 Al, a non-magnetic austenitic stainless steel is known which has a purely austenitic structure. To ensure this structure, a nickel content of between 9 and 15 wt.% is added. This makes the material very expensive to produce.

[0012] From EP 2 455 508 Bl, an austenitic, corrosion-resistant steel with reduced manganese content (8 to 12 wt.%) and a carbon-to-nitrogen ratio (C + N) between 0.6 and 1 wt.% is known. It is further disclosed that the alloy must contain at least 0.3 wt.% nitrogen. Due to the lower manganese content, a complex melting process in a vacuum melting furnace under a nitrogen atmosphere is necessary to achieve the required nitrogen content in the steel alloy. Furthermore, the examples provided disclose that the austenitic alloy contains more carbon than nitrogen. International patent application

[0013] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0014] WO 02 / 02837 Al discloses a corrosion-resistant material for use in media with high chloride concentrations in oilfield technology. This is a chromium-nickel-molybdenum superaustenite characterized by comparatively low nitrogen contents but very high chromium and nickel contents.

[0015] These chromium-nickel-molybdenum steels typically exhibit improved corrosion resistance compared to the previously mentioned chromium-manganese-nitrogen steels. Overall, chromium-manganese-nitrogen steels are a relatively cost-effective alloy composition that nevertheless offers an excellent combination of strength, toughness, and corrosion resistance. The aforementioned chromium-nickel-molybdenum steels achieve significantly higher corrosion resistance than chromium-manganese-nitrogen steels, but are associated with considerably higher costs due to their very high nickel content.

[0016] From EP 2 455 508 Al, a high-strength and corrosion-resistant austenitic stainless steel and its manufacturing process are known. The nickel content is limited to a maximum of 2 wt.%. Through the controlled addition of the interstitial elements carbon and nitrogen (C+N = 0.6 to 1.0 wt.%) and the additional elements manganese (8 to 12 wt.%), chromium (15 to 20 wt.%), tungsten (< 4 wt.%), and molybdenum (< 2 wt.%), a tensile strength of over 850 MPa and excellent pitting resistance are achieved in an atmospheric induction melting process followed by hot forming and water quenching.

[0017] Superaustenitic alloys typically have molybdenum contents > 4 wt.% and a MARC value > 42 to achieve high corrosion resistance. However, molybdenum increases the tendency for segregation, thus increasing the susceptibility to precipitates, particularly the brittle sigma or chi phases. Consequently, these alloys require homogenization annealing, or, at molybdenum contents above 4%, even remelting to reduce segregation. Even then, the tendency for precipitates is so high that dimensions larger than 250 mm cannot be produced without precipitation due to the reduced cooling rate at the center. International patent application

[0018] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0019] Basically, it is necessary that the materials still have a magnetic permeability of p even after cold forming. r exhibit < 1.01.

[0020] Furthermore, such superaustenitic steels typically have a yield strength. P 0.2 of 140 KSI = 965 MPa after cold forming.

[0021] One characteristic value for corrosion resistance is the so-called PRENi6 value. Furthermore, it is common to define the so-called pitting equivalent number using MA COPT ZU: MARC = wt.% Cr + 3.3 wt.% Mo + 20 wt.% N + 20 wt.% C - 0.5 wt.% Mn. A MARC value of 20–42 indicates a corrosion-resistant, austenitic alloy.

[0022] Another characteristic value for corrosion resistance against pitting corrosion is given by the standard ASTM G150: Critical Pitting Temperature Test for stainless steel.

[0023] For the test, samples of the austenitic material with a sample size of 25 x 30 x 5 mm are prepared, ground, and cleaned with deionized water and acetone. The sample is placed in a test solution of 1 molar NaCl (corresponding to 58.45 g NaCl diluted to 2 with deionized water). Electrodes and a thermometer are installed in the test cell for the measurement. Initially, the test solution is kept at a constant 10°C for 10 minutes. The temperature of the test solution is then increased at 1°C / min. The time, temperature, and current density are continuously measured. The temperature is increased until the measured current density exceeds 100 pA / cm² for one minute.

[0024] According to ASTM G150, the CPT (temperature per maximum temperature) is defined as the temperature at which the current density exceeds 100 pA / cm² for one minute. If the measured current density exceeds 100 pA / cm² for one minute at the start of the experiment, the result is considered to be < 10°C. International patent application

[0025] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0026] Austenitic alloys are also known for their use as shipbuilding steels for submarines. These are chromium-nickel-manganese-nitrogen steels, further alloyed with niobium to stabilize the carbon. However, the latter reduces impact toughness. These steels generally contain little manganese and therefore have relatively good corrosion resistance, but they do not achieve the strength and, above all, the toughness of CrMnN alloys used for heavy bars.

[0027] The object of the invention is to create an austenitic drill string component which, with respect to its manganese and nickel content, has a significantly reduced alloy design while simultaneously exhibiting high corrosion resistance, high strength and toughness, as well as good paramagnetic behavior.

[0028] The problem is solved with an austenitic drill string component having the features of claim 4. Advantageous embodiments are characterized in dependent claims.

[0029] Furthermore, it is an object of the invention to provide a method for producing an austenitic drill string component which exhibits high strength and toughness and good paramagnetic behavior in addition to increased corrosion resistance.

[0030] The problem is solved by a method having the features of claim 1. Advantageous further developments are characterized in the dependent dependent claims.

[0031] Any percentages given below are always given in wt.% (weight percent).

[0032] According to the invention, the austenitic drill string component is said to possess a completely austenitic microstructure, in particular without carbides and / or nitrides and / or carbonitrides and / or without deformation martensite, even after cold forming, wherein the magnetic perme- International Patent Application

[0033] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO barkeit p r < 1.01 preferred p r < 1.005. Since ferrite or deformation methylenesite exhibit magnetic behavior, they increase the permeability and should therefore be avoided in this embodiment.

[0034] After the hot forming process to which the cast block was subjected, the yield strength is at P 0.2 > 450 MPa and the impact energy is greater than 250 at 20°C.

[0035] After hot forming, the process is called cold forming. This refers to the plastic deformation of alloys below the recrystallization temperature, resulting in an increase in strength, known as work hardening. The degree of deformation during plastic forming (also called work hardening) is defined as follows: (initial area A0 - final area Al) / initial area A0. If the initial area is 100 mm² 2 and the end surface 40 mm 2 The degree of deformation is calculated using the formula: (100 - 40) / 100 = 0.6 or 60%. After cold working with a degree of deformation of 10–90%, the yield strength R is... P The impact energy is greater than 900 MPa, although values ​​greater than 1100 MPa are achieved in practice. The impact energy at 20°C is greater than 80 J, although values ​​greater than 130 J are achieved in practice.

[0036] The impact strength is determined by the standard DIN EN ISO 148-1.

[0037] The yield strength R P0.2 is determined by the standard EN-ISO 6892-1.

[0038] To increase corrosion resistance, the chromium content is increased, particularly to resist attack in media with high chloride concentrations. The manganese content in the alloy is also reduced. This has the additional positive effect of minimizing the corrosive attack of fretting corrosion, thus increasing the theoretical service life. To ensure that the austenitic drill string component is non-magnetic, it is necessary to use non-ferritic steel alloys. Because the chromium content is increased and the manganese content is simultaneously reduced, the austenitic drill string component must be balanced by the remaining austenite-forming elements, such as nickel. (International patent application)

[0039] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0040] Nitrogen, cobalt, and carbon are adjusted. Empirical investigations have shown that it is particularly advantageous if the formulas A = 0.55 < (C + N) < 0.95 and B = 0.07 < (C / N) < 0.50 apply. This ensures that the microstructure is a purely austenitic structure that meets the required strength and is also free of inclusions such as carbides, carbonitrides, nitrides, and / or deformation martensite.

[0041] Furthermore, it is important that such austenitic drill string components are not only made from the appropriate alloys, but that appropriate post-treatments are also carried out to ensure that a homogeneous, precipitation-free, high-strength and, in particular, high-impact alloy is present.

[0042] Therefore, such austenitic drill string components with a diameter of 80 mm to 450 mm are selected to ensure that the minimum values ​​of the mechanical properties, in particular the 0.2% yield strength, are met. P 0.2 and tensile strength are able to withstand the dynamically changing loads that occur.

[0043] The individual elements, possibly in combination with the other alloying components, are described in more detail below. All information regarding the alloy composition is given in weight percent (wt%). The upper and lower limits of the individual alloying elements can be freely combined within the limits of the invention.

[0044] Carbon (C) is a strong austenite former and has a beneficial effect with regard to high mechanical properties. For this reason, a lower limit of 0.05 wt.%, 0.06 wt.%, 0.07 wt.%, 0.08 wt.%, 0.09 wt.%, or 0.10 wt.% should be defined. To avoid carbide precipitates and embrittlement of the material, an upper limit of 0.30 wt.% should be chosen. Preferably, a carbon content between 0.05 and 0.30 wt.% is provided. International patent application

[0045] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0046] Silicon (Si) serves to deoxidize steel. It also increases strength through the formation of solid solutions. To achieve these effects, a lower limit of 0.05 wt.%, 0.06 wt.%, or 0.07 wt.% is required. However, if silicon is added in excessive amounts, there is a risk of intermetallic phase formation. Since silicon is also a ferrite former, the upper limit is defined by a safety margin. Specifically, silicon can be added in amounts of < 0.50 wt.%, < 0.45 wt.%, < 0.40 wt.%, < 0.35 wt.%, or < 0.30 wt.%. A particularly preferred range lies between 0.05 and 0.30 wt.%.

[0047] Manganese (Mn) increases nitrogen solubility. It was previously assumed that manganese contents of more than 19.00 wt.%, ideally more than 20 wt.%, were necessary for high nitrogen solubility. Surprisingly, with the present alloy, it has been found that high nitrogen solubility is achieved even with low manganese contents, without the need for expensive pressure nitriding. The lower limit for manganese is 8.50 wt.%. The upper limit for manganese is 13.00 wt.%. This is a remarkably low value compared to high-nitrogen materials according to the prior art. Preferably, a manganese content between 8.50 and 13.00 wt.% is used. A particularly preferred range lies between 9.50 and 13.00 wt.%.

[0048] According to literature, the addition of copper (Cu) proves advantageous for resistance in sulfuric acid. However, it has been shown that copper values ​​> 0.50 wt.% increase the tendency for chromium nitride precipitation, which in turn negatively affects corrosion properties. Therefore, the upper limit is set at 0.50 wt.%, 0.15 wt.%, or 0.10 wt.%. The copper content can also be chosen so that it is below the detection limit, meaning no deliberate addition of copper.

[0049] Chromium (Cr) increases the corrosion resistance of the alloy and is also essential for maintaining nitrogen solubility. Chromium contents of 17.00 wt.% or more are necessary for improved corrosion resistance. According to the invention, at least [number of] international patent applications are pending.

[0050] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0051] The product contains 18.00 wt.% and at most 22.50 wt.% chromium. This optimally influences the resistance to pitting and stress corrosion cracking. The lower limit for chromium is 18.00 wt.%, 18.50 wt.%, 19.00 wt.%, 19.50 wt.%, or 20.00 wt.%. The upper limit for chromium can be selected as 22.50 wt.% or 22.00 wt.%. Preferably, a chromium content between 18.00 and 22.50 wt.% is provided. A particularly preferred range lies between 20.00 and 22.00 wt.%.

[0052] Molybdenum (Mo) contributes significantly to corrosion resistance in general and pitting corrosion resistance in particular. To utilize this positive effect of Mo, a minimum content of 0.50 wt.%, 0.60 wt.%, 0.70 wt.%, 0.80 wt.%, 0.90 wt.%, 1.00 wt.%, 1.10 wt.%, 1.20 wt.%, 1.30 wt.%, 1.40 wt.%, or 1.50 wt.% is required. However, molybdenum contents exceeding 5.00 wt.% necessitate electroslag remelting (ESR) or pressure electroslag remelting (PESR) to prevent segregation. Such remelting processes are very complex and expensive. Therefore, a maximum of 5.00 wt.%, 4.50 wt.%, or 4.00 wt.% molybdenum is added. Preferably, a molybdenum content between 0.50 and 5.00 wt.% is provided. A particularly preferred range is between 1.50 and 4.00 wt.%.

[0053] Tungsten (W) has the same properties as molybdenum, thus contributing to increased corrosion resistance and strength. The upper limit for the tungsten content can be 3.00 wt.%, 2.00 wt.%, or 1.00 wt.%. Due to the additional alloying of molybdenum, a lower limit for the tungsten content is not required.

[0054] Nickel (Ni) improves stress corrosion cracking resistance in chloride-containing media. Nickel is also an austenite-stabilizing element. To utilize the positive effects of nickel, a lower limit of 0.50 wt%, 1.00 wt%, 1.50 wt%, 2.00 wt%, or 2.10 wt% is required. With increasing nickel concentrations, the driving force for precipitation also increases. At the specified carbon and nitrogen concentrations, this would lead to undesirable carbide, nitride, and / or carbonitride precipitation. For this reason, the upper limit for nickel is set at 6.00 wt% (International Patent Application).

[0055] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0056] The nickel content is selected to be 5.50 wt.%, 5.00 wt.%, or 4.50 wt.%. Preferably, a nickel content between 0.50 and 6.00 wt.% or 1.50 and 5.50 wt.% is provided. A particularly preferred range is between 2.00 and 5.50 wt.%.

[0057] Cobalt (Co) can be added, particularly as a substitute for nickel. The upper limit for cobalt is 0.50 wt%, 0.40 wt%, 0.30 wt%, 0.20 wt%, or 0.10 wt%. The cobalt content can also be chosen so that it is below the detection limit (i.e., no deliberate addition of cobalt).

[0058] Nitrogen is added to ensure high strength. Furthermore, nitrogen contributes to corrosion resistance and is a strong austenite former. Therefore, nitrogen contents higher than 0.40 wt.%, and particularly higher than 0.45 wt.%, are advantageous. However, to avoid nitrogenous precipitates, especially chromium nitride, the upper limit of the nitrogen content is restricted to 0.80 wt.%, 0.75 wt.%, or 0.70 wt.%. It has been shown that, despite the very low manganese content compared to known alloys, these high nitrogen contents can be achieved in the alloy without pressure nitrogenation. Preferably, a nitrogen content between 0.40 and 0.80 wt.% is used. A particularly preferred range is between 0.45 and 0.70 wt.%.

[0059] If the manganese, chromium, nickel and molybdenum content is within the limits listed above, empirical evidence shows that a particularly advantageous, synergistic effect is achieved when the carbon to nitrogen ratio (C / N) and (C+N) are chosen such that the austenitic drill string component fulfills formulas A and B:

[0060] Formula A [wt%]: 0.55 < (C + N) < 0.95

[0061] Formula B [-]: 0.07 < (C / N) < 0.50, where formula A is given in wt.% and formula B is dimensionless.

[0062] This has surprisingly proven to be particularly advantageous. The ratio according to formula A ensures a fully austenitic microstructure and sufficient strength. International patent application

[0063] Voestalpine BÖHLER Edelstahl GmbH & Co KG

[0064] Schoeller-Bleckmann Oilfield Technology GmbH

[0065] 240549WO

[0066] In this drill string component, the manganese content is reduced to improve pitting corrosion resistance. However, lowering the manganese content also reduces the austenite stabilizers. This is compensated for by increasing the carbon content. Furthermore, the carbon, as an interstitially dissolved element, ensures the necessary strength and also increases the solubility of nitrogen in the austenite. The ratio of (C + N) in the range of 0.60 to 0.90 is particularly advantageous: 0.60 < (C + N) < 0.90.

[0067] The ratio according to formula B is particularly advantageous for this drill string component, as it has a positive effect on the precipitation behavior.

[0068] It is theoretically conceivable to omit carbon from the alloy to meet the ratio specified in Formula A. However, this negatively impacts the strength and austenite stability. Therefore, the carbon / nitrogen ratio must be selected with a lower limit of 0.07, 0.08, 0.09, or 0.10. With increasing carbon content, however, the driving force for undesirable carbide formation also increases. By appropriately adjusting the nitrogen content according to Formula B, surprising effects occur regarding the mutual inhibition of precipitation. These effects are based on an interstitial expansion of the crystal lattice, resulting in more carbon and nitrogen remaining in solution.

[0069] If the levels of manganese, chromium, nickel and molybdenum are within the limits listed above and the ratio of carbon to nitrogen is chosen according to formula B, the thermokinetics of precipitation formation is surprisingly positively influenced.

[0070] For the given elements, precipitation can result in the formation of M₂₃C₆ and / or M₂N. In the case of the carbide M₂₃C₆, the metal-to-carbon ratio is approximately 4:1, while in the nitride M₂N, the metal-to-nitrogen ratio is 2:1. The carbide tends to have a higher precipitation capacity, but because dissolved nitrogen atoms are present in abundance, the precipitation processes inhibit each other, and precipitation is delayed. (International patent application)

[0071] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO postponed. After the final hot forming step and solution annealing, water quenching is required. This makes it possible to produce the drill string component without precipitates. Precipitation-free in this context means that no precipitates such as carbides, carbonitrides, or nitrides are present.

[0072] The ratio of (C / N) is particularly advantageous in the ranges 0.10 to 0.48: 0.10 < (C / N) < 0.48.

[0073] Optionally, boron, aluminum and sulfur may be included as additional alloying elements.

[0074] The alloying elements vanadium and titanium are not necessarily present in this steel alloy. Although these elements contribute positively to nitrogen solubility, high nitrogen solubility can also be ensured in their absence.

[0075] Niobium should not be included in the alloy, as concentrations above 0.015 wt.% can lead to the precipitation of niobium carbides or niobium carbonitrides. For austenitic alloys used in particularly corrosive environments, these precipitates have a detrimental effect; the preferential precipitation at grain boundaries reduces impact toughness. Niobium is typically used only for carbon bonding, which is undesirable in this alloy embodiment. Niobium contents up to 0.03 wt.% are still tolerable, but should not exceed the content of unavoidable impurities.

[0076] The invention thus relates to an austenitic drill string component which has a composition (all values ​​in wt.%) comprising the following elements:

[0077] Carbon (C) 0.05 - 0.30

[0078] Silicon (Si) 0.05 - 0.50

[0079] Manganese (Mn) 8.50 - 13.00 International patent application

[0080] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0081] Phosphorus (P) < 0.05 Sulfur (S) < 0.005 Chromium (Cr) 18.00 - 22.50 Molybdenum (Mo) 0.50 - 5.00 Nickel (Ni) 0.50 - 6.00 Vanadium (V) < 0.50 Tungsten (W) < 3.00 Copper (Cu) < 0.50 Cobalt (Co) < 0.50 Titanium (Ti) < 0.50

[0082] Aluminum (Al) < 0.50 Niobium (Nb) < 0.03

[0083] Boron (B) < 0.01 Nitrogen (N) 0.40 - 0.80

[0084] Residual iron and unavoidable impurities, whereby the following applies:

[0085] Formula A [wt%]: 0.55 < (C + N) < 0.95

[0086] Formula B [-]: 0.07 < (C / N) < 0.50 and where formula A is given in wt.% and formula B is dimensionless.

[0087] Further training stipulates that the drill string component is completely austenitic after cold forming, i.e., free of deformation martensite and / or carbides and / or carbonitrides and / or nitrides.

[0088] Further training requires that the following conditions are met:

[0089] Formula A [wt%]: 0.60 < (C + N) < 0.90

[0090] Formula B [-]: 0.10 < (C / N) < 0.48.

[0091] Further development provides that the chromium content is 19.5 - 22.5 wt.%, particularly preferably 20 - 22.5 wt.%.

[0092] Further training stipulates that the Critical Pitting Temperature (CPT), measured according to the ASTM G150 standard, lies between 25 and 90°C. International patent application.

[0093] Voestalpine BÖHLER Edelstahl GmbH & Co KG

[0094] Schoeller-Bleckmann Oilfield Technology GmbH

[0095] 240549WO

[0096] Further training specifies that the nickel content should be 0.50 - 5.5 wt.%, preferably 1.5 - 5.5 wt.%.

[0097] Further training stipulates that the nickel content should be 2.0 - 5.5 wt.%.

[0098] Further training envisages that the austenitic alloy is obtained through secondary metallurgical treatment of the melt, casting into blocks, immediately followed by hot forging, cold forging and, if necessary, further mechanical processing.

[0099] Further training stipulates that the magnetic permeability |_i r < 1.01 after cold working.

[0100] Further training stipulates that the yield strength, measured according to the standard EN ISO 6892-1, is cold-worked. P 0.2 > 900 MPa.

[0101] Further training stipulates that the impact energy at 20°C, measured according to the standard DIN EN ISO 148-1, is greater than 130 J.

[0102] The invention further relates to a method for producing an austenitic drill string-

[0103] Component, wherein an alloy comprising the following constituents (all details in

[0104] (wt%)

[0105] Carbon (C) 0.05 - 0.30

[0106] Silicon (Si) 0.05 - 0.50

[0107] Manganese (Mn) 8.50 - 13.00

[0108] Phosphorus (P) < 0.05

[0109] Sulfur (S) < 0.005

[0110] Chromium (Cr) 18.00 - 22.50

[0111] Molybdenum (Mo) 0.50 - 5.00

[0112] Nickel (Ni) 0.50 - 6.00

[0113] Vanadium (V) < 0.50

[0114] Tungsten (W) < 3.00 International patent application

[0115] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0116] Copper (Cu) < 0.50 Cobalt (Co) < 0.50 Titanium (Ti) < 0.50 Aluminum (AI) < 0.50 Niobium (Nb) < 0.03 Boron (B) < 0.01

[0117] Nitrogen (N) 0.40 - 0.80

[0118] Residual iron and unavoidable impurities, whereby the following applies:

[0119] Formula A [wt%]: 0.55 < (C + N) < 0.95

[0120] Formula B [-]: 0.07 < (C / N) < 0.50 and where formula A is given in wt.% and formula B is dimensionless, is melted and then treated by secondary metallurgy, the alloy thus obtained is cast into blocks and allowed to solidify, if necessary remelting, then heated and immediately hot-formed by forging, after the last hot-forming step being water-quenched, and after cooling the forgings being subjected to further cold forming and subsequent mechanical processing.

[0121] One advanced training method involves hot forming in several stages, during which the block is reheated, and after the final hot forming stage, solution annealing at 1050 to 1200°C for a duration of 0.5 to 12 hours. Water quenching follows solution annealing.

[0122] Further training stipulates that cold forming is carried out after hot forming, and the degree of cold forming is between 10 and 90%.

[0123] Further training stipulates that the cold-formed, austenitic drill string component has a final diameter of 80 to 450 mm.

[0124] The invention is explained by way of example using a drawing. The drawing shows: International patent application

[0125] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0126] Figure 1: a table showing the components of the drill string component according to the invention;

[0127] Figure 2: highly schematic representation of the manufacturing process;

[0128] Figure 3: a table with three different alloys within the concept according to the invention (A, B, C) and three non-inventive alloys (D, E, F).

[0129] Figure 4: Isothermal phase diagram (calculated with ThermoCalc 2024a, database TCFE 12) for alloy B at 1100°C, with the stable phases: austenite (face centered cubic, FCC), ferrite (body centered cubic, BCC), M23C6, M7C3, and M2N and a gas phase (Gas) and the respective combinations of the stable phases therefrom;

[0130] Figure 5: Mechanical properties of the drill string component from Figure 3 in the solution annealed and cold-worked condition with a degree of deformation of 10 - 90 %

[0131] Figure 6: Corrosion characteristics and microstructure characterization of the alloys

[0132] The first column of the table in Figure 1 shows the elemental composition of the austenitic drill string component according to the invention, which is characterized by increased corrosion resistance, high strength and toughness, and good paramagnetic behavior. These latter positive properties are achievable if the contents of the respective elements are within the limit ranges specified in the second column and satisfy formulas A (0.55 < (C + N) < 0.95) and B (0.07 < (C / N) < 0.50), although not all alloying elements are necessarily present.

[0133] In the present drill string component, it is particularly surprising that nitrogen values ​​exceeding 0.40 wt.% are found despite the low levels of nitrogen solubility-promoting substances in the international patent application.

[0134] Voestalpine BÖHLER Edelstahl GmbH & Co KG

[0135] Schoeller-Bleckmann Oilfield Technology GmbH

[0136] 240549WO

[0137] Elements, for example manganese, can be adjusted without a special electroplating process such as pressure electroslag remelting (DESU) or melting in a vacuum melting furnace under a nitrogen atmosphere.

[0138] Figure 2 shows a highly schematic representation of a possible process for manufacturing the drill string component according to the invention. In the vacuum induction melting unit (VID), the material is simultaneously melted and undergoes secondary metallurgical treatment. Alternatively, the melt can be melted in an electric arc furnace (EAF) and subsequently treated with secondary metallurgy in an argon oxygen decarburization (AOD) converter. The melt is then poured into ingot molds and solidifies into blocks. The solidified blocks are then hot-formed. "Directly" in the context of the invention means that no additional remelting process, such as electroslag remelting (ESR) or pressure electroslag remelting (PESR), is necessary.

[0139] The advantage of the drill string component according to the invention is that homogenization annealing or remelting is not necessary.

[0140] The hot forming process then takes place in several stages. After the final stage, solution annealing is performed at 1050–1200°C for 0.5–12 hours. Following solution annealing, water quenching is carried out. This special process step allows critical temperature ranges to be traversed more quickly and prevents the formation of grain boundary precipitates and / or carbides and / or nitrides and / or carbonitrides. To determine the final properties, further cold forming steps are carried out, such as forging on a long forging machine, with the diameter of the final products ranging from 80 to 450 mm.

[0141] Following cold forming, mechanical processing takes place, which can include turning or peeling, for example. International patent application.

[0142] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0143] The present austenitic drill string component can be produced not only via the manufacturing route described and in particular schematically illustrated in Figure 2, but also by a powder metallurgical production route, whereby the advantageous properties of the alloy can also be achieved.

[0144] Figure 3 shows three different variants of the drill string components and compositions according to the invention, which satisfy formulas A and B. In addition, two reference examples (D and E) are shown, which do not both satisfy formulas A and B and also differ from the intended composition in other ways, and a further reference example F, which satisfies formulas A and B, but whose chromium and nickel content lies outside the specified chemical analysis.

[0145] All six alloys investigated were produced using the same process. All alloys were melted in a vacuum induction melting unit (VID) and subjected to secondary metallurgical treatment. The molten metal was then poured into molds (ingots) where it solidified into ingots. These ingots were subsequently hot-formed in several stages on the P52 forging press. All alloys were then subjected to solution annealing at 1100°C for 8 hours. This was followed by water quenching and an initial characterization of their properties. Cold forming then took place on the long forging press. All alloys were cold-formed to a final diameter of 200 mm, with a cold forming degree of 15% for all alloys. A final characterization of the properties was then performed. To characterize the mechanical properties, samples were taken every 25 mm below the outer surface.

[0146] Figure 4 shows an isothermal phase diagram for alloy B (calculated using the program ThermCalc 2024a, database TCFE 12 at 1100°C). The phase diagram consists of the phase components austenite (face-centered cubic, FCC), ferrite (body-centered cubic, BCC), M₂³C₆, M₇³C₆, and M₂N, and a gas phase (Gas). The ratio (C / N) is plotted on the secondary axis. The aim of the alloys according to the invention is to be in the stable austenite phase. The equilibrium line between austenite and (austenite + M₂³C₆) is shown in the International Patent Application.

[0147] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO lies just above the calculated ratio line of (C / N) = 0.50. Therefore, adhering to the upper limit (C / N) = 0.50 is crucial, as otherwise carbide precipitates will form. For the calculated alloy B, this shows that the alloy lies within the stable austenite phase. It is also evident that if the ratio of formula B were greater than 0.50, the calculated point would shift into the stable phase region of (FCC + M23C6), leading to the formation of undesirable carbide precipitates. For comparison, alloys A and C to F are also shown in the diagram. However, these points have limited validity, as the alloys differ significantly in their chemical analysis. For example, alloys A and C are shown in the phase diagram for alloy B in the boundary region between FCC and (FCC+BCC).Both alloys have a significantly higher nickel content compared to alloy B (2.14 wt% Ni) (alloy A: 5.45 wt% Ni, alloy C: 4.09 wt% Ni). Due to the austenite-stabilizing effect of nickel, these alloys also exhibit pure austenite at 1100°C. In alloys D and E, the BCC phase and the undesired carbide precipitates are present in the calculated phase diagram. A comparison between alloy F and alloy B is not valid due to the nickel content of 8.0 wt% in alloy F. The high nickel content increases the driving force for precipitation formation so strongly that carbide precipitates occur.

[0148] Figures 5 and 6 characterize the six drill string components from Figure 3. The tensile strength Rm, yield strength at 0.2% elongation (Rp0.2), and elongation A5 were determined according to EN ISO 6892-1. The impact strength was measured according to DIN EN ISO 148-1. Slight differences in the mechanical properties are observed in the solution-annealed alloys. All measured values ​​for Rp0.2 are > 450 MPa and Rm is > 850 MPa. These values ​​were lowest for alloy D, which is attributed to the lowest C + N ratio of 0.52. This can be compensated for with an increased C + N ratio. Significant differences in Charpy V impact strength are observed in the work-hardened condition. No values ​​> 74 J were measured for alloys E to F. This is due to the carbide excretions, which are characterized in Figure 6.International patent application.

[0149] Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO

[0150] The biggest difference between the alloys A to C according to the invention and the alloys that are outside the specified chemical analysis is found in the characteristic values ​​for corrosion resistance (standard ASTM G150: Critical Pitting Temperature Test for stainless steel) and in the microstructure characterization.

[0151] The microstructure, including individual phases, can be examined using a scanning electron microscope (SEM) at 20,000x magnification. For this purpose, a 10 x 10 mm sample is cut from the formed block with a diameter of 80–450 mm, preferably directly from the center, as the center of the formed block is of particular interest for characterization. The samples are then ground and polished. Additional etching allows for better identification of the phases. The phases to be determined are austenite, ferrite, deformation-induced martensite, carbides, nitrides, and carbonitrides.

[0152] The microstructure characterization of alloys A to C consistently shows an austenitic matrix – free of carbides, carbonitrides, nitrides, and / or deformation martensite. Alloy D deviates significantly from formulas A and B, with a (C + N) ratio of 0.52 wt.%, which is below the intended limit of 0.55 to 0.95 wt.%. Furthermore, the (C / N) ratio of 0.70 also deviates considerably from the intended limit of 0.07 < (C / N) < 0.50. These deviations, combined with the 200 mm diameter, lead to the formation of carbide inclusions in the alloy. This makes the alloy very poorly suited for corrosion resistance in aggressive media. In alloy E, the (C / N) ratio was increased even further to investigate its effects. This revealed even worse corrosion behavior and a significantly higher carbide content in the microstructure.

[0153] The negative effects of deviations from the intended alloy composition are most clearly seen in the CPT temperature result. In reference examples D to F, this temperature reaches a maximum of 15°C. In contrast to the invention, sample F, according to the MarcOPT formula, is already a superaustenitic alloy (MarcOPT - International Patent Application).

[0154] Voestalpine BÖHLER Edelstahl GmbH & Co KG

[0155] Schoeller-Bleckmann Oilfield Technology GmbH

[0156] 240549WO

[0157] Value = 42.1). Even though alloy F fulfills formulas A and B, 3 vol% carbides can still be detected in the microstructure during microstructural characterization. This is due to the increased nickel and chromium content. If the nickel content exceeds 6 wt%, carbide precipitation is unavoidable during water quenching in the presence of > 0.10 wt% carbon. Thus, the invention is advantageous because the austenitic drill string component with good corrosion resistance has been created with very low manganese and nickel content.By adding carbon and nitrogen according to the ratios described by formulas A and B, it was possible to produce a perfectly austenitic alloy without inclusions, such as carbides, carbonitrides, nitrides, or deformation martensites, which exhibits both high strength and good paramagnetic behavior; even after cold forming, a perfectly austenitic microstructure with a magnetic permeability of pr < 1.005 is present. In addition, the corrosion resistance, as measured by the critical pitting temperature, was improved.

Claims

International patent application Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO Claims 1. Method for producing an austenitic drill string component, characterized in that an alloy comprising the following components (all values ​​in wt.%): Elements Carbon (C) 0.05 - 0.30 Silicon (Si) 0.05 - 0.50 Manganese (Mn) 8.50 - 13.00 Phosphorus (P) < 0.05 Sulfur (S) < 0.005 Chromium (Cr) 18.00 - 22.50 Molybdenum (Mo) 0.50 - 5.00 Nickel (Ni) 0.50 - 6.00 Vanadium (V) < 0.50 Tungsten (W) < 3.00 Copper (Cu) < 0.50 Cobalt (Co) < 0.50 Titanium (Ti) < 0.50 Aluminum (AI) < 0.50 Niobium (Nb) < 0.03 Boron (B) < 0.01 Nitrogen (N) 0.40 - 0.80 Residual iron and unavoidable impurities, whereby the following applies: Formula A [wt%]: 0.55 < (C + N) < 0.95 Formula B [-]: 0.07 < (C / N) < 0.50 and where formula A is given in wt.% and formula B is dimensionless, International patent application Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO is melted and subsequently treated by secondary metallurgy, the alloy thus obtained is cast into blocks and allowed to solidify, remelting if necessary, then heated and immediately hot-formed by forging, after the last hot-forming step a water quench takes place and the quenched hot-formed blocks are subjected to further cold forming and subsequent machining, the hot-forming takes place in several stages, the block is reheated between the hot-forming stages, after the last hot-forming stage a solution anneal at 1050 to 1200°C for a duration of 0.5 - 12h, and after the solution annealing a water quench takes place.

2. Method according to claim 1, characterized in that cold forming is carried out after hot forming, and the degree of cold forming is between 10 and 90%.

3. Method according to claim 1 or 2, characterized in that the cold-formed, austenitic drill string component has an end diameter of 80 - 450 mm.

4. Austenitic drill string component produced by a method according to any of the preceding claims, comprising a composition comprising or consisting of the following elements (all values ​​in wt. %): Carbon (C) 0.05 - 0.30 Silicon (Si) 0.05 - 0.50 Manganese (Mn) 8.50 - 13.00 Phosphorus (P) < 0.05 Sulfur (S) < 0.005 Chromium (Cr) 18.00 - 22.50 Molybdenum (Mo) 0.50 - 5.00 International patent application Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO Nickel (Ni) 0.50 - 6.00 Vanadium (V) < 0.50 Tungsten (W) < 3.00 Copper (Cu) < 0.50 Cobalt (Co) < 0.50 Titanium (Ti) < 0.50 Aluminum (Al) < 0.50 Niobium (Nb) < 0.03 Boron (B) < 0.01 Nitrogen (N) 0.40 - 0.80 Residual iron and unavoidable impurities, whereby the following applies: Formula A [wt%]: 0.55 < (C + N) < 0.95 Formula B [-]: 0.07 < (C / N) < 0.50 and where formula A is given in wt.% and formula B is dimensionless, where the drill string component is completely austenitic after cold working, i.e. free of deformation martensite and / or carbides and / or carbonitrides and / or nitrides.

5. Austenitic drill string component according to claim 4, characterized in that the following conditions are met: Formula A [wt%]: 0.60 < (C + N) < 0.90 Formula B [-]: 0.10 < (C / N) < 0.

48.

6. Austenitic drill string component according to claim 4 or 5, characterized in that the chromium content is 19.5 - 22.5 wt.%, particularly preferably 20 - 22.5 wt.%.

7. Austenitic drill string component according to one of claims 4 to 6, characterized in that the Critical Pitting Temperature (CPT) according to the ASTM G150 standard is between 25 and 90°C. International patent application Voestalpine BÖHLER Edelstahl GmbH & Co KG Schoeller-Bleckmann Oilfield Technology GmbH 240549WO 8. Austenitic drill string component according to one of claims 4 to 7, characterized in that the nickel content is 0.50 - 5.50 wt.% and particularly preferably 1.50 - 5.50 wt.%.

9. Austenitic drill string component according to one of claims 4 to 8, characterized in that the nickel content is 2.00 - 5.

50.

10. Austenitic drill string component according to one of claims 4 to 9, characterized in that the magnetic permeability pr is <1.01 after cold working.

11. Austenitic drill string component according to one of claims 4 to 10, characterized in that the yield strength according to standard EN ISO 6892-1 cold work-hardened po,2 > 900 MPa.

12. Austenitic drill string component according to one of claims 4 to 11, characterized in that the impact energy at 20°C according to the standard DIN EN ISO 148-1 is greater than 130 J.

Images