Hydrogen-conducting pipe component

Abstract

Hydrogen-carrying, cold-drawn pipe component made of a steel alloy which, in addition to iron and melting-related impurities, contains the following elements in mass percent: C: 0.07 - 0.22 Si: 0.10 - 0.55 Mn: 0.30 - 1.60 P: ≤ 0.025 S: ≤ 0.015 Ti: 0.010 - 0.030 V: 0.003 - 0.30 N: 0.008 - 0.025 Al: 0.010 - 0.025 Ca < 0.10 and optionally: Nb: ≤ 0.10 Mo: ≤ 0.50 Cr: ≤ 0.50 Ni: ≤ 1.0 Cu: ≤ 0.20, wherein the microstructure contains more than 95% ferrite + pearlite, with a grain size of Grain size class 9 or finer according to ASTM E112-13(2021), in particular at least 10, wherein the remainder of the microstructure consists of martensite, bainite and retained austenite, wherein the pipe component has a tensile strength of at least 340 MPa, preferably 400 - 850 MPa.

Description

[0001] The invention relates to a hydrogen-carrying pipe component according to the features of claim 1.

[0002] Hydrogen as an energy carrier for fuel cell vehicles is emission-free, but has a low volumetric mass density at room temperature. Compressing hydrogen increases this low volumetric energy density, which significantly simplifies its storage, transport, and use. Suitable high-pressure piping systems are required to transport compressed hydrogen from a tank to a fuel cell stack or an internal combustion engine. In trucks and cars, these systems are typically operated at a hydrogen pressure of 35 MPa or 70 MPa, respectively. The requirements for high-pressure piping systems in hydrogen-powered vehicles, as well as in peripheral systems or similar applications, are high. They must withstand the high hydrogen pressure safely and reliably. Furthermore, they must be protected against corrosion from the hydrogen itself and from other media.

[0003] Stainless steels are preferably used for hydrogen-conducting components. Stainless steels have a minimum chromium content of 16% and nickel content of 10%. Due to the high chromium and nickel content, they are relatively expensive. Furthermore, the material has low strength, so components designed for higher pressure resistance require greater wall thicknesses. This, in turn, increases the weight and thus, in mobile applications, the energy consumption. The increased material usage also leads to higher costs.

[0004] Approaches focused on developing cost-effective, hydrogen-resistant steel grades concentrate particularly on high-strength steels. Conventional, low-alloy carbon steels with tensile strengths between 350 MPa and 630 MPa could theoretically represent an optimal alternative; however, the hydrogen compatibility of low-alloy carbon steels is lower than that of stainless steels.

[0005] The invention is based on the objective of optimizing the alloy composition of low-alloy carbon steels specifically with regard to their use in hydrogen-carrying pipe components and with regard to material costs.

[0006] A hydrogen-carrying, cold-drawn pipe component according to the features of claim 1 solves this problem. The dependent claims relate to advantageous embodiments of the invention.

[0007] The invention relates to a hydrogen-carrying, cold-drawn pipe component made of a steel alloy. Hydrogen-carrying pipe components are, in particular, high-pressure lines or hydrogen tanks for storing hydrogen in stationary or mobile applications. The pipe component according to the invention is, in particular, a piping application of a hydrogen pressure tank system of a motor vehicle. The cold-drawn pipe component used for this purpose consists of a steel alloy which, in addition to iron and melting-related impurities, contains the following elements in mass percent as residue: C: 0.07 - 0.22 To: 0.10 - 0.55 Mn: 0.30 - 1.60 P: ≤ 0.025 S: ≤ 0.015 Of: 0.010 - 0.030 V: 0.003 - 0.30 N: 0.008 - 0.025 Al: 0.010 - 0.025 Ca < 0.10.

[0008] Optionally, the alloy contains the following elements in mass %: Note: ≤ 0.10 Know: ≤ 0.50 Cr: ≤ 0.50 In: ≤ 1.0 Cu: ≤ 0.20

[0009] Carbide-forming elements, such as vanadium, are added in a targeted manner. The addition of these elements improves hydrogen embrittlement (HE) resistance. Due to precipitation hardening, the addition of these elements leads to increased material strength. Nanoscale vanadium carbonitrides (V(C,N)) play a crucial role in this process. They act as hydrogen traps, effectively trapping hydrogen and thus reducing the hydrogen diffusion rate. They also refine the existing austenite grain size, significantly improving HE resistance.

[0010] Coarse vanadium carbonitrides lose their ability to act as strong hydrogen traps and instead act as crack initiation sites, thus reducing their HE resistance. Therefore, only vanadium carbonitride nanoprecipitates with sizes below 60 nm represent effective hydrogen traps.

[0011] Thermokinetic calculations have shown that, for the alloy composition according to the invention, the number of vanadium carbonitride precipitates per unit volume exceeds 1 × 10^18 / m³ at a vanadium content of 0.003 wt.% and is therefore above the TEM detection limit (TEM = transmission electron microscopy). The average size of the vanadium carbonitride precipitates is 10 nm in diameter. The equivalent diameter is determined. With increasing vanadium content, the number of nanoscale vanadium carbonitride precipitates increases. Simultaneously, the hydrogen diffusion coefficient decreases by an order of magnitude. The maximum value of 0.3 wt.% vanadium should not be exceeded, as otherwise the hydrogen halide resistance decreases again with increasing vanadium content.

[0012] Titanium and titanium nitrides have a grain-refining effect by inhibiting recrystallization and austenite grain growth. Furthermore, TiN precipitates serve as nucleation sites for vanadium carbonitrides, thereby increasing their number and thus the number of hydrogen traps.

[0013] Vanadium leads to the formation of vanadium carbonate ditrides V(C,N), which have a grain-refining effect. This grain-refining effect increases the strength and toughness of the material.

[0014] The pipe component is manufactured, in particular, without weld seams, preferably from a hot-rolled and once- or twice-normalized microstructure. For normalization, the pipe component is heated above the Ac3 temperature, held at the target temperature, and slowly cooled to produce a fine-grained microstructure. This achieves a homogeneous distribution of mechanical properties, which improves formability during cold drawing.

[0015] The pipe component according to the invention consists of a ferrite-pearlite steel with high HE resistance due to the addition of vanadium. The pipe component according to the invention is particularly easy to weld and has a carbon equivalent value (CEV) of less than or equal to 0.42%. The carbon equivalent is a measure for assessing the weldability of unalloyed and low-alloy steels. The carbon equivalent combines the carbon content and the weighted proportions of elements that influence the weldability of the steel in a similar way to how carbon would be expected to do. Values ​​below 0.45% indicate good weldability. Higher values ​​require preheating. Above 0.65%, the workpiece is only weldable with increased effort due to martensite formation, which can lead to cold cracking or hardening cracks.

[0016] The CEV value is determined for a carbon content from 0.18 mass% according to the following equation: CEV= C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5.

[0017] Copper, nickel, chromium and molybdenum are optional alloying components.

[0018] As a result, the microstructure consists of more than 95% ferrite and pearlite. The remaining components of the microstructure are martensite, bainite, and retained austenite. The microstructure is exceptionally fine-grained, corresponding to a grain size of size class 9 or finer according to ASTM 112-13 (2021). In particular, the grain size class is at least 10.

[0019] The steel alloy is formed into a cold-drawn tube component, the tube component having a tensile strength of at least 340 MPa. Preferably, the tensile strength is between 400 MPa and 850 MPa. The yield strength Rp0.2 is preferably at least 220 MPa. The elongation at break A is at least 25%.

[0020] The steel alloy preferably contains the following elements in mass percent, in addition to iron and impurities resulting from the melting process: C: 0.09 - 0.22 To: 0.10 - 0.55 Mn: 0.70 - 0.70 P: 0.005 - 0.025 S: 0.002 - 0.015 Of: 0.010 - 0.030 V: 0.030 - 0.30 N: 0.008 - 0.025 Al: 0.010 - 0.025 Ca: 0.0005 - 0,050 and optional Note: ≤0.050 Know: ≤0.30 Cr: ≤0.350

[0021] Furthermore, the steel alloy preferably contains, in addition to iron and impurities resulting from the melting process, the following elements in mass percent: C: 0.09 - 0.22 To: 0.10 - 0.55 Mn: 0.70 - 1.60 P: 0.005 - 0.025 S: 0.002 - 0.015 Of: 0.010 - 0.030 V: 0.050 - 0.30 N: 0.008 - 0.025 Al: 0.015 - 0.025 Ca: 0.0005 - 0,050 and optional Note: ≤0.050 Know: ≤0.30 Cr: ≤0.50 In: ≤0.50 Cu: ≤0.20.

[0022] In a further advantageous embodiment of the invention, the steel alloy consists, in addition to iron and impurities resulting from the melting process, of the following elements in mass percent: C: 0.09 - 0.19 To: 0.20 - 0.55 Mn: 0.90 - 1.50 P: 0.005 - 0.025 S: 0.003 - 0.015 Of: 0.010 - 0.030 V: 0.110 - 0.30 N: 0.008 - 0.025 Al: 0.015 - 0.025 Ca: 0.0010 - 0.010 and optional Note: ≤ 0.050 Know: ≤ 0,30 Cr: ≤ 0.50 In: ≤ 0.50 Cu: ≤ 0.180, and in particular from the following composition: C: 0.07 - 0.17 To: 0.10 - 0.55 Mn: 0.70 - 1.60 P: 0.005 - 0.025 S: 0.002 - 0.015 Of: 0.010 - 0.030 V: 0.003 - 0.30 N: 0.008 - 0.025 Al: 0.010 - 0.025 Ca: 0.0005 - 0,050 and optional Note: ≤ 0.050 Know: ≤ 0.30 Cr: ≤ 0.35.

[0023] The use of the pipe component as a hydrogen-carrying, cold-drawn pipe component in mobile applications requires effective corrosion protection. For this purpose, the hydrogen-carrying pipe component can be coated on one outer surface, preferably only on one side. This coating can be a zinc or zinc alloy coating applied by immersion, optionally in combination with an organic coating, such as a powder coating. Suitable coatings can be applied galvanically or by electrophoretic deposition processes, in particular by cathodic dip coating. The coating is particularly multi-layered and serves to protect the outer surface of the hydrogen-carrying, cold-drawn pipe component from corrosion, especially in its function as a pipeline in a hydrogen pressure tank system, either as a line within the system or as the tank itself.

[0024] The specific application of the hydrogen-carrying, cold-drawn pipe component requires high static and cyclic load-bearing capacity.

[0025] The burst pressure test according to ISO 11114-4:2017 (Method A) is a test procedure for assessing the susceptibility of metals to hydrogen embrittlement. A small, flat disc of the material to be tested is placed between two stainless steel flanges. Pressure is increased from one side of the disc at varying rates of pressure increase until fracture occurs. The burst pressures are then determined. The test is performed using both helium and hydrogen gas. The resulting burst pressures are compared. The ratio between these burst pressures is an indicator of hydrogen compatibility. The lower the ratio of the helium burst pressure to the hydrogen burst pressure, the less susceptible the steel is to hydrogen embrittlement. The helium burst pressure should be equal to or only slightly higher than the hydrogen burst pressure.The helium burst pressure / hydrogen burst pressure factor should be a maximum of 2, preferably a maximum of 1.75, particularly preferably a maximum of 1.50, and especially a maximum of 1.25.

[0026] Steels with a coefficient of performance (COP) of less than or equal to 2.0 are considered hydrogen-compatible. Values ​​close to 1.0 are desirable for high-pressure hydrogen pipeline systems. The steel alloy according to the invention achieves COPs of up to 1.2, and in particular values ​​of up to 1.16. It is therefore a steel alloy suitable for the production of cold-drawn, hydrogen-carrying pipe components, and especially for use in high-pressure hydrogen pipeline systems.

[0027] However, the hydrogen-carrying, cold-drawn pipe component according to the invention also meets high requirements for cyclic pressure loading.

[0028] For this purpose, a cyclic pressure test with hydrogen gas is performed for up to 50,000 pressure cycles at a defined test temperature. The cyclic pressure test is particularly suitable for assessing the effects of cyclic aging under the influence of pressurized hydrogen. Maximum hydrogen-induced damage occurs at a temperature of -60 °C. One pressure cycle lasts 20 to 30 seconds, during which the pressure is increased from 0 to 87.5 MPa and then reduced back to 0 MPa. After up to 50,000 pressure cycles, a burst pressure test is performed, stipulating that an unstressed pipe component (i.e., a pipe component without cyclic pressure testing) is used as a reference pipe and compared to a pipe sample after the cyclic pressure test.The ratio between the determined burst pressures is an indicator of hydrogen compatibility after dynamic loading, wherein the determined burst pressure of the pipe sample is at most 40%, preferably at most 30%, particularly preferably at most 20%, and especially at most 10% lower compared to the reference pipe.

[0029] The pipe component according to the invention is characterized in that the determined burst pressure of the pipe sample is lower compared to the reference pipe.

[0030] It should be noted that with the alloy compositions according to the invention, no significant adverse difference was found between these two burst pressures, i.e., the burst pressure of the unloaded pipe component and the pipe component subjected to the cyclic pressure test. This demonstrates excellent HE resistance.

[0031] Hydrogen is stored at a pressure level of 70 MPa. At a working pressure of 70 MPa and a safety factor of 1.25, this results in 87.5 MPa, corresponding to the test pressure in the cyclic pressure test. The tests have thus confirmed that a burst pressure of at least 80 MPa was determined. The cyclic pressure test was carried out on a pipe according to the features of claim 1 with dimensions of 6.35 mm diameter and a wall thickness of 1.675 mm. The test was performed with hydrogen gas with a purity of at least 99.999%. Regarding the test conditions for the cyclic pressure test, it should be added that, under the same test conditions, the burst pressure of the stainless steel pipe decreased by 1.9% compared to the initial pipe.

Claims

1. Hydrogen-carrying, cold-drawn pipe component made of a steel alloy which, in addition to iron and melting-related impurities, contains the following elements in mass percent: C: 0.07 - 0.22 Yes: 0.10 - 0.55 Mn: 0.30 - 1.60 P: ≤0.025 S: ≤0.015 Ti: 0.010 - 0.030 V: 0.003 - 0.30 N: 0.008 - 0.025 Al: 0.010 - 0.025 Approx < 0,1 and optional: Note: ≤0.10 Mon: ≤0,50 Cr: ≤0.50 Ni: ≤1,0 Cu: ≤0,20, wherein the microstructure contains more than 95% ferrite+pearlite, with a grain size of grain size class 9 or finer according to ASTM E112-13(2021), in particular at least 10, wherein the remainder of the microstructure consists of martensite, bainite and retained austenite, wherein the pipe component has a tensile strength of at least 340 MPa, preferably 400 - 850 MPa.

2. Hydrogen-carrying, cold-drawn tube component according to claim 1, characterized by the fact that The steel alloy contains the following elements in mass percent, in addition to iron and impurities resulting from the smelting process: C: 0.07 - 0.22 Yes: 0.10 - 0.55 Mn: 0.30 - 0,7 P: 0,005 - 0.025 S: 0,002 - 0.015 Ti: 0.010 - 0.030 V: 0.003 - 0.30 N: 0.008 - 0.025 Al: 0.010 - 0.025 Approx 0.0005 - 0,050 and optional: Note: ≤0.050 Mon: ≤0.30 Cr: ≤0.

35.

3. Hydrogen-carrying, cold-drawn tube component according to claim 1, characterized by the fact thatThe steel alloy contains the following elements in mass percent, in addition to iron and impurities resulting from the smelting process: C: 0.09 - 0.22 Yes: 0.10 - 0.55 Mn: 0.70 - 1.60 P: 0.005 - 0.025 S: 0.002 - 0.015 Ti: 0.010 - 0.030 V: 0.050 - 0.30 N: 0.008 - 0.025 Al: 0.015 - 0.025 Ca: 0.0005 - 0,050 and optional Note: ≤0.050 Mon: ≤0.30 Cr: ≤0.50 Ni: ≤0.50 Cu: ≤0.

20.

4. Hydrogen-carrying, cold-drawn tube component according to claim 1, characterized by the fact that The steel alloy contains the following elements in mass percent, in addition to iron and impurities resulting from the smelting process: C: 0.09 - 0.19 Yes: 0.20 - 0.55 Mn: 0.90 - 1.50 P: 0.005 - 0.025 S: 0.003 - 0.015 Ti: 0.010 - 0.030 V: 0.011 - 0.30 N: 0.008 - 0.025 Al: 0.015 - 0.025 Ca: 0.0010 - 0.010 and optional Note: ≤0.050 Mon: ≤0.30 Cr: ≤0.50 Ni: ≤0.50 Cu: ≤0.

180.

5. Hydrogen-carrying, cold-drawn tube component according to claim 1, characterized by the fact that The steel alloy contains the following elements in mass percent, in addition to iron and impurities resulting from the smelting process: C: 0.07 - 0.17 Yes: 0.10 - 0.55 Mn: 0.70 - 1.60 P: 0.005 - 0.025 S: 0.002 - 0.015 Ti: 0.010 - 0.030 V: 0.003 - 0.30 N: 0.008 - 0.025 Al: 0.010 - 0.025 Ca: 0.0005 - 0,050 and optional Note: ≤0.050 Mon: ≤0.30 Cr: ≤0.

35.

6. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 5, characterized by the fact that The steel alloy has a carbon equivalent CEV ≤ 0.42 calculated according to the following equation CEV= C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5.

7. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 6, characterized by the fact that The pipe component has a yield strength Rp0.2 ≥ 220 MPa and an elongation at break A ≥ 25 %.

8. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 7, characterized by the fact that on one side of the pipe component, in particular on the side not carrying hydrogen, at least one coating produced by dipping and / or electroplating and / or electrophoretic deposition and / or powder coating is applied.

9. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 8, characterized by the fact thatIn a burst pressure test according to ISO 11114-4:2017 Method A, the burst pressure of a sample of the steel material of the pipe component with test gas helium in relation to the burst pressure with test gas hydrogen is a maximum of 2, preferably a maximum of 1.75, particularly preferably a maximum of 1.5, and especially a maximum of 1.

2.

10. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 9, characterized by the fact thatA cyclic pressure test with hydrogen gas is carried out over 50,000 pressure cycles at a test temperature of -60°C, wherein a pressure cycle comprises 20 to 30 seconds and wherein in each pressure cycle the pressure is increased from 0 to 87.5 MPa and then reduced back to 0 MPa, wherein a burst pressure test is subsequently carried out under the conditions specified in ISO 11114-4:2017, wherein an unloaded pipe component is used as a reference pipe and compared with a pipe sample after the cyclic pressure test, wherein the determined burst pressure of the pipe sample is at most 40%, preferably at most 30%, particularly preferably at most 20%, and especially at most 10% lower than that of the reference pipe.

11. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 10, characterized by the fact that It has a pressure resistance of at least 80 MPa in hydrogen gas.

12. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 11, characterized by the fact thatthe steel alloy has vanadium carbide precipitates, wherein the vanadium carbide precipitates have a maximum equivalent diameter of 60 nm and wherein the mean equivalent diameter is 10 nm or less.

13. Hydrogen-carrying, cold-drawn tube component according to one of claims 1 to 12, characterized by the fact that it consists of a hot-rolled, cold-drawn and single or double normalized structure, wherein the pipe component is manufactured in particular without weld seams.

14. Hydrogen-carrying, cold-drawn tubular component according to one of claims 1 to 13, characterized by the fact that it is a hydrogen-carrying pipe or a hydrogen tank, wherein the hydrogen tank has at least one end section closed by forming and / or joining with a material bond.

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