JP4528346B2 - FRP container for high pressure hydrogen storage using Cr-Mo steel liner - Google Patents

Description

  The present invention relates to a high-pressure hydrogen storage FRP container in which the outer periphery of a Cr-Mo steel liner is coated with FRP. Specifically, it is an FRP container using a thin-walled Cr—Mo steel liner containing 0.8 to 1.2% by mass of Cr and 0.3 to 0.6% by mass of Mo, and high-pressure hydrogen gas. The present invention relates to an FRP container for high-pressure hydrogen storage, which has a feature of excellent fatigue characteristics under an environment and can be suitably used for a hydrogen fuel tank for a fuel cell vehicle.

  As a measure against global warming, there is an increasing demand for reducing carbon dioxide emissions from automobiles. In order to respond to such demands for the clean energy of automobiles, the popularization of electric vehicles and natural gas vehicles has been studied in the early stages, but recently, the development of fuel cell vehicles has been energetically studied. In order to cope with such a request, it is assumed that a container filled with high-pressure hydrogen gas fuel is mounted on an automobile.

  Compressed natural gas containers for natural gas automotive fuel systems have a maximum filling pressure of 20 MPa or higher, so that FRP is reinforced with metal liners and resin liners with FRP to reduce vehicle loading weight as well as high pressure resistance. A composite container is used. Examples of the metal liner include steel, stainless steel, aluminum or an alloy thereof, titanium or an alloy thereof (Patent Documents 1 and 2). However, the steel liner produced in the example of Patent Document 1 uses a seamless steel pipe equivalent to STH21 as defined in JIS G 3429 (1988), designed to withstand pressure according to the notification of a composite container for a natural gas automobile fuel device based on the container safety regulations. However, it is calculated when the steel liner weight reaches 50 kg per unit length (1 m). For this reason, the weight of the liner portion is excessive as an automobile-mounted pressure vessel, which is not practical. Therefore, a liner using an aluminum alloy has been put into practical use for a vehicle equipped with a compressed natural gas container (Non-Patent Document 1).

  On the other hand, in the case of a fuel cell vehicle equipped with hydrogen, in order to secure the fuel consumption and storage amount of a traveling vehicle while mounting a hydrogen storage container in a limited space of the vehicle, than for a vehicle equipped with a compressed natural gas container, There is a significant demand for lighter and more compact containers. That is, the maximum filling pressure is expected to be increased to 35 MPa and 70 MPa, and it is necessary to have sufficient resistance against hydrogen embrittlement caused by the high-pressure hydrogen gas stored. For this reason, the above-mentioned aluminum alloy liners and resin liners, which have been proven for vehicles equipped with compressed natural gas containers, have been studied in advance as liner materials. The filling pressure 35 MPa container in which the carbon fiber reinforced resin is provided on the outer periphery of these liners is already in a practical stage, and development of increasing the pressure to the maximum filling pressure of 70 MPa is in progress (Non-patent Document 1). In particular, an FRP container that uses a fiber with a specified Young's modulus and elongation at break as a reinforcing fiber layer, and an FRP container that uses an aluminum alloy containing magnesium, silicon, and copper as a metal liner is a hydrogen storage with a filling pressure of 70 MPa. It has been developed as a container (Patent Documents 3 and 4).

  In this way, in hydrogen storage containers for fuel cells, the development of lightweight and high-strength aluminum liners is expected, the thinning of containers with the optimal design has progressed, and the amount of hydrogen storage per container is also expected to increase ( Non-patent document 1). On the other hand, the hydrogen embrittlement characteristics due to the metal liner coming into contact with the stored hydrogen gas, or the fatigue characteristics associated with pressure fluctuations during hydrogen filling, especially the thermal fatigue characteristics associated with temperature changes in the container during filling, The FRP container for high-pressure hydrogen storage to be used is a very important issue, but the actual situation is that little consideration has been made from these viewpoints.

Japanese Patent Laid-Open No. 10-292899 Japanese Patent Laid-Open No. 10-220691 JP 2005-36918 A JP 2007-154927 A

“Current Status and Challenges of Hydrogen Storage Technology”, September 2008, New Energy and Industrial Technology Development Organization Report

  It is an object of the present invention to provide an FRP container for high-pressure hydrogen storage that realizes a lightweight and compact FRP container for high-pressure hydrogen storage and is excellent in fatigue crack generation characteristics and propagation characteristics in a high-pressure hydrogen gas atmosphere.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor has 0.8 to 1.2 mass% Cr and 0.3 to 0.6 mass% excellent in hydrogen embrittlement resistance as a metal liner. The present invention finds that the above problem can be solved by adopting Mo-containing Cr-Mo steel, and further finds that it is more preferable that the Cr-Mo steel has a tensile strength of 830 to 1000 MPa. Was completed.

  That is, the present invention is an FRP container for high-pressure hydrogen storage in which the outer periphery of a Cr-Mo steel liner is covered with FRP, and the Cr-Mo steel contains 0.8 to 1.2% by mass of Cr and 0.3%. It is an FRP container for high-pressure hydrogen storage, which is steel containing ˜0.6% by mass of Mo.

  In the present invention, the Cr—Mo steel preferably has a tensile strength of 830 to 1000 MPa. In addition, the present invention provides a process in which a liner made of Cr-Mo steel forms a bottomed cylindrical body, a step of forming a neck portion by spinning a one-end opening of the bottomed cylindrical body, and obtaining a liner base tube. It is preferable that the liner is manufactured by sequentially performing a step of performing heat treatment by quenching and tempering the liner tube and a step of performing shot blasting on the inner and outer surfaces of the liner tube subjected to the heat treatment.

  In the present invention, the step of forming the bottomed cylindrical body is a step of forming a deep rolled steel plate, a step of forming a seamless steel pipe by spinning, or a step of forming a billet by hot drilling. Preferably, the bottomed cylindrical body is formed by deep drawing a rolled steel sheet.

  The FRP container for high-pressure hydrogen storage of the present invention uses a liner made of Cr—Mo steel containing 0.8 to 1.2% by mass of Cr and 0.3 to 0.6% by mass of Mo. The Cr—Mo steel used in the present invention preferably has a tensile strength of 830 to 1000 MPa. This tensile strength is much higher than aluminum alloy liner containers, resin liner containers, and stainless steel liner containers that have been studied as liner materials so far. It can satisfy the basic characteristics required for FRP containers mounted on automobiles. Therefore, as the liner container increases in strength, the liner thickness can be reduced to increase the storage volume, or the liner thickness can be maintained to reduce the amount of carbon fiber used and the associated cost reduction. . In addition, since the Cr-Mo steel of the present invention is superior in hydrogen embrittlement resistance than conventional Cr-Mo steel, the life until fatigue cracks generated from the inner surface of the steel container in contact with the filled hydrogen is extended. In addition, it has excellent fatigue resistance properties that slow the subsequent propagation characteristics (fatigue crack growth rate).

It is a figure which compares and shows the crack propagation rate test result of the Cr-Mo steel of this invention, and the conventional Cr-Mo steel. It is a figure which compares and shows the relationship between the crack depth progress of the trunk | drum of the Cr-Mo steel of this invention, and the conventional Cr-Mo steel, and the number of repetitions (Thickness 3 is based on the measurement result of FIG. 1). .. Is a diagram showing the result of calculating the number of cycles until a 2 mm liner is penetrated.

  The present invention, as an FRP container for high-pressure hydrogen storage mounted on a fuel cell vehicle, satisfies the basic characteristics of weight reduction and compactness, and also realizes excellent fatigue resistance in a hydrogen gas atmosphere. A liner made of Cr-Mo steel containing ~ 1.2 mass% Cr and 0.3-0.6 mass% Mo is used, and the outer periphery thereof is covered with FRP. The present invention is described in detail below.

Cr-Mo steel in the present invention In the present invention, Cr-Mo steel containing 0.8 to 1.2 mass% Cr and 0.3 to 0.6 mass% Mo is used as a liner material. When Cr—Mo steel having this basic chemical component is used, a tensile strength of 830 to 1000 MPa can be obtained by quenching and tempering heat treatment, and an aluminum alloy liner that has been used or has been studied for use. Compared with a resin liner or stainless steel, for example, a SUS316L liner, it is possible to realize a lighter and more compact container with increased strength. On the other hand, a tensile strength of 830 to 1000 MPa can moderately suppress hydrogen embrittlement sensitivity. In addition, the Cr-Mo steel used in the present invention is, in addition to 0.30 to 0.40 mass% C, 0.40 mass% or less Si, 0.50 / 1.00 mass% Mn, Impurities such as P, S, N and O which are inevitably mixed can be contained. Further, as long as the above-described tensile strength can be obtained at a normal quenching and tempering temperature, Ni may be contained at 2.00% by mass or less, but basically Ni is not contained.

  As shown in Table 1, the Cr—Mo steel used in the present invention is already standardized Cr—Mo steel, for example, chromium molybdenum steel (SCM435 steel) and nickel chromium molybdenum steel (SNCM439 steel specified by JIS). ), The amount of Mo is increased even if the amount of Cr is almost the same, and the amount of Cr is significantly reduced compared to the Cr-Mo steel where the amount of Mo is almost the same. To do. In addition, it is based on not containing Ni. The reason why the present invention has selected such a chemical component is that the high Mo steel is intended to enable high temperature tempering in heat treatment in order to reduce the resistance to hydrogen embrittlement. Therefore, it can be said that the tensile strength is lower than that of the existing Cr-Mo steel.

  The Cr—Mo steel of the present invention is less susceptible to hydrogen embrittlement than the conventional Cr—Mo steel because it has better fatigue crack propagation characteristics in a high-pressure hydrogen gas environment.

  In the present invention, the resistance to hydrogen embrittlement was evaluated based on the fatigue crack growth rate in a high-pressure hydrogen gas environment. Here, the fatigue crack growth rate was measured under the following conditions specified in ASTM E647, and the results are shown in FIG. Further, FIG. 2 shows a result of calculating the number of cycles until the liner having a thickness of 3.2 mm is penetrated based on the measurement result of FIG.

(1) Test material The steel of the present invention was a heat-treated hot-rolled steel sheet having the following chemical components to obtain a test material.
Steel of the present invention (34CrMo44 steel): 0.35% C-0.24% Si-0.69% Mn-0.98% Cr-0.45Mo, YS842MPa, TS939MPa, elongation 16.0%
On the other hand, the Cr-Mo steel as comparative steel quoted the numerical value described in the well-known literature. That is, comparative steel 1 (SCM435 steel) is "NEDO hydrogen station equipment dismantling investigation results December 12, 2008", and comparative steel 2 (SNCM439 steel) is "NEDO fuel cell / hydrogen technology development 2007 Research results report symposium quoted from "Safety Technology Research on Hydrogen Infrastructure (Outline of Results) June 24, 2008".
(2) Shape of test piece Using a compact tension (CT) test piece having a thickness of 6.30 mm from the heat-treated steel plate, the test piece was collected so that the crack propagated along the axial direction of the liner container. .
(3) Introduction of test piece pre-crack The pre-crack length of the notch tip was set to 2 mm so as to be 5% or more of the final crack length specified in ASTM E1820.
(4) Test conditions A load was applied to the test piece in accordance with K-decreasing or K-increasing control specified in ASTM E647. The testing machine used hydraulic servo type Instron 8500, and the crack tip position was measured by the potential drop method. The high-pressure hydrogen gas atmosphere was 62.5 MPa for the steel of the present invention, and a test vessel that can maintain the high-pressure hydrogen confidentiality was designed and manufactured and tested. On the other hand, comparative steel 1 is a test result in a hydrogen gas atmosphere of 45 MPa and comparative steel 2 is a 70 MPa hydrogen gas atmosphere.

  Referring to a separately conducted test in the air, the steel of the present invention showed a slightly larger slope of da / dN with respect to ΔK in the high-pressure hydrogen gas atmosphere than in the air, but no significant difference was observed. Under a high-pressure hydrogen gas atmosphere, when the Cr-Mo steel of the present invention and the conventional Cr-Mo steel are compared, the steel of the present invention has a small crack growth rate and is excellent. Comparative steel 1 (SCM435 steel) showed crack growth rate equivalent to that of the steel of the present invention in the atmosphere, but in hydrogen, the crack growth rate was significantly accelerated and hydrogen embrittlement sensitivity was high. Comparative steel 2 (SNCM439 steel) has a high crack growth rate in the atmosphere and in hydrogen.

  Based on the measurement results of FIG. 1, from the analysis based on BS PD6493, a fatigue crack that progresses from an initial crack (depth: 0.16 mm, length: 25 mm) on the liner inner surface is 3.2 mm in liner thickness. The number of pressure cycles reaching the outer surface was calculated. The results are shown in FIG. In the Cr-Mo steel of the present invention, the number of pressure cycles penetrating the liner thickness of 3.2 mm is 87,300 times, which is much higher than the number of pressure cycles of 11,250 times, which guarantees a 15-year service life of the container. , Indicating no damage caused by fatigue or rupture. On the other hand, in comparative steel 2 (SNCM439 steel), the number of pressure cycles penetrating the liner thickness of 3.2 mm is 8300 times. This is 1/10 or less of the steel of the present invention, and it is impossible to satisfy the number of pressure cycles that guarantee the useful life of the container for 15 years. Moreover, in comparative steel 1 (SCM435 steel), the number of pressure cycles penetrating the liner thickness of 3.2 mm is 16,800 times, satisfying the pressure cycle number that guarantees the useful life of the container for 15 years, but there is a margin. I can say no.

  From the above, the Cr-Mo steel liner containing 0.8 to 1.2 mass% Cr and 0.3 to 0.6 mass% Mo of the present invention is controlled to have a tensile strength of 830 to 1000 MPa. In combination with the appropriate material strength, it can be understood that the crack growth rate is excellent in a high-pressure hydrogen gas environment and the hydrogen embrittlement sensitivity is extremely low.

Liner production The Cr-Mo steel liner of the present invention is obtained by forming a bottomed cylindrical body from a raw material, forming a neck portion by spinning one end opening of the bottomed cylindrical body, and obtaining a liner tube. The liner base tube is manufactured through a process of performing a heat treatment by quenching and tempering, and a step of performing a shot blasting process on the inner and outer surfaces of the liner base pipe subjected to the heat treatment.

  Here, the step of forming the bottomed cylindrical body is any of a step of forming a deep rolled steel plate, a step of forming a seamless steel pipe by spinning, or a step of forming a billet by hot drilling. In particular, a bottomed cylindrical body formed by deep drawing a rolled steel sheet is more preferable.

  Since the Cr-Mo steel liner of the present invention is excellent in hydrogen embrittlement resistance as described above, a bottomed cylindrical body obtained by spinning one end of a seamless steel pipe as a conventional liner pipe as in the prior art. Alternatively, a bottomed cylinder obtained by hot drilling a billet can be used. However, seamless steel pipes are manufactured by continuously casting round steel pieces using a Mannesmann drilling machine. Inclusions and impurities are segregated in the vicinity of the center of the round steel pieces that become the final solidification part of continuous casting. It is inevitable to do. Even after forming into a seamless steel pipe, the surface layer portion in the vicinity of the inner surface of the steel pipe becomes a layer including this segregation part, and there is a very small hardened structure layer resulting from extremely small surface defects or component segregation. For this reason, in a high-pressure container using a seamless steel pipe as a liner element pipe, there is a high possibility that these minute surface defects or hardened layers remain on the inner surface of the high-pressure container. Such a defect does not cause a special problem in a high-pressure vessel for filling with an inert gas. However, when the filling gas is high-pressure hydrogen gas, large pressure fluctuations and high-pressure hydrogen gas environment during gas filling may cause the occurrence of fatigue cracks from microscopic surface defects and hardened layers. There is also a fear of increasing the conversion characteristics. The same applies to a case where a bottomed cylindrical body obtained by hot perforating a billet is used as a liner tube.

  Therefore, if a pipe made by processing a rolled steel plate into a bottomed cylindrical body by deep drawing is used instead of producing a Cr-Mo steel liner by hot drilling from a seamless steel pipe or billet, a fatigue crack will occur. It is more preferable in terms of generation. The rolled steel plate is specifically a thick steel plate or a hot coil (hereinafter referred to as “hot rolled steel plate”). By using a hot-rolled steel sheet as the liner material, it is possible to solve the problem that the central final solidification part of the continuously cast round steel pieces remains near the inner surface of the container product. A healthy structure that does not contain the material can be obtained, and the fatigue crack initiation characteristics can be remarkably improved.

A liner tube from a hot-rolled steel sheet can be produced by the following method.
The hot-rolled steel sheet is cut into an appropriate length and then cut into a circle. After applying the lubricant to the hot-rolled steel sheet, deep drawing is performed by a vertical press. Depending on the dimensions of the container, it is necessary to perform the deep drawing process in two or three stages. During the process, it is better to heat-treat (anneal) the processing blank to soften the work-hardened structure and perform multi-stage deep drawing. . After finishing the bottomed cylindrical long semi-finished product after deep drawing, the thickness of the cylindrical portion is made uniform by flow forming. Subsequently, the one-end opening is cut to an appropriate length, and then subjected to a spinning process and a boss part forming process. Thereafter, a heat treatment of quenching and tempering is performed to adjust the material strength to an appropriate range. After the heat treatment, shot blasting is performed on the entire inner and outer surfaces of the liner, and finally the neck portion is threaded to complete the molding of the container as the liner. In this way, the liner container can produce a one-piece container that does not use any weld seams.

  The production of a plate-like material as a liner container by deep drawing is common for small containers, but a large high-pressure FRP container intended to be mounted on a fuel cell vehicle, or It is not common in large high pressure FRP containers used as pressure accumulators at hydrogen filling stations. The present inventor made it possible to manufacture a steel liner for a large-sized high-pressure FRP container by using a vertical press machine for deep drawing and combining annealing heat treatment in the middle.

  Shot blasting is also applied to the inner surface of the steel liner tube, in addition to removing wrinkle-like micro-defects on the surface layer formed near the inner surface by flow forming, as well as compressive residue directly under the inner surface. The purpose is to positively apply stress and greatly improve the fatigue crack initiation characteristics. In particular, it is preferable to leave a large compressive residual stress in the vicinity of the inner surface of the liner because it can be expected to further suppress the occurrence of fatigue cracks from the inner surface of the liner.

FRP container manufacture Next, FRP is formed on the outer periphery of the formed steel liner. The manufacture of the FRP container at this time is performed by using a known filament winding method that is generally employed. First, after primer-coating the outer surface of the container, an epoxy resin-impregnated carbon or glass fiber is wound around the container surface in order to obtain high strength. The fiber wrapping can be first carbon fiber, then glass fiber, or all carbon fiber or glass fiber. The resin-impregnated fiber is finally dried by heating to cure the resin layer. Thereafter, plastic processing (Autofretague) is performed by water pressure, and a state in which an appropriate compressive residual stress in a range not exceeding the yield strength is applied to the steel liner portion is defined as a final product. After that, the pressure test for product guarantee, the appearance inspection of the container, the painting, the processing of the label, etc. are carried out.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.

  An FRP container using the Cr—Mo steel liner of the present invention that satisfies the specifications shown in Table 2 was prepared.

Here, the used Cr-Mo steel liner was formed by deep-drawing a hot-rolled steel sheet cut out from a hot coil having a thickness of 12 mm, and its chemical composition was as follows (mass%). .
C: 0.35, Si: 0.24, Mn: 0.69, Cr: 0.98, Mo: 0.45, Al: 0.032

A steel liner container having a body plate thickness of 3.2 mm processed using the above chemical components was subjected to quenching-tempering treatment (quenching temperature: 900 ° C., tempering temperature: 645 ° C.). The mechanical properties after the heat treatment are as follows.
Yield strength: 842 MPa, Tensile strength: 939 MPa, Elongation: 16%

  The thickness of the barrel of the Cr—Mo steel liner produced in this example is 3.2 mm. In the case of a conventionally used aluminum alloy liner (grade: Al 6061-T6, YS: 275 MPa or more, TS: 310 MPa or more), the average liner thickness is 10 mm, so the thickness is about 1/3. Decrease. If the outer diameter of the liner is 300 mm (constant), the weight per unit length (1 m) is 24.6 kg / m for the aluminum alloy liner and 23.2 kg / m for the Cr-Mo steel liner. The Cr—Mo steel liner of the present invention is rather lightweight.

  A liner tube was manufactured as described above, and shot blasting was performed on the inner and outer surfaces of the liner tube after heat treatment. Next, FRP was coated on the outer periphery of the liner. In the FRP, a total of 7 layers of 3 layers of hoops and 4 layers of helical layers were wound by a filament winding method, and a glass fiber was wound by 2 layers of helical layers as a carbon fiber protective layer. In order to achieve high strength and light weight of the FRP container, SOFICAR T700SC-12000 manufactured by Toray Industries, Inc. was used as the carbon fiber, and a product of Owens Corning Advancex was used as the glass fiber. Moreover, an epoxy resin was used as the resin.

  The liner made of Cr-Mo steel containing 0.8 to 1.2% by mass of Cr and 0.3 to 0.6% by mass of Mo used in the present invention is an aluminum alloy liner container or a resin liner container. Compared to stainless steel liner containers, the strength is higher, so it is possible to realize a lighter, more compact, lower cost container, and excellent resistance to hydrogen embrittlement. Therefore, the characteristics required for the FRP container for high-pressure hydrogen storage mounted on the fuel cell vehicle using hydrogen gas can be satisfied, which contributes to the practical use of the fuel cell vehicle.

Claims (4)

A high-pressure hydrogen storage FRP container in which the outer periphery of a liner made of Cr-Mo steel is coated with FRP, and the Cr-Mo steel is composed of 0.8 to 1.2 mass% of Cr and 0.3 to 0.6 mass. % Of Mo, steel containing Nb, V, Ti and B, and having a tensile strength of 830 to 1000 MPa under a hydrogen pressure environment of 62.5 MPa according to the test method specified in ASTM E647. Fatigue crack growth rate was measured at the same time, and based on the measurement results, analysis based on BS PD6493 revealed that a fatigue crack that progresses from an initial crack with a liner inner surface depth of 0.16 mm and length of 25 mm is liner. When calculating the number of pressure cycles to reach the outer surface with a thickness of 3.2 mm, it exceeds the number of pressure cycles of 11,250, which guarantees a 15-year service life of the container.
An FRP container for high-pressure hydrogen storage, characterized by excellent fatigue characteristics in a high-pressure hydrogen gas environment.   Cr-Mo steel liner forms a bottomed cylindrical body, a process of forming a neck portion by spinning one end opening of the bottomed cylindrical body to form a liner base pipe, and quenching the obtained liner base pipe The FRP container for high-pressure hydrogen storage according to claim 1, which is a liner produced by sequentially performing a step of performing a heat treatment by tempering and a step of performing a shot blast treatment on the inner and outer surfaces of the liner pipe subjected to the heat treatment.   The step of forming the bottomed cylindrical body is either a step of forming a deep rolled steel plate, a step of forming a seamless steel pipe by spinning, or a step of forming a billet by hot drilling. The FRP container for high-pressure hydrogen storage according to claim 2.   The FRP container for high-pressure hydrogen storage according to claim 2, wherein the bottomed cylindrical body is formed by deep drawing a rolled steel plate.

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