Patent Description:
Examples of a device for storing high-pressure gas include a pressure vessel for storing and transporting high-pressure hydrogen gas used at a hydrogen station or the like. Conventionally, the pressure vessel is manufactured using high-strength low-alloy steel such as Cr-Mo steel. However, in a case where hydrogen is stored in the pressure vessel, when the pressure vessel has a structure in which hydrogen comes into direct contact with a screwable portion constituting an opening portion of the pressure vessel, there is a concern that strength and ductility of a stress concentrated portion (for example, a screw-threaded portion between a male thread and a female thread) in the screwable portion may decrease due to so-called hydrogen environment embrittlement. Such embrittlement of the pressure vessel is not preferable because it may cause a reduction in an accumulation performance of the pressure vessel.

Therefore, in one of the conventional pressure vessels, a structure (a so-called screwable nut type lid structure) is adopted in which a lid-like structure is interposed between a screwable portion and an accumulator chamber, so that the screwable portion and hydrogen do not come into direct contact with each other. With this structure, the conventional pressure vessel suppresses hydrogen environment embrittlement at a screw-threaded portion (for example, roots of threads) between a male thread and a female thread of the screwable portion (see, for example, <CIT> or NPL <NUM>).

In the above-described screwable nut type lid structure, the lid-like structure is normally held at a predetermined position by the screwable portion. In other words, a force exerted on the lid-like structure by gas in the accumulator chamber is transmitted to the screwable portion via the lid-like structure, and finally acts on the screw-threaded portion of the screwable portion. Therefore, in addition to the hydrogen environment embrittlement, there is a concern that a fatigue crack may occur in the screw-threaded portion due to a stress generated in the screw-threaded portion of the screwable portion (particularly, in the vicinity of a first screw thread closest to the accumulator chamber).

From the background as described above, it is desirable for the pressure vessel to suppress both hydrogen environment embrittlement of the screwable portion in the case of storing hydrogen in the accumulator chamber and fatigue crack of the screwable portion due to an internal pressure of the accumulator chamber.

An object of the present invention is to provide a pressure vessel capable of suppressing both hydrogen environment embrittlement and fatigue crack of a screwable portion included in a pressure vessel.

The invention is a pressure vessel as described in claim <NUM>.

According to the first aspect, since the lid portion is provided between the screwable portion and the accumulator chamber, hydrogen is suppressed from coming into direct contact with the screwable portion even when hydrogen is stored in the accumulator chamber. Further, the reinforcing ring provided so as to cover the outer peripheral surface of the cylinder portion (in other words, so as to be fitted to the outer peripheral surface) covers the outer peripheral surface of the cylinder portion corresponding to a part or the whole of the screw-threaded portion between the screwable portion and the cylinder portion. According to experiments and considerations made by the inventors, it becomes clear that the occurrence of a fatigue crack in the screw-threaded portion can be suppressed by arranging the reinforcing ring at such a position (see <FIG> or the like). Therefore, the pressure vessel according to the first aspect can suppress both hydrogen environment embrittlement and fatigue crack of the screwable portion.

[<NUM>] In a second aspect of the present invention, the pressure vessel according to the first aspect <NUM>, further comprising: a seal portion sealing a gap between the lid portion and the cylinder portion, wherein the reinforcing ring is configured such that an end portion of the reinforcing ring on an accumulator chamber side in the axial direction is positioned at a position on the outer peripheral surface corresponding to the seal portion, or at a position closer to the accumulator chamber side in the axial direction than the position on the outer peripheral surface corresponding to the seal portion.

According to the second aspect, the seal portion further appropriately suppresses gas in the accumulator chamber from coming into contact with the screwable portion. Further, the "end portion on the accumulator chamber side" of the reinforcing ring is positioned at a position on the outer peripheral surface of the cylinder portion corresponding to the seal portion, or at a position closer to the accumulator chamber side than the position on the outer peripheral surface of the cylinder portion corresponding to the seal portion. According to the experiments and considerations made by the inventors, it becomes clear that since the end portion of the reinforcing ring is arranged at such a position, the reinforcing ring can suppress the cylinder portion from deforming so as to expand in the radial direction, and the seal portion can seal the gap more reliably (see <FIG>). Therefore, the pressure vessel according to the second aspect can further reliably suppress the hydrogen environment embrittlement of the screwable portion.

[<NUM>] In a third aspect of the present invention, the pressure vessel according to the first or second aspect, wherein the reinforcing ring is configured such that an end portion of the reinforcing ring on an opposite side to the accumulator chamber in the axial direction is positioned at a position on the outer peripheral surface corresponding to an end portion of the screw-threaded portion on an opposite side to the accumulator chamber, or at a position farther away from the accumulator chamber in the axial direction than the position on the outer peripheral surface corresponding to the end portion of the screw-threaded portion on the opposite side to the accumulator chamber.

According to the third aspect, the "end portion on the opposite side to the accumulator chamber" of the reinforcing ring is positioned at a position corresponding to the end portion of the screw-threaded portion or positioned farther away from the accumulator chamber than the position corresponding to the end portion of the screw-threaded portion. According to the experiments and considerations made by the inventors, it becomes clear that the occurrence of the fatigue crack in the screw-threaded portion can be suppressed by arranging the reinforcing ring at such a position (see <FIG>). Therefore, the pressure vessel according to the third aspect can further reliably suppress the fatigue crack of the screwable portion.

[<NUM>] In a fourth aspect of the present invention, the pressure vessel according to any one of the first to third aspects, wherein a difference between the maximum value and the minimum value of a stress generated in the screw-threaded portion is 300MPa or less in a case where a pressure in the accumulator chamber varies within a range of <NUM> MPa or less and <NUM> MPa or more.

According to the fourth aspect, based on the experiments and considerations made by the inventors, it became clear that the difference (hereinafter referred to as a "stress range") between the maximum value and the minimum value of the stress generated in the screw-threaded portion can be reduced since the reinforcing ring is attached to the cylinder portion (see <FIG>, <FIG>). In particular, if the stress range is <NUM> MPa or smaller in a case where the pressure in the accumulator chamber varies within the range of <NUM> MPa to <NUM> MPa, the pressure vessel of the present invention can be used even when the accumulator chamber has a particularly high pressure such as a hydrogen storage vessel at a hydrogen station. In particular, if the cylinder portion is designed using a thin-walled pipe satisfying the above condition and having a safety coefficient of <NUM> or more, it is possible to contribute to reduction in a size of the hydrogen storage vessel at the hydrogen station. Incidentally, in this case, the "safety coefficient" is a value calculated by "the tensile strength of a steel material or the like forming the thin-walled pipe and/or the maximum stress assumed in design of the thin-walled pipe" (see, for example, NPLs <NUM> to <NUM>).

In the present invention, the reinforcing ring is fitted to the cylinder portion in a state of exerting a compressive stress so as to tighten the cylinder portion.

According to the above-mentioned aspect, since the cylinder portion is tightened by the reinforcing ring, the effect of protecting the seal portion and the screw-threaded portion is enhanced, and the hydrogen environment embrittlement and the fatigue crack can be more reliably suppressed. For example, the tightening can be realized by shrink-fitting the reinforcing ring to the cylinder portion.

[<NUM>] In a fifth aspect of the present invention, the pressure vessel according to any one of the first to fifth aspects, wherein a thickness of the reinforcing ring in a radial direction of the cylinder portion is <NUM>% or more and <NUM>% or less of an outer diameter of the cylinder portion.

According to the fifth aspect, based on the experiment and the considerations conducted by the inventors for the sixth aspect, it becomes clear that the reinforcing ring having such a thickness can achieve both effect of protecting the seal portion and the screw-threaded portion and an economic efficiency and weight of the pressure vessel as a product.

[<NUM>] In a sixth aspect of the present invention, the pressure vessel according to any one of the first to sixth aspects, wherein the lid portion comprises an extending portion expanding radially outward of the cylinder portion, wherein the screwable portion comprises a recessed portion recessed radially outward, wherein the extending portion and the recessed portion abut against each other in the axial direction, and wherein the outer peripheral edge of the screwable portion on the accumulator chamber side and the lid portion are separated from each other in the axial direction.

According to the sixth aspect, since the outer peripheral edge (in other words, in the vicinity of the screw-threaded portion) of the screwable portion on the accumulator chamber side is separated from the lid portion, the force exerted on the lid portion by the gas in the accumulator chamber is not easily transmitted directly to the screw-threaded portion. Therefore, the pressure vessel according to the seventh aspect can further reliably suppress the occurrence of the fatigue crack.

[<NUM>] In a seventh aspect of the present invention, the pressure vessel according to any one of the first to seventh aspects, wherein the cylinder portion has a straight tubular and cylindrical shape.

According to the seventh aspect, since the cylinder portion has the straight tubular (that is, a tubular shape that is not curved) and cylindrical shape, it is possible to easily perform a precise machining when the cylinder portion is manufactured as compared with a case where the cylinder portion is curved. Therefore, it is possible to suppress the occurrence of a machining crack on the inner wall surface or the like of the cylinder portion, and to suppress occurrence of the hydrogen environment embrittlement in the cylinder portion due to the machining crack. In addition, it is also possible to increase the work efficiency of inspecting the presence or absence of the machining crack.

[<NUM>] In an eighth aspect of the present invention, the pressure vessel according to any one of the first to eighth aspects, wherein a fatigue crack life is not less than <NUM>,<NUM> times in a case where an annular crack having a depth of <NUM> is assumed as an initial assumed crack in the screw-threaded portion of the cylinder portion, in fatigue crack propagation analysis according to Standard for Ultra High-Pressure Gas Equipment KHKS <NUM> (<NUM>) defined by the High Pressure Gas Safety Institute of Japan.

According to the eighth aspect, since the pressure vessel has a fatigue crack life of <NUM>,<NUM> times or more in fatigue crack propagation analysis according to the above standard, the pressure vessel that can withstand long-term practical use can be provided as the hydrogen storage vessel at the hydrogen station. Incidentally, "<NUM>,<NUM> times" is a value assuming a case where the pressure vessel is subjected to about <NUM> times of pressure increase and pressure decrease per day for about <NUM> years.

According to the present invention, both hydrogen environment embrittlement of the screwable portion in the case of storing hydrogen in the accumulator chamber and fatigue crack of the screwable portion due to the internal pressure of the accumulator chamber can be suppressed.

A pressure vessel <NUM> according to an embodiment of the present invention will be described below.

As shown in <FIG>, the pressure vessel <NUM> of the present embodiment includes a cylindrical cylinder portion <NUM> made of steel that defines an accumulator chamber <NUM> therein, lid portions <NUM> made of metal that is provided so as to close both end portions of the cylindrical cylinder portion <NUM> and each have a passage hole 25D, screwable portions <NUM> made of metal that fix the lid portions <NUM> to the cylindrical cylinder portion <NUM>, and reinforcing rings <NUM> made of metal that are fitted to outer peripheral surfaces 1F of both end portions of the cylindrical cylinder portion <NUM>. As will be described later, pressure receiving surfaces 2A of the lid portion <NUM> facing the accumulator chamber <NUM> directly receive a pressure of high-pressure gas in the accumulator chamber <NUM>. On the other hand, the screwable portion <NUM> is isolated from gas in the accumulator chamber <NUM> by the corresponding lid portion <NUM>. The pressure vessel <NUM> may be used, for example, for storing hydrogen gas.

The cylindrical cylinder portion <NUM> has a straight tubular and cylindrical shape with both end portions opened. Therefore, when the cylindrical cylinder portion <NUM> is manufactured, it is possible to perform a precise machining such as mirror finishing so that a main inner surface 1A of the cylindrical cylinder portion <NUM> is not damaged or cracked. For example, as will be described later, it is possible to perform a quality management so that a machining crack having a depth of <NUM> or greater does not occur on the main inner surface 1A. In addition, it is also easy to inspect a presence or absence of the crack after the cylindrical cylinder portion <NUM> is manufactured. On the other hand, as the conventional pressure vessel, a seamless vessel (for example, a Mannesmann-type bomb or an Ehrhardt-type bomb) that has a shape in which a tube cross section becomes smaller as it approaches the opening portion generally has a smaller opening portion than the cylindrical cylinder portion <NUM>. Therefore, in the conventional pressure vessel, the same inspection as that of the cylindrical cylinder section <NUM> is difficult.

Materials of the cylindrical cylinder portion <NUM>, the lid portion <NUM>, the screwable portion <NUM>, and the reinforcing ring <NUM> are not particularly limited. Manganese steel, chromium molybdenum steel, nickel chromium molybdenum steel or other low-alloy steels (excluding stainless steel) can be used, for example. By using these materials having excellent tensile strength as described above, strength of the pressure vessel <NUM> can be improved. The lid portion <NUM>, the screwable portion <NUM>, and the reinforcing ring <NUM> may be made of the same material as the cylindrical cylinder portion <NUM>, or may be made of another material (for example, carbon fiber reinforced plastic or the like). The lid portion <NUM>, the screwable portion <NUM> and the reinforcing ring <NUM> may be made of different materials.

A method of manufacturing the cylindrical cylinder portion <NUM> is not particularly limited. For example, it is preferable that the cylindrical cylinder portion <NUM> is formed into an integral unit by, for example, forging, extrusion, or the like, which is a machining method with few drawbacks. The main inner surface 1A defines the accumulator chamber <NUM> and receives the pressure of high-pressure gas. It is preferable that the main inner surface 1A of the cylindrical cylinder portion <NUM> is mirror finished to be free from a crack. In particular, the main inner surface 1A is preferably mirror-finished so as to be free from a crack having a depth of <NUM> or greater in a thickness direction of the cylindrical cylinder portion <NUM> and a surface length of <NUM> or greater in the cylindrical cylinder portion <NUM>. By the mirror finishing, a development or propagation of a crack that would be caused by hydrogen environment embrittlement can be suppressed.

Both end portions in an axial direction of the cylindrical cylinder portion <NUM> are formed with bore portions 1B that are recessed radially outward from the main inner surface 1A. A female thread portion 1C into which the screwable portion <NUM> is screw-threaded is provided on an inner peripheral portion of each of the bore portions 1B. However, the female thread portion 1C is not provided in a part of the bore portion 1B on an accumulator chamber <NUM> side.

The screwable portion <NUM> includes a male thread portion <NUM> that has a tubular shape and is screw-threaded into the female thread portion 1C at an outer peripheral portion thereof. The screwable portion <NUM> is attached to both end portions of the cylindrical cylinder portion <NUM>. In this example, an end portion structure of the cylindrical cylinder portion <NUM> including the screwable portion <NUM> is the same at one end and another end of the cylindrical cylinder portion <NUM>. However, the end portion structure of the cylindrical cylinder portion <NUM> may be different at the one end and the other end of the cylindrical cylinder portion <NUM>.

The lid portion <NUM> includes a first shaft portion <NUM> on the accumulator chamber <NUM> side and a second shaft portion <NUM> on an opposite side to the accumulator chamber <NUM>. The lid portion <NUM> includes the passage hole 25D penetrating the first shaft portion <NUM> and the second shaft portion <NUM> in the axial direction of the cylindrical cylinder portion <NUM>.

The first shaft portion <NUM> of the lid portion <NUM> includes a large diameter portion <NUM> expanding radially outward. A portion of the first shaft portion <NUM> closer to the accumulator chamber <NUM> side than the large diameter portion <NUM> extends along the main inner surface 1A of the cylindrical cylinder portion <NUM>. As shown in <FIG>, a seal portion <NUM> such as an O-ring is provided between the first shaft portion <NUM> and the main inner surface 1A. The seal portion <NUM> is arranged at a position slightly away from the accumulator chamber <NUM> than the pressure receiving surface 2A. A recess for arranging the seal portion <NUM> in this manner is provided at an outer peripheral edge of the first shaft portion <NUM> on the accumulator chamber <NUM> side.

The large diameter portion <NUM> and a boundary portion 1D between the main inner surface 1A and the bore portion 1B of the cylindrical cylinder portion <NUM> abut against each other in the axial direction of the cylindrical cylinder portion <NUM>. As a result, the large diameter portion <NUM> (as a result, the lid portion <NUM>) is restricted from moving toward the accumulator chamber <NUM> from the boundary portion 1D.

An extending portion <NUM> having a smaller diameter than the large diameter portion <NUM> and expanding radially outward of the cylindrical cylinder portion <NUM> is provided on the large diameter portion <NUM> on an opposite side to the accumulator chamber <NUM>. In this example, the extending portion <NUM> has a cylindrical shape. However, the shape of the extending portion <NUM> is not particularly limited, and may have another shape other than a cylinder. The extending portion <NUM> may be made up of a plurality of members. The extending portion <NUM> may be formed integrally with the large diameter portion <NUM> or may be formed separately from the large diameter portion <NUM>. In this example, the large diameter portion <NUM> and the extending portion <NUM> are integrally formed.

The second shaft portion <NUM> of the lid portion <NUM> is arranged radially inward of the screwable portion <NUM>. In this example, the second shaft portion <NUM> has a cylindrical shape. However, the shape of the second shaft portion <NUM> is not particularly limited, and may have another shape other than a cylinder. The second shaft portion <NUM> may be made up of a plurality of members.

As shown in <FIG>, the screwable portion <NUM> includes a through hole <NUM> in which the second shaft portion <NUM> is arranged. The screwable portion <NUM> has a recessed portion <NUM> recessed radially outward at an end portion on the accumulator chamber <NUM> side. The recessed portion <NUM> and the extending portion <NUM> abut against in the axial direction of the cylindrical cylinder portion <NUM>. Further, an outer peripheral edge 3A of the screwable portion <NUM> on the accumulator chamber <NUM> side (that is, the portion in the vicinity of the screw-threaded portion <NUM>) and the large diameter portion <NUM> are separated from each other in the axial direction of the cylindrical cylinder portion <NUM> with the recessed portion <NUM> kept in abutment against the extending portion <NUM> in this manner.

When the screwable portion <NUM> is screwed in a direction approaching the accumulator chamber <NUM> from the end portion of the cylindrical cylinder portion <NUM>, the recessed portion <NUM> of the screwable portion <NUM> presses the extending portion <NUM> of the lid portion <NUM> toward the accumulator chamber <NUM>. Accordingly, in a state in which the large diameter portion <NUM> is pressed against the boundary portion 1D of the cylindrical cylinder portion <NUM>, a movement of the lid portion <NUM> in the axial direction is restricted. At this time, since the outer peripheral edge 3A of the screwable portion <NUM> is separated from the large diameter portion <NUM>, the outer peripheral edge 3A does not directly press the lid portion <NUM>. Conversely, in a case where high-pressure gas is stored in the accumulator chamber <NUM>, the force exerted on the lid portion <NUM> by the gas in the accumulator chamber <NUM> is not directly transmitted to the outer peripheral edge 3A. As a result, the force exerted on the lid portion <NUM> by the gas in the accumulator chamber <NUM> is not easily transmitted to the screw-threaded portion <NUM>, and a stress generated in the screw-threaded portion <NUM> can be reduced. Incidentally, a female thread may be formed on an inner surface of the through hole <NUM> of the screwable portion <NUM>, a male thread may be formed on an outer peripheral surface of the second shaft portion <NUM> of the lid portion <NUM>, so that the screwable portion <NUM> and the second shaft portion <NUM> are screw-threaded together.

In the axial direction of the cylindrical cylinder portion <NUM>, the extending portion <NUM> preferably extends to a position away from the accumulator chamber <NUM> than two or more threads of a meshing engagement of the screw-threaded portion <NUM> between the female thread portion 1C and the male thread portion <NUM> on the accumulator chamber <NUM> side. In addition, a length of the extending portion <NUM> in the axial direction is preferably <NUM>% or less than a length L in the axial direction between a position where the seal portion <NUM> is provided and the outer peripheral edge 3A of the screwable portion <NUM>. When the extending portion <NUM> is too short, an effect of reducing the stress generated in the screw-threaded portion <NUM> cannot be sufficiently obtained. The effect increases as the extending portion <NUM> extends longer, and becomes saturated when the extending portion <NUM> reaches a predetermined length. Therefore, the length of the extending portion <NUM> may be set to an appropriate length enough to sufficiently exert the effect of reducing the stress generated in the screw-threaded portion <NUM>.

An outer peripheral surface 22A of the extending portion <NUM> is preferably positioned away from an inner peripheral surface 31A of the through hole <NUM> of the screwable portion <NUM> toward the radially outer side by <NUM>% to <NUM>% of a radial thickness T2 of the screwable portion <NUM> including a radial height (thickness) of the male thread portion <NUM>. However, when the outer peripheral surface 22A of the extending portion <NUM> is too close to the male thread portion <NUM> (for example, in a case where the outer peripheral surface 22A is at a position exceeding <NUM>% of the thickness T2 from the inner peripheral surface 31A), the effect of reducing the stress generated in the screw-threaded portion <NUM> is reduced. In addition, when the outer peripheral surface 22A of the extending portion <NUM> is too far from the male thread portion <NUM> (for example, in a case where the outer peripheral surface 22A is positioned less than <NUM>% of the thickness T2 from the inner peripheral surface 31A), the effect of reducing the stress generated in the screw-threaded portion <NUM> is also reduced.

When a thickness T3 of a ligament portion (that is, a portion positioned radially outward of the extending portion <NUM> including the male thread portion <NUM> of the screwable portion <NUM>) is excessively small, there is a possibility that a problem such as deformation of the ligament portion occurs when a work piece is hit by mistake or the like. The thickness of the ligament portion is preferably <NUM>% or more of a height of the screw thread (a distance between a crest and a root of the thread) in the screw-threaded portion <NUM>, or is preferably <NUM>% or more of a pitch of the thread in the screw-threaded portion <NUM>.

An autofrettaging treatment may be applied to the main inner surface 1A of the cylindrical cylinder portion <NUM>. When applying the autofrettaging treatment, an inner peripheral layer forming the main inner surface 1A of the cylindrical cylinder portion <NUM> is plastically deformed, so that a residual stress is generated in the inner peripheral layer. Accordingly, strength of the main inner surface 1A is increased. On the other hand, when applying the autofrettaging treatment, an outer peripheral layer forming the outer peripheral surface 1F of the cylindrical cylinder portion <NUM> is more likely to be elastically deformed than the inner peripheral layer.

In the pressure vessel <NUM>, the main inner surface 1A can be precisely machined by making the cylindrical cylinder portion <NUM> cylindrical. Therefore, for example, it is preferable to manufacture the cylindrical cylinder portion <NUM> so that a machining crack having a depth of <NUM> or greater does not occur on the main inner surface 1A. In addition, an internal inspection of the cylindrical cylinder portion <NUM> after manufacturing can also be carried out easily and accurately by removing the lid portion <NUM>, the screwable portion <NUM>, or the like. As a result, a quality of the pressure vessel <NUM> is further improved. After the internal inspection is finished, the lid portions <NUM>, the screwable portion <NUM>, or the like can be easily attached to the cylindrical cylinder portion <NUM>.

As described above, in the pressure vessel <NUM> of the present embodiment, the force exerted on the lid portion <NUM> by the gas in the accumulator chamber <NUM> is not directly transmitted from the large diameter portion <NUM> to the outer peripheral edge 3A of the screwable portion <NUM>. As a result, the force caused by the gas in the accumulator chamber <NUM> is not concentrated in a portion (that is, a first screw thread 12A and the vicinity thereof) of the screw-threaded portion <NUM> on the accumulator chamber <NUM> side, and the force can be distributed over a wider range of the screw-threaded portion <NUM>.

In the present embodiment, the reinforcing ring <NUM> is fitted to the outer peripheral surface 1F of each of both the end portions of the cylindrical cylinder portion <NUM>. The reinforcing ring <NUM> preferably has a thickness of <NUM>% or more and <NUM>% or less of an outer diameter of the cylindrical cylinder portion <NUM>. As will be described later, according to experiments and considerations made by the inventors, it becomes clear that the reinforcing ring <NUM> having such a thickness can achieve both effects of protecting the seal portion <NUM> and the screw-threaded portion <NUM> and an economic efficiency and weight of the pressure vessel <NUM> as a product.

The reinforcing ring <NUM> can be fixed to the outer peripheral surface 1F of the cylindrical cylinder portion <NUM> by shrink fitting, for example. However, a method of attaching the reinforcing ring <NUM> to the cylindrical cylinder portion <NUM> is not particularly limited. For example, the reinforcing ring <NUM> may be divided into a plurality of parts, these divided parts may be attached to the outer peripheral surface 1F of the cylindrical cylinder portion <NUM>, and the parts may be joined together by welding or the like. In addition, the reinforcing ring <NUM> is fitted to the cylindrical cylinder portion <NUM> in a state of exerting a compressive stress so as to tighten the cylindrical cylinder portion <NUM>. For example, the tightening can be realized by the shrink fitting. Since the reinforcing ring <NUM> exerts the compressive stress on the cylindrical cylinder portion <NUM>, an effect of protecting the seal portion <NUM> and the screw-threaded portion <NUM> can be further enhanced.

In the present embodiment, both end portions of the cylindrical cylinder portion <NUM> are opened, and the reinforcing rings <NUM> are attached to both end portions. However, in a case where only one end portion of the cylindrical cylinder portion <NUM> is opened, the reinforcing ring <NUM> only needs to be fitted to the opened end portion. The reinforcing ring <NUM> is preferably arranged on the outer peripheral surface 1F of the cylindrical cylinder portion <NUM> so as to be at a position corresponding to a part or the whole of the screw-threaded portion <NUM>. However, the position of the reinforcing ring <NUM> preferably includes a position corresponding to the portion of the screw-threaded portion <NUM> on the accumulator chamber <NUM> side (that is, the first screw thread 12A and the vicinity thereof), and more preferably includes a position corresponding to the whole of screw-threaded portion <NUM>.

The reinforcing ring <NUM> is preferably arranged on the outer peripheral surface 1F of the cylindrical cylinder portion <NUM> so as to be at a position corresponding to the seal portion <NUM>. By reinforcing the vicinity of a portion of the cylindrical cylinder portion <NUM> corresponding to the seal portion <NUM> with the reinforcing ring <NUM>, a sealing performance of the seal portion <NUM> is enhanced. In a case where a distance from the seal portion <NUM> to the screw-threaded portion <NUM> is L, an end portion 4A of the reinforcing ring <NUM> on the accumulator chamber <NUM> side preferably extends a position corresponding to a portion separated by <NUM> from the seal portion <NUM> to the accumulator chamber <NUM> side from a viewpoint of enhancing the sealing performance (see also <FIG>).

The reinforcing ring <NUM> preferably extends to a position corresponding to an end portion (that is, a screw thread 12B in <FIG>) of the screw-threaded portion <NUM> on the opposite side to the accumulator chamber <NUM>. As described above, by covering the position corresponding to the end portion (the screw thread 12B) of the screw-threaded portion <NUM> on the opposite side to the accumulator chamber <NUM> with the reinforcing ring <NUM>, the effect of protecting the screw-threaded portion <NUM> is enhanced. In the case where the distance from the seal portion <NUM> to the screw-threaded portion <NUM> is L, an end portion 4B of the reinforcing ring <NUM> on the opposite side to the accumulator chamber <NUM> preferably extends to a position corresponding to a portion separated by <NUM> from the seal portion <NUM> to the opposite side to the accumulator chamber <NUM> from a viewpoint of protecting the screw-threaded portion <NUM> (see also <FIG>).

The pressure vessel <NUM> of the present embodiment can be used as a hydrogen storage vessel at a hydrogen station so as to supply hydrogen to a motor vehicle equipped with a fuel cell using hydrogen as fuel. For example, the pressure vessel <NUM> can be used to supply hydrogen with a pressure of about <NUM> MPa to the motor vehicle equipped with the fuel cell. In this case, as an example, the pressure vessel <NUM> is subjected to repetition of pressure increase and pressure decrease of <NUM>,<NUM> times for <NUM> years. The pressure vessel <NUM> is light in weight and has a small number of parts while having sufficient strength to withstand such severe applications. In addition, the pressure vessel <NUM> is also excellent in safety and reliability required for the hydrogen station installed in an urban area or the like.

A test was conducted to compare the effects of the pressure vessel <NUM> of the present embodiment and a pressure vessel <NUM> as a comparative example without using the reinforcing ring <NUM>. A sectional view of the pressure vessel <NUM> without using the reinforcing ring <NUM> is shown in <FIG>. The pressure vessel <NUM> has the same configuration as that of the pressure vessel <NUM> of the above-described embodiment (for example, see <FIG>), except that the reinforcing ring <NUM> is not included. Therefore, the description of each member included in the pressure vessel <NUM> will be omitted.

The cylindrical cylinder portion <NUM> of the pressure vessel <NUM> of the comparative example is formed of a thin-walled pipe (an inner diameter ϕ is <NUM>, an outer diameter ϕ is <NUM>). The cylindrical cylinder portion <NUM> has a shape corresponding to "fatigue crack propagation analysis according to Standard for Ultra High-Pressure Gas Equipment KHKS <NUM> (<NUM>) defined by the High Pressure Gas Safety Institute of Japan" (see NPL <NUM>). In a case of using this thin-walled pipe, when the pressure vessel <NUM> is used within a stress range shown in Table <NUM> below, a safety coefficient is <NUM>. Incidentally, in this case, the safety coefficient is a value calculated by "tensile strength of a steel material forming the thin-walled pipe and/or the maximum stress generated in the thin-walled pipe".

In a case where an internal pressure of the pressure vessel <NUM> of the comparative example was repeatedly varied between <NUM> MPa and <NUM> MPa, values of stresses (specifically, a primary principal stress) generated in the screw threads of the screw-threaded portion <NUM> were estimated by a computer simulation. The results of the estimation are shown in Table <NUM> below. Incidentally, the "stress range" in Table <NUM> is a difference between the maximum value and the minimum value of the stress generated in each screw thread. As shown in Table <NUM>, in the pressure vessel <NUM> of the comparative example, the maximum stress generated in the first screw thread 12A of the cylindrical cylinder portion <NUM> is <NUM> MPa. The value of the maximum stress greatly exceeds a yield stress (generally <NUM> MPa) of high-strength steels. In addition, the stress range of the first screw thread 12Ais <NUM> MPa and exceeds <NUM> MPa, which is a criterion for ensuring a fatigue life.

The fatigue crack propagation analysis according to the above-described standard was performed assuming an annular crack having a depth of <NUM> at the screw-threaded portion <NUM> of the cylindrical cylinder portion <NUM> as an initial assumed crack. The presence or absence of the crack was verified by penetrant inspection or magnetic particle inspection. As a result, in the case where the pressure was repeatedly varied between <NUM> MPa and <NUM> MPa, as shown in Table <NUM> below and a graph of <FIG>, a fatigue crack propagation life Na1 of the pressure vessel <NUM> of the comparative example was <NUM>,<NUM> times. The fatigue crack propagation life is synonymous with the allowable number of cycles, and is <NUM>/<NUM> of the number of cycles N at which the fatigue crack penetrates through the cylindrical cylinder portion <NUM>. The fatigue crack propagation life Na1 of the pressure vessel <NUM> of the comparative example is significantly less than <NUM>,<NUM> times required as the hydrogen storage vessel for the hydrogen station. Therefore, in the pressure vessel <NUM> of the comparative example, the fatigue crack propagation life is insufficient as this type of hydrogen storage vessel.

In contrast, the pressure vessel <NUM> of the present embodiment has a structure in which the reinforcing ring <NUM> is attached to the cylindrical cylinder portion <NUM> as shown in <FIG> and <FIG>. In this example, the reinforcing ring <NUM> made of chrome molybdenum steel material SCM35 was used. A length of the reinforcing ring <NUM> in the axial direction of the cylindrical cylinder portion <NUM> is <NUM>. The thickness of the reinforcing ring <NUM> in the radial direction of the cylindrical cylinder portion <NUM> is <NUM>. As shown in <FIG>, in the case where the distance from the seal portion <NUM> to the screw-threaded portion <NUM> is L, the end portion 4A of the reinforcing ring <NUM> on the accumulator chamber <NUM> side extends to a position corresponding to a portion separated by <NUM> from the seal portion <NUM> to the accumulator chamber <NUM> side. The end portion 4B of the reinforcing ring <NUM> on the opposite side to the accumulator chamber <NUM> extends to a position corresponding to the end portion of the screw-threaded portion <NUM> (that is, an end portion 1E of the cylindrical cylinder portion <NUM>). Incidentally, a friction coefficient between the cylindrical cylinder portion <NUM> and the reinforcing ring <NUM> is <NUM>.

The fatigue crack propagation analysis similar to that of the pressure vessel <NUM> of the comparative example was performed on the pressure vessel <NUM> prepared as described above. As a result, as shown in the graph of <FIG>, a fatigue crack propagation life Na2 was improved up to <NUM>,<NUM> times. As described above, it became clear that the effect of improving the fatigue crack propagation life can be obtained by using the reinforcing ring <NUM>.

Next, a relationship between the stress range in the screw-threaded portion <NUM> and the length and arrangement of the reinforcing ring <NUM> was studied.

<FIG> is a view showing distribution of the stress (specifically, the primary principal stress) generated in the pressure vessel <NUM> estimated by the computer simulation in a case of varying the internal pressure of the pressure vessel <NUM> configured to have various dimensions shown in <FIG> between <NUM> MPa and <NUM> MPa. In this example, a stress generated at a point P shown in <FIG> (in the vicinity of the root of the zeroth thread of the cylindrical cylinder portion <NUM>) was maximized. As shown in <FIG>, when a distance from a position of the seal portion <NUM> to the screw-threaded portion <NUM> is a reference distance L, a length from the pressure receiving surface 2A to the end portion 4B of the screw-threaded portion <NUM> on the opposite side to the accumulator chamber <NUM> is <NUM>, a length from the seal portion <NUM> to the end portion 4B of the screw-threaded portion <NUM> is <NUM>, the length of the screw-threaded portion <NUM> is <NUM>, the outer diameter of the reinforcing ring <NUM> is <NUM>, and the length of the reinforcing ring <NUM> is <NUM>.

<FIG> show values of the stress at the point P in <FIG> in the case of varying the length of the reinforcing ring <NUM> (specifically, the position of the end portion 4A) in a state of aligning the end portion 1E of the cylindrical cylinder portion <NUM> with the end portion 4B of the reinforcing ring <NUM>. As shown in a table of <FIG>, it became clear that the stress range was reduced when the length of the reinforcing ring <NUM> on the accumulator chamber <NUM> side was increased. Specifically, the value of the stress range is reduced to <NUM> MPa, and is much smaller than the value (<NUM> MPa) in the case where the reinforcing ring <NUM> shown in Table <NUM> is not provided. Therefore, it became clear that the fatigue crack propagation life could be further improved by setting the length of the reinforcing ring <NUM> as shown in <FIG>. However, even if the position of the end portion 4A of the reinforcing ring <NUM> on the accumulator chamber <NUM> side is changed from a position corresponding to -<NUM> to a position corresponding to -<NUM>, the value of the stress range does not substantially change. Therefore, the optimum length of the reinforcing ring <NUM> is so considered that a distance from the position corresponding to the seal portion <NUM> to the position of the end portion 4A of the reinforcing ring <NUM> is about -<NUM>.

<FIG> show values of the stress at the point P in <FIG> in the case of varying a position of the end portion 4B of the reinforcing ring <NUM> in a state of setting the position of the end portion 4A of the reinforcing ring <NUM> to -<NUM>. It became clear that the stress range was reduced as the position of the end portion 4B of the reinforcing ring <NUM> approached the end portion 1E of the cylindrical cylinder portion <NUM>, and after the position of the end portion 4B exceeded the end portion 1E, the stress range was further reduced until the position of the end portion 4B reached <NUM>. Therefore, it became clear that a reinforcing effect of the screw-threaded portion <NUM> was improved by slightly protruding the end portion 4B of the reinforcing ring <NUM> from the end portion 1E of the cylindrical cylinder portion <NUM> in an opposite direction from the accumulator chamber <NUM>. However, even if the position of the end portion 4B of the reinforcing ring <NUM> is changed from a position corresponding to <NUM> to a position corresponding to <NUM>, the value of the stress range does not substantially change. Therefore, it is considered that the optimum length of the reinforcing ring <NUM> from the position corresponding to the seal portion <NUM> to the position of the end portion 4B of the reinforcing ring <NUM> is about <NUM>.

In a case where the positions of the end portions 4A, 4B of the reinforcing ring <NUM> were set to the optimum values (that is, the end portion 4A: -<NUM>, the end portion 4B: <NUM>), when the fatigue crack propagation analysis similar to that of the pressure vessel <NUM> of the comparative example was performed, the fatigue crack propagation life of the pressure vessel <NUM> was <NUM>,<NUM> times (not shown in the graph of <FIG>). Therefore, the fatigue crack propagation life was significantly improved as compared with <NUM>,<NUM> times in the pressure vessel <NUM> of the comparative example shown in Table <NUM>. Further, the fatigue crack propagation life is sufficiently higher than <NUM>,<NUM> times, which is the number of times of use assumed as a hydrogen storage vessel for the hydrogen station.

As described above, it became clear that the fatigue crack propagation life of the cylindrical cylinder portion <NUM> can be remarkably improved by appropriately determining the positions of both end portions 4A, 4B of the reinforcing ring <NUM>.

The present invention is not limited to the above-described embodiment, and various modifications can be adopted within the scope of the present invention, which is defined by the appended claims. For example, the present invention is not limited to the embodiments described above, and be appropriately modified, improved or the like. Additionally, materials, shapes, sizes, numbers, arrangement positions, or the like of constituent elements in the above-described embodiment are optional and are not limited as long as the present invention can be achieved.

Claim 1:
A pressure vessel (<NUM>) comprising:
a cylinder portion (<NUM>) defining an accumulator chamber (<NUM>) therein;
a screwable portion (<NUM>) arranged inside of both end portions of the cylinder portion (<NUM>), an outer peripheral portion of the screwable portion (<NUM>) being screw-threaded into an inner peripheral portion of the cylinder portion (<NUM>);
a lid portion (<NUM>) arranged at a position closer to the accumulator chamber (<NUM>) than the screwable portion (<NUM>) and comprising a pressure receiving surface (2A) facing the accumulator chamber (<NUM>);
characterized by
a reinforcing ring (<NUM>) fitted to an outer peripheral surface (1F) of the cylinder portion (<NUM>) at each of the both end portions of the cylinder portion (<NUM>),
wherein the reinforcing ring (<NUM>) covers a portion of the outer peripheral surface (1F) corresponding to the whole of a screw-threaded portion (<NUM>) of the cylinder portion (<NUM>) and the screwable portion (<NUM>) along an axial direction of the cylinder portion (<NUM>) and
wherein the reinforcing ring (<NUM>) is fitted to the cylinder portion (<NUM>) in a state of exerting a compressive stress so as to tighten the cylinder portion (<NUM>).