Patent Description:
In a high-pressure hydrogen pressure vessel used for a hydrogen station or the like, a structure in which, for example, a lid is screwed into an opening end of a cylinder (cylindrical body) has been employed, as disclosed in Patent Literature <NUM> and Non-Patent Literature <NUM>. In this hydrogen pressure vessel, the cylinder is filled with hydrogen gas and then the cylinder is sealed by a resin seal member (e.g., O-ring) provided between an inner circumferential surface of the cylinder and an outer circumferential surface of the lid. Therefore, it is difficult for the hydrogen to reach a female thread formed in the opening end of the cylinder and thus hydrogen induced cracking which starts from a root of a thread where stress is concentrated is unlikely to occur.

<CIT> is directed to a high-pressure tank configured so as to suppress accumulation of gas in a space between a valve and a mouthpiece while achieving low cost. To this end, the high-pressure tank includes the mouthpiece and the valve installed on the mouthpiece, and is formed with: a communicating hole that communicatively connects spaces which are formed between the mouthpiece and the valve, and in the valve, respectively, and in which gas having permeated from the tank side may potentially accumulate; and a gas venting hole that connects either of the spaces to the outside of the tank.

<CIT> is directed to a fluid container for containing a fluid under pressure, comprising a tubular member closed by a closure member, said closure member having a tubular part extending generally axially within the tubular member to form at least one peripheral space between the closure member and tubular member, the space being sealed from the inside of the container and having at least one vent passage leading from the space to outside the container.

Incidentally, Non-Patent Literature <NUM> discloses that when low-concentration oxygen is contained in hydrogen gas, a crack growth rate of hydrogen induced cracking is reduced. Further, Non-Patent Literature <NUM> discloses that oxygen is adsorbed on the crack surface of hydrogen induced cracking, which prevents hydrogen from entering the material. As shown in these techniques, it has been known that oxygen prevents hydrogen induced cracking.

The present inventors have found that hydrogen permeates through a resin seal member in a hydrogen pressure vessel filled with high-pressure hydrogen gas even though the amount of hydrogen that permeates through the resin seal member is small. Therefore, it is possible that hydrogen may reach a female thread formed in an opening end of a cylinder and thus hydrogen induced cracking may occur in the cylinder starting from a root of the thread where stress is concentrated.

Other problems and novel features will be made apparent from the following description and the accompanying drawings.

A pressure vessel is disclosed in accordance with independent claim <NUM>. In a hydrogen pressure vessel according to one embodiment, a gap part in which an inner peripheral surface of a cylinder is spaced apart from an outer peripheral surface of a lid is provided between a female thread part of the cylinder into which the lid is screwed, and a resin seal member, and the cylinder includes a first through hole for discharging gas in the gap part into a relief pipe and a second through hole for introducing gas containing oxygen into the gap part formed therein.

According to the embodiment, it is possible to provide a hydrogen pressure vessel capable of preventing hydrogen induced cracking of a cylinder.

Hereinafter, with reference to the drawings, specific embodiments will be described in detail. However, the present disclosure is not limited to the following embodiments. Further, for the sake of clarification of the description, the following descriptions and the drawings are simplified as appropriate.

Hereinafter, with reference to <FIG> and <FIG>, a structure of a hydrogen pressure vessel according to a first embodiment will be described. <FIG> is a cross-sectional view of the hydrogen pressure vessel according to the first embodiment. <FIG> is an enlarged view of an area II in <FIG>. As shown in <FIG>, the hydrogen pressure vessel according to the first embodiment includes a cylinder <NUM>, lids <NUM>, and resin seal members <NUM>. The hydrogen pressure vessel according to this embodiment is, for example, a high-pressure hydrogen pressure vessel for a hydrogen station. The design pressure of the hydrogen pressure vessel is, for example, about <NUM>-<NUM> MPa.

Note that the right-handed xyz three-dimensional orthogonal coordinate systems shown in the respective drawings, which are consistent with each other in these figures, are shown just for the sake of convenience for explaining the positional relation among components. Typically, the xy-plane forms a horizontal plane and the positive direction on the z-axis is the vertically upward direction. In the examples shown in the drawings, the longitudinal direction of the hydrogen pressure vessel is parallel to the x-axis direction. In this way, the hydrogen pressure vessel is typically arranged horizontally.

Referring first to <FIG>, the whole structure of the hydrogen pressure vessel will be described.

As shown in <FIG>, the lids <NUM> are screwed into the respective opening ends of the cylinder <NUM> filled with hydrogen so that they can be opened and/or closed. A space surrounded by the inner circumferential surface of the cylinder <NUM> and the inner end surfaces of the two lids <NUM> is filled with high-pressure hydrogen gas. The inside of the cylinder <NUM> is sealed by the circular resin seal members <NUM> provided between the inner circumferential surface of the cylinder <NUM> and the outer circumferential surfaces of the lids <NUM>.

The inner circumferential surface of the cylinder <NUM> and the inner end surfaces of the lids <NUM> that receive stress from the high-pressure hydrogen gas are each called a pressure resistant part.

Further, the lid <NUM> includes a lid body <NUM> and a nut <NUM>, although the details thereof will be described later.

While a structure in which both end parts of the cylinder <NUM> are opened is employed in the example shown in <FIG>, a structure in which only one end part of the cylinder <NUM> is opened may instead be employed. Further, the outer circumferential surface of the cylinder <NUM> may be reinforced, for example, by a carbon fiber reinforced plastic layer (not shown).

The cylinder <NUM> and the lid <NUM> (the lid body <NUM> and the nut <NUM>) are each made of, for example, a steel material such as manganese steel, chrome molybdenum steel, or nickel-chrome-molybdenum steel. The cylinder <NUM>, the lid body <NUM>, and the nut <NUM> may be made of steel of the same type or steel of different types.

The cylinder <NUM> is, for example, a seamless pipe manufactured by forging or extruding. Regarding the dimensions of the cylinder <NUM>, for example, the internal volume is about <NUM>-<NUM>, the total length is about <NUM>-<NUM>, the inner diameter D (see <FIG>) is about <NUM>-<NUM>, and the thickness t (see <FIG>) is about <NUM>-<NUM>. In order to reduce surface scratches, which cause hydrogen induced cracking, the inner circumferential surface of the cylinder <NUM> may be mirror-finished. For example, it is preferable to eliminate surface scratches having a depth of <NUM> or greater and a length of <NUM> or greater.

Referring next to <FIG>, details of the opening ends of the cylinder <NUM> will be described. Since the structures of the opening ends of the cylinder <NUM> are similar to each other, as shown in <FIG>, the structure of only the opening end of the cylinder <NUM> on the side of the x-axis positive direction will be described in detail in <FIG>.

As shown in <FIG>, in the opening end of the cylinder <NUM>, the inner diameter is enlarged and the inner circumferential surface is threaded. That is, a female thread part 10a is formed in the opening end of the cylinder <NUM>. The nut <NUM> of the lid <NUM> is screwed in the opening end of the cylinder <NUM>.

The lid <NUM> that includes the lid body <NUM> and the nut <NUM> has a structure that is in compliance with a "screwing structure" specified in the standard KHKS <NUM> by The High Pressure Gas Safety Institute of Japan (Non-Patent Literature <NUM>).

As shown in <FIG>, the lid body <NUM> is a cylindrical shaped member with a step having a central axis C that is common to the cylinder <NUM>. The lid body <NUM> includes a flange part 21a. In the lid body <NUM>, a part having a large diameter located on the side of the x-axis negative direction with respect to the flange part 21a is referred to as a large diameter part and a part having a small diameter located on the side of the x-axis positive direction with respect to the flange part 21a is referred to as a small diameter part.

The diameter of the flange part 21a is larger than the inner diameter of the main body part (part other than the opening end) of the cylinder <NUM> but smaller than the inner diameter of the opening end of the cylinder <NUM>. Therefore, the lid body <NUM> can be inserted into the cylinder <NUM> from the opening end of the cylinder <NUM>. The flange part 21a contacts a step 10b between the main body part of the cylinder <NUM> and the enlarged opening end.

As shown in <FIG>, the diameter of the large diameter part of the lid body <NUM> is substantially equal to the inner diameter of the main body part of the cylinder <NUM> and the lid body <NUM> is fitted into the main body part of the cylinder <NUM>. On the other hand, the small diameter part of the lid body <NUM> has an axis diameter that is substantially equal to the inner diameter of the nut <NUM> and is fitted into the through hole of the nut <NUM>. The small diameter part of the lid body <NUM> and the nut <NUM> can be rotated relative to each other. Further, in the example shown in <FIG>, the length of the small diameter part of the lid body <NUM> is substantially equal to the height of the nut <NUM> (the length in the x-axis direction).

The nut <NUM> is a male thread nut having a central axis C that is common to the cylinder <NUM>. That is, the outer circumferential surface of the nut <NUM> is threaded. The nut <NUM> is screwed into the opening end of the cylinder <NUM> while inserting the small diameter part of the lid body <NUM> into the through hole of the nut <NUM>, whereby the lid <NUM> is fixed to the cylinder <NUM>. Specifically, when the nut <NUM> is screwed into the opening end of the cylinder <NUM>, the nut <NUM> moves forward in the x-axis negative direction. When the nut <NUM> presses the flange part 21a against the step 10b of the cylinder <NUM>, the nut <NUM> does not move forward any further and the lid body <NUM> and the nut <NUM> are fixed to the cylinder <NUM>. In this way, the flange part 21a serves as a stopper when the nut <NUM> is screwed into the opening end of the cylinder <NUM>.

The resin seal member <NUM>, which is, for example, an O-ring, is a circular resin member having a central axis C that is common to the cylinder <NUM>. As shown in <FIG>, the resin seal member <NUM> is provided between the inner circumferential surface of the cylinder <NUM> and the outer circumferential surface of the lid <NUM>. More specifically, as shown in <FIG>, the resin seal member <NUM> is fitted into the annular groove 21b formed on the outer circumferential surface of the large diameter part of the lid body <NUM>. That is, the inside of the cylinder <NUM> is sealed by the resin seal member <NUM> that is provided between the inner circumferential surface of the main body part of the cylinder <NUM> and the outer circumferential surface of the large diameter part of the lid body <NUM>.

As shown in <FIG>, a gap part G in which the inner circumferential surface of the cylinder <NUM> is spaced apart from the outer circumferential surface of the lid <NUM> is provided between the resin seal member <NUM> and the female thread part 10a of the cylinder <NUM>. Specifically, a circular gap part G having a band shape is provided in the outer circumference of the flange part 21a of the lid body <NUM>.

In the hydrogen pressure vessel according to this embodiment, besides a through hole (a first through hole) <NUM> that discharges gas inside the gap part G to a relief pipe <NUM>, a through hole (a second through hole) <NUM> that introduces gas including oxygen into the gap part G is formed in the cylinder <NUM>. The gas including oxygen is, for example, but not particularly limited thereto, air. The relief pipe <NUM> is a pipe for safely releasing the hydrogen gas leaked from the inside of the cylinder <NUM> to the gap part G into the atmosphere. In case of an emergency such as a case in which, for example, a defect occurs in the resin seal member <NUM>, the hydrogen gas is released via the relief pipe <NUM>.

As described above, the present inventors have found that hydrogen permeates through the resin seal member <NUM> in the hydrogen pressure vessel filled with high-pressure hydrogen gas even though the amount of hydrogen that permeates through the resin seal member is small. In this case, it is possible that the hydrogen may reach the female thread part 10a of the cylinder <NUM> via the gap part G and thus hydrogen induced cracking may occur in the cylinder starting from a root of the thread where stress is concentrated.

In order to solve the above problem, with the hydrogen pressure vessel according to this embodiment, besides the through hole <NUM> connected to the relief pipe <NUM>, the through hole <NUM> is formed in the cylinder <NUM>. Since the through hole <NUM> is connected to the relief pipe <NUM>, gas including oxygen, i.e., air can be taken into the gap part G from the through hole <NUM> by, for example, natural convection. Since the gap part G communicates with the female thread part 10a of the cylinder <NUM>, oxygen that effectively prevents hydrogen induced cracking reaches a root of the thread of the female thread part 10a. As a result, it is possible to prevent hydrogen induced cracking of the cylinder <NUM> which starts from the root of the thread.

The positions where the through holes <NUM> and <NUM> are formed are not particularly limited as long as they are between the resin seal member <NUM> and the female thread part 10a of the cylinder <NUM>. The closer the positions of the through holes <NUM> and <NUM> are to the pressure resistant part, that is, the closer they are to the resin seal member <NUM>, the larger the effect of stress received from the high-pressure hydrogen gas the cylinder <NUM> is filled with. In particular, stress that occurs in the corner parts of the through holes <NUM> and <NUM> on the inner circumferential surface of the cylinder <NUM> becomes higher. Therefore, the positions where the through holes <NUM> and <NUM> are formed are preferably spaced apart from the resin seal member <NUM> in the x-axis positive direction in <FIG>.

Specifically, it is considered that the stress received from the high-pressure hydrogen gas affects a range of about <NUM>×(r×t)<NUM>/<NUM>[mm] in the x-axis positive direction from the pressure resistant part using the average radius r [mm] and the thickness t [mm] of the cylinder <NUM> shown in <FIG>. The average radius r of the cylinder <NUM> is an average value of the inner radius and the outer radius of the cylinder <NUM>. Therefore, the average radius r [mm] may be expressed as r=(D+t)/<NUM> using the inner diameter D [mm] and the thickness t [mm].

On the other hand, when the through holes <NUM> and <NUM> are too close to the female thread part 10a, the stress that occurs in the female thread part 10a increases.

Therefore, as shown in <FIG>, for example, the through holes <NUM> and <NUM> are formed in the central part in the longitudinal direction (x-axis direction) of the cylinder <NUM> that is opposed to the gap part G.

The through hole <NUM> connected to the relief pipe <NUM> is arranged, for example, but not particularly limited thereto, vertically downward. With this structure, moisture accumulated in the gap part G due to condensation or the like can be discharged along with gas. On the other hand, the through hole <NUM> for introducing oxygen is, for example, but not particularly limited thereto, opposed to the through hole <NUM> via the lid <NUM>. With this structure, oxygen introduced from the through hole <NUM> flows toward the through hole <NUM>, which causes oxygen to be easily distributed throughout the gap part G.

As the diameters of the through holes <NUM> and <NUM> become larger, the stress applied to a stress concentrated part becomes high and cracks that are due to metal fatigue are likely to occur. On the other hand, when the diameters of the through holes <NUM> and <NUM> are too small, release of hydrogen gas and introduction of oxygen is unlikely to occur and it becomes difficult to round the corner parts of the through holes <NUM> and <NUM> on the inner circumferential surface of the cylinder <NUM>. Therefore, the diameters of the through holes <NUM> and <NUM> are each, for example, about <NUM>-<NUM>% of the average radius r [mm] of the cylinder <NUM>. As one example, the diameters of the through holes <NUM> and <NUM> are each about <NUM>-<NUM>.

Further, the corner parts of the through holes <NUM> and <NUM> on the inner circumferential surface of the cylinder <NUM> may be, for example, rounded since sharp corner parts tend to cause cracks that are due to metal fatigue.

A plurality of through holes <NUM> and a plurality of through holes <NUM> may be provided.

Referring now to <FIG>, a structure of a hydrogen pressure vessel according to a comparative example will be described. <FIG> is a cross-sectional view of the hydrogen pressure vessel according to the comparative example. <FIG> is a diagram that corresponds to <FIG>.

As shown in <FIG>, in the hydrogen pressure vessel according to the comparative example, only a through hole <NUM> that discharges gas inside a gap part G to a relief pipe <NUM> is formed in a cylinder <NUM> and a through hole <NUM> that introduces gas including oxygen into the gap part G shown in <FIG> is not formed.

Therefore, oxygen that effectively prevents hydrogen induced cracking cannot be introduced into the gap part G. As a result, hydrogen induced cracking which starts from a root of the thread where stress is concentrated occurs in the cylinder <NUM>. In particular, cracking is more likely to occur at a root of the thread that is closer to the gap part G.

Note that hydrogen induced cracking in the above hydrogen pressure vessel is a fatigue failure due to repeated filling and release of the high-pressure hydrogen gas.

As described above, in the hydrogen pressure vessel according to this embodiment, the through hole <NUM> that introduces gas including oxygen into the gap part G is formed in the cylinder <NUM>. Therefore, oxygen that effectively prevents hydrogen induced cracking can be introduced into the gap part G from the through hole <NUM>. Since the oxygen introduced into the gap part G reaches the root of the thread of the female thread part 10a, hydrogen induced cracking of the cylinder <NUM> which starts from the root of the thread can be reduced.

Referring next to <FIG>, a structure of a hydrogen pressure vessel according to a second embodiment will be described. <FIG> is a cross-sectional view of the hydrogen pressure vessel according to the second embodiment. <FIG> is a diagram that corresponds to <FIG> according to the first embodiment.

As shown in <FIG>, in the hydrogen pressure vessel according to the second embodiment, a through hole <NUM> that introduces gas including oxygen into a gap part G is connected to a check valve CV via an introduction pipe <NUM>. The other structures are similar to those of the hydrogen pressure vessel according to the first embodiment shown in <FIG>.

Like in the hydrogen pressure vessel according to the first embodiment, in the hydrogen pressure vessel according to the second embodiment as well, oxygen that effectively prevents hydrogen induced cracking can be introduced into the gap part G from the through hole <NUM>. As a result, hydrogen induced cracking of the cylinder <NUM> which starts from a root of a thread can be reduced.

Further, since the through hole <NUM> is connected to the check valve CV in the hydrogen pressure vessel according to the second embodiment, gas inside the gap part G is not discharged from the through hole <NUM>. Therefore, in case of an emergency such as a case in which, for example, a defect occurs in the resin seal member <NUM>, hydrogen gas is safely released into the atmosphere from the relief pipe <NUM> via the through hole <NUM> instead of being released from the through hole <NUM>.

On the other hand, in the hydrogen pressure vessel according to the first embodiment, in the above case, the hydrogen gas may be released via the through hole <NUM>. However, even when hydrogen gas is released via the through hole <NUM> in the hydrogen pressure vessel according to the first embodiment, the amount of the hydrogen gas that is released is so small that there is no particular safety concern.

Referring next to <FIG>, a structure of a hydrogen pressure vessel according to a third embodiment will be described. <FIG> is a cross-sectional view of the hydrogen pressure vessel according to the third embodiment. <FIG> is a diagram that corresponds to <FIG> according to the first embodiment.

As shown in <FIG>, in the hydrogen pressure vessel according to the third embodiment, a through hole <NUM> that introduces gas including oxygen into a gap part G is connected to a pump P via an introduction pipe <NUM>. The other structures are similar to those of the hydrogen pressure vessel according to the first embodiment shown in <FIG>.

Like in the hydrogen pressure vessel according to the second embodiment, a check valve CV may be provided in the introduction pipe <NUM> provided between the through hole <NUM> and the pump P.

Since the hydrogen pressure vessel according to the third embodiment includes the pump P, it is possible to forcibly introduce oxygen that effectively prevents hydrogen induced cracking into the gap part G from the through hole <NUM>. As a result, it is possible to reduce hydrogen induced cracking of the cylinder <NUM> which starts from a root of a thread more efficiently than in the hydrogen pressure vessel according to the first embodiment.

Referring next to <FIG>, a structure of a hydrogen pressure vessel according to a fourth embodiment will be described. <FIG> is a cross-sectional view of the hydrogen pressure vessel according to the fourth embodiment. <FIG> is a diagram that corresponds to <FIG> according to the first embodiment.

As shown in <FIG>, in the hydrogen pressure vessel according to the fourth embodiment, a relief valve RV is provided in a relief pipe <NUM>. The relief valve RV is closed when the pressure of a gap part G is an atmospheric pressure and is opened when the pressure of the gap part G is raised up to a predetermined pressure from the atmospheric pressure. The other structures are similar to those of the hydrogen pressure vessel according to the third embodiment shown in <FIG>.

Like in the hydrogen pressure vessel according to the second embodiment, a check valve CV may be provided in the introduction pipe <NUM> which is provided between the through hole <NUM> and the pump P.

Like in the hydrogen pressure vessel according to the third embodiment, the hydrogen pressure vessel according to the fourth embodiment includes a pump P. It is therefore possible to forcibly introduce oxygen that effectively prevents hydrogen induced cracking into the gap part G from the through hole <NUM>.

The hydrogen pressure vessel according to the fourth embodiment further includes the relief valve RV in the relief pipe <NUM>. Therefore, by raising the pressure inside the gap part G, the oxygen partial pressure in the gap part G can be increased while preventing permeation of hydrogen in the resin seal member <NUM>. As a result, hydrogen induced cracking of the cylinder <NUM> which starts from a root of a thread can be prevented more efficiently than in the hydrogen pressure vessel according to the third embodiment.

While the disclosure made by the present inventors has been specifically described based on the embodiments, it is needless to say that the present disclosure is not limited to these embodiments and may be changed in various ways without departing from the scope of the appended claims.

Claim 1:
A hydrogen pressure vessel comprising:
a cylinder (<NUM>) filled with hydrogen;
a lid (<NUM>) screwed into a female thread part (10a) formed in an opening end of the cylinder (<NUM>); and
a circular resin seal member (<NUM>) provided between an inner circumferential surface of the cylinder (<NUM>) and an outer circumferential surface of the lid (<NUM>), wherein
a gap part (G) in which the inner circumferential surface of the cylinder (<NUM>) is spaced apart from the outer circumferential surface of the lid (<NUM>) is provided between the female thread part (10a) of the cylinder and the resin seal member (<NUM>), a first through hole (<NUM>) for discharging gas in the gap part to a relief pipe (<NUM>) and a second through hole (<NUM>) for introducing gas including oxygen into the gap part (G) are formed in the cylinder (<NUM>),
characterized in that
the hydrogen pressure vessel comprises the relief pipe (<NUM>),
and in that
the first through hole (<NUM>) and the second through hole (<NUM>) are formed at positions between the resin seal member (<NUM>) and the female thread part (10a) of the cylinder (<NUM>).