fusible plug

Abstract

A fusible plug suitable as a safety device for a high-pressure gas container is provided. It is characterized in that the fusible plug for a high-pressure gas container has a communication hole filled with a low-melting-point alloy, and a porous metal sintered body is pressed into at least a part of the length direction of the communication hole, and the low-melting-point alloy is impregnated into all or a part of the porous metal sintered body to be in a solidified and composite state. The low-melting-point alloy is preferably an alloy with a melting point of 110 °C. In addition, as the porous metal sintered body to be pressed in, a porous metal sintered body having pores with a porosity of 30% or more and 50% or less in terms of area ratio, and having pores with a diameter exceeding 5 μm in 80% or more of all the pores in terms of area ratio is preferred. As the porous metal sintered body, a porous austenitic stainless steel sintered body is preferred.

Description

Technical Field

[0001] The present invention relates to a fusible plug, and particularly to a fusible plug that is installed in a high-pressure gas container and can discharge the gas inside the high-pressure gas container in a short time when the high-pressure gas container is exposed to abnormal high temperature, preventing the container from being damaged. Background Art

[0002] Heretofore, a fusible plug has been used as a safety device for high-pressure containers or equipment. The fusible plug functions as a safety valve as follows: when a container or equipment is exposed to high temperature due to a fire or an accident, etc., before the container or equipment is damaged due to an increase in internal pressure, the plug is opened and the contents are discharged to the outside. As an example of such a fusible plug, for example, there is the "fusible plug" proposed in Patent Document 1. The fusible plug described in Patent Document 1 has a threaded portion for connecting to a high-pressure device formed at one end, has a communication hole inside, and a low-melting-point metal (alloy) is filled in the communication hole, and has a structure in which a porous member is connected at the other end, and the low-melting-point alloy can also penetrate into the porous member. In the fusible plug described in Patent Document 1, if the high-pressure container or equipment reaches an abnormal high temperature, the low-melting-point alloy filled in the communication hole melts, the communication hole is liberated, and the contents inside the high-pressure container or equipment are discharged to the outside through the porous member, preventing the high-pressure container, etc. from being damaged.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-331016. Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In order to avoid situations such as explosion and breakage caused by an increase in the internal pressure of a high-pressure container as described above, in a high-pressure gas container, a safety device of a fusible plug for quickly discharging the contents (gas) is also required. However, the low-melting-point alloy used in the fusible plug is expensive, and in order to reduce its usage amount, there is a strong tendency to miniaturize the fusible plug, and in addition, it is combined with the tendency of simplifying the safety device, and a structure directly loaded with pressure by the fusible plug is required. Due to such a situation, there is a problem that an effective fusible plug has not been developed for a fusible plug installed in a high-pressure gas container and properly operating as a safety device.

[0008] In view of the problems of the above-mentioned prior art, the present invention aims to provide a fusible plug with excellent pressure resistance, which is suitable as a safety device for high-pressure gas containers. Herein, the "high pressure" refers to a pressure of 70 MPa or more. In addition, "excellent pressure resistance" means a pressure resistance of 87.5 MPa or more.

[0009] Solution to the problem

[0010] In order to achieve the above object, the inventors of the present invention have devotedly studied the structure of a fusible plug that can operate properly even under high pressure. Generally, the low-melting-point alloy used in the fusible plug has low strength. Therefore, there is a problem that when exposed to high pressure, the low-melting-point alloy filled in the fusible plug is displaced, and the content (gas) inside the high-pressure gas container sometimes flows out to the outside. Then, as a method for strengthening the low-melting-point alloy filled in the communication hole of the fusible plug, it is thought to use a porous material having many pores into which the molten low-melting-point alloy can be impregnated.

[0011] The inventors of the present invention thought that first, the porous material is pressed into the communication hole of the fusible plug, and then the low-melting-point alloy is impregnated into all or part of the porous material and compounded. Thus, there is an opinion that it is possible to stably increase the strength of the low-melting-point alloy filled in the communication hole of the fusible plug. Even when the fusible plug is installed in a high-pressure gas container, the content (gas) will not flow out to the outside during normal times. In the case of encountering abnormal high temperature or the like, the low-melting-point alloy melts, easily opens the plug, and enables the content (gas) inside the container to flow out of the container.

[0012] The present invention is further studied and completed based on the related opinion. That is, the gist of the present invention is as follows.

[0013] [1] A fusible plug for a high-pressure gas container, which is a fusible plug installed in a high-pressure gas container, characterized in that it has a communication hole, has a porous material assembled in at least a part of the length direction of the communication hole, and the low-melting-point alloy is impregnated into all or part of the porous material and compounded.

[0014] [2] The fusible plug for a high-pressure gas container according to [1], characterized in that the low-melting-point alloy is an alloy with a melting point of 110 ± 5.5 °C.

[0015] [3] The fusible plug for a high-pressure gas container described in [1] or [2], characterized in that the porous material has pores with a porosity of 30% or more and 50% or less in terms of area ratio, and has pores with a diameter exceeding 5 μm in 80% or more of all the pores in terms of area ratio, and is a porous metal sintered body having a flexural strength of 50 MPa or more according to the flexural strength test specified in the Japan Powder Metallurgy Industry Association Standard JPMAM09-1992.

[0016] [4] The fusible plug for a high-pressure gas container described in [3], characterized in that the porous metal sintered body is a porous austenitic stainless steel sintered body.

[0017] [5] The fusible plug for a high-pressure gas container described in any one of [1] to [4], characterized in that the compressive yield strength of the region where the low-melting-point alloy is impregnated in the porous material and compounded is 1.5 times or more the compressive yield strength of the low-melting-point alloy.

[0018] [6] The fusible plug for a high-pressure gas container described in any one of [1] to [5], characterized in that it has a pressure resistance of 87.5 MPa or more at an ambient temperature of 85°C.

[0019] Effects of the Invention

[0020] According to the present invention, even in an environment of high-pressure gas, generally, the gas in the container does not flow out to the outside. On the other hand, when exposed to abnormal high temperatures, the communication holes are easily opened, and the contained substance (high-pressure gas) can be released, which is effective as a safety device for high-pressure gas containers, and a low-cost fusible plug can be provided, which has a remarkable effect in the industry. In addition, by using a fusible plug using a porous austenitic stainless steel sintered body as the porous material, there is also an effect that a fuse plug with improved corrosion resistance and capable of withstanding long-term use can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is an explanatory diagram showing an example of the cross-sectional structure of the fusible plug of the present invention.

[0022] Figure 2 It is an explanatory diagram showing an overview of the method for measuring the compressive yield strength. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention is suitable as a fusible plug for a high-pressure gas container.

[0024] The fusible plug of the present invention is installed in a high-pressure gas container and functions to quickly release the gas inside the high-pressure gas container to the outside when the high-pressure gas container is exposed to an abnormal high temperature or the like, and usually functions in a manner that does not release the gas inside the high-pressure gas container to the outside.

[0025] The fusible plug has a communication hole penetrating therethrough in a manner that connects the high-pressure gas container to the outside. A low-melting-point alloy is filled into the communication hole and is usually solidified in a state of being impregnated in a porous material, and the communication hole is closed by the composite low-melting-point alloy. On the other hand, in the case of an abnormal high temperature, the low-melting-point alloy melts and melts out from the porous body to the outside, so that the communication hole is opened, and the content (gas) inside the container can be quickly released to the outside. In addition, the fusible plug of the present invention is made of the same materials as ordinary fusible plugs, such as brass and stainless steel, and is manufactured by ordinary methods such as cutting to form a desired shape and size.

[0026] In the fusible plug 1 of the present invention, after the porous material 3 is pressed in a manner that occupies a part of the length direction of the above-mentioned communication hole 2, the low-melting-point alloy 4 is impregnated into all or a part of the porous material 3 to become a solidified and composite state. Figure 1 This state is schematically shown in. The fusible plug 1 is connected to the high-pressure gas container 10 by means of a threaded portion or the like, and the low-melting-point alloy bears a predetermined high pressure. In addition, the communication hole may also have a stepped cross-section so that the filled low-melting-point alloy or the like does not ooze out to the outside due to the pressure from the high-pressure side.

[0027] That is, in the fusible plug 1 of the present invention, the low-melting-point alloy 4 is impregnated into all or a part of the porous material 3 pressed into the communication hole 2 to become a composite state. Thus, even when installed in a high-pressure gas container, the high pressure of the gas from inside the container is borne by the low-melting-point alloy in the communication hole, and the low-melting-point alloy does not shift, and the gas inside the container usually does not leak to the outside. The low-melting-point alloy impregnated into all or a part of the porous material 3 and made composite is strengthened by the porous material, and becomes a state of maintaining high strength as a whole compared with the strength of only the low-melting-point alloy. In addition, as schematically shown in Figure 1 (a) and (b), the low-melting-point alloy 4 is sometimes also filled into the communication hole 2 other than the porous material 3. However, as shown in Figure 1 (c)-(h), in the present invention, from an economic point of view, it is also preferable to minimize the low-melting-point alloy 4 filled into the communication hole 2 other than the porous material 3. In addition, if the low-melting-point alloy can maintain the desired strength and sealing performance, the impregnation / composite of the low-melting-point alloy can also be used as a part of the porous material.

[0028] The low melting point alloy filled into the communication hole of the fusible plug only needs to be an alloy suitable for the desired melting point, and there is no need for special limitation. The low melting point alloy is an alloy composed of two or more metals selected from Bi, Sn, In, Ag, Zn, etc. From the viewpoint of easily obtaining a low melting point, alloys such as bismuth Bi / indium In type, bismuth Bi / indium In / tin Sn type, bismuth Bi / indium In / silver Ag type are preferred. In the present invention, since it is installed in a high-pressure gas container, from the viewpoint of the stability of functional characteristics in terms of safety, as the low melting point alloy used, an alloy with a melting point of 110 ± 5.5 °C is preferred. As such a low melting point alloy, a 67 mass% Bi - 33 mass% In alloy is exemplified.

[0029] In the present invention, as the porous material pressed into the communication hole of the fusible plug, from the viewpoint of easily ensuring the desired strength, a porous metal sintered body is preferred. As the porous metal sintered body, the following porous metal sintered bodies can be exemplified: having pores with a porosity of 30% or more, preferably 50% or less in terms of area ratio, and pores with a diameter exceeding 5 μm in the pores having an area ratio of 80% or more relative to all pores.

[0030] When the porosity of the pores in the porous metal sintered body is less than 30% in terms of area ratio, when impregnating the low melting point alloy, the molten metal of the low melting point alloy does not impregnate into the pores of the porous sintered body, and the low melting point alloy cannot be strengthened. In addition, when exposed to an abnormal high temperature, even if the low melting point alloy melts and is released to the outside and the communication hole "opens", the gas in the container cannot be quickly released to the outside. On the other hand, if the porosity exceeds 50% in terms of area ratio, there may be too many pores and the strength may decrease, and it may deform under high pressure, and the strengthening of the desired strength of the low melting point alloy becomes insufficient. Therefore, the porosity of the porous metal sintered body is preferably 30% or more and 50% or less. In addition, when the pores with a diameter exceeding 5 μm in the pores have an area ratio of less than 80% relative to all pores, the amount of micro pores increases, and the molten metal of the low melting point alloy is difficult to impregnate into the pores of the sintered body, and it becomes difficult to ensure the desired strength. Due to such a situation, the porous metal sintered body is preferably a porous metal sintered body as described above, having a porosity of 30% or more, preferably 50% or less in terms of area ratio, and pores with a diameter exceeding 5 μm in the pores having an area ratio of 80% or more relative to all pore areas.

[0031] As such a porous metal sintered body, a porous austenitic stainless steel sintered body is preferably used. The fusible plug of the present invention is used in a high-pressure gas environment indoors and outdoors. Therefore, the porous metal sintered body is preferably a porous austenitic stainless steel sintered body having excellent corrosion resistance. The porous austenitic stainless steel sintered body also has excellent resistance to hydrogen embrittlement and is thus also suitable for use in a high-pressure hydrogen gas environment. In addition, examples of austenitic stainless steels include SUS 201, SUS202, SUS 301, SUS 302, SUS 303, SUS 303Se, SUS 304, SUS 304L, SUS 304N1, SUS 304N2, SUS 304LN, SUS 305, SUS 309S, SUS 310S, SUS 316, SUS 316L, SUS 316N, SUS 316LN, SUS316J1, SUS 316J1L, SUS 317, SUS 317L, SUS 317J1, SUS 321, SUS 347, SUH 660, etc.

[0032] In addition, the porous metal sintered body is subjected to a flexural strength test according to the provisions of the Japan Powder Metallurgy Industry Association Standard JPMA M09-1992 (corresponding to the ISO standard ISO3325) to obtain the flexural strength. The porous metal sintered body is preferably a porous metal sintered body having a flexural strength of 50 MPa or more. When the flexural strength of the porous metal sintered body is less than 50 MPa, sufficient strength as a fusible plug for a high-pressure gas container cannot be ensured even when the low-melting-point alloy is compounded in a state of being impregnated in the porous material. Therefore, the flexural strength of the porous metal sintered body is preferably 50 MPa or more. In addition, it is more preferably 100 MPa or more.

[0033] In addition, in the fusible plug of the present invention, preferably, in the communication hole, the compressive yield strength of the region where the low-melting-point alloy is compounded in a state of being impregnated in the above-mentioned porous metal sintered body is 1.5 times or more the compressive yield strength of only the low-melting-point alloy. In the fusible plug of the present invention, when at least a part of the porous metal sintered body is assembled in the length direction of the communication hole, but the compressive yield strength of the region where the low-melting-point alloy is compounded in a state of being impregnated in the porous metal sintered body is less than 1.5 times the compressive yield strength of only the low-melting-point alloy, the desired strengthening of the strength of the low-melting-point alloy cannot be achieved, and a fusible plug having the desired pressure resistance for a high-pressure gas container cannot be obtained. In addition, it is more preferably 2.0 times or more.

[0034] In addition, "having a desired pressure resistance" as described herein means a state in which, when the fusible plug is connected to a high-pressure gas container, it resists a given high pressure applied to the fusible plug and no leakage of the inclusion is observed. If the fusible plug of the present invention has the above-described configuration, it has a pressure resistance of 87.5 MPa or more.

[0035] Next, a preferred manufacturing method of the above-described porous metal sintered body will be described.

[0036] After mixing alloy powder, graphite powder, and lubricant powder as raw materials to obtain a mixed powder, the mixed powder is charged into a metal mold and press-molded to obtain a green compact, and the green compact is sintered to obtain a porous metal sintered body.

[0037] As the raw material powder, the alloy powder used is preferably an alloy powder having a particle size distribution adjusted to pass through a 30-mesh sieve (hereinafter, also referred to as less than 30 mesh or -30 mesh) and not pass through a 350-mesh sieve (hereinafter, also referred to as more than 350 mesh or +350 mesh). If there are particles of -350 mesh, the amount of minute pores with a diameter of less than 5 μm increases, and it becomes difficult for the molten metal of the low-melting alloy to infiltrate into the pores of the sintered body, making it difficult to ensure the desired strength.

[0038] In addition, for the alloy powder used, from the viewpoints of oxidation resistance and corrosion resistance during press-fitting into the fusible plug, austenitic stainless steel powder having the above-described particle size distribution is preferred. In addition, as preferred austenitic stainless steels, examples include SUS 201, SUS 202, SUS 301, SUS 302, SUS 303, SUS 303Se, SUS 304, SUS 304L, SUS304N1, SUS 304N2, SUS 304LN, SUS 305, SUS 309S, SUS 310S, SUS 316, SUS 316L, SUS316N, SUS 316LN, SUS 316J1, SUS 316J1L, SUS 317, SUS 317L, SUS 317J1, SUS 321, SUS347, SUH 660, etc. In addition, as the lubricant used, examples include zinc stearate.

[0039] In addition, the forming method of the green compact is not particularly limited, but it is preferable to use a forming punch or the like. The green compact formed into a given shape is sintered to become a porous sintered body having a given shape. In addition, it is preferable to adjust the sintering conditions so as to achieve the above-described porosity and so that the flexural strength obtained by a flexural strength test in accordance with the provisions of JPMA M09-1992 is 50 MPa or more.

[0040] Press the thus obtained porous material (porous metal sintered body) into the communication hole of the fusible plug. In addition, regarding the pressing of the porous material, it is preferably pressed in such a manner as to occupy the entire cross-section in a part of the length direction of the above-mentioned communication hole. The pressing length of the porous material may be determined according to the exposed environment and does not need to be particularly limited. As long as it can strengthen the length of the low-melting-point alloy to such an extent that the low-melting-point alloy does not shift according to the exposed high pressure. For example, in an environment of high pressure: 87.5 MPa, if it is a porous material (porous metal sintered body) with a flexural strength of 50 MPa or more, it is preferably pressed about 3 mm to 15 mm in the length direction of the communication hole.

[0041] Next, after pressing a part of the porous material (porous metal sintered body) into the length direction of the communication hole of the fusible plug, the low-melting-point alloy is further filled into the communication hole in a molten state, and the low-melting-point alloy is impregnated into all or a part of the porous material (porous metal sintered body) in a solidified and compounded state.

[0042] Thus, the low-melting-point alloy filled into the communication hole is strengthened by the porous material (porous metal sintered body), and as a whole, it becomes a state of maintaining a high strength of 1.5 times or more compared to the compressive yield strength of only the low-melting-point alloy.

[0043] Hereinafter, the present invention will be further described based on examples.

[0044] [Examples]

[0045] Manufacture a brass fusible plug 1 having a communication hole 2 penetrating therethrough inside. The communication hole 2 has a stepped structure as shown. Then, the porous metal sintered body 3 is pressed in from the high-pressure gas container 10 side (diameter: 9 mmφ side) of the communication hole 2. The length of the pressed porous metal sintered body is 9 mm. Figure 1 As shown, the high-pressure gas container 10 is connected to one of the obtained fusible plugs 1 via a threaded portion, and at an ambient temperature of 85°C, a high pressure (87.5 MPa) is applied to the low-melting-point alloy in the communication hole to evaluate the pressure resistance as a fusible plug.

[0046] Next, a low-melting-point alloy (67 mass% Bi - 33 mass% In alloy: melting point 110°C) is filled into the communication hole into which the porous metal sintered body has been pressed in a molten state, and the low-melting-point alloy is impregnated into the pressed porous metal sintered body to form a fusible plug in a solidified and compounded state. In addition, the following fusible plug is taken as an existing example: instead of pressing the porous metal sintered body, the communication hole is filled with the low-melting-point alloy so as to fill the entire communication hole.

[0047] As Figure 1 shown, the high-pressure gas container 10 is connected to one of the obtained fusible plugs 1 via a threaded portion, and at an ambient temperature of 85°C, a high pressure (87.5 MPa) is applied to the low-melting-point alloy in the communication hole to evaluate the pressure resistance as a fusible plug.

[0048] In addition, the pressed porous metal sintered body is manufactured by the following method.

[0049] Lubricant powder is blended, mixed, and kneaded into alloy powder (steel powder) of the component categories shown in Table 1 to obtain a mixed powder. In addition, the blended alloy powder (steel powder) is SUS316 steel powder that has been pre-classified and adjusted to the particle size distribution shown in Table 1. Next, the obtained mixed powder is loaded into a metal mold and press-formed by forming stamping to obtain a green compact of a predetermined size (size: approximately 9 mmφ).

[0050] [Table 1]

[0051]

[0052] Next, these green compacts are sintered at a sintering temperature of 1100 to 1350 °C to obtain a porous metal sintered body (porous austenitic stainless steel sintered body). The total porosity of the obtained porous metal sintered body is determined by density measurement. The density measurement is based on the Archimedes method. In addition, regarding the ratio of micro pores to all pores, the cross-section of the sintered body in the stamping direction is photographed with an optical microscope, and the total area of micro pores with a diameter of 5 μm or less and the area of all pores are obtained by image analysis, and the ratio is calculated as (total area of micro pores with a diameter of 5 μm or less) / (area of all pores). In addition, the measurement positions are three places on the circumference.

[0053] In addition, a flexural strength test piece (width: 10 mm, thickness: 6 mm, length: 40 mm) specified in JPMA M09-1992 is taken from a sintered body manufactured by the same manufacturing method as the above-mentioned porous metal sintered body to perform a flexural strength test, and the flexural strength is calculated and shown in Table 2. The rollers used for the test have a diameter of 5 mm, and the center-to-center distance (distance between supports) of the supporting rollers is 20 mm. In addition, the flexural strength is calculated using the following formula.

[0054] Flexural strength = (3 × F × L) / (2 × b × h 2 )

[0055] Here, F: Load at the time of specimen fracture (N)

[0056] L: Distance between supports (mm)

[0057] b: Width of specimen (mm)

[0058] h: Thickness of specimen (mm)

[0059] In addition, compression test pieces (test piece size: φ9 mm × 8 mm) were taken from the region where the low-melting-point alloy was impregnated into the porous metal sintered body, solidified, and compounded, and the region composed only of the low-melting-point alloy without being impregnated into the porous metal sintered body, and compression tests were carried out. The compression yield strengths were calculated respectively. Among them, the region where the low-melting-point alloy was impregnated into the porous metal sintered body, solidified, and compounded was the region formed by pressing the porous metal sintered body as in the same manner as the above-described example of the present invention, further filling the communicating pores with the low-melting-point alloy, and impregnating, solidifying, and compounding the low-melting-point alloy into the porous metal sintered body. The compression test was carried out as Figure 2 shown by placing the compression test piece on the fixed base, loading and compressing the test piece at a displacement speed of 1 mm / sec via the compression working jig, and calculating the compression stress at the yield point as the "compression yield strength". The ratio of the compression yield strengths was calculated from the obtained results: (compression yield strength of the compounded region) / (compression yield strength of the region composed only of the low-melting-point alloy). The obtained results are listed and shown in Table 2.

[0060] [Table 2]

[0061]

[0062] Thus, the sintered body suitable for the scope of the present invention pressed into the communicating pores of the porous metal sintered body is a porous material having a flexural strength of 50 MPa or more, and impregnating and compounding the low-melting-point alloy, so that it has a compression yield strength 1.5 times or more higher than that of the case of only the low-melting-point alloy.

[0063] The evaluation results of the pressure resistance of the fusible plug are shown in Table 3.

[0064] Even if any of the examples of the present invention (fusible plugs) are exposed to an ambient temperature of 85°C, displacement of the low-melting-point alloy does not occur, and they do not break either, so no release of inclusions is observed. If the fusible plug is heated to about 120°C, the low-melting metal melts and the release of inclusions is observed. Thus, it can be said that the fusible plug of the present invention has a pressure resistance of 87.5 MPa or more at an ambient temperature up to 85°C. On the other hand, in the comparative examples outside the scope of the present invention, breakage or gas leakage occurs.

[0065] In addition, in the existing examples where the porous metal sintered body was not pressed into the communicating pores, no displacement of the low-melting-point alloy was observed at an ambient temperature of 85°C, and of course, at room temperature either.

[0066] [Table 3]

[0067]

[0068] Symbol Explanation

[0069] 1 Fusible Plug

[0070] 2 Connecting Hole

[0071] 3 Porous Material (Porous Metal Sintered Body)

[0072] 4 Low Melting Point Alloy

[0073] 10 High Pressure Gas Container

Claims

1. A fusible plug for a high-pressure gas container, which is a fusible plug installed in a high-pressure gas container, is characterized in that, It has communicating pores, a porous material assembled in at least a part of the longitudinal direction of the communicating pores, and is formed by impregnating all or a part of the porous material with a low melting point alloy and making it composite. The porous material has pores with a porosity of 30% or more and 50% or less in terms of area ratio, and pores with a diameter exceeding 5 μm among all pores with an area ratio of 80% or more, and is a porous metal sintered body with a flexural strength of 50 MPa or more according to the flexural strength test specified in the Japan Powder Metallurgy Industry Association Standard JPMA M09-1992.

2. The fusible plug for a high-pressure gas container according to claim 1, characterized in that, The low melting point alloy is an alloy with a melting point of 110 ± 5.5 °C.

3. The fusible plug for a high-pressure gas container according to claim 1, characterized in that, The porous metal sintered body is a porous austenitic stainless steel sintered body.

4. The fusible plug for a high-pressure gas container according to any one of claims 1 to 3, characterized in that, The compressive yield strength of the region where the low melting point alloy is impregnated in the porous material and made composite is 1.5 times or more the compressive yield strength of the low melting point alloy.

5. The fusible plug for a high-pressure gas container according to any one of claims 1 to 3, characterized in that It has a pressure resistance of 87.5 MPa or more at an ambient temperature of 85 °C.

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