JPH0419431B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a leak test method.

(Prior Art) Generally, a leak test is performed to check whether a container has cracks or the like.

In this leak test, the inside of the container is pressurized (hereinafter referred to as pressurization method) or depressurized (hereinafter referred to as depressurization method) to bring the inside of the container to the test pressure.
The container is closed from the fluid pressure source, and subsequent pressure fluctuations within the container are detected using a pressure gauge or the like. In the pressurization method, if the pressure decreases, it is determined that gas is leaking from the container, and in the depressurization method, if the pressure increases, it is determined that there is a leak.

Figures 6 and 7 are graphs showing the pressure fluctuations in the container over time in the case of the leak test using the conventional pressurization method and the leak test using the depressurization method, respectively, and these graphs will be explained below. .

In the case of the pressurization method, the test pressure Pt is reached ₁ hour after the start of pressurization. At this time, the temperature of the gas inside the container rises above the outside air temperature due to the pressurization. Therefore, if the container is closed from the fluid pressure source immediately after the above t ₁ hour elapses, that is, immediately after the test pressure Pt is reached, heat is radiated from the container to the outside air and the temperature of the gas inside the container decreases, resulting in a decrease in the temperature of the gas inside the container. The pressure decreases as shown by the solid line A in FIG. 6 even if there is no leakage of gas from the container, and stabilizes after _t4 hours have elapsed. Also, the pressure inside the container is the test pressure.
After Pt is reached, if the container is kept connected to a pressure source for up to t ₂ hours or t ₃ hours and the container is maintained at the above test pressure Pt, and then the container is closed, the pressure inside the container will decrease, although the amount of pressure drop will decrease. It decreases as shown by solid line B or solid line C, respectively, and stabilizes at t ₄ hours. and,
If the pressure inside the container is maintained at the test pressure Pt for up to t ₄ hours and then the container is closed, the pressure fluctuations will disappear because the gas temperature inside the container has already reached equilibrium with the outside temperature.

In the case of the reduced pressure method, a phenomenon opposite to that in the above-mentioned pressurized method occurs. That is, the test pressure Pt' is reached after t1 _' time has elapsed from the start of pressure reduction. At this time, the temperature of the gas inside the container is lower than the outside temperature due to the reduced pressure. Therefore, if the container is closed from the fluid pressure source immediately after the above-mentioned time t ₁ ' has elapsed, i.e., immediately after the test pressure Pt' has been reached, the container will absorb heat from the outside air and the temperature of the gas inside the container will increase. The pressure inside increases as shown by the solid line A' in FIG. 7, and stabilizes after time _t4 ' has elapsed. Furthermore, after the pressure inside the container reaches the test pressure Pt', if the container is maintained at the test pressure Pt' with the container as a pressure source until time _t2 ' or time _t3 ', then the container is closed. , the pressure inside the container rises as shown by solid line B' or solid line C', respectively, and stabilizes at time t ₄ '. If the container is closed after maintaining the pressure inside the container at the test pressure Pt' until time _t4 ', the gas temperature inside the container has already reached an equilibrium state with the outside temperature, so there will be no pressure fluctuation and the pressure will decrease. becomes constant.

As is clear from the above explanation, if a leak test is performed by closing the container before t ₄ hours or t ₄ ′ hours, natural pressure fluctuations due to temperature changes of the gas inside the container and pressure due to leakage from the container will occur. It was difficult to accurately determine the presence or absence of a leak because both fluctuations were detected at the same time.

Therefore, in practice up to t ₄ hours or t ₄ ′ hours,
In other words, the test pressure is maintained by communicating the container with a pressure source until the temperature inside the container reaches an equilibrium state with the outside temperature.
After continuing to maintain Pt, the vessel is closed and pressure fluctuations are detected to ensure accuracy in leak tests.

(Problems to be Solved by the Invention) As mentioned above, since the leak test is performed after waiting until the temperature inside the container naturally equilibrates with the outside temperature, the leak test takes a long time.
It was inefficient.

(Means for Solving the Problems) The present invention was made to solve the above problems, and its gist lies in the following two leak test methods.

(A) In the leak test method, in which a positive test pressure is applied inside the test object and the sealing quality of the test object is judged from the subsequent pressure fluctuation inside the test object, first the positive pressure source and the test object are is connected to apply an initial pressure greater than the test pressure to the inside of the test object, then the test object is cut off from the positive pressure source, and the pressure inside the test object is released to the outside of the test object. By reducing the pressure inside the object to the above test pressure, the temperature inside the object to be tested almost matches the outside temperature, and,
A leak test method characterized in that the airtightness of the test object is judged from the subsequent pressure fluctuation inside the test object.

(B) In a leak test method in which a negative test pressure is applied inside the test object and the sealing quality of the test object is determined from the subsequent pressure fluctuation inside the test object, first the negative pressure source and the test object are to apply an initial pressure smaller than the test pressure to the inside of the test object, then cut off the test object from the negative pressure source, and introduce fluid into the test object to bring the inside of the test object above the above level. The temperature inside the object to be inspected is made to almost match the outside temperature by increasing the pressure to the test pressure, and the quality of the airtightness of the object to be inspected is determined from the subsequent pressure fluctuation inside the object to be inspected. Leak test method.

(Function) In the case of a leak test using the pressurization method, an initial pressure greater than the test pressure is first applied inside the test object, and then the pressure inside the test object is released to the outside of the test object to reduce the pressure to the test pressure. By doing so, when performing a leak test using the depressurization method, an initial pressure smaller than the test pressure is first applied inside the test object, and then fluid is introduced into the test object to increase the pressure to the test pressure. By doing so, the temperature inside the test object reaches an equilibrium state with the outside temperature faster than the natural transition, and the test pressure inside the test object can be brought to a stable test pressure in a short time. .

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings from FIG. 1 to FIG. 3.

FIG. 1 shows a schematic flow diagram when performing a leak test using the pressurization method of the present invention. A regulator 3, a pressure gauge 4, a solenoid valve _SV1 ,
A pressure switch 5 and a solenoid valve SV ₃ are arranged.
These solenoid valves SV ₁ and SV ₃ are connected to the pressurized air source 1 and the container 2.
It is used to cut off or open communication between The piping line 11 is connected to branch piping lines 12 and 1 between the solenoid valve SV ₁ and the pressure switch 5.
3, a solenoid valve SV ₄ for exhaust is arranged in the branch piping line 12, and a solenoid valve SV ₂ for pressure relief and a throttle valve 6 are arranged in the branch piping line 13. Also, the piping line 1 between the solenoid valve SV ₃ and the container 2
1 is connected to a pressure sensor 7 via a branch piping line 14.
is connected. This pressure sensor 7 has a built-in diaphragm (not shown) and electromagnetically detects the deformation of this diaphragm, and a port on one side of the diaphragm is connected to the branch piping line 14.
with the other port open to the atmosphere. The electromagnetic valves SV ₁ , SV ₂ , SV ₃ , SV ₄ and the pressure switch 5 are sequentially controlled.
Note that before pressurization, the pressure inside the container 2 is equal to the outside air pressure.

Next, the leak test procedure will be explained over time according to the time chart shown in FIG. 2 and the pressure transition graph shown in FIG. 3.

One cycle of a leak test consists of a pressurization process, a depressurization process, a first equilibrium process, a second equilibrium process, a detection process,
It consists of an exhaust process, the pressurization process time T ₁ , the combined time required for the depressurization process and the first equilibrium process T ₂ ,
The second equilibrium process time T ₃ , the detection process time T ₄ , and the exhaust process time T ₅ are set by a timer.

In the pressurizing process, the solenoid valves SV ₁ and SV ₃ are in an open state, and the solenoid valves SV ₂ and SV ₄ are in a closed state. As a result, pressurized air is supplied from the pressurized air source 1 to an initial pressure by the regulator 3 in the middle of the piping line 11.
The pressure is reduced to Po and supplied to the container 2. The pressure inside container 2 gradually increases and exceeds the test pressure Pt,
The initial pressure Po is reached after a time Ta has elapsed from the start of pressurization. Then, during the remaining time Tb of the pressurization process,
The pressure inside the container 2 is maintained at the initial pressure Po.

The H contact (High contact) of the pressure switch 5 is set to be higher than the test pressure Pt and slightly lower than the initial pressure Po, and when this H contact is turned ON, the pressure inside the container 2 reaches the test pressure Pt. If the above conditions are confirmed and the H contact does not turn ON, the leak test will not proceed to the next step.

Simultaneously with the end of the pressurizing step, the solenoid valve SV ₁ closes while the solenoid valve SV ₃ remains open, and at the same time, the solenoid valve SV ₂ opens to proceed to the depressurization step. container 2
is closed off from the pressurized air source 1 by the solenoid valve SV ₁ ,
The supply of pressurized air to the container 2 is stopped, and the air stored downstream of the solenoid valve SV ₁ passes through the branch piping line 13 and is released from the solenoid valve SV ₂ and the throttle valve 6 to the outside air. The pressure inside the container 2 gradually decreases.

When the pressure drops to the test pressure Pt, the L contact (Low contact) of the pressure switch 5 is turned on, the solenoid valve SV ₂ is closed, and the process moves to the first equilibrium step.

In the first equilibrium step, only the solenoid valve SV ₃ is in the open state. At the end of the first equilibrium step, the solenoid valve SV ₃ is also closed, and the second equilibrium step begins. In the first equilibrium step and the second equilibrium step, the pressure inside the container 2 is stable and the test pressure Pt is maintained.

The time it takes to obtain the above stable test pressure Pt,
In other words, the total time of the above pressurization process time and depressurization process time is the stable test pressure in the conventional method.
The time required to obtain Pt is much shorter than _t4 . The reason is presumed to be as follows.

The air temperature within the container 2 increases until it reaches the initial pressure Po immediately after the start of pressurization, and decreases during the time Tb during which the initial pressure Po is maintained. But this time Tb
is short, so it does not drop until it reaches equilibrium with the outside temperature. In the next depressurization step, pressurized air is released, and the air temperature inside the container 2 is lowered by this release and brought into equilibrium with the outside air temperature. In this way, the temperature inside the container 2 is forcibly brought into equilibrium with the outside air temperature without waiting for natural heat dissipation, so that a stable test pressure Pt can be achieved in a short time.

After the second equilibration step, a detection step is performed. That is, the pressure inside the container 2 is reduced by the branch piping line 14.
is guided to the pressure sensor 7 and detected as a gauge pressure relative to the outside atmospheric pressure. Note that the electrical signal of the detected pressure from the pressure sensor 7 is amplified and sent to the pressure gauge, and the gauge pressure is displayed on this pressure gauge. If this gauge pressure does not fluctuate, the sealing performance of the container 2 is confirmed, and if the gauge pressure decreases, air is leaking from the container 2, and poor sealing performance is confirmed. After the above detection process is completed, the process moves to the exhaust process. In the exhaust process, the solenoid valve
SV ₃ and SV ₄ are opened, and the air in the container 2 is released through the branch piping line 12.

This completes one cycle of the leak test, and the time required for one cycle can be reduced to about 1/3 compared to the conventional method described above.

In addition, after the pressure reduction process in the above example, the container 2
In order to stabilize the air pressure within the initial pressure
Differential pressure ΔP between Po and test pressure Pt and initial pressure Po
The maintenance time Tb must be set within a predetermined range.

If the above differential pressure ΔP is larger than the upper limit of the predetermined range,
The temperature drop inside the container 2 due to depressurization becomes too large and temporarily drops below the outside temperature, so after the end of depressurization, that is, after the container 2 is closed, the pressure increases until the air temperature inside the container 2 reaches equilibrium with the outside temperature. I did it,
The detection process cannot be performed until the pressure stabilizes. Also, if the differential pressure ΔP is smaller than the lower limit of the predetermined range,
Because the temperature inside the container 2 due to depressurization is not sufficiently lowered to the outside temperature, the pressure decreases until the air temperature inside the container 2 reaches equilibrium with the outside temperature after the end of the depressurization, that is, after the container 2 is closed. , the detection step cannot be performed until the pressure stabilizes.

Similarly, if the above-mentioned maintenance time Tb is longer than the upper limit of the predetermined range, the air temperature inside the container 2 during this maintenance time Tb decreases so much that it approaches the outside temperature, so that the temperature inside the container 2 decreases in the next pressure reduction step. The temperature drops below the outside temperature. For this reason, after the end of pressure reduction, that is, after the container 2 is closed, the pressure increases until the air temperature within the container 2 reaches equilibrium with the outside air temperature, and the detection step cannot be performed until the pressure stabilizes. Also,
If the maintenance time Tb is shorter than the lower limit of the predetermined range, the temperature drop inside the container 2 during this maintenance time Tb is very small, and the temperature inside the container 2 due to the next pressure reduction will not drop to the outside temperature. After the completion of the process, that is, after the container 2 is closed, the pressure decreases until the air temperature within the container 2 reaches equilibrium with the outside temperature, and the detection step cannot be performed until the pressure stabilizes.

The differential pressure ΔP and the maintenance time Tb have a correlation. That is, if the pressure difference ΔP is increased, the maintenance time Tb can be shortened, and if the pressure difference ΔP is small, the maintenance time Tb needs to be lengthened. initial pressure
It is preferable to shorten the test time by increasing Po and increasing the differential pressure ΔP, but these Po, ΔP
is determined depending on the strength of the container 2, etc.

Note that the above ΔP and the maintenance time Tb may be somewhat outside the above ranges, and even in this case, the test time will be longer than the ideal case, but it can be shorter than the conventional method.

In addition, FIG. 4 shows a flow diagram of another embodiment, and parts that are the same as those in the first embodiment are given the same reference numerals and explanations are omitted, and the points that are different from the first embodiment are described below. Explain.

Downstream from the pressure switch 5, the piping line 11 is divided into two piping lines 11a and 11.
A solenoid valve SV ₃ is arranged in each piping line 11a, 11b. Both of these two solenoid valves SV ₃ are opened and closed in the same manner as the solenoid valve SV ₃ of the first embodiment. And one piping line 11a
Container 2 as the inspection target is connected to
Connected to the other piping line 11b is a reference container 2', which is a container of the same dimensions and made of the same material as the container 2, and which has been previously confirmed to be leak-free. or,
The downstream side of the solenoid valve SV ₃ of each piping line 11a, 11b is connected to both input ports of a pressure sensor 7 via a branch piping line 14a, 14b, and this pressure sensor 7 is connected via a differential amplifier 8. It is connected to the differential pressure gauge 9.

The time chart and pressure transition graph in the second embodiment are the same as those in the first embodiment. However, in the detection process, container 2 and piping line 1
The pressure inside 1a, 14a is detected by a pressure sensor 7 as a differential pressure between the pressure in the reference container 2' and the piping lines 11b, 14b, and is displayed by a differential pressure gauge 9.
Since differential pressure detection is used as described above, detection can be performed with high sensitivity. Note that the reference container 2' has the same dimensions as the container 2 and can offset pressure fluctuations caused by external factors, but when this external factor is small, the reference container 2' can be omitted.

FIG. 5 shows a third embodiment of the invention. In this embodiment, the piping line 1 downstream of the pressure switch 5 is
1 is equipped with a three-way solenoid valve SV ₅ for exhaust. An orifice 16 is provided in the piping line 11 between the solenoid valve SV ₅ and the pressure switch 5, and the pressure difference on both sides of the orifice 16 is detected by the sensor 7 via branch piping lines 17a and 17b. The output of the sensor 7 is amplified by a differential amplifier 8 and displayed by a differential pressure gauge 9.

Further, a bypass line 18 is connected to the piping line 11 in parallel with the orifice 16, and this bypass line 18 is provided with a solenoid valve _SV6 .

In the third embodiment, with the container 2 connected to the connection port at one end of the piping line 11, the exhaust solenoid valve SV ₅ is brought into communication between the container 2 and the pressurized air source 1. In this state, pressurization and depressurization steps are performed in the same manner as in the previous embodiment, and the inside of the container 2 is brought to a stable test pressure Pt in a short time. After this, the solenoid valve SV ₆ is switched from open to closed to close the bypass line 18 and start the detection process. If there are no cracks in the container 2 and there is no leakage of pressurized air, no air will flow through the orifice 16 and no pressure difference will occur between its ends, so the differential pressure gauge 9 will display zero. container 2
If there is a leak from the container 2, pressurized air is supplied to the container 2 through the orifice 16 to compensate for the pressure drop caused by the leak, so a pressure difference is created between the two ends equal to the pressure loss at the orifice 16. . This is displayed on the differential pressure gauge 9 to notify the user of a leak. In addition, if the leakage is large, pressurized air is supplemented from a tank 19 connected to the piping line 11.

After the above detection, the solenoid valve SV ₅ is switched to discharge the pressurized air inside the container to the outside.

Although the above-mentioned first, second, and third embodiments have been described using a leak test using a pressurization method, a leak test using a depressurization method can also be performed based on the same concept. In the case of the reduced pressure method, see Figures 1 and 4.
5, a negative pressure air source (negative pressure source) is used instead of the pressurized air source 1, but the other configurations and operations are the same as in the pressurization method. Specifically, the container is connected to a negative pressure air source, the inside of the container is set to below the test pressure, and after maintaining this state for a certain period of time,
What is necessary is to isolate the container from the negative pressure air source, introduce outside air into the container, increase the pressure to the test pressure, and after a certain period of time, detect whether or not fluid has flowed into the negative pressure container. In this method, the temperature of the fluid in the container rises during the pressure increase and reaches equilibrium with the outside temperature in a short time, resulting in a stable test pressure. The change in pressure due to this pressure reduction method can be represented in FIG. 3 by setting the vertical axis to negative pressure.

Furthermore, as shown by imaginary lines in FIGS. 1, 4, and 5, a cylinder 21 containing a piston 20 may be connected to the piping line 11 instead of the solenoid valve SV ₂ . In the case of the pressurization method, the rod 22 connected to the piston 20 is pulled during the depressurization process. In the case of the pressure reduction method, press the rod 20 during the pressure increase step.

This invention is not limited to the above-mentioned embodiments, and various embodiments are possible. For example, the fluid is not limited to air, but may also be gas or a liquid such as water or oil.

(Effects of the Invention) As explained above, according to the present invention, the inside of the object to be inspected can be quickly brought to a stable test pressure, and therefore the leak test can be speeded up. The effect is produced.

[Brief explanation of drawings]

The drawings from FIG. 1 to FIG. 3 show an embodiment of the leak test method according to the present invention.
FIG. 1 is a schematic flow diagram, FIG. 2 is a time chart, and FIG. 3 is a pressure transition graph.
Further, FIGS. 4 and 5 are schematic flow diagrams of other embodiments different from each other. Furthermore, Fig. 6,
FIG. 7 is a graph of pressure changes in the conventional pressurization method and depressurization method for leak testing. 1... Pressurized air source (positive pressure source), 2... Container, Pt... Test pressure, Po... Initial pressure.

Claims (1)

[Scope of Claims] 1. In a leak test method in which a positive test pressure is applied to the inside of the test object and the sealing quality of the test object is determined from the subsequent pressure fluctuation inside the test object, first a positive pressure source is used. and the above-mentioned test object to apply an initial pressure higher than the above test pressure inside the above-mentioned test object, and then cut off this test object from the above positive pressure source to reduce the pressure inside the test object to the outside of the test object. The inside of the test object is depressurized to the above test pressure to bring the temperature inside the test object almost to the outside temperature, and then the quality of the airtightness of the test object is judged from the subsequent pressure fluctuation inside the test object. A leak test method characterized by: 2. In a leak test method in which a negative test pressure is applied inside the test object and the sealing quality of the test object is determined from the subsequent pressure fluctuation inside the test object, the negative pressure source and the above test object are first connected. connect to apply an initial pressure smaller than the test pressure inside the test object, then cut off the test object from the negative pressure source, introduce fluid into the test object, and bring the inside of the test object to the test pressure. The leak test is characterized in that the temperature inside the test object is made to almost match the outside temperature by increasing the pressure to a maximum temperature, and the quality of the airtightness of the test object is determined from the subsequent pressure fluctuation inside the test object. Method.