JP3028898B2 - Pipe leak defect location measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the position of a leak defect in a tube, for example, a helium leak test for measuring the position of a leak defect in a heat transfer tube used in a multi-tube heat exchanger using helium gas. More specifically, the pipe outer space outside the tube to be inspected is filled with a search gas at a higher pressure than the tube inner space inside the tube, and a one-way flow is generated in the gas in the tube inner space, A probe is inserted into the internal space from one end of the tube to be inspected and moved, and at each insertion position of the probe, the gas in the tube collected by the probe is supplied to a search gas detector, and the content of the search gas is determined. The present invention relates to a method for measuring the position of a leak defect in a tube by measuring an insertion position of the probe when a measured value changes, thereby obtaining a position of a leak defect in the tube to be inspected.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring the position of a leak defect in a pipe as described above, a method described in Japanese Patent Application Laid-Open No. 57,797 / 1982 is known. According to the publication, helium gas is injected into the inside of the body of the multi-tube heat exchanger, and gas in the heat transfer tube is sucked from one end of the heat transfer tube to generate a one-way flow in the heat transfer tube. The purpose is to measure the position of the leak defect by using the mutation point indicating the presence or absence of the defect. In forming the suction means, the gas inside the heat transfer tube is sucked with an ejector effect by driving a blower or the like by connecting an end portion of the heat transfer tube to an exhaust duct.

However, according to the above-described method for measuring the position of a leak defect in a pipe, the measured position of the leak defect may still cause a large error with respect to the actual position of the leak defect. In other words, in the conventional defect position measuring method, the balance between the diffusion speed of the helium gas and the suction speed of the gas in the tube has not been properly attained. Therefore, there is a problem that many operations are required to improve the measurement accuracy, and as a result, a long time is required for the measurement operation and the subsequent repair operation.

[0004]

In view of such a problem,
SUMMARY OF THE INVENTION An object of the present invention is to provide a method of measuring a position of a leak defect in a pipe, which can accurately measure the position of a leak defect in the pipe in a shorter time than before.

[0005]

In order to achieve the above object, a method of measuring the position of a leak of a pipe according to the present invention is characterized in that a pipe outside space outside a tube to be inspected is placed inside a pipe outside space. Filling the search gas in a higher pressure state and causing a one-way flow in the gas inside the tube inside the tube interior space, inserting a probe into the tube inside space from one end side of the tube to be inspected, and moving the probe. At each insertion position, the gas in the tube collected by the probe is supplied to a search gas detector, and the insertion position of the probe when the measured value of the content of the search gas changes is measured, thereby leaking the tube to be inspected. In the method for obtaining a defect position, the flow rate of the unidirectional flow of the gas in the pipe is set within a certain range, and the probe is rotated to collect gas in the pipe with respect to the pipe to be inspected. In changing the pores of phase. The probe may be coupled along a line next to the probe, and the probe may be rotated by an operation below the line. The inspected tube is a heat transfer tube in a heat exchanger,
The pipe outer space is an inner space of a body surrounding the heat transfer thin tube,
The search gas may be helium gas. The unidirectional flow velocity of the gas in the pipe is 2.1 cm / sec.
It is desirable to set within the range of 4.8 cm / sec or less. On the other hand, the characteristics of the suction device used in the method for measuring the position of a leak defect in a pipe according to any of the above are two types of valves and two types of valves.
It is to equip with various kinds of flow meters in parallel.

[0006]

First, smoke was simulated in order to investigate the behavior of the search gas entering the inside of the pipe from the position of the leak defect. As shown in FIG. 4, when a one-way flow F is generated in the gas inside the pipe 60 and smoke is introduced from the leak defect 60a, when the flow rate of the gas in the pipe is low as shown in FIG. 60a on the opposite side from the
Smoke 70 diffuses to a position much lower than the above, whereas when the flow velocity of the gas in the pipe is high as shown in FIG. It was found that smoke 70 was flowing to the downstream side in a state where it hardly spread. Further, by appropriately adjusting the flow rate of the gas in the pipe, as shown in FIG.
A boundary layer (hereinafter, referred to as an “air curtain” in the present specification) between a portion including smoke due to leakage and a portion not including smoke due to leakage spreads at a position substantially at the same height as 0a. There was found.

Incidentally, the outer diameter of the probe is formed to be considerably smaller than the inner diameter of the tube in order to facilitate insertion and withdrawal into the tube, so that the tip of the probe does not always exist at the center inside the tube. There is also a high possibility of moving along the wall. In the conventional measurement method, the air curtain of the search gas may be in a state as shown in FIGS. 4A and 4C, and the position of the leak defect is measured by the position of the probe tip in the diameter direction of the tube. Since there was a possibility that a large error occurred in the measurement, it was necessary to repeat the measurement operation.

According to the experiments performed by the inventor, the results of which are shown in Tables 1 and 2 below, the flow rate of the unidirectional flow of the gas in the pipe is within a certain range, particularly, 2.1 cm / sec to 4.8 cm / sec. By setting it within the range, the tip of the probe is 10 mm in front of the leak defect position, regardless of the side of the tube wall where the leak defect exists, the side opposite to this defect, and any intermediate position between them. It has been found that the value of the search gas detector becomes about twice the value of the background at the position of the degree.
That is, from the above simulation and the tendency of Tables 1 and 2 below, within the range of the above flow velocity, the air curtain of the search gas is spread along the diameter direction of the tube, and the tip of the probe having the gas sampling hole is Regardless of the position in the diameter direction of the tube to be inspected, it is possible to penetrate the air curtain of the search gas at a position substantially at the same height as the leakage defect.

In the present invention, by setting the flow velocity of the one-way gas in the pipe within a certain range, the air curtain of the search gas is widened along the diameter direction of the pipe. Then, by rotating the probe to change the phase of the gas sampling hole in the probe with respect to the tube to be inspected, it is possible to confirm that the air curtain is spread along the diameter direction of the tube. it can. Further, according to the feature of the suction device, since two types of valves and two types of flow meters are provided in parallel, the flow rate of the one-way flow can be continuously adjusted.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. In this embodiment, as shown in FIG. 1, an experimental apparatus is configured using a full-scale model of one heat transfer thin tube in a multi-tube heat exchanger. This experimental device 1
In general, an inverted U-shaped heat transfer thin tube 3, which is a tube to be inspected having a leak defect, a pseudo trunk 5 provided at a leak defect portion, and a helium gas serving as a search gas is supplied to the pseudo trunk 5. A cylinder 7, a probe 9 inserted into the tube from one end side of the heat transfer thin tube 3, a helium detector 11 which is an example of a search gas detector for detecting gas in the tube collected by the probe 9,
It comprises a suction device 13 for sucking gas from the other end of the heat transfer thin tube.

As shown in FIG. 2, the pseudo trunk 5 provided in the heat transfer thin tube 3 surrounds the leak defect 3a formed in the heat transfer thin tube 3 in an airtight state, and helium extending from the cylinder 7 is provided. It is connected to the supply pipe 5a to partially reproduce the body of the heat exchanger. That is, a portion surrounded by the pseudo trunk portion 5 and the heat transfer thin tube 3 corresponds to the tube outer space 5b which is the inner space of the body and the outside of the heat transfer thin tube. In the present embodiment, the leakage defect 3a is reduced to 0.
The helium gas supply pressure was set to a gauge pressure of about 0.5 kg / cm ² G, and the tube outer space 5b was set to the tube internal space 3 inside the heat transfer thin tube 3.
The pressure is higher than a. The heat transfer thin tube 3 has a total length of about 18 m and an inner diameter of about 20 mm.

The suction device 13 comprises a vacuum pump 13a, a flow meter, and valves 13b and 13c. The suction tube 14 extending from the suction device 13 and the heat transfer thin tube 3 are airtightly connected via a stopper 15. Although a reciprocating piston pump is used as the vacuum pump 13a, other types may be used, and the exhaust system port is located at a place isolated from the insertion side of the probe. The valves 13b, 13c and the flow meter are connected in parallel to the circuit in two systems.
The flow rate can be continuously adjusted within the range of / min and the range of 0 to 20 l / min. That is, by adjusting the valve, the gas in the pipe in the pipe internal space 3b is sucked at a predetermined flow rate, so that the gas in the pipe can generate a one-way flow F at a predetermined speed.

As the probe 9, as shown in FIG. 2, a sniffer probe which is a cone-shaped rod having a diameter of about 9 mm and which collects gas in a tube from a very fine hole 9a penetrating the center is used. It is. The base of the probe 9 is a sampling tube 9 b for guiding the sampled gas to the helium detector 11.
Is linked to The sampling tube 9b has a buckling strength enough to push the probe 9 into the heat transfer thin tube 3. In this embodiment, in order to change the position of the tip of the probe 9 in the diameter direction of the heat transfer thin tube 3, the diameter 6
A wire 17 of about mm is arranged along the side of the probe 9 at a distance of about 1 mm, and these are wound together with a vinyl tape and joined. Then, the lower part of the number line 17 is bent into an L-shape to constitute an operation unit (not shown) for changing the phase of the probe 9 with respect to the leakage defect 3a. In this embodiment, the probe 9 has the same phase as the leak defect 3a (B in the figure), the probe 9 has a phase rotated by 90 ° from the leak defect 3a (Q in the figure), and the probe 9 has the same phase as the leak defect 3a. 180
Sampling is performed at three points when the phase is rotated by ° (H in the figure). The sampling tube 9b is provided with a scale (not shown) for measuring the distance from the tip of the inserted probe 9 to the entrance of the heat transfer thin tube 3, and in this embodiment, the position of the leak defect 3a is determined. Since it is known, the distance from the position of the leak defect 3a to the tip of the probe 9 can be measured.

The helium detector (helium leak detector) 11 includes a mass spectrometer adjusted for helium measurement, and further includes an exhaust device including a rotary pump and an oil diffusion pump, a vacuum gauge, a trap, and the like. I have. The gas in the tube collected by the suction force of the exhaust device is sent to the mass spectrometer, where the helium gas concentration is measured as a relative value. The concentration of helium gas contained in the atmosphere is defined as a background value. When the measured helium gas concentration is higher than the background value, the helium gas concentration downstream of the one-way flow F from the leak defect position 3a of the heat transfer thin tube. The tip of the probe 9 is located at the side position.

Tables 1 and 2 show the measurement results obtained by the above-mentioned experimental apparatus. The probe 9 is inserted from the upstream side of the one-way flow to the downstream side (the coupling side of the suction device 13), and at each insertion position, the phase of the probe 9 with respect to the leakage defect 3a is changed by the operation unit of the line 17 at each insertion position. Alternately, three points corresponding to B, Q, and H were collected. The temperature of the equipment is almost normal. In the table, the sign of the measurement position is negative, which means that the tip of the probe 9 is on the upstream side of the one-way flow F from the leak defect 3a, and the sign of the measurement position is positive. Means that the tip of the probe 9 is located downstream of the leak defect 3a.

[0016]

[Table 1]

[0017]

[Table 2]

According to Tables 1 and 2, when the suction amount by the suction device 13 is 0.4 to 0.9 l / min, when the distance from the leakage defect is changed from -20 mm to -10 mm, the helium detector 11 The measured value of the helium gas content has changed at least twice the background value in any of the phases B, Q, and H. Therefore, it can be seen that, regardless of the position of the probe 9 in the diameter direction of the heat transfer thin tube 3, the existence position of the leak defect 3a can be almost surely measured from a position about 10 to 20 mm upstream of the leak defect 3a. That is, in the same suction amount range, the air curtain of the search gas is located on the upstream side 10-2 of the leak defect 3a.
It is considered that it is formed between 0 mm, and the position of the leak defect 3a can be indirectly known by penetrating this air curtain with the probe 9 and knowing the position of the air curtain. When the suction rate is 0.3 l / min or less, the measured value gradually increases from between 20 mm and 30 mm on the upstream side of the leak defect 3a, and the change is slow.
Further, when the suction amount is 1.0 l / min or more, the change in the value of the phase B is small, which results in undesirable results for accurate measurement of the leak defect position. An appropriate suction amount of the suction device 13 by the present experimental apparatus is 0.4 l / min or more and 0.9 l / min. Considering that the inner diameter of the heat transfer thin tube is 20 mm, these values are replaced with the flow rate in the heat transfer thin tube 3 by the following equation.

0.4 × 1000 / (1.0 × 1.0 × π × 60) ≒ 2.1 [cm / sec] 0.9 × 1000 / (1.0 × 1.0 × π × 60) ≒ 4.8 [cm / sec] In order to perform a proper measurement, the flow rate of the one-way flow F of the gas in the pipe should be approximately 2.1 cm / sec or more and 4.8 cm.
It must be set within the range of / sec or less.

At the downstream position where the helium gas is further diffused approximately 150 mm from the leak defect 3a, since the helium gas is diffused substantially uniformly and the flow rate of the gas in the pipe is known, the measured value of the helium detector is used to determine the defect hole size. You can know the absolute value. That is, the value of the helium detector is measured using a standard test port whose hole size is known and a calibration gas whose helium gas concentration is known, and the size of the defective hole can be calculated by using these values. it can. However, it is assumed that the defective hole has a cylindrical straight pipe shape.

First, a general formula for calculating a defective hole is obtained. When the gas flow is treated as a compressible fluid, Q = π × d ⁴ × (P ₁ −P ₂ ) / (128 × μ × l)-(a) where P ₁ , P ₂ : pressures at the inlet and outlet [kgf / m
² ] Q: Leakage amount [m ³ / sec] l: Defect length (thickness of thin tube material) [m] μ: Viscosity coefficient of helium gas [kgf · sec / m ² ] d: Leak defect is round hole Time diameter [m]

Here, when the equation (a) is modified, a general equation for obtaining the diameter d of the leak defect hole is obtained. d = [128 × μ × 1 × Q / π × (P ₁ −P ₂ )] ^1/4 )-(b) In the following, using the measurement result at a flow rate of 0.6 l / min and a measurement position of +150 mm, a defect was obtained. Determine the dimensions of the hole. First, Table 3 shows values for calibration of the helium detector.

[0023]

[Table 3]

From the results in Table 3, 51 [div] / 5 [ppm] = 10.2 [div / ppm] 480 [div] / 5 [ppm] = 9.6 [div / ppm] Is the average of both, 9.9d
iv.

Flow rate 0.6 l / min, measuring position +150 mm
The average of the measurement results is determined. (1400 + 1400 + 1300) / 3 = 1367 [div] The average concentration of helium gas leaked from the defective hole into the heat transfer tube is (1367-51) /9.9 = 132.9 [ppm]. The amount of helium gas generated is: Q = 132.9 x 10 ^-6 x 600/60 = 1.329 x 10 ^-3 [cm ³ / sec]

Here, the viscosity coefficient μ of helium is 19.93.
× 10 ^-6 [kgf · sec / m ² ], thickness of heat transfer thin tube l = 1.2 × 10
^-3 [m], the absolute pressure P ₁ = 1.5 × 10 ⁴ [kgf / m ² ] outside the capillary and the absolute pressure P ₂ = 1.0 × 10 ⁴ [kgf / m ² ] inside the capillary
Using Equation (b), the diameter d of the hole of the leak defect is determined. d = [128 × 19.93 × 10 ^-6 × 1.2 × 10 ^-3 × 1.33 × 10 ^-9 /3.14×(1.5-1.0)×10 ⁴ ] ^1/4 ≒ 2.26 × 10 ^-5 [m] = 22 .6 [μm]

Next, as a second embodiment of the present invention, a method of measuring the position of a leak defect in a heat transfer thin tube in a multi-tube heat exchanger will be described. As shown in FIG. 3, the heat exchanger 20 is generally divided into two parts by partitioning the inside of the case 21 up and down by a tube sheet 23 and dividing the lower part of the case 21 left and right by a partition wall 25. To form an inverted U-shaped heat transfer thin tube 3
Is fixed to the tube sheet 23 so that each end thereof is individually communicated with the partition chambers 27 and 29. Originally, in a multi-tube heat exchanger, a very large number of heat transfer thin tubes are provided, but only one representative tube is drawn in this figure. A steam transfer pipe 33 provided with a gate valve 31 and a transfer water pipe 37 provided with a transfer water valve 35 communicate with the body 21, respectively. The partition chambers 27 and 29 communicate with the high-temperature side pressure vessel through primary water pipes (not shown). Then, by heating the high-temperature primary water flowing from one partition chamber 27 through the heat transfer thin tube 3 to the other partition chamber 29, the secondary water supplied from the transfer water pipe 37 becomes steam and reaches the steam transfer pipe 33. . In addition, each partition room 2
Manholes 27a, 29a for inspection are located at the lower part of 7, 29.
Are opened, and are sealed by a lid (not shown) during normal operation.

The probe 9, the helium detector 11, the suction device 13 and the like 13 are constructed in substantially the same manner as in the first embodiment, except that the probe 9 is not along the line, and the valve 13d and the flow meter In that a bypass switching valve 13e which is normally closed is provided in parallel with the above. Also,
A gauge is provided on the sampling tube 9b connected to the probe 9 so that the insertion position of the tip of the probe 9 can be measured. Prior to the measurement of the location of the leak defect, the insides of the partition chambers 27 and 29, the heat transfer thin tube 3 and the inside of the body 21 are sufficiently dried by decompression, and the partition valve 31 and the transfer water valve 35 are closed. Helium gas is injected into the inner space 21a of the body surrounded by the thin tube 3, the tube sheet 23, and the body 21 at the ultimate pressure (gauge pressure) of about 10 kg / m ² G. In addition, a known method is used to check which heat transfer thin tube has a leakage defect.

First, the suction pipe 14 of the suction device 13 is attached to one end side of the heat transfer thin tube 3 having the leakage defect through the manhole 29a by the pinion 15, and the suction amount is 0.4 to 0.9.
l / min (Converted to the gas flow velocity in the pipe, 2.1 to
The gas in the tube is sucked at a rate of about 4.8 cm / sec). Then, the sampling tube 9b is held by hand, and the probe 9 is moved from the other end of the heat transfer thin tube 3 to the tube internal space 3 through another manhole 27a.
Insert into b. At this time, a few meters are inserted at first, and when the measured value of the helium detector 11 becomes large, it is returned slightly and the measurement is performed again. When the measured value is still large, it is returned again. Insert them sequentially at a shorter pitch. At each measurement point, the probe 9 is moved to the next measurement point after waiting about 90 seconds or more in consideration of the response time of the helium detector 11. By repeating this operation several times, it is possible to measure the probe insertion position when the measured value of the helium gas content changes,
Finally, the location of the leak defect can be obtained. Before the start of the measurement operation or when the measured value is unstable, it is conceivable that helium gas is retained in the heat transfer thin tube 3. Therefore, the switching valve 13e is operated to temporarily increase the suction amount. The retained helium gas may be discharged.

Next, in order to evaluate the size of the hole of the leak defect, when the position of the leak defect is almost determined, the tip of the probe 9 is pushed in so as to be located further downstream than the position of the leak defect. At this time, the probe 9 is pushed until the measured value of the helium detector 11 does not largely change.
If the measurement is performed where the leaked helium gas is almost uniformly diffused in the gas in the tube, the size of the hole of the leak defect can be obtained more accurately by comparison with the standard value. It is sufficient to insert about 150 mm further downstream than the position of the leak defect 3a. The size of the hole can be determined by using the measured value and the above-described formula (b) and the like. In the present embodiment, the measurement sensitivity of the helium detector is easily and practically adjusted using the standard test port and the standard test gas in the portion upstream of the heat transfer thin tube and the leak defect position where no leak defect occurs. Calibration can be performed and the size of the leak defect hole can be known more accurately. Note that the present invention can be particularly suitably implemented for a vertical heat exchanger as the heat exchanger 20.

Next, another embodiment will be described. In the above embodiment, the direction of insertion of the probe 9 and the direction of the one-way flow F generated in the gas in the pipe by the suction device 11 are the same, but these directions may be opposite to each other. That is, air may be supplied at a constant flow rate from one end of the heat transfer thin tube using a pump, and a probe may be inserted from the other end of the heat transfer thin tube. When the value is about the ground value, the existence of the leak defect position can be known.

Although helium gas is used as a search gas to be detected by the search gas detector 11 in the above embodiment, other gas such as ammonia gas or chlorofluorocarbon gas may be used. A type not including a mass spectrometer can also be used. Further, in the above embodiment, the present invention is applied to the heat transfer thin tube of the multi-tube heat exchanger. However, the present invention can be applied to other types of heat exchangers and tubes other than the heat exchanger. Furthermore, the present invention is not limited to room temperature,
It can be performed in a temperature range of about 0 to 100 ° C. In addition,
In each of the above embodiments, the probe was inserted manually.
It may be inserted through a rod with a clamp or by using a robot.

[0033]

As described above, according to the method for measuring the location of a leak defect in a pipe according to the present invention, the air curtain is formed by changing the phase of the gas sampling hole in the probe with respect to the pipe to be inspected. It can be confirmed that it spreads along the diameter direction, and the leak defect position can be measured quickly and accurately.

[Brief description of the drawings]

FIG. 1 is an overall view of an apparatus for implementing a method for measuring a position of a leak defect in a pipe.

FIG. 2 is an enlarged view of a main part showing a relationship between a probe and a heat transfer thin tube, where (a) is a longitudinal sectional view and (b) is a schematic transverse sectional view.

FIG. 3 is an explanatory diagram for implementing a method of measuring a position of a leak defect in a pipe in a heat exchanger.

FIG. 4 is a longitudinal sectional view showing a simulation of a method for measuring the position of a leak defect in a pipe due to smoke, wherein (a) shows a case where the flow rate of gas in the pipe is low, and (b) shows a case where the flow rate of gas in the pipe is appropriate. (C) shows the case where the flow velocity of the gas in a pipe is high, respectively.

[Explanation of symbols]

 3 Tube to be inspected 5b, 21a Tube outer space 3b Tube inner space F Unidirectional flow 9 Probe

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Imamura 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Inside Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Hiromizu Nakajima Hyogo, Hyogo-ken 1-1-1, Wadazakicho, Ward Mitsubishi Heavy Industries, Ltd., Kobe Shipyard (72) Inventor Fumio Fujita 1-1-1, Wadazakicho, Hyogo-ku, Kobe, Hyogo Prefecture, Japan Kobe Shipyard (72) Inventor: Satoru Higashi 1-1 1-1 Wadazaki-cho, Hyogo-ku, Kobe City, Hyogo Prefecture Inside Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (56) References JP-A-57-98797 (JP, A) JP-A-5-40071 (JP, A) Japanese Utility Model Showa 58-51248 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01M 3/00-3/40

Claims (5)

(57) [Claims] 1. A tube inside space (3b) inside a tube outside space (5b, 21a) outside a tube to be inspected (3).
At a higher pressure, the gas is filled with the search gas and a one-way flow (F) is generated in the gas in the pipe inside space (3b). A probe (9) is inserted and moved from the probe, and at each insertion position of the probe (9), the gas in the tube collected by the probe (9) is supplied to a search gas detector, and the content of the search gas is measured. In the method for measuring the position of a leak defect of a tube to be inspected (3) by measuring the position of insertion of the probe (9) when the value changes, the one-way flow (F) of the gas in the tube is obtained. Is set within a certain range, and the probe (9) is rotated to change the phase of the gas sampling hole (9a) in the probe (9) with respect to the test tube (3). Pipe leakage Position measurement method. 2. A wire (17) beside the probe (9).
The method according to claim 1, wherein the probe (9) is rotated by operating the lower part of the line (17). 3. The tube to be inspected (3) is a heat transfer thin tube in a heat exchanger, the tube outer space is an inner space (21a) of a body surrounding the heat transfer thin tube, and the search gas is helium gas. 3. The method for measuring the position of a leak defect in a pipe according to claim 1. 4. The pipe according to claim 1, wherein a flow rate of the one-way flow (F) of the gas in the pipe is set in a range from 2.1 cm / sec to 4.8 cm / sec. Leak defect location measurement method. 5. A suction device used in the method for measuring the position of a leak defect in a pipe according to claim 1, comprising two types of valves (13b, 13c) and two types of flow meters in parallel. Suction device.