JPS5824717B2 - Method for detecting minute leaks in heat exchanger tubes - Google Patents

Description

[Detailed Description of the Invention] Conventionally, when checking the integrity of heat exchanger heat transfer tubes, etc. in service, water pressure or air pressure is used to check for leakage by checking for water droplets or bubbles. Microcracks caused by intergranular corrosion, etc., which occurred in other areas could not be detected.

In particular, when a leak in the steam generator of a pressurized water nuclear power plant is discovered using a secondary water radiation monitoring device and the operation is stopped and investigated, the leak location cannot be found using the conventional inspection method described above.

The present invention relates to an improvement of a method for detecting minute leaks in heat transfer tubes of a heat exchanger that overcomes these difficulties. a heat exchanger comprising: discharging the primary and secondary fluid;
After the secondary fluid circulation space in the outer shell is evacuated and the heat transfer tube is heated, helium gas is injected and pressurized into the secondary fluid circulation space, and helium gas leaked into the heat transfer tube is detected. Its purpose is to detect micro-leakage in heat exchanger heat exchanger tubes, which can easily find micro-leakage tubes among the thousands of heat exchanger tubes in a short time. The point is to provide a method.

As described above, the present invention provides a heat exchanger comprising heat exchanger tubes through which a primary fluid flows and an outer shell in which the heat exchanger tubes are disposed and through which a secondary fluid flows. Since the secondary fluid circulation space in the outer shell is evacuated and the heat exchanger tube is heated, it is possible to release as much moisture as possible from minute cracks generated in the heat exchanger tube and the like.

Thereafter, helium gas was injected and pressurized into the secondary fluid circulation space, and the helium gas leaked into the heat transfer tube was detected, so that the water volume remained in the micro cracks without being evaporated by vacuum heating. Even if the helium gas is leaked by overcoming the surface tension of the moisture, the presence of the minute crank can be detected.

Furthermore, when the present invention detects the presence of microcracks that have occurred in heat transfer tubes, etc., a rubber balloon is attached to the end of the heat transfer tube, and the expansion of the balloon makes it extremely easy to remove microcracks from the heat transfer tube. can be found in.

The present invention will be described below with reference to the illustrated embodiment. Reference numeral 1 denotes a blade pressure water type steam generator for nuclear power plants, and the steam generator 1 is divided by a tube plate 2 into a primary water chamber 3 and a secondary water chamber 4. Further, the primary water chamber 3 is partitioned into two chambers 3a and 3b by a partition plate 5, and both ends of a heat transfer tube 60 arranged in the secondary water chamber 4 penetrate the tube plate 2, and one end thereof is connected to one water chamber 3a of the primary side water chamber 3, and the other end is connected to the other water chamber 3b of the primary side water chamber 3.
The main steam pipe 7 connected to the top of the secondary water chamber 4 and leading to the turbine has a main steam isolation valve 8 and a main steam check valve. 9 are interposed in series, and the secondary water chamber 4 is connected to the main steam isolation valve 8.
A paint valve 10, an atmosphere release valve 11, and a vacuum stop valve 12 are connected in parallel to the main steam pipe 1, and the vacuum stop valve 12
A vacuum pump 13 is connected to.

Furthermore, a water supply isolation valve 1 is connected to a water supply pipe 14 connected to a substantially central portion of the secondary water chamber 4 and leading to a water supply pump (not shown).
5 and a water supply check valve 16 are interposed in series.

Furthermore, an isolation valve 18 is interposed in a blowdown line 17 connected to the bottom of the secondary water chamber 4 and leading to a blowdown tank (not shown). A line 19 leading to a helium gas source (not shown) is connected to the down line 17, and a blowdown system stop valve 20 is interposed in the line 19.

The exhaust port of the hot air heater 22 is connected to the manhole 2, la, 21b of either one of the downstream water chambers 3a, 3b.

The illustrated embodiment is constructed as described above, so that the main steam isolation valve 8 leading to the secondary water chamber 4, the vent valve 10, the atmosphere release valve 11, the feedwater isolation valve 15, the isolation valve 18 and the stop valve 20 are connected to the secondary water chamber 4. By operating the vacuum pump 13 after opening only the vacuum stop valve 12, the secondary water chamber is brought to a degree of vacuum below the saturation pressure of the temperature inside the secondary water chamber 4 of the steam generator 1. 4 Make a vacuum inside.

Next, the hot air heater 22 is operated for the time required for the estimated amount of water droplets in the clevis portion in the tube sheet 2 to evaporate, and the hot air is flowed into the steam generator heat transfer tube 6, and the surface of the heat transfer tube 6, especially the tube Water droplets at the clevis in the plate 2 are evaporated.

After circulating hot air for a specified time and confirming that the degree of vacuum in the secondary water chamber 4 has been sufficiently maintained, the vinyl sheet 23 is
The primary side Himuro manhole 21a.

21b is closed, the helium gas concentration in the steam generator-next side water chamber 3 is measured with a helium gas detector, and the blowdown system stop valve 20 is opened to supply helium gas to the steam generator secondary side water chamber 3. inject into chamber 4 and increase its pressure to 2-3 k'1
lclt f & pressurize After further pressurizing helium gas,
By measuring the helium gas concentration in the primary side water chamber 3 with a helium gas detector and comparing it with the helium gas concentration before helium gas injection, the helium gas is transferred from the steam generator secondary side water chamber 4 to the primary side water chamber 3. (Since helium gas exists in the atmosphere, it is necessary to measure the helium gas concentration before helium gas is injected.)

If leakage of helium gas from the steam generator secondary side water chamber 4 to the primary side water chamber 3 is detected, the vinyl sheet 2
3 was removed, and both ends of the several thousand heat transfer tubes 6 were fitted with blind rubber plugs 2.
4 and close the primary water chamber 3a.

If the rubber balloon 25 is attached to the rubber stopper 24 fitted to either end of the tube 3b, the rubber balloon 25 attached to the leaking heat transfer tube 6 will swell with the leaked helium gas and leak. It is very easy to find the heat exchanger tubes 6 that are

As described above, in the embodiment, since a leakage test using water pressure is not performed, water does not seep into the microcracks, and microcracks in the heat exchanger tubes 6 can be found very easily and accurately within a short period of time.

Although the present invention has been described above with reference to embodiments, it goes without saying that the present invention is not limited to such embodiments, and that various design modifications may be made without departing from the spirit of the present invention. be.

[Brief explanation of the drawing]

FIG. 1 is a piping diagram illustrating an embodiment of the method for detecting minute leaks in heat exchanger tubes according to the present invention, and FIG. 2 is an enlarged longitudinal sectional side view of the main parts thereof. 1... Pressurized water type nuclear power plant steam generator, 2...
Tube plate, 3... Primary side ice chamber, 4... Primary side water chamber, 5.
... Partition plate, 6... Heat exchanger tube, 7... Main steam pipe, 8...
- Main steam isolation valve, 9... Main steam backflow valve, 10... Vent valve, 11... Atmosphere release valve port, 12... Vacuum stop valve, 13... Vacuum pump, 14... Water supply pipe, 15.
... Water supply isolation valve, 16 ... Water supply check valve, 17 ... Blowdown line, 18 ... Isolation valve, 19 ... Line, 20 ... Blowdown system stop valve, 21 ... Manhole, 22... Hot air heater, 23... Vinyl sheet, 24... Blind rubber 125... Rubber balloon.

Claims (1)

[Claims] 1. In a heat exchanger comprising a heat exchanger tube through which a primary fluid flows and an outer shell in which the heat exchanger tube is arranged and a secondary fluid flows, the primary and secondary fluids are discharged and the secondary fluid flows in the outer shell. A heat exchanger heat exchanger tube characterized in that after the space is evacuated and the heat exchanger tube is heated, helium gas is injected and pressurized into the secondary fluid circulation space, and helium gas leaked into the heat exchanger tube is detected. Micro leakage detection method.