GB/T 15823-2009Non-destructive testing -- Test methods for helium leak testing (English PDF)

4.1 Pre-leak testing

Before adopting a more sensitive testing method, a pre-leak testing can be

When performing pressure/vacuum leak testing, the indicating-type pressure gauge shall be directly connected to the tested part, or connected to the tested part from the remote end; so that the tester can easily observe these pressure gauges/vacuum gauges during the whole process of testing.

For large vessels or systems under test that require one or more pressure gauges/vacuum gauges, it is recommended to use a recording-type pressure gauge/vacuum gauge, to replace one of the two or more indicating-type pressure gauges/vacuum gauges.

4.3.1.4 Application

When Appendix A ~ Appendix C require the use of other types of pressure gauges/vacuum gauges, they can be used separately instead of the corresponding number of indicating-type or recording-type pressure gauges; or can be used in combination.

4.3.2 Temperature measuring device

When Appendix A ~ Appendix C require temperature measurement, the temperature measuring device shall pass the verification.

4.3.3 Standard leak

The standard leaks used for helium mass spectrometer leak testing can be divided into the following two categories:

a) Permeable standard leak - It shall be a permeable leak of glass or quartz that has been melted and calibrated. It has a helium leak rate of 1×10-11

Pa · m3/s ~ 1×10-7 Pa · m3/s; shall pass the verification.

b) Channel-type standard leak - It shall be a channel-type leak calibrated with helium that allows the tracer gas to pass through a tube. It shall have a leak rate equal to or less than the product of the required testing sensitivity and the actual percentage concentration of tracer gas. It shall pass the verification.

5.1 Preparation for testing

5.1.1 Surface preparation

The surface of the tested part shall be free of oil, grease, paint and other dirt that may hinder the testing. When liquids are used to clean the parts, or the water pressure test or hydro-pneumatic test is performed before the leak testing, the tested parts shall be fully dried before the testing.

5.1.2 Seal

Before testing, plugs, cover plates, sealing grease, glue, or other suitable materials that can be easily removed after leak testing shall be used to seal all holes. The sealing material shall not contain tracer gas.

5.1.3 Testing temperature

The minimum temperature of the tested parts during the testing shall be in accordance with the requirements of each appendix; or in accordance with the provisions of relevant product design documents and of procurement technical conditions for hydraulic, hydro-pneumatic or pneumatic tests of the tested parts.

The minimum or maximum temperature during testing shall not exceed the temperature allowed by the leak testing method or technique used.

5.1.4 Pressure/vacuum (pressure limit)

Unless otherwise specified in the relevant design documents and procurement technical conditions, components, which need to be subjected to pressure leak testing, shall not be tested at a pressure exceeding 25% of the design pressure.

5.2 Testing timing

Leak testing should be performed before hydraulic or hydro-pneumatic testing.

If the acceptance party considers it necessary, a leak testing can be performed again after the hydraulic or hydro-pneumatic testing. The pressure vessel shall not be evacuated unless it is confirmed by design calculation.

5.3 Testing methods and techniques

Common helium leak testing methods and techniques are shown in Table 1.

The specific requirements of various helium leak testing methods and techniques listed in Table 1 are shown in Appendix A ~ Appendix C.

m) Post cleaning method;

n) Personnel qualifications.

A.2.2 Equipment and apparatus

A.2.2.1 Instruments

A helium mass spectrometer capable of sensing and measuring trace amounts of helium shall be used. One or more of the following signal devices shall be used to indicate leak:

a) Meter - A meter on or attached to an instrument;

b) Audible device - Loudspeaker or earphone capable of emitting audible signals;

c) Indicator lamp - An indicator lamp that can emit visible light.

A.2.2.2 Auxiliary equipment

When needed, the following auxiliary equipment can be used:

a) Voltage stabilizer - When there is voltage fluctuation in the power supply line, a voltage stabilizer shall be connected to the instrument;

b) Suction gun - All parts that need to be inspected shall be scanned with a suction gun. The suction gun is connected to the instrument with a section of bellows. In order to shorten the response time and purification time, unless the testing device is specially designed to obtain a short response time and purification time with a longer hose, the length of the hose shall be about 4570 mm.

A.2.2.3 Calibrated standard leak

The calibrated standard leak can be a permeable or channel-type standard leak according to 4.3.3 of this Standard. The type of standard leak used shall be determined according to the sensitivity requirements of the instrument or equipment, or according to relevant design specifications.

A.3 Calibration

A.3.1 Instrument calibration

A.3.1.1 Preheating

Before calibrating with the verified standard leak, the instrument shall be energized to preheat. The minimum time for preheating shall be in accordance l) Scan distance, speed and method;

m) Acceptance criteria;

n) Personnel qualifications.

B.2.2 Equipment and apparatus

B.2.2.1 Instruments

A helium mass spectrometer capable of sensing and measuring trace amounts of tracer helium shall be used. One or more of the following signal devices shall be used to indicate leak:

a) Meter - A meter on or attached to an instrument;

b) Audible device - Loudspeaker or earphone capable of emitting audible signals;

c) Indicator lamp - An indicator lamp that can emit visible light.

B.2.2.2 Auxiliary equipment

When needed, the following auxiliary equipment can be used:

a) Voltage stabilizer - When there is voltage fluctuation in the power supply line, a voltage stabilizer shall be connected to the instrument;

b) Auxiliary pump system - When the testing equipment needs to use the auxiliary vacuum pump system, the absolute pressure and pump speed of the system shall enable the testing sensitivity and response time to meet the requirements;

c) Multi-directional joints - Pipes and valves that can correctly connect the instrument vacuum gauge, auxiliary pump, standard leaks and tested parts;

d) Tracer probe - Connected to a 100% helium source; a valve with a small opening is used at the other end to adjust the helium flow;

e) Vacuum gauge - The range of the vacuum gauge shall be able to measure the absolute pressure when the evacuated system is tested. The location of the vacuum gauge used in large systems shall be as far away as possible from the inlet of the pump system.

B.2.2.3 Calibrated standard leak

The calibrated standard leak can be a permeable or channel-type standard leak.

The type of standard leaks shall be selected according to the instrument or sensitivity requirements, or according to design specifications.

B.3 Calibration

B.3.1 Instrument calibration

B.3.1.1 Preheating

Before calibrating with the verified standard leak, the instrument shall be energized to preheat. The minimum time for preheating shall be in accordance with the regulations of the instrument manufacturer.

B.3.1.2 Calibration

In accordance with the operation and maintenance manual of the instrument manufacturer, the instrument shall be calibrated with the permeable standard leak described in 4.3.3 a) of this Standard, so that it is at the best or adequate sensitivity. The sensitivity of the instrument is at least 1×10-10 Pa · m3/s.

B.3.2 System calibration

B.3.2.1 Standard leak size

Connect the verified channel-type standard leak described in B.2.2.3 to the component; and as far as possible away from the connection between the leak detector and the component. When calibrating the testing system, the verified standard leak shall be opened.

B.3.2.2 Scan rate

When the evacuated parts reach sufficient vacuum, connect the helium mass spectrometer to the system. Calibrate the system by tracing the probe nozzle across the standard leak. The probe nozzle shall be within 6 mm from the standard leak. For the known flow rate of the 100% helium tracer probe, the scan rate for the testing system shall not exceed the rate at which leak from the standard leak can be detected.

B.3.2.3 Response time

During system calibration, it shall observe the time required for the appearance of an indicator signal and for the instrument output to stabilize. It is generally desirable that this time be as short as possible, to reduce the time required to determine the leak position.

B.3.2.4 Calibration frequency and sensitivity

l) Acceptance criteria;

m) Personnel qualifications.

C.2.2 Equipment and apparatus

C.2.2.1 Instruments

A helium mass spectrometer capable of sensing and measuring trace amounts of tracer helium shall be used. The leak shall be indicated by the meter on or attached to the test instrument.

C.2.2.2 Auxiliary equipment

When needed, the following auxiliary equipment can be used:

a) Voltage stabilizer - When there is voltage fluctuation in the power supply line, a voltage stabilizer shall be connected to the instrument;

b) Auxiliary pump system - When the testing equipment needs to use the auxiliary vacuum pump system, the absolute pressure and pump speed of the system shall enable the testing sensitivity and response time to meet the requirements;

c) Multi-directional joints - Pipes and valves that can correctly connect the instrument vacuum gauge, auxiliary pump, standard leaks and tested parts;

d) Shield - Any suitable cover or container, such as a plastic bag, with an intake pipe used as multiple nozzles;

e) Vacuum gauge - The range of the vacuum gauge shall be able to measure the absolute pressure when the evacuated system is tested. The location of the vacuum gauge used in large systems shall be as far away as possible from the inlet of the pump system.

C.2.2.3 Calibrated standard leak

The permeable standard leak described in 4.3.3 of this Standard shall be used.

Unless otherwise specified in the relevant design specifications, its maximum helium leak rate is 1×10-7 Pa · m3/s.

C.3 Calibration

C.3.1 Instrument calibration

C.3.1.1 Preheating

Before calibrating with the verified standard leak, the instrument shall be energized to preheat. The minimum time for preheating shall be in accordance with the regulations of the instrument manufacturer.

C.3.1.2 Calibration

According to the operation and maintenance manual of the instrument manufacturer, use the permeable standard leak described in 4.3.3 a) of this

Standard, to confirm whether the instrument is in the best condition or has sufficient sensitivity. The sensitivity of instrument to helium is at least 1×10-10

Pa · m3/s.

C.3.2 System calibration

C.3.2.1 Standard leak size

Connect the calibrated standard leak with 100% helium as described in 4.3.3 to the component; and keep it as far away as possible from the connection between the leak detector and the component.

C.3.2.2 Response time

The components are evacuated to an absolute pressure sufficient to allow the helium mass spectrometer to be connected to the system. The verified standard leak shall be opened to the system.

The standard leak shall remain open until the instrument signal becomes stable.

The time when the verified standard leak opens to the component and the time when the output signal increases to stabilize shall be recorded. The time elapsed between the two readings is the response time. Record the stable instrument reading M1.

C.3.2.3 Background reading

The background reading M2 is determined after measuring the response time.

The calibrated standard leak closes the testing system. When the instrument reading reaches a stable level, record the instrument reading M2.

C.3.2.4 Initial calibration

The initial system sensitivity S1 shall be calculated according to formula (C.1):

Where:

......