GB-T 16876-1997 Liquid Nitrogen Container Layered Vacuum Test
1. Scope
This standard specifies the requirements, inspection methods, and inspection items for liquid nitrogen container layering vacuum test, which are mainly applicable to vacuum test of all kinds of liquid nitrogen containers.
2. Normative references
The following documents are essential to the application of this standard. For dated references, only the version cited applies to this standard. For undated references, the latest version (including all amendments) applies to this standard.
GB/T 2423.1 Environmental testing - Part 1: General and guidance
GB/T 16876-1997 Liquid nitrogen container layering vacuum test method
3. Requirements
3.1 Before the test, clean up the container. Before testing, the container shall be degreased and decontaminated to ensure that the sealing surface of the container is clean, flat and free of grease.
3.2 The test pressure and test time shall be consistent with the relevant requirements of the manufacturer.
3.3 During the vacuum test, it is necessary to pay attention to the sound and temperature changes of the container, and to ensure that the container does not deform and deform significantly or leak.
4. Apparatus
4.1 Vacuum pump
4.1.1 For vacuum tests in the range of 0.1MPa~0.03MPa, vacuum pumps can be selected from those specified in GB/T 2423.1.
4.1.2 For vacuum tests below 0.03MPa, two types of vacuum pumps can be selected: one with the pump inlet connected to the container respectively by a separate throttle (which can control the rate of evacuation), and the other with the container inlet and outlet connected in series to the pump inlet. The latter should use a vacuum oil-filled pump.
4.1.3 Vacuum pumps shall have the necessary pumping speed, air tightness and exhaust performance to meet the specified test requirements.
4.2 Vacuum measuring instruments
Vacuum measuring instruments suitable for measuring the pressure in the container should be selected from those specified in GB/T 2423.1.
4.3 Connecting pipe
The connecting pipe should be made of seamless steel or stainless steel tube or quick connector pipe with the same inner diameter size and length suitable for the vacuum pump and the container.
4.4 Auxiliary tools
If necessary, other necessary tools and apparatuses should also be prepared, such as hammers and block heads.
5. Test steps
5.1 Connection
5.1.1 First, the connecting pipe and the vacuum pump should be sealed and connected at both ends, and then the connecting pipe should be connected to the inlet port of the container.
5.1.2 When the exhaust rate must be adjusted, adjust the exhaust throttle (for vacuum tests between 0.1MPa and 0.03MPa).
5.2 Vacuum
5.2.1 After the connection is completed, start the vacuum pump and start vacuum until the pressure in the container is less than the specified value. When the pressure is lower than the specified value, the test is successful.
5.2.2 During the vacuuming process, the sound of the container and the change of temperature should be observed, and the deformation and leak of the container should be prevented.
5.3 Pressure maintenance
5.3.1 After the pressure test is completed, the time for maintaining the vacuum should be started and the pressure in the container should be monitored at the same time.
5.3.2 Every 10 minutes, the temperature of the container wall and the pressure in the container should be recorded. The pressure fluctuations during the test should not exceed 0.003MPa.
6. Inspection items
6.1 In the course of the test, the pressure shall be maintained for 20 minutes, and the pressure fluctuations shall not exceed 0.003MPa.
6.2 The leakage in the range of 0.1MPa-0.03MPa can be judged by observing the movement of the thermometer. For vacuum tests below 0.03MPa, the test should be conducted in accordance with the manufacturers instructions.
7. Marking
7.1 After the vacuum test is passed, a label should be affixed to the container as a permanent reminder.
7.2 The contents of the label should include: type (nominal volume), prescribed vacuum value, test date, test personnel and other necessary items.