Welding Quality Inspection - Sealing Inspection

Welding quality inspection refers to the inspection of welding results with the aim of ensuring the integrity, reliability, safety and usability of the welded structure. In addition to the requirements for welding technology and welding process, welding quality inspection is also an important part of quality management of welded structures.
Here to talk about welding quality inspection methods: sealing test.
So how to test the sealing of welded joints?
In general, the following ways can be used to test:
1, sinking test
Used for small vessels or pipelines subject to small internal pressure. Test before the container or pipe filled with a certain pressure (0.4-0.5MPa) of compressed air, and then sinking to test the sealing, such as leakage; the water must be bubbles occur. This is also a common means of checking whether a bicycle inner tube is leaking.
2,Water test
The static pressure generated by the weight of the water to test the structure of the leakage phenomenon. Visual inspection is the main, applicable to the general welded structure is not subject to pressure but requires a seal.

3,Ammonia leakage test
Usage and coal pumping leakage test is the same, its sensitivity is higher than the kerosene leakage test. Before the test in the weld to facilitate the observation of one side of the paste soaked with a mass fraction of 5% of HgNO3, aqueous solution or phenolphthalein reagent of white paper or bandage, and then filled with ammonia in the container or add a volume fraction of 1% nitrogen compressed air.
If there is any leakage, it will flood the white paper strip or bandage with color spots. A 5% HgNO3 aqueous solution is immersed in black spots and phenolphthalein reagent is immersed in red spots.
4,Kerosene leakage test
It is used for welding structure which is subject to small internal pressure and requires a certain degree of sealing. Kerosene permeability, very suitable for weld sealing test. Before the test in the weld to facilitate the observation of one side of the brush lime water, in a little later in the weld on the other side of the brush with kerosene, such as penetrating defects, lime layer will be flooded with kerosene spots or kerosene band. Observation time is 15-30min.
5,Helium mass spectrometry test
Helium mass spectrometry test is currently the most effective means of sealing test, helium mass spectrometer sensitivity is very high, can detect the volume fraction of 10-6 helium. Before the test, the container is filled with helium, and then leakage is detected on the outside of the container weld. The disadvantages are the high cost of helium and the long inspection period.
Although helium has a very strong penetration, but very small gaps (such gaps can not be detected by other means) of the penetration of a long time, some thick-walled containers often up to tens of hours of leak detection. Appropriate heating can accelerate the speed of leak detection.
6,Gas tightness test
Airtightness test is a boiler, pressure vessels and other important requirements of airtightness of the welded structure of the conventional means of inspection. The medium is clean air, the test pressure is generally equal to the design pressure. Test pressure should be increased step by step.
After reaching the design pressure, in the weld or sealing surface of the outer side of the coating of soapy water and soapy water whether bubbling for the test basis. Because of the explosion risk of airtightness test, it should be carried out after the hydrostatic test is qualified.
Airtightness test is not the same as air pressure test:
1, its purpose is different, airtightness test is to test the tightness of the pressure vessel, air pressure test is to test the pressure strength of the pressure vessel. Secondly, the test pressure is different, airtightness test pressure for the design pressure of the container, air pressure test pressure for the design pressure of 1.15 times.
Pneumatic test is mainly to test the strength and sealing of the equipment, airtightness test is mainly to test the tightness of the equipment, especially small penetrating defects; airtightness test focuses more on whether there is a small leakage of the equipment, pneumatic test focuses on the overall strength of the equipment.
2,Using medium
Pneumatic test is generally used in the actual operation of air, air tightness test, in addition to air, if the medium of toxicity is relatively high, does not allow leakage or easy to penetrate, the use of ammonia, halogen or helium.
3,Safety accessories
Pneumatic test, do not need to install safety accessories on the equipment; airtightness test is generally installed in the safety accessories can be carried out only after the completion of (tolerance).
4,Order
Air tightness test needs to be carried out after the completion of pneumatic or hydraulic test.
5,Test pressure
Pneumatic test pressure is 1.15 times the design pressure, internal pressure equipment also need to multiply the temperature correction factor; air tightness test medium for air test pressure for the design pressure, such as the use of other media, should also be adjusted according to the media.

6. Occasions for use
Pneumatic test: Priority is given to the use of hydraulic test, if due to the structure of the equipment or support reasons can not be used when the hydraulic test, or equipment volume is large when the general use of pneumatic test. Air tightness test: the medium is highly or extremely hazardous medium, or does not allow leakage .
Pneumatic test belongs to the pressure test, in order to verify the equipment pressure strength. Air tightness test belongs to the tightness test, in order to check the sealing performance of the equipment.