Welding quality inspection refers to the inspection of Metal Welding Service results for the purpose of ensuring the integrity, reliability, safety and usability of welded structures. In addition to the requirements of welding technology and welding process, welding quality inspection is also an important part of welding structure quality management.
This time we will talk about the welding quality inspection method: sealing test.
So how to test the tightness of the welded joint?
In general, the following methods can be used for detection:
1. Submerged test
Used for a small vessel or pipe subject to low internal pressure. Before the test, the container or pipeline is filled with a certain pressure (0.4-0.5mpa) compressed air, and then submerged to test the tightness, such as right leakage; there must be bubbles in the water. This is also a common way to check whether the inner tube of a bicycle is leaking.
2, water test
The static pressure generated by the dead weight of water is used to test whether the structure has leakage. Mainly by visual inspection, applicable to the general welding structure which is not pressurized but requires sealing.
3. Ammonia leakage test
Its use is the same as the coal extraction leakage test, and its sensitivity is higher than the kerosene leakage test. Before the test, a white paper strip or bandage soaked in 5% HgNO3, aqueous solution or phenolphthalein reagent was pasted on the side of the weld to facilitate observation, and then the container was filled with ammonia or compressed air with 1% nitrogen.
If there is a leak, it will make a stain on the white paper strip or bandage. Immersion mass fraction of 5%HgNO3 aqueous solution for black spot, immersion phenolphthalein reagent for erythema.
4. Kerosene leakage test
For welding structures are subject to small internal pressure and required to have a certain tightness. Kerosene has strong permeability and is very suitable for weld sealing inspection. Before inspection, it is easy to observe one side of the weld brush lime water, and brush kerosene on the other side of the weld after drying. If there are penetrating defects, the lime layer will appear coal oil spots or kerosene belts. The observation time was 15-30min.
5. Helium mass spectrometry test
The Helium mass spectrometry test is the most effective means of sealing test at present. helium mass spectrometer is very sensitive, can detect the volume fraction of 10-6 helium. Before the test, fill the container with helium, and then check the leakage on the outside of the container weld. The disadvantages are the high price of helium and the long inspection period.
Although HELIUM IS EXTREMELY PENETRATING, IT TAKES A LONG TIME TO PENETRATE VERY SMALL CREVICES (SUCH CREVICES CANNOT BE DETECTED BY OTHER MEANS), AND some thick-WALLED CONTAINERS ARE often detected for tens of hours. Proper heating can speed up the leak detection.
6. Air tightness test
Air tightness test is a routine inspection method for boilers, pressure vessels and other important welding structures requiring air tightness. The medium is clean air, and the test pressure is generally equal to the design pressure. The pressure should be increased step by step during the test.
After reaching the design pressure, apply soapy water on the outside of the weld or sealing surface and check whether the soapy water is bubbling. Due to the risk of explosion in the air tightness test, it should be carried out after passing the hydrostatic test.
Air tightness tests and air pressure tests are not the same:
1, its purpose is different, the air tightness test is to test the tightness of the pressure vessel, pressure test is to test the pressure strength of the pressure vessel. Secondly, the test pressure is different. The air tightness test pressure is the design pressure of the vessel, and the air pressure test pressure is 1.15 times of the design pressure.
Air pressure test is mainly to test the strength and tightness of equipment, air tightness test is mainly to test the tightness of equipment, especially small penetration defects; the air tightness test focuses more on whether the equipment has a small leak, while the air pressure test focuses on the overall strength of the equipment.
2, the use of media
Air pressure test is generally used in practical operation, air tightness test in addition to air, if the medium is relatively high toxicity, does not allow leakage or easy penetration, ammonia, halogen or helium gas.
3. Safety accessories
When air pressure tests, there is no need to install safety accessories on the equipment; under normal circumstances, the air tightness test can not be carried out until the safety accessories are installed (capacitive gauge).
4, order
The air tightness test should be carried out after the air pressure or hydrostatic test is completed.
5. Test pressure
The air pressure test pressure is 1.15 times the design pressure, and the internal pressure equipment needs to multiply the temperature dressing coefficient; when the air tightness test medium is air, the test pressure is the design pressure. If other media are used, it should be adjusted according to the condition of the medium.
6, use occasion
Pressure test: the priority is to use hydraulic test, if the equipment structure or support reasons can not be used hydraulic test, or the equipment volume is large when the general use of pressure test. Air tightness test: medium is highly or extremely hazardous medium, or no leakage is allowed.
The pressure test belongs to a pressure test, in order to check the bearing strength of equipment. air tightness test belongs to compactness test, in order to check the sealing performance of equipment.