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Six methods to detect the tightness of welded joints

Views: 1     Author: Site Editor     Publish Time: 2022-05-20      Origin: Site

Submersion test 


For small containers or pipes with low internal pressure. Fill the container or pipeline with compressed air with a certain pressure (0.4-0.5MPa) before inspection. Then submerge in water to check the tightness, such as right leakage; bubbles must occur in the water. This is also a common means of checking for leaks in bicycle inner tubes.


water test 


Use the static pressure generated by the dead weight of water to check the structure for leakage. Based on visual inspection, it is suitable for general welded structures that are not under pressure but require tightness.


Ammonia leak test


The purpose is the same as that of the kerosene leakage test, and its sensitivity is higher than that of the kerosene leakage test. Before the test, paste a white paper strip or bandage soaked with 5% HgNO3, aqueous solution or phenolphthalein reagent on the side of the weld that is easy to observe, and then fill the container with ammonia gas or add 1% nitrogen compression. Air. If there is a leak, it will stain the white strip or bandage. The dark spots were soaked in a mass fraction of 5% HgNO3 aqueous solution, and the erythema was soaked in phenolphthalein reagent.


Kerosene Penetration Test 


It is used for welded structures that are subject to small internal pressure and require a certain degree of sealing. Kerosene has strong permeability and is very suitable for sealing inspection of welds. Before inspection, brush lime water on one side of the weld for easy observation. After drying, brush kerosene on the other side of the weld. If there is a penetration defect, kerosene spots or kerosene bands will appear on the lime layer. The observation time is 15-30min.


Helium mass spectrometry 


Helium mass spectrometry test is the most effective means of tightness inspection at present. The helium mass spectrometer is extremely sensitive and can detect helium with a volume fraction of 10-6. Before the test, the container is filled with helium, and then the leak is detected on the outside of the welding seam of the container. The disadvantage is that helium is expensive and the inspection cycle is long. Although helium has extremely strong penetrating power, it still takes a long time to penetrate very small gaps (such gaps cannot be detected by other means), and the leak detection of some thick-walled containers often takes up to tens of hours. Appropriate heating can speed up leak detection.


Air tightness test 


Air tightness test is a routine inspection method for boilers, pressure vessels and other important welded 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 to the outside of the welding seam or sealing surface and check whether the soapy water is bubbling. Due to the danger of explosion in the air tightness test, it should be carried out after the hydrostatic test is qualified.

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