Welded joint refers to the contact of two or more parts to be welded together. Or a joint of two or more parts joined by welding method, including a weld, a fusion zone and a heat affected zone. The mechanical properties of welded joints are determined by their chemical composition and structure. Therefore, the factors affecting the chemical composition of the weld and the structure of the welded joint all affect the performance of the welded joint.

Sinking test

Used for small vessels or pipes subjected to low internal pressure. Before inspection, the container or pipe should be filled with compressed air at a certain pressure (0.4-0.5MPa). Then sink water to check the tightness, such as right leakage; Bubbles must occur in the water.

Water holding test

The static pressure generated by water dead weight is used to check whether the structure has leakage phenomenon. Based on visual inspection, it is suitable for general welding structure which is not compressed but requires sealing.

Ammonia leakage test

The use is the same as that of kerosene leakage test, and its sensitivity is higher than that of kerosene leakage test. Before the test, paste a white strip or bandage soaked with 5% HgNO3, aqueous solution or phenolphthalein reagent on the easy observation side of the weld, and then fill the container with ammonia or add compressed air with 1% nitrogen. If there is leakage, it will stain the white paper strip or bandage. The solution of 5%HgNO3 was black spot, and the solution of phenolphthalein was erythema.

Kerosene penetration test

It is used for welding structure with small internal pressure and certain sealing requirement. Kerosene has strong permeability and is very suitable for sealing inspection of welds. Before inspection, brush lime water on the side of the weld for observation, and brush kerosene on the other side of the weld after drying. If there are penetration defects, the lime layer will spill coal oil spots or kerosene belts. The observation time was 15-30min.

Helium mass spectrometry test

Helium mass spectrometry test is the most effective means of sealing test at present. Helium mass spectrometer is very sensitive and can detect helium with volume fraction of 10-6. The container was filled with helium before the test, and the leak was detected outside the weld of the container. The disadvantage is the high price of helium and the long inspection period. Although helium gas is highly permeable, it takes a long time to penetrate the smallest gaps that cannot be detected by other means, often in tens of hours in some thick-walled vessels. Proper heating can speed up leak detection.

Air tightness test

Air tightness test is a conventional test means for boiler, pressure vessel 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 on the outside of the weld or sealing surface and check whether the soapy water is bubbling. Because of the risk of explosion in the air tightness test, it should be carried out after the water pressure test is qualified.