The 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 methods, including a weld, a fusion zone, and a heat-affected zone. The mechanical properties of welded joints are determined by their chemical composition and organization. Therefore, the factors that affect the chemical composition of the weld and the structure of the welded joint affect the performance of the welded joint.

1. Sinking test

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

2. The water test

The static pressure generated by the water's own weight is used to check the structure for leakage. Based on visual inspection, it is suitable for general welding structures that are not under pressure but require sealing.

3. Ammonia leakage test

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

4. Kerosene penetration test

It is used for welding structures that are subject to small internal pressure and require certain tightness. Kerosene is highly permeable and is very suitable for sealing inspection of welds. Before the inspection, brush lime water on the side of the weld for easy observation, and brush kerosene on the other side of the weld after drying. If there is a penetration defect, the lime layer will spill 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 the sealing test at present, helium mass spectrometer is very sensitive and can detect the volume fraction of 10-6 helium. Before the test, the container is filled with helium, and the leak is detected on the outside of the weld of the container. The disadvantage is the high price of helium and the long inspection cycle. Although helium is extremely permeable, it still takes a long time to penetrate very small cracks (such cracks cannot be detected by other means), and the detection of leaks in some thick-walled vessels often takes tens of hours. Proper heating can speed up leak detection.

6. Air tightness test

The 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 on the outside of the weld or sealing surface and check whether the soapy water bubbles. Because of the risk of explosion in the air tightness test, it should be carried out after the hydraulic test is qualified.