Necessary inspection of welded joints is an important measure to ensure welding quality.

Therefore, after the workpiece welding should be according to the product technical requirements of the weld corresponding inspection, where does not meet the technical requirements allowed defects, need to be repaired in time.

The inspection of welding quality includes three aspects: appearance inspection, nondestructive inspection and mechanical performance test. These three are complementary to each other, and the main nondestructive testing.

(1) Appearance inspection

Appearance inspection is generally based on naked eye observation, and sometimes 5-20 times magnifying glass is used for observation.

Through the appearance inspection, the weld surface defects can be found, such as edge biting, welding tumors, surface cracks, pores, slag inclusion and penetration. The shape dimension of the weld can also be measured by the solder joint detector or sample.

(2) Non-destructive testing

Inspection of slag, porosity, crack and other defects hidden in the weld.

At present, X-ray inspection, ultrasonic inspection and magnetic inspection are commonly used.

X-ray inspection is to use X-ray to take pictures of weld seams and judge whether there are internal defects, the number and type of defects according to the negative image. According to the technical requirements of the product to assess whether the weld is qualified.

If there is a defect in the weld, the ultrasonic beam is reflected back to the probe and is accepted, and then reflected waves appear on the fluorescent screen. According to the comparison and identification of these reflected waves and normal waves, the size and location of defects can be determined.

Ultrasonic flaw detection is much simpler than X-ray, so it is widely used.

However, ultrasonic inspection can only be judged by operating experience, and no inspection basis can be left.

Magnetic flaw detection can also be used for internal defects that are not deep from the weld surface and for microscopic cracks on the surface.

(3) water pressure test and air pressure test

For pressurized vessels requiring sealing, hydrostatic test and/or air pressure test shall be carried out to check the sealing and bearing capacity of the weld.

The method is to inject 1.2-1.5 times the working pressure of clean water or equal to the working pressure of the gas (mostly with air) into the container, stay for a certain time, and then observe the pressure drop in the container, and observe the leakage phenomenon outside, according to these can assess whether the weld is qualified.

(4) Mechanical property test of welding test plate

Nondestructive inspection can find the inherent defects of the weld, but it can not explain the mechanical properties of the metal in the heat affected zone of the weld, so sometimes the welded joint should be tensile, impact, bending and other tests. These tests are carried out by test plates.

The test plate shall be welded together with the longitudinal seam of the cylinder to ensure consistent construction conditions, and then the mechanical properties of the test plate shall be tested. In actual production, only the welding joints of new steel are tested in this respect.

Welding defects and Inspection Welding defects In the process of welding production, due to the influence of various factors in design, technology and operation, welding defects often occur.

Welding defects not only affect the appearance of the weld, but also may reduce the effective bearing area of the weld, resulting in stress concentration and fracture, which directly affects the reliability of the welding structure.

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