The analysis of some factors that will affect ultrasonic flaw detection

Factors that affect the detection accuracy of ultrasonic flaw detectors are: detection object, temperature, surface roughness, magnetic field, adhesion material, shape characteristics of the defect, acoustic impedance of the defect, and surface characteristics of the defect (such as smoothness).

1, the impact of materials

It is thought that the speed of sound of an object like steel, even if it contains many different alloy components, is essentially constant. However, in many other materials, such as many non-ferrous metals or plastics, the change in the speed of ultrasonic propagation is very significant, thus affecting the accuracy of the measurement. If the material to be tested is not isotropic, then the speed of sound will be different in different directions. In this case, the average speed of sound over the detection range must be used to calculate. The mean value is obtained by measuring a reference block whose sound speed is equivalent to the mean sound speed of the block to be measured.

2. The influence of temperature

The speed of sound varies with the temperature of the material. If the instrument calibration is carried out in a relatively low temperature environment, and the instrument is used in a relatively high temperature environment, this situation will cause the test results to deviate from the true value. To avoid this effect of temperature, the method is to preheat the reference block before calibrating the instrument to achieve the same ambient temperature as the use; Alternatively, the measured value is multiplied by a temperature influence factor.

3, the impact of surface roughness

The surface roughness of the inspected part has an effect on the quality of the inspected part. As the roughness increases, so does the impact. Rough surfaces can cause systematic and unexpected errors, which should be overcome by increasing the number of measurements at different positions during each measurement.

4. Effects of attachment materials

The attached material must be removed before the inspection to ensure that the probe of the instrument is in direct contact with the surface of the part under test.

5. The influence of magnetic field

The strong magnetic field generated by the surrounding electrical equipment can seriously interfere with the inspection work.

Requirements for technicians in the operation of flaw detection machines

No matter what kind of work scene is inevitably people-oriented, people's safety is always the first place in the safety of production, even in some seemingly very safe posts also need to pay attention to a lot of safety matters.

Portable magnetic particle flaw detection machine has a series of safety protection requirements in its working process, and the requirements for the staff operating the machine are also very high. There are generally three kinds of protection principles for magnetic particle flaw detection with X-ray or X-ray irradiation, namely shielding protection, distance protection, and time protection.

Operating magnetic particle flaw detection machine itself is also a professional technology, due to the professional knowledge of the flaw detection personnel, practical experience, responsibility and other reasons, may make the inspection quality can not meet the inspection requirements.

Therefore, the safety supervision department to carry out the necessary supervision of non-destructive testing, to ensure the quality of inspection requirements and operator safety will be very important.

So what are the specific requirements? Take a look:

1, should have the necessary professional knowledge, including the simple principle of magnetic particle flaw detection machine, magnetic particle flaw detection and shortcomings, what defects can be found, the scope of application of magnetic particle flaw detection machine, commonly used magnetic particle flaw detection machine types and performance, the main factors affecting the sensitivity of magnetic particle flaw detection machine.

2, should have the necessary practical skills, including the identification of X-ray film exposure conditions are normal, film blackness and sensitivity to meet the requirements, the difference between the true and false defects of the film, the identification of the nature of the defect on the film, the evaluation of the film grade, understand the magnetic particle flaw detection machine process and the whole process.

The practical skills to master the observation and evaluation of negatives should be stronger than the general flaw detection personnel, otherwise it will not be able to monitor.

Workpiece crack common judgment scheme:

(1) The magnetic particle diagram is the first information to analyze the crack defects, and its characteristics are: the shape and distribution of the magnetic particle diagram are generally the description of the shape and distribution of the crack; The magnetic particle pattern is affected by the width, depth, shape and magnetic permeability of crack.

② It is necessary to understand the process of the parts before magnetic particle detection, because the cracks have sources and rules to follow.

(3) The shape and distribution characteristics of the cracks found in the general magnetic inspection are determined by the maximum normal stress of the parts and the internal situation of the parts during the process, so the formation, shape, size and distribution of the cracks are the result of the superimposed of these two factors.

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