Characteristic analysis and function of Nondestructive Testing Technology

Date：2022-02-21 14:29:00Views：1246

Nondestructive testing is to use the acoustic, optical, magnetic and electrical characteristics of materials to detect whether there are defects or non-uniformity in the tested object without damaging or affecting the service performance of the tested object, and give information such as the size, location, nature and quantity of defects. With the continuous improvement of testing requirements, nondestructive testing technology has widely adopted digital technology and has gradually entered the measurement field. For example, for the measurement of geometric quantities and material characteristic parameters, it is necessary to monitor and control the continuous stability of instrument indexes according to certain procedures, so as to improve the reliability of testing results.

(1) Characteristics of ultrasonic testing

Ultrasonic technology is a widely used nondestructive testing technology, which mainly depends on the different conditions of reflected waves to analyze the internal defects of specified targets. This nondestructive testing technology is relatively safe and does not need special protection. It has the characteristics of simple operation and low cost in practical application. However, affected by the characteristics of the technology itself, this testing method also has its own disadvantages in nondestructive testing.

There are three main disadvantages:

First, it is limited by the appearance of the tested object. Nondestructive testing can only be carried out for solids with regular shape. When the surface of the tested object is uneven or the shape is irregular, the ultrasonic testing results will be affected, with large deviation and lack of reference value.

Second, limited by material and defect shape. It is insensitive to the volume defect reaction inside the tested object, and can not analyze the internal defect shape of the tested object in time and effectively. When the material and particle of the tested object are different, it will also affect the accuracy of ultrasonic testing.

Third, limited by NDT experience. Because this testing method is not intuitive, it largely depends on the working experience of NDT personnel. It has a certain subjectivity in judging the welding quality, which may lead to the non objectivity of the testing results.

(2) Radiographic characteristics

Radiographic testing has a good sensitivity to volume defects in the tested objects, and can detect a variety of internal defects of welding parts, such as slag inclusion, incomplete penetration, porosity and so on. When X-ray testing is used, the defective parts inside the metal welding joint can be detected, and the position and volume of the notch can be judged by the penetration strength of the ray. However, there are some problems in the application of this nondestructive testing method:

First, high environmental requirements. Before radiographic testing, the irradiation environment shall be prepared in advance. If there is a problem of improper ray penetration position, it will also affect the welding quality test results.

Second, the preparatory work is demanding. In order to ensure the accuracy of radiographic testing and reduce the side effects of testing, NDT personnel are required to prepare for testing in advance, and the operation of the whole NDT process is difficult.

Third, compared with other detection methods, the whole detection time of radiographic detection method is longer, and the operation is difficult and the cost is high, so it has some limitations in popularization.

Specifically, the functions of NDT are as follows:

1. Ensure the quality of workpiece or equipment and ensure the safe operation of equipment. Nondestructive testing is used to ensure the product quality, so that under the specified service conditions and within the expected service life, part or the whole of the product will not be damaged, so as to prevent equipment and personnel accidents.

2. Improve the manufacturing process. We can first make samples or test products according to the predetermined manufacturing process and carry out nondestructive testing on them. We can use nondestructive testing to observe whether the process of manufacturing samples is appropriate. In this way, we can improve the process while observing until Zui we determine the manufacturing process that meets the quality requirements.

3. Reduce manufacturing costs. The purpose of reducing manufacturing cost can be achieved through nondestructive testing. Proper and correct nondestructive testing in the process of product manufacturing can prevent the workpiece from being processed and scrapped after Zui, which will waste man hours, so as to reduce the manufacturing cost.

Ultrasonic nondestructive testing has made great progress in recent decades. It has become a common means of nondestructive testing of materials or structures. Because ultrasonic testing can be carried out online, ultrasonic is harmless to human body and does not change the operation state of the system, it has been widely used in the nondestructive testing of materials or structures.