On the significance of Nondestructive Testing Technology

Date：2021-09-15 15:41:01Views：1725

Nondestructive testing is a new comprehensive application technology in the third testing industry. On the premise of not damaging the service performance of the tested object, it applies a variety of physical principles and chemical phenomena to effectively inspect and test all kinds of engineering materials, parts and structural parts. One of the main purposes of NDT is to provide real-time process quality control for raw materials, semi-finished products, finished products and product components of discontinuous processing (such as multi process production) or continuous processing (such as automatic production line), especially to control the metallurgical quality of product materials and production process quality, such as defect condition, organization state Coating thickness monitoring, etc. at the same time, the quality information learned through the detection can be fed back to the design and process department, so as to further improve the design and manufacturing process to improve the product quality, and receive the effect of reducing scrap and repaired products, so as to reduce the manufacturing cost and improve the production efficiency.

The research content of nondestructive testing mainly includes two aspects: Nondestructive Testing and nondestructive evaluation. The former is to detect the presence or absence of defects; The latter is to quantitatively measure the defects on the basis of the former, so as to evaluate the quality of defective materials and products or measure some physical and mechanical properties of materials and products (such as internal residual stress, microstructure, coating thickness, etc.). It can be seen that nondestructive testing technology is adopted in the production and manufacturing process to timely detect and control various defects in the original and processing process, so as to prevent raw materials and semi-finished products that do not meet the quality requirements from flowing into the next process, avoid the waste of labor, manpower, raw materials and energy caused by futility, and promote the improvement of design and process, That is to avoid "insufficient quality" of the final product.

Nondestructive testing and its evaluation technology plays an important role in controlling and improving product quality, ensuring the reliability of materials, parts and products, ensuring the safe operation of equipment, improving production efficiency and reducing cost. It is not only an essential technical means for the development of modern industry, science and technology, but also an important link of comprehensive "quality management" Nondestructive testing plays an active role in all stages from processing and manufacturing, finished product inspection to in-service testing.

1. Design stage

The quality of products depends largely on the design level. During the design, the structural form of the product is selected, and the inspection, test methods and acceptance standards are formulated, which determines the performance, reliability and maintainability of the product. In the 1980s, the United States promulgated the military standard mil-i-6870e nondestructive testing requirements for aircraft and missile materials and parts. In this standard, it is clearly proposed that each design unit should consider the actual ability of nondestructive testing to ensure that the structural design requirements are consistent with the sensitivity, resolution and reliability of nondestructive testing. At the same time, each design unit is required to establish a nondestructive testing technical requirements review department to review the part drawings, categories, allowable defect types and sizes, key parts, nondestructive testing methods and specifications Acceptance standards, items requiring nondestructive testing in use and maintenance, etc. shall be reviewed.

2. Development and production stage

The design drawings and data are distributed to the development and production department. The first task of the production department is to obtain raw materials that can manufacture parts that meet the design requirements. In addition to the chemical composition and mechanical properties, the requirements for raw materials must also include the requirements for nondestructive testing. For example, in the early stage of the development of Qin alloy parts, due to the low metallurgical level at that time, there was the problem of uneven structure caused by uneven composition, which was not allowed. In the specification, it was stipulated that ultrasonic testing must be carried out to strictly control the clutter level within a certain range.

Nondestructive testing is often considered to increase the inspection cost, so as to increase the manufacturing cost. However, if the nondestructive inspection is carried out correctly in the appropriate link in the manufacturing process, the subsequent invalid process can be avoided, so as to reduce the manufacturing cost. For example, if defects are detected after welding, rework is required. Rework takes a lot of man hours or is difficult to repair. Therefore, nondestructive testing can be carried out in the middle stage before the completion of welding. After it is proved that there are no defects, the welding can be continued. In this way, it may not be necessary to repair after welding. For another example, when machining castings, it is sometimes not allowed to have defects such as residues, pores or cracks on the machined surface, which can also carry out nondestructive testing on the parts to be machined before machining. Through non-destructive testing, there is no need for machining where defects will appear after processing. By adopting the above method, it can avoid becoming unqualified products due to defects after machining, so as to save machining hours.

In order to manufacture products according to the specified quality requirements, first of all, it is necessary to know whether the manufacturing process adopted is appropriate. First, make samples or test products according to the predetermined manufacturing process and carry out nondestructive testing. While observing the inspection results, improve the manufacturing process, and repeat the test, and finally determine the product manufacturing process that meets the quality requirements. For example, in order to determine the welding specification, the sample can be made according to the predetermined welding specification for radiography, then the welding specification can be corrected according to the flaw detection results, and finally the welding specification that can meet the quality requirements can be determined. When manufacturing castings, in order to determine the casting process design, radiographic flaw detection can also be used to improve the position of gate and riser according to the occurrence of defects, and finally determine the casting process design. These are examples of non-destructive testing used to improve manufacturing processes. According to the characteristics of various nondestructive testing methods and skillfully using these methods, the manufacturing process can be easily improved.

However, it must be noted that the use performance of the same specific product is the same, but the raw materials and product manufacturing processes are different. The NDT methods and technologies to be adopted and the corresponding result evaluation contents may be very different. If the NDT is applied blindly, the reliability may not be improved. Therefore, it is necessary to study when to conduct appropriate nondestructive testing, select the most appropriate testing method and apply the correct testing technology.

3. Use phase

In order to ensure the reliability of use, the user department must conduct reliable nondestructive testing on the designated parts according to the cycle and method specified by the design department and the testing rules of specific parts submitted by the manufacturing department. These testing results are very important for improving the design, manufacturing and testing level, so as to ensure the service performance and prolong the service life of the products. High temperature, high pressure, high speed and high efficiency are the symbols of modern industry, which are based on high-quality products. The high quality of products is based on high-quality design and high-quality process level. In the production process, from the nondestructive testing of raw materials to the nondestructive testing of final products, through a series of nondestructive testing, judge the quality of design, raw materials and manufacturing process, find out the factors that can cause damage, and then improve them, so as to minimize the probability of product damage. It can be said that modern industry is based on nondestructive testing. It is difficult to find any other discipline branch, which covers profound technical knowledge, many basic research fields and a wide range of application fields, which can be compared with nondestructive testing.

In addition, the use of nondestructive testing technology can also control the quality level of materials and products within the range suitable for the use performance requirements according to the acceptance standards, so as to avoid the so-called "excess quality" caused by infinitely improving the quality requirements. Nondestructive testing technology can also determine the location of defects through testing, and use some defective materials or semi-finished products without affecting the design performance. For example, the defects are within the machining allowance, or local grinding or repair is allowed, or the processing technology is adjusted to make the defects located at the parts to be removed, so as to improve the utilization rate of materials, Obtain good economic benefits.

Therefore, nondestructive testing technology plays an important role in reducing production and manufacturing costs, improving material utilization, improving production efficiency, and making products meet the requirements of service performance (quality level) and economic benefits at the same time.