Non-destructive testing technology development process gone through three stages: nondestructive testing stage, non-destructive testing stage and non-destructive evaluation stage. The first stage is a non-destructive testing, detection and discovery defects, the second stage is a non-destructive testing, not only detect defects, including probe test pieces some other information, such as the structure, nature, status, and trying to pass the test, to obtain more information, nondestructive evaluation is the third stage, it requires not only a defect is discovered the probe test pieces of the structure, the nature, status, also requires access to a more comprehensive, more accurate and comprehensive information, such as the shape and size of the defect, position, orientation, inclusions, defects in parts of the organization, the residual stress, combined with imaging technology, integrated application of knowledge of automation technology, computer data analysis and processing technology, materials, mechanics, fracture mechanics, the quality of the specimen or product and performance given a comprehensive and accurate evaluation.

Commonly used in non-destructive testing methods: radiographic testing, ultrasonic testing, magnetic particle testing, penetrant testing, eddy current testing, acoustic emission testing. Production to meet the demand, and along with the progress of modern science and technology, non-destructive testing methods and increasing variety, laser, infrared, microwave, LCD technology is used in addition to several of the above-mentioned method, non-destructive testing. The generation of non-destructive testing technology is the basis for the development of modern science and technology. For example, x-radiography is used to detect industrial product defects found in the German physicist Roentgen X-ray generated after ultrasonic testing in the two world wars and the rapid development of the sonar and radar technology developed on the basis of Magnetic particle testing is built on the basis of the theory of electromagnetism, and the penetration detection thanks to the progress of physical chemistry.

With the development of modern industry, product quality and structure of the security, the reliability of the ever-increasing demands due to the non-destructive testing techniques have advantages does not destroy the specimen, the detection sensitivity, the increasingly widespread application. Currently, non-destructive testing techniques in many domestic industries and sectors, such as machinery, metallurgy, oil and gas, petrochemical, chemical, aerospace, shipbuilding, railways, electricity, nuclear industry, weapons, coal, non-ferrous metals, construction, etc., are widely used .

Application of non-destructive testing technology advantages:
Discover defects and improve product quality
Application of non-destructive testing technology, the specimen internal defects can be detected by the naked eye can not see, and many hard to see with the naked eye can detect small defects in test specimen surface quality, by non-destructive testing methods. The reliability of the test results, because of the wide range of applications of non-destructive testing techniques for defect detection, high sensitivity, and therefore commonly used in the manufacturing process of container and other products inspection and final quality inspection.
Destructive testing, detection is completed at the same time, the specimen is damaged, destructive testing can only be carried out sampling. Destructive testing, nondestructive testing without damage to the specimen will be able to complete the testing process, so non-destructive testing product one hundred percent inspection or individually examined. Many important materials, structures or products are guaranteed to be foolproof, and only means of non-destructive testing, in order to provide an effective guarantee for quality.
Second, effective guarantee of the safe operation of equipment
Even if it is a design and manufacturing quality full compliance with the specification requirements of container damage accidents may occur after a period of use, this is due to the harsh operating conditions of the equipment status changes, for example, due to the high temperatures and stresses the role of lead material creep fatigue alternating stress due to fluctuations of temperature, pressure, stress concentration sites from under the corrosive effect of the wall thinning or material deterioration. The above factors may make the equipment originally exist, the manufacturing specification allows small defects expansion cracking, or kind or another newborn defects so that they had no defects in the equipment, and ultimately lead to equipment failure. In order to protect the use of safety in the use of boiler and pressure vessel must be regularly tested, timely detection of defects to avoid the accident.
Third, to promote the improvement of the manufacturing process
In production, in order to understand the manufacturing process sufficient suitability of advance technology test. In process test, often to process samples for nondestructive testing, and to improve the manufacturing process in accordance with the detection result, and ultimately determine the ideal manufacturing process. For example, in order to determine the welding process specification, in the welding test the welding specimen radiographic. Subsequent correction of welding parameters according to the test results, and eventually be able to achieve the quality requirements of the welding process. In another example, during the casting process design by the defects of the of radiographic penetration test pieces happening, which improved the position of gate and riser, to finalize a suitable casting process.
Fourth, to save money, reduce production costs
For non-destructive testing, often considered to increase the cost of testing, so that the increase in manufacturing costs in the product during the manufacturing process. However, if in the appropriate part of the middle of the manufacturing process correctly performed nondestructive testing, is to prevent the waste of the subsequent step of reducing rework, lower scrap rates, thereby reducing manufacturing costs. For example, in the thick plate welding If, after the completion of the welding, non-destructive testing found excessive defects need repair, to spend many hours of work or difficult to repair. Welded to half the first time non-destructive testing, confirm and then continue welding defects exceeding such destructive testing costs increase, but the total manufacturing cost reduction. In another example, machining, casting sometimes appears on the surface allowed machine plus slag, porosity, cracks and other defects, before machining to be subjected to processing site implementation of the non-destructive testing, a portion of the defect is discovered without further processing, thereby reducing the rejection rate, saving machining hours.

Application of non-destructive testing, should pay attention to the problem:
1, compatible with the destructive testing
The most important feature of the non-destructive testing is testing, so under the premise of no damage to materials, workpiece and structure of non-destructive testing, product inspection rate can reach 100%. However, not all projects and targets need to be tested can be carried out non-destructive testing, nondestructive testing technology limitations. Some test only destructive testing, Therefore, in the current non-destructive testing can not be completely replaced by destructive testing. In other words, the evaluation of a workpiece, materials, machinery and equipment, the results of non-destructive testing and destructive testing results compared with each other and cooperate in order to make an accurate assessment. Such as liquefied petroleum gas cylinders also burst test in addition to non-destructive testing. Boiler tube weld, sometimes to cut the sample do metallographic and fracture test.
2, the correct choice for the detection timing
When conducting non-destructive testing, must be in accordance with the purpose of the non-destructive testing, correct choice of the timing of the implementation of non-destructive testing. For example, ultrasonic testing of forgings, general arrangement forging been roughing, drilling, milling, grinding and final machining, because the scanning surface is relatively flat, better coupling may interfere with testing holes, slots, and Taiwan has not been processed, found quality problems processing easier, less loss, but also, for example, to check high-strength steel weld with or without delay crack, NDT timing of implementation, you should arrange for the completion of welding 24h later. To check whether the correct heat treatment process, it should be non-destructive testing after the implementation of the timing on the heat treatment. The correct selection of the implementation of the timing of non-destructive testing, in order to successfully complete the testing, correct evaluation of the quality of products.
3, a reasonable choice of non-destructive testing methods
Nondestructive testing applications, the detection method itself has limitations, can not be applied to all the workpiece and all defects, in order to improve the reliability of the detection result, before detection must, according to the subject matter of the material, structure, shape, size, expected may produce what kind, what the shape of the defect, in what part of what direction analysis under these circumstances, then according to the individual characteristics of the non-destructive testing methods to select the most suitable detection method. For example, lamination defects of the steel sheet because of its extending direction is parallel to the plate, is not suitable ray detector should select ultrasonic detection. Check the surface of the workpiece small cracks should not choose ray and ultrasonic detection, should choose the magnetic particle and penetrant testing. In addition, the choice of non-destructive testing methods and applications should be fully recognized that the purpose of detection is not a one-sided pursuit of the kind of excessive demands "high quality", but at the same time to ensure adequate security to ensure economic . Only in this way will the selection and application of non-destructive detection method is correct and reasonable.
4, a variety of non-destructive testing methods integrated application
NDT applications must recognize any kind of non-destructive testing methods are not a panacea, each of the non-destructive testing methods has its own advantages, but also has its drawbacks. Therefore, the application of non-destructive testing, if possible, not only children-ways, and as much as possible, while a non-destructive testing methods, in order to ensure that a variety of detection methods complement each other, so as to obtain more information. , But also the knowledge of the the other detection from the use of non-destructive testing outside to take advantage of the knowledge of the relevant materials, welding, machining process and product structure, combined judge, for example, ultrasonic crack defect detection sensitivity, but the characterization is not must have its shortcomings, the advantages of the ray is qualitatively more accurate defect, the combination of the two to use, will be able to ensure that test results are reliable and accurate.