Application scope and safety precautions of NDT technology

Date：2022-01-13 16:06:18Views：1427

Nondestructive testing is a test method to check the surface and internal quality of the inspected parts without damaging the working state of the workpiece or raw materials. The purpose of nondestructive testing is to improve the manufacturing process, reduce the manufacturing cost, improve the possibility of products and ensure the safe operation of equipment. Any industry with large physical equipment or infrastructure may use some kind of non-destructive testing. Nondestructive testing has been widely used in many important industries around the world. Now mainly introduce its application scope and safety precautions.

ultrasonic examination

It is a nondestructive testing method to detect defects by using the reflection property of ultrasonic wave at the interface in the medium and the attenuation law when it propagates.

Scope of application:

1. Longitudinal wave can be used to detect inclusions, cracks, tube shrinkage, white spots, delamination and other defects in metal ingots, billets, medium and heavy plates, large forgings and products with simple shape;

2. The circumferential and axial cracks, scratches, pores, slag inclusions, cracks, incomplete penetration and other defects in the pipe can be detected by shear wave;

3. Surface defects on castings with simple shape can be detected by surface wave;

4. Defects in thin plates can be detected by plate wave.

Magnetic particle inspection

It is a nondestructive testing method that uses the interaction between magnetic leakage field and magnetic powder to show the surface and near surface defects of ferromagnetic materials.

Scope of application:

1. Detect the discontinuities on the surface and near surface of ferromagnetic materials that are very small and the gap is very narrow (for example, cracks with a length of 0.1mm and a width of micron can be detected), which are difficult to be seen visually;

2. It can detect raw materials, semi-finished products, finished workpieces and parts in service, as well as plates, profiles, pipes, bars, weldments, steel castings and forged steel parts, and can find defects such as cracks, inclusions, hair lines, white spots, folding, cold insulation and looseness.

Radiographic inspection

It is a non-destructive testing method to detect defects by using the different absorption of penetrating rays by the tested workpiece.

Radiography has been widely used in the internal quality inspection of welds and castings, such as welds of various pressure vessels, boilers, ship hulls, oil and gas pipelines, pressure castings in various cast steel valves, pump bodies, petroleum drilling, chemical and oil refining equipment, precision cast turbine blades, various aluminum magnesium alloy castings for aviation and automobile industries, etc.

Penetrant flaw detection

It is a nondestructive testing method for detecting open defects on the surface of materials based on the principle of capillary action.

Scope of application:

1. Detect the surface opening defects of (steel, heat-resistant alloy, aluminum alloy, magnesium alloy, copper alloy) and non-metallic (ceramic, plastic) workpieces, such as cracks, porosity, pores, slag inclusion, cold insulation, folding and oxidation scars. These surface opening defects, especially subtle surface opening defects, are generally difficult to find by direct visual inspection.

2. It can detect magnetic materials, non-magnetic materials, ferrous metals, non-ferrous metals, non metals, weldments, castings, calendered parts, forgings, machined parts, etc.

Let's take another look at the safety precautions for the use of NDT methods, which are summarized as follows:

First, reasonably select nondestructive testing methods

In the application of nondestructive testing instrument, due to the limitations of the testing method itself, it can not be applied to all workpieces and all defects. In order to improve the reliability of the testing results, it is necessary to predict what kind, shape and direction of defects may occur according to the material, structure, shape and size of the tested object before testing, According to the analysis of the above situations, and then select the most appropriate testing method according to the respective characteristics of NDT methods. For example, the delamination defect of steel plate is not suitable for radiographic testing because its extension direction is parallel to the plate, and ultrasonic testing should be selected. For the inspection of small cracks on the workpiece surface, magnetic particle and penetrant testing should be selected instead of radiographic and ultrasonic testing. In addition, when selecting nondestructive testing methods and applications, we should fully realize that the purpose of testing is not to unilaterally pursue the "high quality" of products with excessive requirements, but to ensure the economy of products while ensuring full safety. Only in this way can the selection and application of nondestructive testing methods be correct and reasonable.

Second, comprehensive application of various nondestructive testing methods

In the application of nondestructive testing, we must realize that any nondestructive testing method is not omnipotent. Each nondestructive testing method has its own advantages and disadvantages. Therefore, in the application of nondestructive testing, if possible, do not only use one nondestructive testing method, but use multiple methods at the same time as much as possible, so as to ensure that various testing methods learn from each other, so as to obtain more information. In addition, the information obtained from other tests other than non-destructive testing, knowledge of materials, welding and processing technology and product structure shall be used for comprehensive judgment. For example, ultrasonic has high sensitivity to crack defect detection, but inaccurate characterization is its deficiency, while the advantage of ray is that the characterization of defects is more accurate, and the two are used together, It can ensure that the test results are reliable and accurate.

Third, cooperate with destructive testing

The biggest feature of nondestructive testing is that it can be tested without damaging materials, workpieces and structures. Therefore, after nondestructive testing, the inspection rate of products can reach 100%. However, not all items and indicators that need to be tested can be subject to nondestructive testing, and nondestructive testing technology has its own limitations. Some tests can only use destructive testing. Therefore, nondestructive testing can not completely replace destructive testing at present. In other words, for the evaluation of a workpiece, material, machinery and equipment, the results of nondestructive testing and destructive testing must be compared and matched with each other in order to make an accurate evaluation. For example, in addition to nondestructive testing, explosion test shall be carried out for LPG cylinders. For boiler pipe welds, sometimes samples shall be cut for metallographic and fracture inspection.

Fourth, correctly select the detection time

During NDT, the time of NDT implementation must be correctly selected according to the purpose of NDT. For example, the ultrasonic flaw detection of forgings is generally arranged after forging and rough machining, and before final machining such as drilling, slot milling and fine grinding. At this time, the scanning surface is flat and the coupling is good. The holes, slots and platforms that may interfere with the flaw detection have not been machined, so it is easy to deal with quality problems and less loss. For example, In order to check whether there is delayed crack in the weld of high-strength steel, the implementation time of NDT should be arranged 24 hours after the completion of welding. To check whether the heat treatment process is correct, the implementation time of NDT should be carried out after heat treatment. Only by selecting the right time to implement nondestructive testing, can we successfully complete the testing and correctly evaluate the product quality.

The above is the relevant contents of the application scope and safety precautions of nondestructive testing technology compiled by the core testing team. I hope it will be helpful to you. Chuangxin testing is a professional testing organization for electronic components. At present, it mainly provides integrated circuit testing services such as capacitance, resistance, connector, MCU, CPLD, FPGA and DSP. Specializing in functional testing of electronic components, incoming appearance testing of electronic components, anatomical testing of electronic components, acetone testing, X-ray scanning testing of electronic components and RoHS component analysis testing. Welcome to call, we will serve you wholeheartedly!