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32 questions to be clear about NDT!

Jun 22, 2018

1.What is NDT/NDT?

(1) non-destructive testing is a test method to check the surface and internal quality of the inspected parts without damaging the workpiece or raw materials.

(2) NondestructiveTesting: NondestructiveTesting (NDT)

2.What are the commonly used methods of detection?

According to the research and analysis of NASA, nondestructive testing methods can be divided into six categories and about 70 types. However, in practical application, the following kinds are common:

Conventional nondestructive testing methods include:

- Ultrasonic Testing (UT);

- Radiographic Testing (RT);

- Magnetic particle Testing (MT);

- Penetrant Testing (PT);

- Eddy current Testing (ET);

Unconventional nondestructive testing techniques include:

- Acoustic Emission (AE);

- Leak Testing (UT);

- Optical Holography Holography;

- Infrared Thermography of thermal imaging;

- Microwave detection Testing

3.What is the basic principle of ultrasonic inspection?

There are many kinds of ultrasonic testing equipment, but in the actual testing process, pulse reflection ultrasonic testing equipment is the most widely used. Generally in homogeneous material, the existence of defects will cause material discontinuity, the discontinuous and acoustic impedance caused by inconsistencies, often by reflection theorem, we know that ultrasonic wave in two different acoustic impedance of the medium of the boundary surface reflection will occur with the size of the reflected energy and acoustic impedance difference on both sides of the interface between media and the size of the interface orientation,. The pulse reflection ultrasonic flaw detector is designed according to this principle.

At present most of the portable pulse reflection type ultrasonic flaw detector are A scanning mode, namely so-called A scan display mode display is the abscissa of the ultrasonic propagation time in tested materials or propagation distance, ordinate is ultrasonic reflection wave amplitude. , for example, there is a defect in a steel workpiece, as a result of the existence of the defect, the defect and steel materials formed between a different medium, the interface between the interface between the acoustic impedance is different, after the launch of ultrasonic wave in the interface, the reflection occurs (see figure 1), and was accepted by the probe to the reflected energy, abscissa in the display screen of a certain position will be displayed a reflected wave waveform, the abscissa of depth in this position is the defects in the tested materials. The height and shape of the reflected wave vary from defect to defect, reflecting the nature of defect.

4.What are the advantages of ultrasonic testing compared with X-ray testing?

Ultrasonic testing has the advantages of high sensitivity, short period, low cost, flexibility, high efficiency and no harm to human body. The disadvantage is that the work surface needs to be smooth, requiring experienced inspectors to identify the types of defects, and there is no direct perception of defects. Ultrasonic testing is suitable for testing thick parts.

5.What are the main features of ultrasonic testing?

(1) when the ultrasonic wave propagation in a medium, has the character of reflection on the different quality, and the interface, such as defects, defect is equal to or greater than the size of the ultrasonic wave length, the ultrasonic reflected on defects, flaw detector reflection wave can be displayed; If the size of the defect is even smaller than the wavelength, sound waves will bypass the radiation and cannot be reflected.

(2) the wave sound has good directionality, the higher the frequency, the better the directionality. It radiates to the medium with a narrow beam, which is easy to determine the location of defects.

(3) the transmission energy of ultrasonic wave is large, for example, the energy transmitted by the ultrasonic wave with a frequency of 1MHZ (100hz) is equivalent to one million times of the sound wave with the same amplitude and a frequency of 1000HZ (Hertz).

6.What may be the cause of the disappearance of the bottom wave when the ultrasonic inspection is carried out?

(1) major defects in the near watch;

(2) absorption defect; 

(3) major tilt defects;

(4) the oxide coating is not well combined with the steel plate.

7.What are the three principles for selecting K value of ultrasonic testing probe?

(1) sound beam scan the entire weld section;

(2) the sound beam should be perpendicular to the main defect as far as possible;

(3) sufficient sensitivity.

8.What are the three cases of defects identified in the jb1150-73 standard?

(1) multiple reflected waves with no bottom waves but defects.

(2) there are only a number of disordered defect waves without bottom waves.

(3) both defect waves and bottom waves exist simultaneously.

9.The distance specified in jb1150-73 - what is the purpose of the amplitude curve?

Distance -- amplitude curve is mainly used to determine the size of defects, which provides a basis for acceptance criteria.

Scrap line -- the maximum allowable equivalent of defect determination;

Quantitative line -- the control line that determines the size and length of defects;Testing line - detection starting sensitivity control line.

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