Detection testing is the use of acoustic, optical, magnetic and electrical properties of substances, in the absence of damage or does not affect the use of the performance of the object to be tested on the premise of the surface of the inspected parts and the internal quality of the inspection of a means of testing to detect the presence of defects or inhomogeneities in the object to be inspected.
- Scope of weld flaw detection:
- the inspection of weld surface defects. Check the weld surface for cracks, unwelded and weld leakage and other welding problems.
- Internal cavity inspection. Check the surface for cracks, scratches, craters, bumps, skinning, drawing lines, spots, corrosion and other defects.
- Excess inspection. Check whether there are residual internal chips, foreign objects and other excess material in the inner cavity of the product.
- state check. When some products (such as worm gear pumps, engines, etc.) work, according to the technical requirements of the project specified in the endoscopy.
- Detection methods:
1. penetration detection PT
Penetration testing is mainly used for non-destructive testing of surface opening defects. Such as cracks, folds, air holes, cold segregation and porosity. It is not limited by the structure and chemical composition of the material. It can inspect not only metal materials, but also non-porous materials such as plastics, ceramics and glass.
The permeability display is intuitive and easy to judge. The operation method is fast and simple. Defects in any direction can be detected by operation, but there are some limitations. It can only detect defects with openings on the surface, and cannot effectively detect defects that are blocked by contaminants or with openings closed after mechanical treatment (polishing, grinding, etc.)). It is also not suitable for inspecting workpieces made of porous loose materials and workpieces with rough surfaces. Its developer is effective for an optimal observation time of 8-10 minutes. And in general it cannot be used at the same time with magnetic particle flaw detection; the magnetic suspension applied by its magnetic powder will block the openings of defects. Under special requirements, you can do penetration flaw detection first, and then do magnetic particle flaw detection, but the detection rate will be very low, no practical significance.
2. Magnetic particle testing MT
Magnetic particle flaw detection is mainly used to detect surface and near-surface defects in carbon steel, alloy structural steel, precipitation hardening steel and electrical steel. As discontinuous magnetic traces accumulate on the surface of the inspected workpiece, the shape, position and size of the discontinuities can be visualised and their nature can be roughly judged. The sensitivity of magnetic particle flaw detection is also very high, and the width of detectable defects can reach 0.1 μm, and some discontinuities buried up to several millimetres or even a dozen millimetres can be detected.
Magnetic particle flaw detection is virtually unlimited by the size and shape of the part being inspected, and uses a variety of magnetisation techniques to check each part for defects. Its process is relatively simple, fast inspection speed and low cost. However, it cannot inspect non-ferromagnetic metals such as aluminium, magnesium and copper, nor can it inspect non-metallic materials such as rubber, plastics, glass and ceramics. Can not test austenitic stainless steel, mainly used for hull welds, diesel engine parts, steel forgings, cast steel parts of the inspection.
Magnetic particle inspection is only applicable to ferromagnetic materials; can only detect surface and near-surface defects; it has a strong ability to detect cracks.
3. Ultrasonic flaw detection
Ultrasonic flaw detection is widely used in industry, mainly applied to forgings, rolled parts, welds, castings and so on. It is suitable for ferrous, non-ferrous and non-metallic materials and parts.
Ultrasonic waves are suitable for detecting plane defects, such as cracks, folds, interlayers, unwelded and unfused. As long as the ultrasonic beam is perpendicular to the crack plane, a high defect echo can be obtained. However, it is not sensitive enough to spherical defects such as pores and slag, and the radiation is low.
4. ray flaw detection
X-ray flaw detection is one of the earliest and most commonly used non-destructive testing methods.
The principle is based on the X-ray penetration of the object after the attenuation of different degrees to identify defects within the object, thus producing different blackness images on the negative. Defect images are intuitive and easy to locate qualitatively and quantitatively. It is applicable to various materials such as metal and non-metal.
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