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Magnetic Flux Leakage Detection (MFL) Method Details

What Is mfl testing and How Does It Work?

mfl magnetic flux leakage testing (MFL) refers to the nondestructive testing technology that the surface and near surface defects form a magnetic leakage field on the surface of the material after the ferromagnetic material is magnetized, and the magnetic leakage field is detected to find defects.

When magnetizing the ferromagnetic material under test with a magnetic saturator, the magnetic induction line in the material will be constrained in the material if the material is continuous and uniform, and the magnetic flux is parallel to the surface of the material. There is almost no magnetic induction line passing through the surface, and there is no magnetic field on the tested surface.

However, when there are defects of cutting magnetic lines of force in the material, the change of defects or structure state on the surface of the material will change the permeability. Because the permeability of the defect is very small and the magnetic resistance is very large, the magnetic flux in the magnetic circuit will be distorted, and the magnetic induction line will change the way. In addition to a part of the magnetic flux passing through the defect directly or bypassing the defect inside the material, some of the magnetic flux will leave the surface of the material, bypass the defect through air and enter the material again, forming a leakage magnetic field at the surface defect of the material. We can detect the distribution and size of the leakage magnetic field through the magnetic sensor, so as to achieve the purpose of non-destructive testing.

Magnetization Methods in Magnetic Flux Leakage System

The magnetization method of MFL detection system plays an important role in MFL detection, which affects the magnetic field signal of the detected object. From the perspective of magnetization range, it can be divided into local magnetization and overall magnetization; from the perspective of magnetizing magnetic source, it can be divided into alternating magnetic field magnetization method, direct current magnetic flux leakage method and permanent magnet magnetization method.

The method of alternating magnetic field magnetization uses alternating current to excite the electromagnet to magnetize. With the increase of current frequency, the depth of magnetization decreases. After magnetization, the ferromagnetic material does not produce remanence and does not need demagnetization.

In the method of DC magnetic field magnetization, the electromagnet is excited by DC current to produce magnetic field for magnetization, and the magnetization intensity can be achieved by controlling the current; in the method of permanent magnet magnetization, the permanent magnet is used as the excitation magnetic source, and its effect is equivalent to the fixed DC magnetization.

Permanent magnet can use rare earth permanent magnet, aluminum nickel cobalt permanent magnet and so on. Generally, it uses rare earth permanent magnet, which has high magnetic energy and small volume. Remanence will be produced by using DC magnetization and permanent magnetization. Demagnetization depends on the specific requirements, and there is no specific requirements for the detection speed parameters. The selection of magnetization is generally aimed at ensuring the detection sensitivity and reducing the magnetizer so that the magnetic field generated by defects or structural features can be detected.

Key Applications of Magnetic Flux Leakage Technology

In addition to the appearance and near appearance crack defects, the biggest advantage of MFL detection is that it can find the corrosion pit and other defects inside the tank from the outside, and it does not need to polish the surface of the tank, which is suitable for online detection of the tank. At present, online detection of the tank is the most urgent method for users, which can reduce unnecessary downtime and reduce the cost of inspection. In addition, MFL detection can also determine some characteristic dimensions of defects, such as depth and length. Magnetic flux leakage detection is widely used in tank online detection. The magnetic flux leakage detection technology of the outer wall of the vessel is used to reflect the defects of the inner wall of the vessel, especially the severity and distribution of the corrosion on the inner and outer surfaces.

Besides, magnetic flux leakage testing equipment can also be used to detect the defects of mobile pressure vessels that can not be inspected internally when they are in parking inspection such as unmanned holes. At present, there is no good inspection method for the equipment that can not be inspected internally except by endoscope, and it may not be able to effectively observe the condition of the internal and external surfaces due to the reasons, for example, the cover of the internal and external surface media can not be removed. Magnetic flux leakage detection can be used for scanning detection when the outer surface is covered with paint layer, and the size and depth of corrosion pit on the inner wall can be detected from the outside, so as to reduce the increased inspection cost due to unnecessary parking and grinding, and also reduce the labor intensity. The on-line magnetic flux leakage detection can generally understand the internal and external surface states of the tank body and the distribution of defects. The magnetic flux leakage detection results of key equipment and important parts can be archived as a reference for regular spot check, so as to predict the thinning rate of the tank car wall thickness and ensure that the equipment can be safely transported to the next inspection cycle.

For more information about magnetic flux leakage testing procedure and ndt testing, please feel free to contact us!

 

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Magnetic Flux Leakage Testing Equipment

What is flux leakage
magnetic flux leakage testing equipment is widely used for non-destructive inspection of ferromagnetic materials. Magnetic flux leakage testing (MFL) helps detect corrosion, pitting and material loss in steel structures, pipelines, storage tanks and other industrial components.

magnetic flux leakage principle
The basic magnetic flux leakage principle used in mfl testing equipment is to magnetize ferromagnetic steel with a powerful magnetic field.  When used in combination with other methods, it provides a quick and inexpensive assessment of the workpiece of ferromagnetic materials. With the advancement of technology, people are paying more and more attention to the automation of the inspection process. This not only reduces the labor intensity of the inspection work but also improves the reliability of the test results and reduces the influence of human factors.

The MFI magnetic flux leakage testing method is a highly automated magnetic flux testing technology. The magnetic flux leakage principle is that after the ferromagnetic material is magnetized, the surface and near-surface defects form a leakage magnetic field on the surface of the material, and defects are detected by detecting the leakage magnetic field. In this sense, magnetic particle detection technology is commonly used in pressure vessel inspection. However, it is customary to use the method of measuring the leakage flux with a sensor as the magnetic flux leakage ndt detection, and the magnetic flux to detect the leakage flux. The method is called magnetic particle detection and they are juxtaposed into two detection methods.

Benefits of Magnetic Flux Leakage Testing
MFL testing equipment is highly sensitive to corrosion, pitting and material loss in ferromagnetic materials. magnetic flux leakage inspection also supports high-speed testing, making it suitable for industrial applications such as steel tubes, pipelines, storage tanks and components used in power plants and oil fields.

Application of Magnetic Flux Leakage Testing

magnetic flux leakage technology can improve asset safety by identifying corrosion and material loss before serious structural failure occurs. In addition, MFL technology has been shown to reduce operating costs by helping operators avoid costly shutdowns caused by corrosion or other material loss.

 

In addition to its use in oil & gas applications, magnetic flux leakage testing has been applied to assets in other industrial sectors including power generation plants; chemical manufacturing facilities; paper mills; steel mills; transportation systems (including railroads); offshore drilling platforms; defense installations; and municipal water treatment facilities.

 

Magnetic particle testing can only detect surface and near-surface crack defects, and it needs surface grinding when testing. It is only suitable for the detection of workpiece discontinuation. In addition to the surface and near-surface crack defects, the MFI magnetic flux leakage inspection can also find the corrosion inside the workpiece from the outside. Defects such as pits, and do not need to be polished on the surface of the workpiece, suitable for on-line inspection of workpieces. On-line inspection of workpieces is currently the most urgent method for users, which can reduce unnecessary parking and reduce inspection costs. In addition, the magnetic flux leakage detection can also quantify the depth and length of defects. Although the application of magnetic flux leakage detection technology is rarely used in workpiece inspection, it has the advantages that magnetic particle detection does not have, so its application prospect is very broad.

 

As a non destructive testing equipment manufacturer and supplier, we have been committed to developing and manufacturing high-quality and high-performance NDT equipment to provide customers with the best quality service.

 

There are many eddy current testing companies, but we are one of the best choices for you.

 

For more information about eddy current testing, please feel free to contact us!

 

Benchtop Magnetic Flux Leakage Testing Equipment

MFI Magnetic flux leakage test refers to the formation of a leakage magnetic field on the surface of a test piece after it is magnetized due to defects on the surface or near-surface of the test piece. People can detect defects by detecting changes in the leakage magnetic field.

Briefly describe the limitations of the magnetic flux leakage detection method.

The limitations of the magnetic flux leakage detection method are as follows: 

1. It is only applicable to ferromagnetic materials.  

2. Detection sensitivity is low.

3. The quantification of defects is rough.  

4. Due to the shape of the workpiece to be inspected, the leakage magnetic field method is not suitable for detecting test pieces with complicated shapes because the sensor detects the leakage flux.  

5. Magnetic flux leakage is not suitable for cracking very narrow cracks, especially closed cracks. It was found in the experiment that cracks with very narrow cracks, magnetic particle flaw detection and magnetic flux leakage inspection failed to produce an indication of injury and injury.

Briefly describe the application range of magnetic flux leakage detection technology. 

1. The application of magnetic flux leakage detection in the steel industry: in steel mills, it is mainly used for inspection of steel structural parts, billets, round bars, bars, steel pipes, welds and steel cables.  Make sure the finished product is in good condition.  On many occasions, users will not receive steel products that have not been inspected by steel mills and third parties.  Users often use magnetic flux leakage testing before manufacturing, which ensures the manufacturer's technical requirements for the product. Such inspections are often carried out by an independent inspection company or the user's quality assurance department.  

2. The application of magnetic flux leakage testing detection in the petrochemical industry: the installation of oil and gas pipelines (including buried pipelines), storage tank floor or the recovery of oilfield steel pipes.  

3. Other applications: regular in-service inspection of used steel cables, wire ropes, and chains.

BKN's bench top mmagnetic flux leakage testing equipment are capable of detecting workpieces efficiently and accurately.

 

As a non destructive testing equipment manufacturer and supplier, we have been committed to developing and manufacturing high-quality and high-performance NDT equipment to provide customers with the best quality service.

 

There are many non destructive testing machine suppliers, but we are one of the best choices for you.

 

For more information about eddy current testing, please feel free to contact us!