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Selection of flaw detection method

【Regarding EDDIO】Non-distractive Inspection Technique that EDDIO using

About ECT: Eddy Current Testing

Eddy current testing is explained in JIS Z 2316 as below.

Definition

Testing method that evaluate flaw, thickness, form, material, etc., by using change of eddy current occurred on test material.

Principle

Eddy Current Testing is based on the induction of current in the conductor. The amount of measurement and analysis are related to distribution of induced current. The volume of measurement is expressed as an amount of vector in the Gaussian plane, since magnetize the material with alternating current.
The eddy current distribution for depth direction of material, follows the physical laws. Therefore, the density of current is markedly decreased proportionately to increase of depth.

Items affect the measurement
  1. Permittivity of material
  2. Magnetic permeability of material
  3. Size and form of material
  4. Geometrical relation between probe for eddy current test and the material
    → More detail information can be obtained by indicating measurement amount on Gaussian plane
Advantages
  1. Available to use contactlessly to products.
  2. Available to use without contact medium such as water.
  3. Available to carry out a test at high speed.

（Above are from JIS Z 2316）

Features in practical aspect

  1. Available to automate the test, since inspection result can be obtained as an electrical output.
  2. Fast test speed, since the inspection is contactless.
  3. No need to do preprocessing and post processing for the inspection.
  4. The part of inspection is limited to rather simple form

About Eddy Current Tester

Flaw detection principle

Putting coil on conductor and applying a current generates Eddy current in conductor.
Detecting the change of eddy current by characteristic of material, and presence of flaw

Flaw detection method
Encircling type
Encircling type Rotary type Probe method

MLFT：Magnetic Leakage Flux Testing

Magnetic leakage flux testing is explained in JIS Z 2319 original draft revision as below.

Principle

Magnetize the ferromagnetic material by Magnetizer. Then magnetic flux leaks from the material if there is discontinuity part on the material such as flaw. Magnetic Leakage Flux Testing method is the technique that detect the flaw by measuring the magnetic intensity and distribution of magnetic flux leaked from this flaw. Magnetic Leakage Flux Testing method is the non-destructive testing method which suitable to carry out an inspection in the midway part of steel production line, an inspection of machine-parts, a maintenance of wire probe, because magnetic sensor scan the material without contact, and it enables to complete the test at high speed.
（Above are from JIS Z 2319 original draft revision）

There are no big differences between eddy current testing method about the “Items affect the Measurement”, “Advantages” and “Features in practical aspect”, except it is not affected by permittivity.

Items affect the measurement

  1. Magnetic permeability of material
  2. Size and form of material
  3. Geometrical relation between probe for eddy current testing and the material
    → More details can be obtained by showing measurement amount on Gaussian plane

Advantages compare to other inspection method

  1. Available to use contactlessly to products.
  2. Available to use without contact medium such as water.
  3. Available to carry out a test at high speed.

Features in practical aspect(same as ECT)

  1. Enable to automate the test, since inspection result can be obtained as an electrical output.
  2. Enable to automate the test, since inspection result can be obtained as an electrical output.
  3. No need to do preprocessing and post processing for the inspection.
  4. The part of inspection is limited to rather simple form

The part of inspection is limited to rather simple form

Flaw detection principle
Flaw detection method
Rotary type Scan type

Differences and features among Eddy Current Testing（ECT）, Magnetic Leakage Flux Testing（MLFT）

Differences and features among Eddy Current Testing（ECT）, Magnetic Leakage Flux Testing（MLFT）and other inspection method for detecting surface flaw, are shown on below table:

EDDIO flaw detection method Other flaw detection method
Eddy Current Magnetic Flux Leakage Magnetic Particle Penetrant Test
Principle Detect the tubulence of eddy current by a sensor(coil), to utilize electromagnetic induction. Magnetize the material and detect the magnetic flux leaking from the flaw by a sensor Magnetize the material, attach magnetic powder to the magnetic flux leaking from the flaw, and observe it visually Spray the penetrant, and visually observe leaching of the colored liquid with capillary phenomenon at flaw part.
Visual check △（Partially available） × ◎ ◎
Automatic test ◎ ◎ ×（There are case of automated one partially） ×
Preparation for testing Not necessary Not necessary Mostly not necessary Necessary（Cleaning and developping is needed）
Necessity of skill Not necessary Not necessary Necessary Necessary
Test speed High speed High speed Low speedVisual inspection takes time Super low speedvisual inspection + inspection preparation take time
Direction of flaw LimitedProbe shall scan cross the flaw at right angle LimitedMagnetic line shall cross flaw at right angle LimitedMagnetic line shall cross flaw at right angle No limit
Saving and uses of test result Easily process and accumulate the data as digital data, since flaw data can be earned as electric signal. Easily process and accumulate the data as digital data, since flaw data can be earned as electric signal. Test result can not be saved, so sketching or photographing is needed Test result can not be saved, so sketching or photographing is needed
Maintenance and management Necessary to check performance regularly by standard test piece. Necessary to check performance regularly by standard test piece. Contamination and density management of magnetic powder(liquid) is necessary. Also inspector health care management is necessary. Necessary to be proficient to carry out this test method. Skill management of inspector is necessary.
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