Crack detection

What is Crack Detection?

Crack detection is a process of detecting defects in non-porous materials or surfaces, such as metals, ceramics and plastics. Without effective crack detection, repair methods will be faulty.

What is Surface crack detection?

This is the measurement of the extent of cracks on the surface of a material (usually a solid material such as metals, plastics and ceramics.

How does crack detection work?

methods of detecting cracks in metals; it simply involves inducing electric currents inside the object being tested and then observing the electromagnetic response. When this test is set up properly, a defect in the metal or other solid object being tested will create a response that can be measured immediately.

The alternating current method of crack detection is mostly used in ferrous and non-ferrous metals; it can be used in detecting rusts. This simple process involves the passage of an un-disturbed current through the object,

What are crack detection methods?

There are three methods of crack detection especially for carbon steel, these are;

  • Magnetic particle testing or inspection,
  • Liquid penetrate inspection,
  • Eddy current testing method, and
  • Eddy current array (ECA).

The magnetic particle testing or inspection is a type of crack detection method that works by simply magnetising the region that is being tested, and then applying a wet suspension or solid ferrous particles. The magnetic flux will simply leak because air will not support magnetic field and the presence of air also suggests that a surface or sub-surface discontinuity is happening in the area being tested.

The liquid penetrant inspection usually involves the use of a dye and it is a very low-cost method of inspecting surface breaking defects, especially in non-porous materials. This method of crack detection can be used in detecting hairline cracks, porosity on the surface of material, leakages in new products and fatigue cracks present in in-service components. The liquid penetrant inspection makes use of low surface/tension fluid to penetrate dry surfaces, to detect flaws.

Eddy current testing is a method of crack detection applicable to surface and sub-surface defects. This process makes use of electro-magnetic induction to detect surface defects.  The Eddy current array is another form of crack detection that involves the use of multiplexed coils to test a larger area. This version of Eddy current testing is designed to minimise the interface between testing coils and then cover much larger surface areas during testing.  This method of testing is required mostly when greater speeds of testing are required.

Crack Detection Applications

Crack detection is applicable in many ways, these include;

  • Surface defects in Casting
  • Surface defects in Forging
  • Surface defects Welding

Crack detection uses:

Crack detection can be used in so many ways, the commonest among which are;

  • To detect porosity causes on the surface of a new non-porous material such as plastic, metals and ceramics.
  • To detect fatigue cracks that can lead to bigger cracks in a solid material in the future.
  • To detect leakages in new products.
  • Can be used in detecting the effectiveness of coatings and paints on a solid material.
  • It can be used in generating computerised records on the surface and sub-surface deterioration.
  • It can be used as a cleaning method on the surface of material.
  • It can be used in conducting a post-inspection analysis.

Eddie current crack detection:

The simplest form of Eddie crack detection involves the use of a coiled copper wire that can be excited by passing an alternating current, to create a magnetic field around the coil. As the coil approaches the conductive material being tested, the current in the coil opposed to the current in the material will be induced, and any defect in the conducting material being tested will create a disturbance along the path of the eddy currents. The disruption to the paths of the Eddy current, caused by defects on the surface of the material being evaluated, can be measured through Impedance variations in the copper coil.

Metal crack detection:

A typical metal crack detection is necessary to detect flaws in metals, for instance, a typical welding defect may be caused by the lack of complete fusion of the weld to the base metal, this will eventually create cracks and porous conditions inside the weld. The use of metal crack detection involves non-destructive methods of evaluating the geometry of defects in metals. Without adequate metal crack detection, heavy loads plus continuous bending and flexing can cause metal fatigue, and this may eventually lead to catastrophic accidents.

 

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