Thursday, April 20, 2017

Dye penatration test

Aim of the experiment: - To perform Dye/Liquid penetrant test.

Apparatus required:-Cleaner, penetrant, developer, and specimen.

Principle: - This method is used to detect surface defect /discontinuity of material on the basis of their surface properties. The penetrants are visible at the discontinuity of material.

Theory:-Dye penetration test is commonly used for detection of surface cracks. This process is used for finding subsurface crack of ferrous material or nonferrous materials. This process cannot inspect surface crack of porous material like chalk, wood, refractory material etc. The dye penetrant test complete in three step.

1. Cleaning the surface
2. Penetrating the penetrant
3. Pouring the developer in the surface

The principle of dye penetrant test is that the liquid used to enter small opening such as crack or flaws are porosity by capillary action. The capillary action is that type of action which provide the movement of liquid against the gravity. The rate and extent of capillary action are depend on certain properties like

1. Surface tension between liquid and solid material
2. Viscosity of liquid
3. Adhesion or cohesion for liquid
4. Penetrate affectivity

For the liquid to penetrate effectively the surface of material must be completely clean of all material that would affect the inherence of liquid into the crack. After cleaning the liquid penetrant is applied evenly and allowed for some time (5-10 min) called dwell time to permit penetration of liquid into all the surface crack. Than the extra liquid is penetrant from the surface is completely removed either by cloths or wet dryer. Than the developer is used on the surface thoroughly and evenly and provided some time to absorb the penetrant from the crack. After certain time the crack positions bleed out the penetrant on the surface and gives the idea about presence of crack.

Procedure:-

1.The surface of the specimen is prepared for the examination.
2.Once the surface is cleaned and dried the penetrant is applied all over the surface.
3.Dwell time is provided.
4.Excess penetrant is removed.
5.A thin layer of developer is provided in the surface of the specimen.
6.Inspection is performed in the apropreate light.
7.The surface is cleaned for the next examine.

Application:-

1.Used to locate surface bracking defect.
2.Casting and welded surface defect can be examine.
3.Forging cracks ,lops ,burst, can be examine.
4. Rolled product and lamination defect can be examine.
5.can determine volume of defect.

Advantages:-

1.This method have high sensitivity to small surface cracks.
2.Large volume and large area can be tested rapidly at very low cost.
3.Indications of cracks are produced directly on the surface and constitute the visual representation of defect.
4.Liquid penetrants ,devolopers and associated equipments are relatively low.

Disadvantages:-

1.Dye penetrant test only detect the surface defect it cannot detect subsurface and internal defects.
2.This process is not usefull for determination of flaws or cracks in pouros material.
3.Penetrating of specimen is criticlr simce contamination can maskor the surface crack.
4.Surface roughness can affect the inspection sensitivity.
5.post cleaning is required.