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LIQUID (DYE) PENETRATION TEST (D.P.T.)

LIQUID (DYE) PENETRATION TEST

INTRODUCTION
A liquid penetrant test is non-destructive type of testing to detect flaws that are open to the surface. e.g. cracks, seams, laps, lack of bond, porosity, cold shuts etc. can be effectively used not only in the inspection of ferrous metals but is especially useful for non-ferrous metal products and on non-porous, non-metallic materials such as ceramics, plastics and glass.

PRINCIPLE OF OPERATION
The principle of liquid penetrant test is that the liquids used enter small openings such as cracks or porosities by capillary action. They are influenced by factors such as the condition of the surface of material and the interior of the discontinuity. For liquid to penetrate effectively, the surface of the material must be thoroughly cleaned of all material that would obstruct the entrance of the liquid into the defect. After cleaning, the liquid penetrant is applied evenly over the surface and allowed to remain long enough to permit penetration into the possible discontinuities. The liquid is then completely removed from the surface of the component and either a wet or dry developer is applied. The liquid that has penetrated the defect will then bleed out onto the surface and the developer will help delineate them. This will show the location and general nature and magnitude of any defect present.

PROCEDURE FOR LIQUID PENETRANT TESTING 
This procedure covers Liquid Penetrant Examination by solvent/water removable process using visible penetrant for detecting discontinuities that are open to the surface of weldment and materials of any shape or size required by drawings, specifications and codes.



1. REQUIREMENTS
  • Pre-cleaner 
  • Penetrant 
  • Cleaner 
  • Developer 
2. SURFACE PREPARATION
The surface to be inspected and adjacent areas within shall be free from dirt, grease, scale or any other extraneous matter that would obscure surface openings or interfere with the test.

3. PRE-TEST CLEANING
Thoroughly clean the test area with cleaner and then wipe to dry with cotton waste. Allow surface to dry by normal evaporation for two minutes. Take adequate care to ensure proper surface condition prior to application of the penetrant.

4. TEMPERATURE
During testing the material temperature shall be between 6deg.c. and 52deg.c.
5. APPLICATION OF THE PENETRANT
Apply liquid penetrant by spraying or brushing to cover adequately and allow a minimum dwell time of I 0 minutes.

6. REMOVAL OF EXCESS PENETRANT
Wipe penetrant applied area with cotton waste. Continue cleaning till all traces of visible penetrant is removed. Take care to avoid use of excess cleaner and deposition of any contaminating material, which may lead, to misinterpretation of the test results. Allow the surface to dry by normal evaporation for 2 to 3 minutes.

7. APPLICATION OF DEVELOPER
Apply developer by spraying to give a thin uniform coat & maintain a developing time of minimum 7 minutes to maximum 30 minutes.

8. INTERPRETATION AND EVALUATION OF INDICATION
  • Only indications with major dimensions greater than 2mm shall be considered. 
  • A linear indication is one having length greater than 3 times width 
  • A rounded is one circular or elliptical shape with length equal to or less than 3 times width. 
  • Any questionable or doubtful indications shall be re-examined to determine whether they are relevant or not.


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