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Pt presentation
- 1. Liquid Penetrant Testing (PT) Satyakiran School of NDT BU-3, SFS, Outer Ring Road, pitampura, Delhi-110088, India Ph: 91-11-27345252, 27342948; satyakiran@vsnl.com
- 2. www.satyakir an.com Introduction PT is one of the oldest NDT techniques. Earliest forms of penetrant inspection was the use of carbon black on glazed pottery. This method can be used to detect defects in a wide range of components provided that the defect break the surface of the material. However liquid penetrant testing can be done only on non-porous materials such as all metals amd alloys, non metals (plastic, polymers, glassware)
- 3. www.satyakir an.com There are five essential steps in PT 1. Cleaning and Surface preparation 2. Application of Penetrant 3. Removal of excess penetrant 4. Development 5. Observation and Inspection
- 4. www.satyakir an.com Characteristics of a Penetrant • Penetration ability – to enter into extremely fine defects or openings. • Surface tension & Wettability - to maintain a continuous film over the part • Fluidity – ability to drain away through the opening. • Solubility – capability to dissolve in contaminants possible in defects. • Washability – capability to removing penetrant from the part without dragging out penetrant trapped in defects.
- 5. www.satyakir an.com Characteristics of a Penetrant contd... • Stability – composition should not change over a wide range of temperature and humidity. • Resistance to drying during the test • Viscosity – To control fluidity and washability • Ignition point – higher to be inflammable • Chemical composition – to resist corrosion and reaction with the part
- 6. www.satyakir an.com Visibility of a penetrant 1. Colour contrast method – Deep red colour against white contrasting background of developer. 2. Fluorescent method – Glowing green- yellow or orange colour under ‘black light’ (near UV)
- 7. www.satyakir an.com Characterization of penetrant systems 1. Water-washable system – lower sensitivity, low cost, used for bulk goods in field inspection 2. Solvent-removable system – medium sensitivity, general purpose 3. Post emulsification system – high sensitivity and expensive, used in critical inspections (Based on penetrant removal method)
- 8. www.satyakir an.com Developer should posses following properties: • Absorption – developer must be easily wetted by the penetrant in the flaw and absorptive to suck back., • Application – must be easy to apply and capable of forming thin and uniform surface coating • Background masking – interference from background colours should be masked and provide contrasting background for indications • Physical characteristics – It must have grain size and shape to easily disperse the penetrant in the flaw, so that clearly defined indication is attained. Must neither be hygroscopic nor excessively dusty. • Chemical characteristics – must not contain ingredients harmful to the parts.
- 9. www.satyakir an.com Limitations • Only surface breaking flaws can be detected • Part material should be non porous • Affected by part temperature Advantages • Low cost, no instrumentation • No need higher operator competence and experience
- 11. www.satyakir an.com Removal of oxide, rust, weld spattrer etc: Wire brushing, or abrasive blasting followed by chemical cleaning When a number of small parts involved: Ultrasonic cleaning To clean all narrow openings: Vapour degreasing
- 12. www.satyakir an.com Penetration dwell time: 5 to 30 minutes
- 13. www.satyakir an.com • Water spray: Less than 50 psi • Solvent: Wipe with a moist cloth or absorbent paper • Post-Emulsifying: Emulsifier shall be applied by spraying or dipping. Emulsification time is critical and determined experimentally (never exceed 5 min.)