Dpt Methods123.Doc

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A Liquid usually Red (called PENETRANT) is applied to the testsurface to form a uniform layer over the surface. Adequate time(called DWELL) is provided for the penetrant to seep into cavities

open to surface. A suitable method of cleaning (CLEANER) is used

to remove only the excess penetrant left on the surface. Then thedye that has seeped into discontinuities is made to come out & form

an indication on a contrasting background (called DEVELOPER).The evaluation of the indication so obtained can reveal lot of useful

information about the test surface. As a later development, dyes

which FLOURESCE under ultraviolet light, are employed for abetter delectability

LIQUID PENETRANT TEST ( LPT )

PRINCIPLE



PENETRANT TESTING MATERIALS

• PENETRANTS/DYE

• EMULSIFIER

• SOLVENT CLEANER/REMOVER

• DEVELOPER




PENETRANTS

FLURESCENT:-Penetrant utilises penetrants that are usually green in colorand flouresce(shine) brilliant under Ultraviolet light(back light) Fluorescenceis a property of some materials to absorb Ultravoilet light & give out visiblelight

VISIBLE:- Penetrant Utilises a penetrant that is usually re in color andproduces sharply visible red indications in contrast to the white backgroundof the developer under visible light.

DUAL SENSITIVITY PENETRANT

Fluorescent testing methods more sensitive over all visible method.




Properties of Penetrant

• Chemical stability and uniform consistency

• Good Wettability

• Low Viscosity

• Sufficient Brightness

• Chemical Inertness to containers & test materials

• Slow drying characteristics

• Ease of removal

• In-offnesive Odour

• Low Toxicity

• Resistance to UV light &/or heat

• Low cost

• High flash point




EMULSIFIERS

Emulsifier are liquids that make the excess penetrant water washable andhence aid the process of excess penetrant removal.

LIPOPHYLIC:- emulsifiers are essentially oil based and work by diffusinginto excess penetrant making it washable in water. The emulsification

action is fast and continues as long as it is in contact with excesspenetrant. The time for emulsification is dependent on the particularemulsifier, its concentration, emulsification rate, test piece surface conditionetc.

HYDROPHYLIC:-emulsifier are slow acting. Pre-rinsing with coarse wateris done to reduce ‘emulsification tine and penetrant contamination’

It is always preferable to find EMULSIFICATION time by experimentation





Penetration Add emulsifier Solution & diffusion begin

Diffusion proceeds Rinsing Clean surface



SOLVENT CLEANER/REMOVERS

Solvent cleaners are chemicals that are used to remove penetrants.

FLAMMABLE - FREE OF HALOGENS

NON FLAMMABLE - HALOGEN CONTAINING




DEVELOPERS

The purpose of the developers is to increase the visible contrast of visiblepenetrant indications in normal visible penetrant testing and to increase thebrightness of fluorescent indications in fluorescent penetrant testing.

Types of Developers are:-

• Dry Powder

• Water Soluable

• Water suspendible

• Non-aqueous solvent suspendible




PROPERTIES OF DEVELOPERS

• It must be capable of providing a contrast background in color contrast

penetrant testing

• It must be produce its own fluorescence

• It must be easy to apply & form a thin, uniform coating over a surface

• It must be easily wetted by the penetrant and capable of exposingpenetrant from a defect

• It must have a good blotting action

• It must be easy to remove after inspection




PENET RANT EMULSIFIER CLEANER DEVELOPER

VISIBLE LIPOPHYLIC WATER DRY POWDER

WATER WASHABLE HYDROPHYLIC HALOGENATED WATER SOLUABLE

POST-EMULSIFIABLE SOLVENT WATER

SOLVENT REMOVABLE HALOGEN-FREE SUSPENDIBLE

FLOURESCENT SOLVENT NON-AQUOUSWATER WASHABLE SOLVENT

POST-EMULSIFIABLE SUSPENDIBLE

SOLVENT REMOVABLE


SELECTION OF PENETRANT MATHODS:




BASIC STEPS INVOLVED IN LPT

.SURFACE PREPARATION / PRE- CLEANING

.PENETRANT APPLICATION

.EXCESS PENETRANT REMOVAL

.DEVELOPER APPLICATION

.DEVELOPING TIME

.EXAMINATION & EVALUATION

.RECORDING

.POST-CLEANING



ADVANTAGES OF LPT

• The method has high sensitivity to small surface discontinuity

• Large areas and large volumes of parts/materials can beinspected rapidly and at a Low cost

• Parts with complex geometry shapes are routinely inspected

• Penetrant materials and associated equipment are relatively

inexpensive.




LIMITATIONS OF DPT

• Can not give the indication for depth.

• Poor repeatability of test.

• Chemical handling and proper disposal is required

• Not suitable for porous material.

• Not applicable for hidden defects(only for surface defect)

• Precleaning is critical as contaminants can mask defects.

• Surface finish and roughness can affect inspection sensitivity




LIQUID PENETRANT STANDARDS

ASME SEC-V (ARTICLE - 22)

SE-165-91

Standard Practice for Liquid Penetrant Inspection Method.

SE-1209-91

Fluorescent Penetrant Examination using water washable process.

SE-1219-91

Standard Testing Method for Fluorescent Penetrant Examination using

Solvent removable Process

SE-1220-91

Standard Test Method for visible Penetrant Examination using solvent

removable




REQUIREMENTS OF NDT PERSONNEL QUALIFICATION

SNT – TC – 1A - Recommended Practice for Non-destructive

Testing Personnel Qualification and Certification.

ASNT – CP – 189 - ASNT Standard for Qualification and Certification

Of Non-destructive Testing Personnel.

ASNT - American Society For Non-destructive Testing Personnel.

ISNT - Indian Society For Non-destructive Testing Personnel.

LEVEL OF QUALIFICATION

Level I - Operator

Level II - Inspector / Interpretor

Level III - Authorise to write a NDT procedure and Training &

Certification of NDT Personnel.

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Dpt Methods123.Doc