PENETRANT TESTING (PT)

 Penetrant inspection is an extension of visual inspection

 Used for detecting surface-breaking discontinuities like cracks, laminations, porosity etc
on any non-absorbent material's surface.

 A brightly coloured visible dye or a fluorescent dye is applied on the well cleaned
surface and allowed to penetrate in to surface-breaking discontinuities by capillary
action.

 After some time of soaking, the excess liquid penetrant is removed from the surface and
a developer applied.

 The developer draws penetrant out of any cracks by reverse capillary action to produce
indications on the surface.

 The indication are seen under either normal visible light or under dark UV Light

 These indications are broader than the actual flaw and are therefore more easily visible.
Inspection of the indications

Normal Light
OR
Dark (UV) Light
Basic Requirements:

1. Cleaner / Penetrant remover

- Water jets, solvent spray, alkaline, steam, vapour,
detergents

2. Penetrant

- liquid dye

- can be applied by spraying, painting and dipping

3. Developer

- Chalk powder (dry or wet)

4. UV (Black) light source

 Wave length of UV light = 10 – 380 nm
 Wave length of dark light = 320 – 380 nm
 PENETRANTS

 Penetrants are specialized liquids used to detect surface-breaking defects in materials.

 They work by seeping into cracks and other discontinuities, making them visible under
specific lighting conditions.

A penetrant must possess some important characteristics.

 good wettability - spread easily over the surface

 be drawn into surface breaking defects by capillary action.

 remain in the defect but remove easily from the surface of the part.

 remain fluid

 be highly visible or fluoresce brightly

 not be harmful to the material being tested or the inspector.

Penetrants come in two basic types.

Type 1 - Fluorescent Penetrants

Can be seen only under dark light, excellent sensitivity, costlier

Type 2 - Visible Penetrants

Can be seen in normal visible light, moderate sensitivity, cheaper
Penetrants are classified based on their sensitivity:

S1 = Low Sensitivity
S2 = Medium Sensitivity
S3 = High Sensitivity
S4 = Ultra-High Sensitivity

Penetrants are also classified based on the washability:

Method A = Water Washable systems

Method B = Post-Emulsifiable, Lipophilic systems
Method C = Solvent Removable systems
Method D = Post-Emulsifiable, Hydrophilic systems
 DEVELOPER

 The role of the developer is to pull the trapped penetrant material out of defects and
spread it out on the surface of the part

 Should be highly absorptive

 Simply chalk powder either in dry from or dissolved in water or solvent

 The six forms

Form A – Dry Powder

Form B – Water Soluble
Form C – Water Suspendable
Form D – Non-aqueous Type 1 Fluorescent Dye
Form E – Non-aqueous Type 2 Visible Dye
Form F – Special Applications
 Dark Light (UV) Source

 Wave length = 320 nm to 400 nm

 Lamp filter cleanliness & quality is very important

 Min warm up time is = 15 min

 Dark light intensity = min 1000 mW / cm2

 Distance between UV light and test surface = 15” or 381mm

 Proper calibration is required for every 6 months

Radiometer
 PT Procedural Steps
1. Cleaning / Precleaning:
 Is done to make the surface opening flaws to act like excellent capillars.

 The surface must be free of oil, grease, water, or other contaminants that may prevent
penetrant from entering flaws.

 Chemical mode of cleaning is more preferred than mechanical mode.

 Solvent cleaning
 Aqueous cleaning
 Vapour cleaning
 Steam cleaning
 Ultrasonic cleaning
 Surface preparation by grinding, machining, or other methods may be necessary where
surface irregularities could mask indications of unacceptable discontinuities.

 But, Precautions shall be made with the mechanical cleaning not to close the
discontinuities open to the surface.

 Etching of the cleaned surfaces may be necessary to open the discontinuities.

 Prior to all liquid penetrant inspections, the surface to be examined and all adjacent
areas within at least 25mm (1”) shall be dry and free of dirt, grease, lint, scale, welding
flux, weld spatter, oil and other extraneous matters that could obscure surface openings
or otherwise interfere with the examination.

 Once cleaning is over, dry the component at least for 1 min

Contaminant free
surface

Defect
Part
2. Application of Penetrant
 An appropriate dye system is selected based on the factors like sensitivity required,
materials cost, number of parts, size of area requiring inspection, and portability.

 Then the selected dye is applied uniformly to the surface of the part.

 This applied penetrant seeps into any surface openings or cracks due to capillary action.

 Then it is allowed to be on the surface for some time = Dwell time

 The dwell time is important because it allows the penetrant the time necessary to be
drawn into a defect

 Usual dwell time is = 5 – 60 mins, but for most the practical cases, it is about 15mins.

 The dye can be applied by spraying, brushing, or dipping

 Dye

Excess Dye

Required Dye Defect

Part

 After application, excess penetrant shall be allowed to drain while allowing for minimum
penetration (dwell) time stated in accordance with standards unless otherwise specified
by the client in a more restrictive manner.

 Dwell time (The length of time the penetrant must remain on the part to allow proper
penetration) should be as recommended by the penetrant manufacturer.

 Under any circumstances, the dwell time shall not exceed the maximum recommended
by the manufacturer.
3. Removal of Excess Penetrant

 After the specified dwell time has been elapsed, any penetrant remaining on the surface
shall be removed.

 The penetrant removal procedure must effectively remove the penetrant from the surface
of the part without removing an appreciable amount of entrapped penetrant from the
defect.

 If the removal process extracts penetrant from the flaw, the flaw indication will be
reduced by a proportional amount (over washing)

 If the penetrant is not effectively removed from the part surface, false & non relevant
indications may come (under washing)
Excess Dye

Required Dye
Component
 Depending on the dye system used, the excess dye may be removed by

i. Cleaning with solvents

ii. Direct rinsing with water
iii. First treating the part with an emulsifier and then rinsing with water.

 In method C, excess dye is removed with a dry or slightly moistened LINT FREE cloth of
solvent cleaner, taking care to minimize removal of penetrant from possible
discontinuity.

 Flushing the surface with solvent cleaner, following the application of the penetrant and
prior to developing is prohibited.
Water Cleaning – Method A

Water = DM water
Temp = 10o – 32oC
Pressure = < 40psi
Angle = 45o
Distance = 8 – 10”
Water Cleaning after emulsification – Method B&D

Draining
4. Developing:

 A developer is applied to pull the trapped penetrant out the defect and spread it on the
surface

 The dye coming to the surface by reverse capillary action and forming an indication

 Apply the non-aqueous wet developer (Form D or E) directly to the area being inspected,
by spraying from the aerosol container.

 The non-aqueous developer evaporates rapidly at room temperature and therefore does
not require the use of a dryer.

 Areas being inspected shall be sprayed in such a manner so as to assure complete

coverage with a thin, even film of developer.

 Dipping or flooding parts with non-aqueous developer is prohibited.

 Parts should be allowed to develop for a minimum of 10 minutes and no more than 2
hours before inspecting.

 Otherwise fading effect will takes place

 Red visible or Fluorescent indication on a white background

 Developer

Dye Defect

Part

Defect
Indication Developer

Defect

Part
5. Inspection and interpretation

 Inspection shall be carried out after the applicable developer dwell time to allow for
bleed out of penetrant from discontinuities into the developer coating.

 It is good practice to observe the bleed out while applying the developer as an aid in
interpreting and evaluating indications.

 Visible Penetrants (Type 2) = Normal light (> 1000 lux)

 Fluorescent Penetrants (Type 1) = UV light (320nm – 400nm)

 The light source, technique used, and light level verification is required to be
demonstrated, documented, and maintained on file.

 All indications shall be evaluated in accordance with the referencing code or

Specification.

 Relevant indications are those that result from mechanical discontinuities

 Any questionable or doubtful indications shall be re-tested to verify whether or not

actual defects are present. Visual inspection is the final step in the process.

 Flaw type and location can be obtained

 ACCEPTANCE CRITERIA
(ASME BPVC Section VIII)

1. Indications greater than 1.6mm considered as relevant.

2. All linear indications are unacceptable.

(Length of the indication is more than 3 times of width of the indication)
3. Rounded indications with max dimension in any one side more than 4.8 mm are
unacceptable.

4. Two indications placed apart with in 1.6mm are unacceptable.

5. More than 10 indications in a 6 in2 area are unacceptable.

< 1.5mm – Non relevant

> 1.5mm - relevant Space <1.6mm - Unacceptable

> 1.5mm – relevant – unacceptable defects

> 1.5mm, but < 4.8mm – relevant – acceptable defects 6 in2 area

> 4.8mm – relevant – Unacceptable defects

6. Documentation and Report preparation

 All relevant indications shall be recorded as specified by the referencing Code Section.

 As a minimum,
 the type of indications (linear or rounded),
 location and extent (length or diameter or aligned) shall be recorded.

 A suitable record format may be developed and used for this documentation purpose

 This format must contain all relevant information about the test with drawings of the
component and flaws

7. Post cleaning
Upon completion of the test, in cases where residual penetrant or developer could interfere
with subsequent processing or with service requirements, a suitable technique, such as a
water rinse or solvent soak for cleaning may be employed.
 Format No: PT C2

IOCL 3 On site
Pipe steel weld
ASTM E 165-02 As welded
ASME B31.1 27oC 20mm

Visible Penetrant Testing Pipe steel weld

SKL – SP1 Spotcheck
SKC S Spotcheck
SKD – S2 Spotcheck

Solvent spray cleaning

Spraying 15 mins
Spraying 15 mins
8000 lux -
 METHOD C - SOLVENT WASHABLE

 Method C penetrants require a solvent to remove them from the part.

 Basically dyes are oil based substances, so that they can be removed from the surface
only with solvents like acetone

 Hence, a solvent is usually sprayed over the dyed surface

 The same cleaner used for cleaning is used as penetrant remover

 Possibility for incomplete removal of excess dye from the surface of the part – Under
washing

 Incomplete removal of excess dye may lead to false & non relevant indications which
may confuse the inspector

 Huge chance for False indications which is not during the inspection of high critical
components
Solvent cleaning
 METHOD A - WATER WASHABLE

 They are removed from the part by rinsing with water

 They contain an inbuilt emulsifying agent (detergent)

 They are referred to as self-emulsifying penetrants

 Easy and complete removal of excess dye is possible

 However, there is a possibility of removing the penetrant from the flaws also, leading to
missing of sensitivity – Over washing

 EASY WASHING, but POOR SENSITIVITY

METHOD A - WATER WASHABLE
VISIBLE PENETRANT
 POST EMULSIFICATION

 They are developed to overcome the limitations of methods both A and C

 Conventional method C penetrant is applied on the component

 Then a separate emulsifier is added externally

 This emulsifier converts the oil based dye to water washable dye

 Only the dye on the defect free surface is alone converted into water washable

 There is no over washing as well as under washing

 Better sensitivity and easy washing

Emulsifier

Dye
 METHOD B – POST EMULSIFIABLE (LIPOPHILIC)
 Lipophilic systems make use of oil-based emulsifiers

 After the emulsifier has coated the surface of the object, the emulsifier diffuses into the
penetrant and the resulting mixture is easily removed with a water spray.

 Contact time is very crucial parameter here

 METHOD D – POST EMULSIFIABLE (HYDROPHILIC)
 They use an emulsifier that is a water soluble detergents that contain solvents and
surfactants.

 They remove the excess penetrant with mechanical and chemical action

 They break up the penetrant into small quantities and prevents these pieces from
recombining or reattaching to the surface of the part.

 The mechanical action of the rinse water removes the displaced penetrant from the part
and causes fresh remover to contact and lift newly exposed penetrant from the surface.

 Here, no diffusion takes place and hence contact time is not a crucial parameter
Method D
VISIBLE PENETRANT TESTING
Method D
Advantages

• Can detect surface defects better than VT.

• Can inspect parts with irregular shapes easily.
• Fast method of inspection and indications are visible directly on the specimen surface.
• Considered low cost compared to many other NDT methods.
• Is a very portable inspection method.

Limitations

• Can not detect subsurface and internal flaws

• Cannot inspect ceramics and powder metallurgy components
• Pre-cleaning of components is a critical step for better flaw detectability.
• Results are qualitative